Author Topic: Another 6 x 26 Knee Mill CNC conversion  (Read 42145 times)

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Another 6 x 26 Knee Mill CNC conversion
« on: July 14, 2012, 08:21:50 AM »
Hi All,

New kid on the Mad Modder block here. I've just discovered this site when trawling for info on CNC conversion.
I've had a Myford VMC mill from new for the last 20 years or so and have been thinking sporadically about conversion to CNC for about half that time. Usually after a tedious session of pecking out profiles from a long list of Excel generated coordinates. :lol:

The VMC is quite similar to the generic 6 x 26 that appears worldwide with a range of badges with the exception that it does not have the fine quill feed that virtually all other 6 x 26 machines I've seen.
The original data sheet is here
and



I've had a Heidenhain 2 axis DRO on it since new and a few years back swapped the DC motor I was using for get variable speed for a 3 phase 1hp induction motor and a Siemens Micromaster inverter that I run from 10Hz to 100Hz giving a range of 20% to 200% of the designed spindle speeds. The machine has had light hobby use from new and is still in pretty good condition.

A few years back I decided that in order to learn a little about stepper motors and drivers to change the homebrew X feed from a windscreen wiper motor and worm gearbox to a direct drive 3Nm stepper motor (that is about 400 of your strange 'merkin oz-inches  :lol:) Currently I still have the 4mm pitch feedscrew and the 3Nm motor is just about man enough to turn it.


My background is in electronics research and development so I tend to be an experimenter using suck it and see iterative methods rather than detailed paper design and build. Well that is my excuse anyway!
Throughout this conversion, I will have to make any parts needed using the target mill supplemented by Myford ML7RB for any turning and milling whilst the VMC is inoperable. This might turn into quite a challenge and as a last resort might be begging/borrowing time in other workshops :doh:

As I'm very much a novice in the area of CNC, I'm not proposing to make this write up a blow by blow account of how to do a CNC conversion. There are better threads here and elsewhere written by professional engineers for that sort of use.
I intend to post various sub topics here of my approach on the basis that it might just be of interest and maybe stimulate a discussion.

One such topic is my attempt to balance the load of the knee on the Z axis using a gas spring.

My first task was to estimate the weight of the knee. I wound it right up to the top of the slide, locked the Z axis and released the Z axis feed nut. Once SWMBO was out of the way, I used the bathroom scales to measure the force on the nut which was around 1000kN. Put another way - about the same as I weigh :bugeye:

The vertical travel is around 350mm and I found I could buy an adjustable gas spring with 1200kN force and 400mm travel here
http://www.sgs-engineering.com/gas-struts/range/nitride/adjustable/10mm-rod/gsv10-400

These springs are filled with nitrogen and oil and must be fitted cylinder uppermost to keep the seals moist and the gas inside.
The spring is mounted centrally under the knee about 30mm away from the Z slideways.
I drill a clearance hole through the cast base and the sheet steel stand underneath with a starrett type hole saw. Pretty heavy going through 10mm thick cast iron and the sheet steel 100mm below. None too pretty result but it did the job!




I used a length of 1" iron water pipe welded to a mild steel flange to house and support the piston end of the spring.



and



An M6 cross bolt (not shown) was fitted at the lower end of the pipe to support the piston end that was screwed into a short length of 22mm diameter steel bar. The cylinder is also 22mm diameter so the piston end is kept roughly central. Once is had 100Kg of knee pressing down, it won't be going anywhere!

To mark the underside of the knee casting I turned up a pointed steel plug to fit inside the tube flange and lowered the knee onto it - result one centre dot that I could then use a punch to enlarge.



Drilling and tapping the casting  M8 was a bit awkward with a right angle drive cordless drill and a small tap wrench with removable tommy bar.

Here is a the ball end fitted ready to receive the gas spring cylinder. There is a choice of end fittings available included in the price of the gas spring.



Getting the spring into position is a bit tricky. uncompressed it is 850mm long before any end fittings are added.

I need to jack the knee up another 80mm above its usual maximum position. So by locking the knee, undoing the nut and inserting spacers underneath, I could use the Z screw to achieve this.



With the cylinder fitted to the knee casting I could then remove the spacers and refit the nut securing screws.

Winding the knee up and down felt most peculiar. Remember we have 1200kN force upwards and 1000kN imposed by the knee. So it take MORE effort to lower the knee than raise it :D

I then used a spring balance and the feedscrew handle to measure the difference in torque need to raise and lower the table whilst gently letting some gas out of the spring one fart at a time remembering that there is no way back if I let too much out!

I've used these springs before and it is actually fairly easy - a sub one second burst makes a small but measurable difference.

I've now got it balanced quite nicely now and it takes about a 2kg pull at 200mm radius - about 4Nm to move the table in either direction.

My next step is to attach a stepper in place of the handle and see how well or otherwise that works. A 12Nm motor  and matching driver are on order from Zapp and some timing pulleys from http://www.beltingonline.com/ - a new supplier to me but the prices seem good. Lets hope the service matches!

More in a few days with luck.
I hope this is of interest - comments welcome
Bob




Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #1 on: July 14, 2012, 09:38:16 AM »
Bob,
I think you need to rethink the 12 Nm motors, they are far to big and powerful for this machine.
problem with large motors is the detent torque needed to overcome the rest position. To overcome this take time and power with the result that the motors are slow and in short moves of which a lot of CNC moves are they spend most of their time accelerating and not running at the speed they should.

As an idea that big Beaver CNC of mine which i know you have seen uses 7Nm motors direct driving onto 0.2" pitch ballscrews which is close to 5mm pitch and has no problems.

John S.
John Stevenson

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #2 on: July 14, 2012, 09:50:28 AM »
Thanks for your input John. I guess I was afraid of not having enough power to lift the knee especially as I'm hoping not to have to use a ballscrew for the Z axis if I can help it.
I did consider the comments about 12Nm speed in Rob's 6 x 26 thread and will be using much more agile motors for X & Y.
I'm still of two (or three minds!) whether to put a stepper on the quill for majority of the Z operations.

Any thoughts on  CNCing the quill  would be of great interest especially interlinking it with a powered knee. Can Mach 3 cope with two Z drivers?

TIA

Bob

Offline loply

  • Sr. Member
  • ****
  • Posts: 260
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #3 on: July 14, 2012, 10:20:12 AM »
Hi Bob,

Far from an expert but I have done quite a bit of reading as I'm slowly gathering bits for CNC'ing my mill and lathe.

I note that individuals are often concerned about not having enough power for their Z axis, yet I can't ever find a reference to anybody ever having a problem with this.

Cheers,
Rich

Offline Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #4 on: July 14, 2012, 11:25:54 AM »
Hiya Bob  :wave:

Welcome to the collective :borg:

Very glad to see you are sharing your build with us. I will be following!

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #5 on: July 14, 2012, 12:15:18 PM »
Hiya Bob  :wave:

Welcome to the collective :borg:

Very glad to see you are sharing your build with us. I will be following!

Eric

Thanks for the welcome Eric.

I dunno about followers - I think I need some leaders too  :lol:

Bob

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #6 on: July 14, 2012, 05:00:45 PM »
Did a search because I had read an article by Tony Jeffee when he converted his X3 and did some tests on the Z axis.

He was using the largest type 23 motor at the time sold by ARC. These are 2.2Nm motors and he was driving a 2mm pitch ball screw directly.

End of the day he finished up putting a set of bathroom scales on the bed and pushed down. He bailed out at 137Kg because he didn't want to break the scales.

When we were doing the X3 conversion kits we were using the same motors with 4mm pitch screws, direct drive on X ans Y and 2:1 reduction on the Z. No complaints and no problems.

Later WM series machines have had 5mm pitch screws and the 3Nm motors fitted again direct on X and Y, 2:1 reduction on Z. Again no problems.

In your case Bob with the gas strut on the knee Zapps 5504 or 6004 motors driving a 16 x 5 screw would be more than enough and faster than Robs setup.

[edit] The VM-B I am doing will have 16 x 5 screws, 3 Nm motors, direct on X and Y and 2:1 on the Z and run at 72 volts driving the larger ARC drivers. I do not see any problems with this setup.

John S.
John Stevenson

Offline doubleboost

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 1619
  • Country: gb
  • Newcastle Upon Tyne
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #7 on: July 14, 2012, 05:47:27 PM »
Hi
Bob
I also have a 626 mill  :doh: :doh:
Although i have no intension of doing a cnc conversion , i will be copying your gas strut mod  :thumbup: :thumbup:
My mill has a 6 inch riser block so i will need a bit more stroke on the ram
I have been looking  at car tail gate  struts but your link has convinced me not to be such a "tight arse" and just buy one for the job
Good luck with your conversion (you have some good people on this forum ready to help )
John

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #8 on: July 15, 2012, 07:00:21 AM »
I thought I replied to this last night but can't see it this morning? But I did have a few drinks.......

The riser block that I have does not add any Z travel but just increases the daylight under the quill nose so the same 400mm gas spring will still do the job. In fact a 350mm would possibly do but it makes it all the more critical to align the knee travel to the spring travel.

Bob

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #9 on: July 15, 2012, 07:06:45 AM »
Bob,
This is true about aligning, any sideways force on the rod will wear the seal and they soon start to leak.
Don't ask  :wave:
Contrary to popular engineering practice if you can get as much bag and flop in the mounting and allow it to self centralise the better it is.
John Stevenson

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #10 on: July 15, 2012, 07:15:47 AM »
Very true John.

My comment use of the word alignment was probably a bad choice. I just meant that using a 400mm strut meant that it was less critical to get the vertical position of the strut right so that it did run out of steam when the knee was at max height or indeed limit the knee travel at the lowest point.
Sort of being lazy on the measurements. In any case the supplier I linked to does not sell 350mm struts and one who does
http://www.strutsdirect.co.uk/components/variable-force-gas-struts-sd03.php does not offer the in line ball & socket end fittings.

Bob

Offline doubleboost

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 1619
  • Country: gb
  • Newcastle Upon Tyne
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #11 on: July 15, 2012, 08:35:23 AM »
Hi
Bob
Just had a bit measure up 400 will be ideal (360 )travell before the screw comes out of the nut
John

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #12 on: July 15, 2012, 10:44:27 AM »
I've just been sent this link by Ron Ginger about his conversion. It is for a 8 x 28 mill but it's pretty similar to the 6 x 26.

http://plsntcov.8m.com/JetMill/Jet.html

Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #13 on: July 19, 2012, 08:54:42 AM »
I've been starting to think about ballscrews for the X and Y slide whilst waiting for parts to arrive for the Z axis.

There is plenty of room in the area of the Y screw but the X axis is going to be tight. I'm trying to minimise the machining needed once I have the mill in pieces. Even though a mate has offered me use of his mill to make parts, I don't want to impose on him too much.

I've decided on 20mm ballscrews and Zapp have a couple of ball nuts with a 34mm body diameter which will just fit in with 1mm clearance. However, the flange is 57mm diameter with two flats 40mm across and I wanted to see how they would fit before splashing the cash.

I made a replica of the flange from 1/2" aluminium.



The cut out in one side was in the hope that I could slot it over the 1" diameter feedscrew but no such luck  :doh:
So the end of the table had to be taken off which in the end gave a much better view of the problem.

There is very little room arounf the existing nut.



I clamped the flange to the table end.



and marked the table to show where it interferes



I considered that machining that much off the table would weaken the dovetail too much and so marked the flange where it would interfere.



Removing that much from the ball nut flange will destroy one mounting hole but I reckon the remaining 3 should be enough especially if I add some sort of clamp around the body of the nut as well.

I think I've done enough to satisfy myself that the X ballscrews can be made to fit even though it seems a bit brutal to attack a brand new nut in this way.

The next job, whilst I have the table end/bearing carrier off is to counter bore the inside face to admit the ballnut flange and to open out the bore to take a second bearing. Straight forward faceplate work on the lathe. This will allow room for two opposed A/C bearings (7204-2RS) to support the ballscrew

Current bearing is a 6303z which has the same OD as the a/c ones (47mm) but a 17mm bore to suit the old feedscrew. The new ones are 20mm bore which will be ideal for my ballscrew end adaptors.

That's all for now folks.

Bob



Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #14 on: July 19, 2012, 10:30:16 AM »
Sounds like you have a plan Bob  :thumbup:

It is a bit tight getting these parts into a mill that was not designed to take ballscrews  :palm:


Rob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #15 on: July 19, 2012, 12:52:19 PM »
Yes Rob, things are starting to come together - at least to an outline plan.

I have to confess to everyone about an error in my first post. I got my N & kN mixed up :doh: :doh:

The knee weighs about 100kg thus exerting 1000N

The gas spring is rated at 1200N

Sadly I still weigh more than 100kg - the only bit I got right. :lol:

Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #16 on: July 19, 2012, 02:04:31 PM »
I got a bit more done this afternoon.

I bored the bearing housing to take the second bearing.



A spare 6204ZZ fitted for the photo together with the original 6303Z just visible



Dummy flange fitted to illustrate the counterbore. The X axis traverse stop will continue to be the breaing housing hitting the saddle as per original design and not risk damaging the ball nut.




Everything has arrived now for the Z drive. 1/2" plate, motor, timing pulleys & belt so that will be the next job.

Bob

Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #17 on: July 19, 2012, 03:48:43 PM »
Hi Bob  dose this mean its now a three CNC horse race  , Yourself  ,Mr JS and I  ,I will lay odds i will come last  :palm:


Looking forward to seeing what you make from your 1/2" plate  :dremel:


Rob

Offline dsquire

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 2275
  • Country: ca
  • Kitchener, Ontario, Canada
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #18 on: July 19, 2012, 03:54:45 PM »
Hi Bob  dose this mean its now a three CNC horse race  , Yourself  ,Mr JS and I  ,I will lay odds i will come last  :palm:


Looking forward to seeing what you make from your 1/2" plate  :dremel:


Rob

Rob

That may be but I am willing to bet yours is the shiniest. Especially with that patented trade secret camera process you use.  :lol: :lol: :lol:

Cheers

Don
Good, better, best.
Never let it rest,
'til your good is better,
and your better best

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #19 on: July 19, 2012, 06:19:53 PM »
Hi Bob  dose this mean its now a three CNC horse race  , Yourself  ,Mr JS and I  ,I will lay odds i will come last  :palm:


Rob

No way my VM-B has took back seat, done a little drag engraver the other week as it was needed, the shop clear out after getting rid of the big TOS is taking longer than I thought.

Problem is damn customers, no matter how much you swear at them, take the pi$$ and be as obnoxious as possible the bastards still keep coming back.

Keep getting phone calls about the new laser and when can they deliver it but so far nowhere finished to put it, mind you once it does hit the deck that's another diversion.
John Stevenson

Offline DMIOM

  • Hero Member
  • *****
  • Posts: 676
  • Country: gb
  • Isle of Man
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #20 on: July 20, 2012, 03:34:57 AM »
..........Problem is damn customers, no matter how much you swear at them, take the pi$$ and be as obnoxious as possible the bastards still keep coming back........

No, you've missed the point - if you're still providing top-notch services (even if they're not chrome-plated) then they'll keep coming back!   maybe its even the Gordon Ramsay effect?   :lol:

Quote
...........Keep getting phone calls about the new laser and when can they deliver it but so far nowhere finished to put it....

Tell you what, I'd be very glad to help - I'll look after it & get it run-in for you, rent-free  :thumbup:

Dave

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #21 on: July 23, 2012, 11:49:02 AM »
I got some more work in on the Z axis drive over the weekend.

I machined up a plate to hold the motor onto the Z axis shaft and in the process managed to make it 6mm too short  :bang:
So I can't tension the belt properly  :doh:



Viewed from the rear to show the motor.



A shorter belt should have been delivered this morning but Parcel Farce sent it to the Gatwick Airport depot instead of my local one which is Southampton Airport  :doh: Hopefully it will turn up tomorrow.

However I could not wait to give it a quick try out. So I raided my electronics junk box and cobbled together a 60v supply and connected up the driver in test mode which turns the motor slowly.
So by no means a realistic test but the table moves under power! :D



Click picture to view short video clip.

The manual handle was left attached to show the rotation. Obviously this would normally not be fitted!

Bob

Offline Ronkh

  • Jr. Member
  • **
  • Posts: 35
  • Country: england
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #22 on: July 23, 2012, 01:29:45 PM »
Nice going Bob but for God's sake disengage otherwise watch yer nut's!  :lol:
Just me!

Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #23 on: July 23, 2012, 03:52:30 PM »
 :thumbup:  nice going Bob  :clap: :clap: :clap:


Rob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #24 on: July 23, 2012, 04:00:18 PM »
Thanks Guys

 :thumbup:

Trying to decipher the Chinglish manual for the driver now..... :bang:

Bob

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #25 on: July 23, 2012, 04:39:04 PM »
Starts off "Do not place in the sunshine room "

Best one I saw was on a parts list, it listed Part No.#1234 as Water Buffalo.
Had a look for Part No.#1234 on the illustrated parts list and it was a Hydraulic Ram !!   :Doh:
John Stevenson

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #26 on: August 08, 2012, 02:15:41 PM »
Its been a while since I posted but I have been busy designing and starting to make parts.

One of my design criteria is to retain manual operation via the handwheels and the built in dials from the original machine which are 4mm per turn.
The new ballscrew is 5mm pitch and is right handed. The drive is therefore require to correct for these 'challenges'

This is a cross section through the Y axis drive.



At the top left is the new ball screw supported by a pair of AC bearings. The screw spindle has a 26 tooth HTD pulley secured by grubscrews and to this is bolted a 25 tooth 2 module spur gear. This gear meshes with a home made anti backlash 20 tooth gear which drives the handwheel and original dial.

The gears both correct the pitch ratio and provide a reversal of rotation.

The 26 tooth pulley is connected to a similar pulley (1:1 ratio) via the belt. The lower HTD pulley has been bored to take a needle roller bearing and is free to rotate on the motor shaft.
A simple pin clutch is permanently driven by the motor and when the spring loaded pin is engaged by pulling and rotating the knob by 90 degrees picks up on one of the 4 holes in the pulley.

Now for the pics

The top htd pulley showing the recess for the AC bearing preload adjustment nut



View of the other end showing the 25 tooth gear




This is the completed clutch mounted on a dummy motor shaft



and the component parts.

Dummy shaft - not pretty but functional for testing



The lower HTD pulley with needle roller and four holes for the clutch pin.



This is the driven part of the clutch with the pin withdrawn



and with the pin in the locked position



The external view of the clutch with the pin withdrawn.



Rotating the pin by 90 degrees allows the clutch to move to the engaged position.

This is the sprung loaded pin and the knurled operating knob which also acts a cover for the mechanism.




The two spur gears were purchased ready made ( life is too short!) from  http://www.technobotsonline.com/ and arrived next day!

The teeth are 20mm wide and I parted the 20 tooth one into two halves and machined the recesses for the torsion spring.



The spring installed



and the two halves re-assembled



After parting off and cleaning up the tooth width is 17.5 mm so I reduced the tooth width on the 25 tooth gear to match.
I've yet to see how effective the antibacklash device is. The spring allows about half a turn (10 teeth) maximum so reasonable scope for adjustment.


I've shown the details for the Y axis here but there are similar requirements for the X axis.  The only difference being the the original X feed screw is the same hand as the ballscrew and so the geared drive is not required.  Instead, the 5:4 ratio is provided by a 30 & 24 tooth htd belt on the right hand end of the table and a 1:1 motor drive will be fitted on the left hand end

Thanks for looking.

Bob







Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #27 on: August 08, 2012, 03:46:15 PM »
very interesting Bob ,, clever bit of design work  :clap: :clap: :clap: :clap: :clap:


Rob

Offline loply

  • Sr. Member
  • ****
  • Posts: 260
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #28 on: August 08, 2012, 04:42:28 PM »
Hi Bob,

Real nice bit of work. Question - Is the clutch pin tapered so that it will always achieve a tight (zero backlash) fit?

Are you confident you won't have backdrive issues since you're using ballscrews here? It's quite a big mill to have manual handles on ball screws...

Cheers,
Rich

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #29 on: August 08, 2012, 05:01:41 PM »
Hi Rich,

Yes, the pin slides in a reamed hole and has a 2 degree taper and locates in a parallel hole. My aim was for minimal backlash, automatic take up for wear due to the spring loaded pin and yet trying to avoid it jamming due to the taper. Time will tell how that all works out.

To be honest I don't know if back drive will be a problem or not. I've read conflicting reports. I'm very much a beginner in all this and once I become more proficient in using the CNC, I expect to use manual mode less. I can always nip up the carriage locks a bit?
At the moment it take me longer to draw an item fully than make it. That hopefully will change
What I really need is a back of envelope to gcode interpreter  :lol:

Bob

Offline loply

  • Sr. Member
  • ****
  • Posts: 260
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #30 on: August 08, 2012, 05:16:26 PM »
Bob,

I needn't have asked about the taper really  :thumbup:

It's interesting that you've made manual mode possible. I'm converting my lathe to CNC at the moment and plan to do my mill at some point and initially wanted to retain manual mode.

Having thought about it I decided against - Using the CNC software you can essentially operate in 'manual' mode anyway by simply jogging the axes using the keyboard, the difference being you can set the jog speed precisely and you get a DRO for free.

The only downside is that the PC needs to be turned on and it won't work if you have an electrical fault, so the mechanical backup is good in that respect!

Cheers,
Rich

Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #31 on: September 05, 2012, 08:06:21 AM »
were be these photos you promised Bob  :poke:  :D

Any how , still moving crap around in the shop today , found dis .





Any good to you ? 


Rob

Offline DaveH

  • Hero Member
  • *****
  • Posts: 1413
  • Country: za
  • Kempton Park, South Africa
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #32 on: September 05, 2012, 10:11:32 AM »
Bob,

Very nice work  :thumbup: :clap: :bow:
 :beer:
DaveH
(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #33 on: September 05, 2012, 10:22:47 AM »
I've been in the wood workshop today - that is my excuse anyway!
Thanks for your offer Rob - I'll send a pm next.

Ok So I've now got an ever increasing selection of parts made most of which seem to fit  :bugeye:



Firstly a couple of the clutches that connect the stepper motor to the htd pulley or not depending on the position of the knob.

These are fixed to the motor shaft and supported by an oil seal which should keep swarf out of the mechanism hopefully.

Next the ball nut housings:-
X axis which needs the odd shape to fit under the table



and the simpler Y axis one where there is plenty of room




This is the X feedscrew extension which enabled me to save the cost of having custom machining done on the screw.



This is the X motor mount, clutch housing and belt drive which will fit on the left hand end of the X screw via the extension above



It needs a 75mm spacer block to keep it out of the way




and the complete assembly less motor to put it in context



When fitted the spacer is at the top and the motor to the rear of the table - again to keep it out of the way.

The X axis handwheel end has the 4:5 ratio belt drive and fits to the right hand end of the table. It is narrow enough to tuck inside the saddle and not limit the X travel.



the two lugs at the top mount onto the table end casting.

The Y axis addition shown below comprises the functions of the both the above parts

Motor mount, clutch, 4:5 ratio drive to the handwheel complete with direction reversal anti-backlash gear and a 1:1 drive to the Y axis feed screw.



and



Kicking around in the parts box are the inevitable spacers and bushes




I'm just waiting for the feedscrews to arrive from Zapp and do a trial fit of a few parts and then to take the table, saddle and knee off my mill and take them over to a friends workshop so I can do some machining on them to mount the ballnut carriers and anything else I've forgotten to do.


In a few weeks, I hope to have it all back together and usable as a manual machine once more whilst I think about the electrical/electronic aspects of the project. I have some other stuff to sort out then and might not be back on this project till after Christmas :doh:

Cheers

Bob





Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #34 on: September 06, 2012, 10:54:57 AM »
 :bow: :bow: :bow: :bow:  Dam fine machining Bob  :bow: :bow: :bow: :bow:

You have been busy  :dremel: worth the wait  , i like your design to keep the manual operation of the machine ,clever  :smart:


Rob 

Offline Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #35 on: September 06, 2012, 11:02:51 AM »
I agree Bob... That looks pretty darn good!

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #36 on: September 06, 2012, 11:49:20 AM »
:bow: :bow: :bow: :bow:  Dam fine machining Bob  :bow: :bow: :bow: :bow:

You are very kind Rob but its nowhere near the quality of your work.  :clap:

Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #37 on: September 06, 2012, 11:50:14 AM »
Thanks Eric - I'll pay you later OK?

Bob

Offline AdeV

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 2434
  • Country: gb
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #38 on: September 06, 2012, 12:54:27 PM »
:bow: :bow: :bow: :bow:  Dam fine machining Bob  :bow: :bow: :bow: :bow:

You are very kind Rob but its nowhere near the quality of your work.  :clap:


It's not that, you're not using the special filter that Rob has on his camera, the one that removes machining marks & makes everything look like it was chrome plated....  :lol:
Cheers!
Ade.
--
Location: Wallasey, Merseyside. A long way from anywhere.
Occasionally: Zhengzhou, China. An even longer way from anywhere...

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #39 on: September 06, 2012, 05:08:28 PM »
Bloody hell have I got to buy 'another' Juju doll ?
John Stevenson

Offline Ned Ludd

  • Full Member
  • ***
  • Posts: 207
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #40 on: September 07, 2012, 06:38:47 AM »
John, I think you will find they are more effective if you make your own, commercial ones are never the same as home grown, or am I thinking of Tomatoes? :doh:
Ned
I know enough to do what I do, but the more I know the more I can do!

Leafy suburbs of NW London

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #41 on: September 07, 2012, 07:45:55 AM »
Bloody hell have I got to buy 'another' Juju doll ?

I thought you must have a second one already? The fcuk-up fairy has been hovering around my workshop during the build.
I had terrible trouble with some M6 taps that just would not cut any perceptible depth of thread in clearance holes the other day :bang: :bang:

Bob

Offline John Stevenson

  • In Memoriam
  • Hero Member
  • *****
  • Posts: 1643
  • Nottingham, England.
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #42 on: September 07, 2012, 09:46:52 AM »
Funny that, i sometimes get the same problem but just by a fluke I discovered that the oversize hole is the *exact* right size for a helicoil, Phew, another ones lives another day  :med:
John Stevenson

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #43 on: September 07, 2012, 12:30:41 PM »
Good Tip John- Thanks

Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #44 on: September 09, 2012, 09:32:31 AM »
I'm kicking my heels a bit on this project at the moment waiting for parts.

Zapp say they will send out my ballscrews & nuts on Monday so until then I'm thinking about lubrication.

Just made up these to fit pipes onto  the ball nuts and a for instance oil adapter to screw into various places for oiling the ways.

The brass banjos have got little o rings set in the faces as I could not find my little stash of Dowty seals :bang: and I have  whole baccy tin of 5/16 x 7/16 O rings that I could find!



I expect I'll use clear pipe finally but just grabbed some black pneumatic nylon to check the fit as it was handy.

Lets hope posty is early on Tuesday!!


Cheers

Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #45 on: September 13, 2012, 04:48:51 AM »
Heels duly kicked for a while and now I have the ball screws and nuts in from Zapp.


Here is the nut fitted to the Y axis mount



Space is very tight on the X axis and earlier in the thread, I found that I needed to trim a bit of the nut flange.
I spoke to Zapp who assured me that the flange sa simply for mounting and did not contain any of 'the works'
They failed to mention that the flange is hardened however.

Sensitive souls should look away now.......




Time to get out the angle grinder :bugeye: :bugeye:

Lots of masking tape around the whole nut apart from the corner of the flange - it looked like it was going into an operating theatre!
Wet cloths handy to cool the patient brow at regular intervals

One of those ever so handy 1mm thick cutting discs and away I went.  Sorry no video clips just an end result.



One final last check though the parts I'd made to make sure I had not further need for a working mill and the strip down starts ready to machine the saddle & knee castings on a friends mill next week.


Bob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #46 on: September 18, 2012, 04:55:05 PM »
I spent Monday in my mates workshop attacking my Myford VMC castings on his Myford VME
It was a full day and I did not take any pictures of work in progress.
Making a bit more room for the X axis nut in the underside of the table was a bit of a pig with hard spots knocking the edges of the cutter so in the end the angle grinder was the only answer and then back to the mill. I only had to take of 2mm but it took about 2 hours :bang:

This morning I started the assembly. In with the Z axis screw. Another tight spot is in the knee and I needed a bit more room over the top of the Z axis gear to allow the Y ball nut to pass over the top.
I ended up by putting a 2mm washer (black one in the photo) under the thrust bearing.



Above the thrust bearing there is a spacer and needle roller bearing.



The spacer is an addition as the original arrangement allowed the helical gear to rub on the knee casting. This can't happen with a spacer fitted.

On with the knee and fit the gears



Adjust the gib strip and we have a working knee.



This also shows the enlarged opening in the top surface of the knee to maximise the Y travel and fit in the larger ballnut.

This photo is the underside of the saddle casting with a shallow pocket about 1.5mm deep for the Y nut carrier



And the carrier and nut in place



Until the ball screw is fitted, it is vital that a tube is retained to stop the balls falling out hence the wire through the nut.

In order to fit the saddle on to the dovetails, the nut carrier had to be removed and then fitted up though the underside to the knee. Bit awkward but doable - thank heavens for ball ended allen keys!



And in with the ball screw




I have made a start on the X axis by fitting the screw into the nut and mounting it onto the top surface of the saddle.



This shows the X axis bearing carrier that bolts onto the table, I have bored this out to accept the nut flange which wins back another 12mm of table travel.

This shows the screw at the end of its travel.




I'm stuck now until some small socket cap screws arrive in the post - tomorrow?? These hold on a oil feed to the nut - there is just no room to use the intended oil port on the flange so I'm feeding oil in at the other end.

I'll show that in the next set of photos.

That's all for now folks!

Bob







Offline NickG

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 1890
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #47 on: November 03, 2012, 11:53:13 AM »
Hi Bob,

Thanks for pointing this out, I'll be following along too now!  :thumbup:

Crikey, there's some work gone into this one too   :bugeye:


Looks great, keep up the good work.

Nick
Location: County Durham (North East England)

Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #48 on: November 03, 2012, 12:13:57 PM »
 :scratch: dunt no how i missed your last couple of posts Bob  :bang:

Very nice  :thumbup: , I will make sure I keep an eye out in the new year for when you resume work on the mill  :dremel:


Rob

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #49 on: November 03, 2012, 12:44:20 PM »
Rob, Something you might be interested in......

I wanted something to protect wiring and oil pipes across the moving section between slides and the static parts of the machine.

On the leesprings website I found tucked away in their tension spring section 'spring by the mile' well by the 3 foot length anyway.

I chose some made from just under 0.7mm wire and about 8mm bore/10mm OD and it looks the business. Minimum order is 5 lengths part no LEC026D-36-S  http://www.leespring.com/uk_product_spec.asp?partnum=LEC026D36S&springType=E&subType=
It is a tolerable screw in fit into m10 x 1.0 threaded hole to make terminations for it

There are various other sizes  - browse their extension spring catalogue around page 70 ish and scan though for free length of 12, 24 or 36" which make them stand out from the other springs.



In one place it says MOQ 10 off - elsewhere it is 5 off - I had no problems ordering on line for just 5 - I did have to wait a week or so for stock but it was worth it. I'm very pleased with them

Bob

Rob.Wilson

  • Guest
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #50 on: November 03, 2012, 01:28:03 PM »
 :thumbup: Nice one Bob .

I will have a look , i was planning on using spiro rap I use at work , steel spring may be a better job .


Rob

Offline TrueBlue

  • Newbie
  • *
  • Posts: 2
  • Country: au
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #51 on: April 27, 2013, 01:50:52 AM »
Hello 9fingers -  I have a similar mill to this which I purchased about 10 years ago, and I cam considering a CNC conversion for it.  Well perhaps a bit more than consider as I have purchased the drives for the stepper motors already :-)

Anyway, I was wondering why you chose the path of modifying the knee, with the need for the gas strut etc, rather than just modifying the quill.   This is the route I am thinking of taking.   My logic is that it appears simpler and I don't think I need z travel much large than 100mm or so.


Alan

Offline 9fingers

  • Jr. Member
  • **
  • Posts: 75
  • Country: gb
    • Info on Induction motors (Heavily UK based!)
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #52 on: April 27, 2013, 04:33:45 AM »
Hi Alan,

I decide to move the knee after considering that 87mm (my quill travel) might not be enough in the future and that I was not confident of adequate rigidity when milling in X or Y axes with the quill unlocked relying on the stepper to hold the quill.
Devising a quill drive (my Myford VMC has no quill fine feed unlike later clones from Warco etc) and a motor power locking system seemed more difficult than the knee method.
I did consider doing both, but whilst Mach3 can handle 4 driven axes, I was advised that it does not support two of them being in the same direction and being able to sum the two (or perhaps decide how to apportion a wanted Z travel between the two).

Good luck with your conversion. Maybe we will see a thread describing your work here soon?

Cheers

Bob

Offline TrueBlue

  • Newbie
  • *
  • Posts: 2
  • Country: au
Re: Another 6 x 26 Knee Mill CNC conversion
« Reply #53 on: April 27, 2013, 06:30:02 AM »
Thanks Bob,  that clarifies it.   
             
My mill  is of the Warco type and does have the fine feed which can be engaged or dis-engaged.   So I think that is the way I will go. :)

I have already converted a Sieg X3 Mill to CNC but I did not document that exercise, but I will this conversion in a separate thread.

Alan
« Last Edit: April 27, 2013, 07:05:42 AM by TrueBlue »