Author Topic: Set-Over Centre  (Read 46874 times)

Offline Raggle

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Re: Set-Over Centre
« Reply #25 on: February 21, 2012, 04:04:00 PM »
I'd call this optical and guaranteed vertical punching

http://www.schsm.org/html/marv_klotz_29.html

see the next 2 pages to complete your understanding.

(I still haven't made mine :) )

Ray
still turning handles  -  usually the wrong way

Offline wongster

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Re: Set-Over Centre
« Reply #26 on: February 21, 2012, 06:48:55 PM »
Cool stuff!  Thanks Ray.

Offline Fergus OMore

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Re: Set-Over Centre
« Reply #27 on: February 24, 2012, 03:07:22 AM »
I've just sent what is as near a copy of George Thomas's simple centreing device 'explanation' and drawing as I dare without  infringing copyright.

The device is so simple that there is virtually nothing that I can add.

Can anyone else- add or explain please? :doh:

Offline wongster

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Re: Set-Over Centre
« Reply #28 on: February 24, 2012, 10:23:22 AM »
Hi Norman,

I received the jpg of the 2 pages, thanks.  Can't really read it as the jpg is a little too small and when enlarged, the text is to blur to make out any word.

Regards,
Wong

Offline Fergus OMore

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Re: Set-Over Centre
« Reply #29 on: February 24, 2012, 11:37:42 AM »
I'm afraid that for reasons of copyright, I am unable to copy. I deliberately only tried to print the drawing.

Simply make a D bit- or don't make one. If you use a bit of .500 round- all you allow for is 0.250 at the edge of the work rather than zero with a centreing device.
« Last Edit: February 24, 2012, 12:17:26 PM by Fergus OMore »

Offline Miner

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Re: Set-Over Centre
« Reply #30 on: February 24, 2012, 02:45:02 PM »
Wong,
Everybodys methods and favorite techniques are a bit different. When it needs it, I make a layout as a general check for miscounting handwheel turns. But if your leadscrews are in pretty good shape and dependable for measurement? I don't use any center punch marks at all. Locating your marks and starting the hole with a center drill by coordinate measurement works real well. It does take a bit of time and practice to get fully used to using that system though. That's where those edge finders come in. If it was good enough system to use for the super accurate Moore jig borers and grinders? Then it's more than good enough for me. Having dial indicators for measureing the slide movements, Or a DRO makes the job that much easier. It is a bit slower way to work since your using a center drill to start, Then switching over to your drill. But if you factor in the fairly accurate center punching time, This method could be a bit quicker.

If my memory is correct, It's called the Cartesian coordinate system? But the correct name is not that important. It's the technique that is.

Pete

Offline Fergus OMore

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Re: Set-Over Centre
« Reply #31 on: February 24, 2012, 03:43:17 PM »
Yes, it's the cumulative  Descartes stuff which many of us use.  It is far less prone to making mistakes with 'Simple Arithmetic' going from making what is in effect establishing a zero at each centre drilling. Of course the zero, may not be accurately determined.

Someone mentioned 'Tubal Cain'- not this Johnny Come Lately but the Tom Walshaw variety and he set off to knock the so called experts who were all called to centre on two scribed lines- and none of them could.

Interesting stuff. And it all gets worse with worn leadscrews 'et al' :smart:



 

Offline wongster

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Re: Set-Over Centre
« Reply #32 on: February 24, 2012, 08:58:02 PM »
Thanks all for your input. I'll go it without centre punch for the next piece and use a corner as reference. Using the centre hole location is convenient the drawings uses that as the reference. I read from one book (can't recall the name) that if the drawings uses a certain point as the datum, all measurements are relative to that datum. Using a corner of the workpiece is more convenient for me as I'm more familiar with it.

Regards,
Wong

Offline wongster

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Re: Set-Over Centre
« Reply #33 on: February 26, 2012, 11:40:47 AM »
The Base

I started off my Sunday morning redoing the dimensions of the Base of the Set-Over Centre using the bottom right corner of the workpiece as datum (hope I'm not using the wrong word here).  The drawings from Hemingway have the location of all features relative to the centre 5/16" BSF tap hole, which I followed when fabricating the Slide.  Counting the number of turns on the dial is easier with the datum from the bottom right corner and I was moving the table in one direction, thus not having to worry too much about backlash.

The stock was cut almost to length on the bandsaw and trimmed to 3" as called out in the plan.  This is the 2nd time I'm hitting the exact dimension - a real boost of confident.  Wishing for more as I progress...


Redoing the drawings with the bottom right corner of the workpiece as datum.
 

The stock was held in the vise and carefully tapped down to ensure full contact on the parallels beneath.  The layout lines can be seen in the pic.  No punch mark this time as advised in the forum.


Measuring the tip of the Proxxon Edge Finder. It actually measures 0.2", kind of strange from Proxxon which has everything else in metric.


Finding the edge in Y axis.  The table was moved over by half of the tip of the Edge Finder to zero the spindle axis to the edge of the workpiece. X was next.


Centre drilling of the 5 holes for later operations.  This is the first time I centre drill all the holes before drilling.  I always like to centre drill and drill through each hole before moving to the next location to reduce the number of times I have to move the table (and save on counting...).


Drilling the holes using 1/4" drill.


A pair of machinist clamp was deployed as limits for the slot to be milled.  There are 2 slots in this part; one connecting the 2 holes on the right and the other, the last 2 holes on the left.  This will save me from having to count the number of turns I've made to focus on the job at hand.  I plan to make mill stops in the near future for all 3 axes to ease the process.


Begin milling the slot with a 1/4" slot drill. I started with depth of 0.2mm per pass but went on to 0.5mm.


Slot done.  The 3/8" slot 1/4" deep was next.


A piece of scrap used as depth stop for the Z axis.  Wanted to use machinist clamp for this but I couldn't locate the other 2 pieces I bought.


Done! Time to test if the cap screw will fit.


Unfortunately not... The supplied 1/4" BSF cap screw's head measures slightly larger than 3/8" and the 3/8" slot drill from Sherline cut the slot at 0.372".  The 0.372" seems to be consistent with the slot I did in the Slide before widening.  I will be buying another one locally for further testing.

Till the next session, be blessed.







Offline andyf

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Re: Set-Over Centre
« Reply #34 on: February 26, 2012, 12:19:47 PM »
[quote)... The supplied 1/4" BSF cap screw's head measures slightly larger than 3/8" and the 3/8" slot drill from Sherline cut the slot at 0.372".  The 0.372" seems to be consistent with the slot I did in the Slide before widening.  I will be buying another one locally for further testing.

[/quote]
Hi Wong
Turning the head of the screw down by a few thousandths would be easier than widening the slot.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline wongster

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Re: Set-Over Centre
« Reply #35 on: February 26, 2012, 12:30:10 PM »
Hi Andy,

You're right.  I may do just that.

One question which I need your input.  I'm re-reading the part on screw cutting the 5/16" BSF to provide a tighter fit.  Does screw cutting means using the lathe to cut the thread using a single point tool?  I'm not sure if I can do that with my proxxon.  This is my first encounter with BSF.

Regards,
Wong

Offline DaveH

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Re: Set-Over Centre
« Reply #36 on: February 26, 2012, 01:16:15 PM »
Wong,

Nicely done :thumbup: :clap:  good use of the tool makers clamps.

The 5/16" BSF can always be changed to a 'near' metric one.
If one uses a split die it can be allowed to cut on the high side, adjusted until you are happy with the fit. Also if the threaded part is long, then at least a partial cutting on the lathe keeps it on the straight and narrow. The final 50% of the thread is completed with the die.

 :beer:
DaveH
(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline wongster

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Re: Set-Over Centre
« Reply #37 on: February 26, 2012, 06:23:03 PM »
Hello DaveH,

I've the split die  :D  I'll give that a shot.  The female tap hole has already been done, there goes my chance to change to a near metric one.  My experience so far on using a die to cut threads have not been at all pleasant, even with a chamfer at the end of the workpiece.  Let's hope I'm able to get it on this time and change the experience.

Regards,
Wong

Offline MadNick

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Re: Set-Over Centre
« Reply #38 on: February 27, 2012, 08:52:13 AM »
Glad to see you are getting stuck in!

BTW I found the same problem with cap bolts, the diameter of the head can vary. The time I didnt check this I had to take a few thou off as has been recommended - I made and used a mandrel to do this.

Nick

Offline wongster

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Re: Set-Over Centre
« Reply #39 on: February 27, 2012, 09:40:51 AM »
Hi Nick,

Do you have a pic of your mandrel?

Regards,
Wong

Offline andyf

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Re: Set-Over Centre
« Reply #40 on: February 27, 2012, 09:50:01 AM »
Wong, I had to turn down and slightly reduce the length of the heads on a load of them. I took a bit of round bar, drilled and tapped it (M5 in my case) in my 3-jaw, then screwed each Allen bolt in to it and did the turning. The tool pressure tends to screw the bolt tighter into the bar, si it is secure.

Andy
(with apologies for interrupting you and Nick)
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline wongster

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Re: Set-Over Centre
« Reply #41 on: February 27, 2012, 11:39:23 AM »
Hi Andy,

Thanks! Didn't realize it is as simple as that! I imagined something more complex... Silly me.


Regards,
Wong

Offline Tony Wells

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Re: Set-Over Centre
« Reply #42 on: February 27, 2012, 01:31:33 PM »
You may also see issues with the concentricity of head vs threads. Fasteners generally aren't regarded as precision components. It's standard practice to make allowance for heads not running true with threads.
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Offline wongster

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Re: Set-Over Centre
« Reply #43 on: February 27, 2012, 06:06:11 PM »
I'm now wondering the reason why the plan calls for 3/8" slot for the screw head given that the 2 screws provided has diameter of their head at 3/8" being the smallest when measuring at one side of the head.  If I'm to press it in, I wouldn't be able to move them easily.  I'll do as Andy said, to trim the head just a tiny bit to have it seat in the slot.

Regards,
Wong

Offline wongster

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Re: Set-Over Centre
« Reply #44 on: March 03, 2012, 11:59:52 PM »
I continued with the work on the Base and completed it over 2 sessions of about 2 hours each.  I took it very slowly when milling the other slot with a 10mm slot drill due to the vibration and loud noise.  The feel on the handwheel while feeding didn't feel smooth at all.  This may be caused by the ER16 spindle chuck I'm using which extended the tool out quite a bit.  I didn't have that problem when using the Sherline's endmill holder but the largest holder I've from Sherline is 3/8"...  Some rectification was done to the Slide's slot as one side is tapered.  The 2 components now fit nicely together and the sliding one against the other is smooth.  4 more parts to complete before I can call this done.



Moving over to the start.  The more I use the mill, the more confident I get in getting to the spot I want using the handwheels.  The right limit of the slot was set with the tool maker's clamp on the right of the job against the saddle.



Moving to the left limit and setting the clamp.



Milling the 1/4" slot with the Sherline 1/4" slot drill.  The Sherline's endmill holder in use here.



Slot done.



The 10mm slot drill in the ER16 collet chuck was employed to cut the counterbore slot.  To set the depth, I plunge the slot drill to the depth of 1/4" and fit another piece of the toolmaker's clamp on the column bed.



Slot done.  I went at 0.25mm per pass to minimise vibration.  The cap screw sit flush with the top surface of the Base.



The centre hole enlarged to 6.4mm to tap 5/16" BSF.


Testing fit.  No side wobbling encountered.  I'm pretty pleased  :)

The instruction calls for the 2 x 2BA holes to be done on the drill press.  I was running out of time to set up the drill press (its under the bench...) and so stand the part in the vise and carry on.



Locating the side and dialed to the centre of the workpiece.



Centre drill and drill through with a 4mm.  I'm at the limit of the z travel...



A piece of card stock used at the back to check if I'm right in the middle.  Not too bad..

The part was then flipped over to drill and tap the other 2BA hole on the other side.  This completes the work on the Base.



View from the back where the 2MT Arbor will be screwed in from.



The front.  I'm wondering if the screws are a little too long.  The drawing shows them as almost flushed with the surface.  Can those who did this confirm if I need to shorten the screws?

The rest of the work will be mostly done in the lathe.  From the plan, I'm left with making the 2 adjustment screws, the Centre, and the 2MT Arbor.

I'm hoping to get back to the shop real soon!

Regards,
Wong

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Offline DaveH

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Re: Set-Over Centre
« Reply #45 on: March 04, 2012, 07:08:12 AM »
Wong,

That is very nicely done, good use of the toolmakers clamps- clever idea.  :thumbup: :clap:

Milling is at the best of times a slow process, and you did a good job with your mill :clap: :clap: :clap:

Looking good :thumbup: :thumbup: :thumbup:

 :beer:
DaveH

(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline wongster

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Re: Set-Over Centre
« Reply #46 on: March 04, 2012, 07:16:27 AM »
Hi Dave,

Thanks. Really feel good everytime I read your comments despite knowing that I did screw up on some parts. Thanks for the encouragement!

Regards,
Wong

Offline krv3000

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Re: Set-Over Centre
« Reply #47 on: March 04, 2012, 10:32:31 AM »
HI wong Very well done

Offline Fergus OMore

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Re: Set-Over Centre
« Reply #48 on: March 04, 2012, 02:11:11 PM »
Question! How are you going to cope with the three dimensional effect of Pythagoras when all is said and done.

Euclid only did it in two dimensions, if I recall :coffee: 


Offline Miner

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Re: Set-Over Centre
« Reply #49 on: March 04, 2012, 03:11:15 PM »
Norman,
The dude that thought that up was bit behind times. If? I'm reading your referances correctly, A dial indicator across the top till it reads true will straighten out that theroy. Royal did much the same on their no longer built screw adjustable centers with a built in level.

Pete