Author Topic: Servo Driven 4th Axis for CNC Mill  (Read 66643 times)

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #25 on: January 09, 2014, 02:50:36 PM »
Then of course the other end. This cover is oil filled within, but there was no gasket or other sealing, so it went back with a smear of Blue Hylomar which is usually pretty good stuff
Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #26 on: January 09, 2014, 02:58:20 PM »
Next in sequence needs to be the brake assembly, so I can't put off deciding what to do with the broken bit. I think that it is probably a steel forging - could be cast possibly but it's steel not cast iron.

I decided to silver braze it first - if it proves not to be strong enough the fall back plan is to turn off the end, axially drill and tap it, and bolt a cheek on the end. Bally awkward thing to clamp. I ended up 'buttering' both parts with silver braze, holding one in the vice and the other in pliers and putting them roughly together, letting it cool a bit, then clamping them together with extended mole grips and re-melting. It's important to not only keep the alignment but minimise the thickness of the joint. The silver braze will absorb some of the steel and alloy with it if thin enough.

Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #27 on: January 09, 2014, 03:05:28 PM »
Although the brazed joint is nice and even, the operating 'face' of the shoe isn't perpendicular to the shaft as it should be. The part must have bent before it broke. I'll skim the face tomorrow - the intermittent cut will show if it's just stuck on with flux or has properly brazed  :lol:

 . . so onwards and upwards !


Andrew
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #28 on: January 10, 2014, 03:43:43 AM »
So up early and skimmed the brake shoe. Happily the brazing stood up to the intermittent cut - ended taking about 45 thou off both sides. Remains to be seen if it stands up to working conditions !

Andrew
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #29 on: January 10, 2014, 08:49:40 AM »
So - now to re-assemble the brake and see if it works.

Here's the assembly:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #30 on: January 10, 2014, 08:50:41 AM »
And here's where it has to go:
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #31 on: January 10, 2014, 08:52:51 AM »
Ah . . it won't go in as an assembly - needs assembling in situ  :bang:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #32 on: January 10, 2014, 08:58:13 AM »
So that WAS all good fun  :lol:

Now did it work ?

No - it broke first time I actuated it  :bang:

I'm not entirely surprised, so we'll have to revert to plan B  :clap:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #33 on: January 10, 2014, 08:59:55 AM »
So first make a suitable disk chosen from the extensive stocks of quality traceable bars made from a handy bar end  :clap:

Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #34 on: January 10, 2014, 09:03:56 AM »
Trim it roughly to size by taking big gulps with a beefy end mill, then fettle it a bit so that it fits. (by heck it was TIGHT !)

There is presumably quite a torque on the brake shoe when operated, so before I loctited the screw in, I welded the 'heel' of the sector to the shaft. Then it was a case of re-assembly in situ AGAIN !
« Last Edit: January 10, 2014, 10:37:14 AM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #35 on: January 10, 2014, 09:06:30 AM »
 :ddb: :ddb: :ddb: Well I'm pleased to say it works  :ddb: :ddb: :ddb:

I've re-assembled the air actuator rack and cylinder, and am operating it blowing air from an air duster in the appropriate port for 'brake' or 'release'
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #36 on: January 10, 2014, 09:09:20 AM »
There is a solenoid valve that fits on the end of the cylinder that diverts the two ports so one releases when the other operates (otherwise the inactive side of the cylinder would be blocked shut). I've not mounted it yet as it's coils seems to be 110 V and I need to operate on 24 V . I will probably re-wind the coil - it's all a bit of a mess currently :
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #37 on: January 10, 2014, 09:10:58 AM »
So with a few ups and downs at least this phase of the build has had a happy ending  :thumbup:

. . .lots more to do yet on this project. Probably the motor mount is next on the list

Andrew
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #38 on: January 12, 2014, 10:16:05 AM »
A bit of playing around with CAD and some careful measurements showed that it was just possible to make a flange to convert from the end fixing SEM servo motor to the flange mount with external screws needed to be able to adjust the 4:1 gear train mesh for minimum back lash. The original stepper motor relied on oversized holes to get some movement, but as I was CNC'ing the flange I opted to give the hole a slot form with a 2 mm 'travel'

So first we have a CAD drawing and a 20 foot long bar of 100 mm x 20 mm bar stock
« Last Edit: January 12, 2014, 10:46:52 AM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #39 on: January 12, 2014, 10:19:36 AM »
Now in an ideal world that flange would have been 110 mm square, but you use what you have  :lol:

So all we need do is slice a 100 mm chunk off in the Pedrazzoli cold cut off saw, and remove the bits we don't want - how hard can it be  :ddb:
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #40 on: January 12, 2014, 10:26:32 AM »
There that was easy wasn't it  :thumbup:

Well yes, but I confess that is the third flange I made  :( First one I broke a 6 mm carbide end mill as it was starting the hold down slots and it left too much mess to re-use. Second one was perfect except when I revised my careful measurements of hole centres and did an average of hole to hole spacing, although my figure was correct I put the wrong one in the CAD drawing  :bang:

Still, third time lucky and now we have a flange that fits and looks reasonably presentable. Here it is as a mock up with the motor balanced on top in it's eventual home. Not bolted on yet as I'm awaiting some 5/16" UNF cap head bolts to hold it on.
Andrew Mawson
East Sussex

Offline Brass_Machine

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #41 on: January 12, 2014, 10:28:47 AM »
Your shop seems to be well stocked with tools... I like how you take this problem and solve it taking all issues in stride with a matter of fact attitude.

Eric
Science is fun.

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

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #42 on: January 12, 2014, 10:33:24 AM »
Thanks Eric, hills are there to be climbed  :lol:

Now I reckon that there is an oddity there  :scratch:

If you look carefully there is a horizontal cap screw that used to bear on the original stepper motor flange to adjust gear mesh, but it is pushing the gears OUT of mesh, not as I would expect, INTO mesh. Presumably a pair of gears will tend to separate if anything when they are under load and running, not pull into each other, so I would have expected that adjuster to work the other way. I may bolt something to the side of my flange to take a screw with a pad on the end that would allow uncrewing the adjuster to pull the assembly to bring the gears further together. All suggestions welcome.

Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #43 on: January 12, 2014, 10:46:12 AM »
So the next thing to sort is the fitting of a suitable pinion to the SEM motor shaft. The original stepper motor had a nice accurate 16 mm shaft, and a 20 tooth 1.5 mod gear fixed by 5 mm key and a grub screw, with the grub screw trapped by a circlip. I would have liked to re-use this gear, if only for economy, but the SEM motor shaft is a rather under sized 5/8" resulting in a 4 thou slop.

I had considered that perhaps Loctite would bridge the gap, but better sense prevailed and I bought a replacement with a 'pilot bore' from HPC gears. Loctite say up to 1.5 thou gap and mine would be 2 thou circularly.  Incidentally let me pour praise on HPC. A phone call at 15:30 on Friday resulted in the postman bringing me their parcel on Saturday morning - how fast is that ! They also were able to provide some drive pulleys and a belt that I need for the encoder, but more of that later.

So I need to mount the gear in a collet, bore it to the rather arbitrary motor shaft diameter, and slot a key way to match the 1/8" key in the shaft.

I've also decided to fit a single lip oil seal to the shaft of the motor, as the gears run in an oil bath.

« Last Edit: January 12, 2014, 11:50:50 AM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #44 on: January 13, 2014, 05:50:48 AM »
This morning I've bored the gear hub to size, broached it's keyway, and drilled and tapped for a 6mm grub screw to line up with an existing and convenient flat on the servo motor shaft
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #45 on: January 13, 2014, 08:02:19 AM »
I can't mount the motor yet as those 5/16" UNF cap screws haven't arrived, so time to investigate the ROD450B/125 encoder and it's mount.

The TNC355 Heidenhain controller can only accept either 18,000 or 36,000 counts per rotary table revolution. Now my table worm has a ratio of 90:1 and the gear train has a ratio of 4:1 and the encoder gives 125 count per rev. Multiplying up we get 90 x 4 x 125 = 45,000. Divide  36,000 by this  and we get 0.8, or a ratio of 20:25.

Somehow I need to gear the servo motor to the encoder, slowing the encoder by a factor of 20:25

Here are the bits we are dealing with
Andrew Mawson
East Sussex

Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #46 on: January 13, 2014, 08:10:52 AM »
The current plan is to mount the encoder at the side of the servo motor on a specially milled housing allowing me to run a timing belt between them. The servo motor will have a 40 tooth pulley, and the encoder a 50 tooth one. Mounting the encoder facing the other way will shorten the whole assembley which is a 'good thing'

Masking tape mock up below  :ddb:

Andrew
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #47 on: January 14, 2014, 07:57:09 AM »
This morning's job was to make an adapter for the ROD450B encoder. It was to allow movement on slots to tension it's drive belt, and to bring the shaft position to the same axial point as the SEM servo motor.

Only two little 'funnies' during this process:

Firstly we had a power cut as I was downloading the G code file to Heidenhain controller from my PC, it wouldn't have been an issue, but I'd not saved the CAD drawing of the cut outs - no big deal as it's only a few minutes work to re-do it

Secondly, for some reason Featurecam refused to cut one of the adjusting slots, claiming that the tool was too big despite using the same tool for the other identical slot. I had to lie to it !

So here we are:

a/  the blank adapter cut from another bit of that (was) 20 foot plank of 100 x 20 aluminium - the notch is for clearance on the servo motor

b/ same thing holding the encoder

Andrew
Andrew Mawson
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Offline awemawson

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #48 on: January 15, 2014, 07:10:12 AM »
Today the Postman brought me the oil seal for the Servo Motor shaft, and the 5/16" UNF cap screws, so I've been able to mount the motor and try the gear mesh, which seems ok. No doubt it'll sound better when filled with oil - it's just lightly oiled at the moment as I'm not convinced the original housing flanges are oil tight and while it's on the bench I don't want it dribbling everywhere !

The servo motor is 140 volts 26 amps peak, so I was surprised how it runs quite well on 24 volts at less than an amp for testing.

Now I'm working on the CAD for the housing that holds the encoder onto the back of the servo motor, fighting tangent snap modes in Featurecam  :scratch:

Andrew
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Offline Pete.

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Re: Servo Driven 4th Axis for CNC Mill
« Reply #49 on: January 15, 2014, 09:52:34 AM »
How does the machine Interface with the 4th axis drive electronics Andrew? Do they simply both comply to a standard?