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Alexander Engraver to CNC Miller Conversion

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philf:
An update to my machine.

Since I first got the CNC running I realised that keeping with the ACME screw for the Z Axis was never going to be satisfactory.

The stepper drove the screw via a 1:4 timing belt drive reduction and then a 1:2 hypoid bevel gear. I had problems with speed and backlash.



I recently bought a Steinmeyer 25mm x 5 pitch C5 zero backlash ballscrew off eBay for £70 which was a bargain.

First job was to design in the ballscrew. I wanted to make a unit which could be easily fitted in the bosses for the Z nut and the Z bearing.



It was too long (850mm and I needed 370mm) and neither end was machined.

I used my home made toolpost grinder to shorten the screw. (Before anyone says anything - I did cover the lathe and thoroughly cleaned it afterwards even though I knew no abrasive particles had got through.) The ballscrew was protected with cling film.



Because the ends of the screw were plain I had to put a centre in one end so I put one end in a collet and supported the other end in the fixed steady so that I could face and centre it.



Using a carbide tool I turned down the screw. The screw was hardened to a depth of about 3mm and the surface finish was excellent. Once I got through to the tough core the finish deteriorated and I ended up using a HSS tool to finish the diameter for the bearings.



At Harrogate I treated myself to a set of external screwcutting inserts and a holder. They made a neat job of the 15mm x 1 pitch thread.



I wondered about trying to cut a keyway in the screw for the pulley but the screw was so hard I decided just to machine a couple of flats at 120 degrees and to make matching tapped holes in the pulley.





The complete assembly:



And in the machine:



I've lost about 75mm of Z travel as a consequence of the mod but hopefully have done away with backlash and I know that I can run it at three times the speed of the ACME. (It would probably run faster but 1,000mm/min is fast enough for me.)

Final job is to make a curtain out of something flexible to stop stray chips getting on to the ballscrew.

Then I must get back to work on my clock and my loco.

Phil.

Rob.Wilson:
Very nicely done Phil  :bow: :bow: :bow: cracking job :thumbup:

Rob

philf:

--- Quote from: RobWilson on June 11, 2013, 04:43:04 PM ---Very nicely done Phil  :bow: :bow: :bow: cracking job :thumbup:

Rob

--- End quote ---

Thanks Rob.

How's your machine progressing?

Nice little T & C grinder you've just acquired.

I have a Quorn T & C which was bequeathed to me by a mate.

I've just been watching a video of someone using his CNC mill to sharpen the flutes on end mills with a 4th axis - hmmmm...............



This guy has done some excellent CNC videos.

:beer:

Phil.

Meldonmech:
Hi Phil,

                  Smart  conversion, well modded, are you going to cut your clock plates on the machine?


                                                   Cheers  David

philf:

--- Quote from: Meldonmech on June 12, 2013, 02:50:55 AM ---Hi Phil,

                  Smart  conversion, well modded, are you going to cut your clock plates on the machine?


                                                   Cheers  David

--- End quote ---

Hi David,

That's the plan. I will also cross out all the wheels on it. I'll cut the wheel teeth using my 4th axis and a fly cutter (I'll cut the tooth form for the flycutter on the CNC.)

Cheers.

Phil.

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