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Servo Driven 4th Axis for CNC Mill

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awemawson:
Its been an ambition to have a 4th axis on my CNC mill for several years, and to this end I've been collecting suitable bits. Frequently people adapt manual rotary tables, in fact I did one myself many years ago using a stepper motor and a 4" table, but to be properly integrated into my Beaver Partsmaster it needs to be servo driven.

The other issue is that standard rotary tables end up on the left side of the mill table so that the motor sticks out forwards - as I have an automatic 16 station tool carousel on that side my 4th axis needs to be a mirror image

awemawson:
I thought I'd cracked the problem when I 'caught' a Nikken 4th axis positioner on ebay a few years back - but when it arrived it proved to be stepper driven not servo  although it is 'handed' correctly :bang:

Never mind, prompted by the success of Jim McCracken on the CNCZone forum getting his working I've decided to put a servo motor on the table of the Nikken


So this is what was there originally:

awemawson:
And here are the bits that together hopefully will drive the table in future:

a/ SEM HT 30H4 -44 with ROD450B 125 count sine wave encoder and integral tachometer (more about the encoder later!)

b/ Bosch Servo drive card rescued from a Bridgeport Interact

c/ Bosch special choke for servo card from same source

awemawson:
So far I have removed the stepper motor and started dismantling the rotary table. The table has a pneumatically operated locking brake, and it had jammed in the on state. Fighting my way into the mechanism proved to be anything but simple, and has required making some special tooling, but I'll leave you to ponder on this shot of the bit that had me stumped for a couple of days, while I go and have my supper  :ddb:

awemawson:
Ok so what's the big deal?

Well firstly from the top there is little indication what you are dealing with, and there seems to be two concentric threads and a retainer with two forms of locking. The retainer has been slit so that a hex headed bolt pinches the slit gripping the thread, and also there is a grub screw bearing on an almost detached 'crescent' of thread to press it into a locked state. They really didn't want that to come adrift!

The grub screw was in a most inaccessible place and didn't seem to have a standard hex socket - I ended up grinding the end off a 3 mm one so it was short enough, then gently reducing its a/f size a few thou with a diamond file.

The retainer is bored for a pin wrench - so first of al I applied my Facom adjustable pin wrench. The retainer won and I sheared the pin on the wrench - lucky they screw in !  :bang:

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