[BMSTECH]

:nono:I need to delete this

[komatias]

Hi John,

I too have a KRV that I am about to convert. I have the ballscrew lengths for the X and Y axis but the dealer could not tell me the diameter off hand.

Would you be able to tell me what diameter your screws are?

[BMSTECH]

I think that they are 25mm with 5mm pitch

[BMSTECH]

I am back to convert my Z axis to CNC.
My mill could be fitted with a Z axis mechanism made by Proto Trak as shown in a previous post fitted to a larger KRV 3000 mill.
I don't want to reinvent the wheel or waste time on a flawed design.
I have removed the quill feed trigger mechanism.
I would like to replace the treaded rod with a ball screw that actuates the quill via the feed stop yoke.
My ball screw would be located where the threaded rod was, not in front of it as with Proto Trak and many other designs.
A 1605 250mm ball screw could pass up through the lower treaded rod mount, a ball nut-yoke made and bearings mounted.

[BMSTECH]

The original treaded rod is supported by a 3/8" hole in the top mount and a 5/8" hole in the lower. As it just moves up and down during operation, these are clearance holes that measure 9.85mm and 16.05mm. The centre of the holes are 18mm from the face behind. A modified BF12 floating bearing would be mounted below the top support and a modified BK12 fixed bearing below the lower support at the Quill nose. A 1605 ball nut would need 2mm ground off the flange to clear the face and more off the LHS to clear the original ruler blocks. A new Yoke that accommodates the ball nut would be minimised in height to maximise Quill travel.

[BMSTECH]

The ball screw would be driven from the lower end by a T5 timing pulley around 40mm diameter. The shaft end would extend around 40mm below the Quill nose. A small 200W AC servo motor would be mounted close by on a angle bracket supported from the LHS face of the mill.
So if you are following this so far, Is it a crazy idea? Has someone done this already? Will it work well?

[komatias]

I will send you detail of how i did mine in a fw weeks when i am back from holidays

[BMSTECH]

The Advantages of this design.

Small, low profile size that fits neatly on the face of the Mill head.

The ball screw is mounted very close to the quill minimising the leverage on the Yoke and reducing the flex that others have experienced here.

The small 200W Servo Motor uses a Drive that is compatible with the existing X and Y Drives.

No modification to the mill face that prevents return to standard manual feed mode.

Mounting is independent of the Tramming adjustment.

Around 100mm of Quill travel should be adequate for most jobs.

The Disadvantages.

The modified Bearing blocks would be attached to the face by drilling and tapping the face.

A 16mm Ball screw is the largest that will fit through the lower mount, will this be adequate?

The Ball nut flange needs to be modified.

Around 10mm of Quill travel will be lost due to the thickness of the BF12 floating bearing.

Another 10mm of Quill trave will be lost due to the length of the ball nut.

The timing pulleys will hang around 40mm lower than the Quill nose.

[BMSTECH]

My ballscrew and bearings arrived today. I reduced the very end of the shaft beyond the keyway from 10mm to 9.7mm diameter so it would just locate in the top mount on the mill face. I tilted the mill face 90 degrees to the left to photograph ballscrew supported by the mill face mounts. Around 7mm needs to be removed from the base of the BF12 and BK 12 bearing blocks.
BK12 shown upside down on ballscrew.

[BMSTECH]

See what you can make of my sketches.

[chevydyl]

im starting a build on an Acer 3VS, Bridgeport clone, but i am looking at a ProtoTRAK K4 for desing influence, where did you get the 16t pulley for the motor side? i too have 19mm shafts on my Allen Bradley servo motors. they are 2.2kw motors but are drive limited to 1kw, the Stock Drive component pulleys have a hub,and i dont want that, plus the shipping from them is $$$ ive googled and searched ebay for a 16t HTD 5M pulley with the only luck being stock drive, or outside of US company but also has the hub
thanks
BTW your private message storage is full

[BMSTECH]

I have used Google Sketch UP to model a new quill yoke that accommodates the slightly modified ball nut. The model looks hollow because I am new to 3D drawing and I don't know how to fix it?

[BMSTECH]

Turning and milling the new ball nut yoke for the quill.

[BMSTECH]

New Yoke detail

[BMSTECH]

Fit New Yoke to Quill with original Cap Head screw.

Fit 16mm Ballnut with notched flange to Yoke with 6x M5 screws.

Remove dummy ball retainer shaft as new 16mm Ballscrew is treaded through via the lower guide hole.

Check clearances and alignment of shaft with upper guide hole in preparation for mounting zero backlash bearings .

[BMSTECH]

The ballscrew as supplied new from China had a 0.06mm run out in the middle over a screw length of just under 200mm. It needed a deflection of around 2mm to tweek it back to less than 0.02mm. Run out was then checked at both ends of the screw and was found to be concentric with the machined bearing surfaces just beyond the screw section. Run out of the coupling end of the shaft was then checked and 0.06mm was measured just 50mm from the bearing surface. By supporting the shaft at the floating end and the coupling end tip and pressing at the coupling end of the screw section, the run out of the thrust bearing section of the shaft was corrected to less than 0.02mm. With the shaft then supported in V blocks at each end on the 10mm diameter sections, run out was checked all along the shaft and was less than 0.02mm in each zone. The shaft was binding in the same place with each rotation when the thrust bearing block was tightened up. This is a lot better now but not perfect. Still got work to do getting the thrust bearing block mounted and aligned to my satisfaction.

[BMSTECH]

Designing a Servo Motor mounting plate and selecting suitable timing pulleys and a belt.

[BMSTECH]

My timing pulleys and belt arrived from Naismith. The small pulley needs to be mounted on a 12mm shaft which leaves nothing to secure it. I decided to make my own with more meat for the keyway and grub screw. I drilled 12 x 7/64" holes on a 18.3mm PCD 15mm deep in the end of an aluminium shaft and then turned the OD to 18.3 to expose half the drilled holes. With the edges hand filed, it looks like it will do the job.

[LeeWay]

That looks great. I have never taken the time to make any gears myself other than a few wooden ones that were more decorative. Those were hand made.

I have seen a few different ways to tackle this sort of thing. Looks like yours will certainly do the job well.
Since you already had the factory made pulley, I would have went a different way. I would have added a collar on it instead. Held in place with epoxy. Then bored it out. Just seems like less math to me. I'm down with less math when possible.

Also I have not seen any steppers that have a keyway. Do most servo's use one? Seems like a much more reliable method than dual sets screws alone, but does add to the cost I'm sure.

[BMSTECH]

Hi Leeway,
The Math is pretty easy with 12 teeth each 30 degrees apart. Just need to have the radius 9.15mm and half the radius 4.575mm and half root 3 by radius 7.924mm. My X and Y axis is CNC controlled so I just typed in the MDI G0X4.575Y7.924 and changed from positive to negative as I moved around the PCD. There would be minimal wall thickness when the 12mm bore is machined in the 12 tooth pulley that I purchased from Naismith. Both flanges would fall off and there is very little to epoxy a collar to. The only option would have been to epoxy the pulley to the motor shaft. I have some more details about the servo motors in previous posts.
John