[cffellows]

A few months ago I took some tentative steps to begin the process of converting my RF-30 to CNC. I bought some SF1605 ball screws with ball nuts. These had no machined ends, just ball screw end to end. I also bought some NEMA 23 Steppers rated at 3 amps, 370 Oz In. I finally began work on in earnest on this project about a week ago. I made ball nut attachments to replace the lead screw nuts. I also machined down the ends of the (Hardened) ball screws with a carbide insert. And began making the machined extensions for the ball screws to fit my milling table ends.

Here's the original Y-axis lead screw nut and the attachment I made out of aluminum...

Attachment 208016

The new assembly shown in place on the underside of the Y-axis carriage...

Attachment 208018

And the machined extension added to the assembly...

Attachment 208020

With the ball nut attachment block...

Attachment 208022

And the assembly in place on the Mill / Drill...

Attachment 208024

Today I began work on the X-Axis ball screw machined extensions...

Attachment 208026

I have also today ordered a Gecko G540 4 axis stepper controller/driver.

Chuck

[Bubba]

Chuck,
Excellent start! Sounds like you have studied the situation and have a well thought out plan. Look forward to watching your progress.

[cffellows]

Thanks, Bubba. Here's the attachment for the X-axis ball nut. It's made from 2" x 2" x 1/4" angle iron. It's been cut and milled to the shape you see here. Also, the contact surfaces have been milled flat and square.

Attachment 208208

Here's a couple of pictures of the X-axis assembly.

Attachment 208210

Attachment 208212

The timing pulley is temporarily mounted on this end so I can turn the screw. In the end, there will be a hand wheel on this end and the timing pulley / stepper motor on the other end.

Chuck

[Bubba]

Chuck,
Couple of thoughts.
When I did mine, I found after a short period of time the X axis mount would loosen up for some reason (even though it was locktited) so I drilled a couple of holes and inserted spring type roll pins and have had any movement in over 10 years.
As for hand wheels, I lost mine based on several conversations that I had in various forums. Haven't missed them at all. The jog keys and MDI commands are more than adequate for moving the table around. Some also indicated the handles present two potential problems. One is of course during rapids, your rotation rate is way above what one can do by hand and the handle will unbalance the assembly and the other is that flying handle can do bodily damage to you if you get in the way!

Also, a question as to what bearings your using for the ball screws? I notice your keeping the original castings.

[cffellows]

The handles are easily removable. I'll probably take your advice and leave them off and only put them on if needed for some reason.

The sealed ball race is a 17mm x 30mm and will be installed opposite from the end which has dual thrust bearings. I hadn't planned on installing any ball bearings on the Y-axis since it also has the thrust bearings. I assume the thrust bearings will handle the lateral load of the timing belt to the stepper motor?

Chuck

[Bubba]

Actually, I "think" in the original setup, the bearing surface for the lateral load was the cast iron of the mount and the thrust bearings did only that (handle thrust load). But then again, I could be wrong.
Just make sure you take all the axial "slop" out when you assemble things to remove as much backlash as you can.

[cffellows]

Yes, of course, you're right. The shaft does not bear against the ID of the thrust bearing. I could replace the thrust bearings with regular ball races, but don't know who well they would stand up to the thrust.

I'm planning to use dual 1/4" x 20 set screws at 90 degrees on the outer collars to maintain pressure against the thrust bearings. I'm kind of worried that these might keep working loose, especially after your experience on the ball nut mount...

Dang, nothing's ever simple, is it???

Chuck

[Bubba]

I used angular contact bearings (7291) in the original mount. As I remember, had to do a little boring to get them to slip in. IF you go that route, be sure to cut a relief so the inner race can spin and not bind on the mount. Don't ask how I know about that one>})

[cffellows]

The mill/drill is back in play, ball screws and nuts installed on both X and Y axes.

Attachment 208330

Attachment 208332

Both axes move freely with no binding and there is no discernible backlash. Next I'll work on installing the stepper motors, then on to the Z-axis.

Chuck

[Bubba]

Looks real nice!
Be careful if you try to manually mill with those ball screws as they will back feed real easy.

[691175002]

I have a soft spot for the RF30 since it was my first conversion. The round column is a real bear though, especially since the quill becomes a floppy mess once you extend two or three inches.

Gotta be real creative to use both drills and endmills in the same setup.

[cffellows]

I'm concerned about the best way to fix the timing belt pulleys to the ball screws. the ball screw assembly has dual opposing thrust bearings on either side of a web in the end piece which screws to the table. A shoulder on the assembly presses against the inner thrust bearing and the timing pulley presses against the outer thrust bearing. Minimizing backlash requires the timing belt pulley to be held firmly against the outer thrust bearing.

My initial plan is to secure the timing pulley to the shaft using two 1/4" x 20 set screws at 90 degrees. I would cut shallow contact flats on the shaft. Anybody have any input on how well this will work? Any other suggestions for securing the pulley to the shaft? I feel like I need some kind of adjustment which precludes the use of spring pins.

Chuck

[Bubba]

Chuck,
When I put my pulleys on the shaft, they are held rotationally by use of a key. Then the end of the shaft is threaded and the assembly is tightened up to remove all backlash in the bearings using a nut backed up by a jam nut to make sure it all stays together.

[LeeWay]

The best way is with a nut of course as Art mentioned.
Second best is a keyway and set screw combo.
Sets screws would probably be my last option with the third being through drilled roll pin and seat it tightly with Bellville washers.
Not a good choice for really small shafts, but yours looks stout enough that through drilling an 1/8" hole won't take too much away.
Looking good, BTW.
I have the HF geared head round column mill that I intended to cnc initially. The spindle is what deterred me for awhile. Then getting a Novakon Torus killed that project.

[hoss2006]

My initial plan is to secure the timing pulley to the shaft using two 1/4" x 20 set screws at 90 degrees. I would cut shallow contact flats on the shaft. Anybody have any input on how well this will work? Any other suggestions for securing the pulley to the shaft? I feel like I need some kind of adjustment which precludes the use of spring pins.

Chuck

I've done this many times and it works great. Put a dab of loctite threadlocker on the setscrews and it won't slip or come loose.
Hoss

[cffellows]

Thanks for the input! I think I will go with the intermediate solution of a key and a setscrew. Pretty easy to implement and gives me the added security of the key.

An another note, I'm wondering if I could get by with a smaller stepper on the Z-axis? The ratio of stepper rotation to axis movement is the same on all three axes, with shaft at 1/2 motor speed. The X & Y steppers are 370 oz in. Would a 175 oz in on the Z axis be too little ooomph?

Chuck

[cffellows]

Got started on the Z-axis mount. Here's a picture of what will be the stepper motor mount. It's 3.625" x 5.25"

Attachment 208734

I decided to mount the plate on the face of the Z-axis crank assembly.

Attachment 208732

I don't think two, 10-24 screws is enough support, so I decided to add a couple more.

Here I'm making a drilling jig to bore the two extra holes in the casting.

Attachment 208736

It will also serve as a drilling guide for boring the mounting holes in the aluminum plate.

Attachment 208738

And here is the casting with the two addition threaded holes.

Attachment 208740

Here's the mounting plate with the mounting holes in place.

Attachment 208742

Next I'll need to machine the mounting holes for the stepper motor and finish machining the contours around the outside.

Chuck

[Bubba]

Chuck,
Make sure you make a spacer go go behind your mounting plate to fill the space between the mounting plate and support the bearing race as it will move in and out if you don't. Measure and make it accurately as this is one part of controlling backlash. IIRC, I made mine out of a short piece of pipe. Also, loosen the two screws that hold the fine downfeed housing to the mill head and tap it forward to take up some of the backlash in the pinion gear for the quill. Makes all the difference in the world in backlash.

[cffellows]

Chuck,
Make sure you make a spacer go go behind your mounting plate to fill the space between the mounting plate and support the bearing race as it will move in and out if you don't. Measure and make it accurately as this is one part of controlling backlash. IIRC, I made mine out of a short piece of pipe. Also, loosen the two screws that hold the fine downfeed housing to the mill head and tap it forward to take up some of the backlash in the pinion gear for the quill. Makes all the difference in the world in backlash.

Thanks, Bubba, I saw that recessed bearing and figured a spacer would be in order to keep it in place.

This morning I finished the Z axis mounting bracket.

Attachment 208786





I would liked to have done it on the Tormach down at the TechShop, but I'm still struggling with getting a drawing processed all the way through FreeMill, the free CAM program I'm using for the moment. So, I just machined it manually. Boy, you're right about the axes unwinding on you if you don't have the locks clamped down nice and tight. Even with a 3/16, 2 flute endmill running at pretty high RPM I could see the slot beginning to creep on me.

[Bubba]

Looks great! You should be up and running shortly:})