Enco Table Top CNC Retrofit

[cmnewcomer]

I know this subject has been beaten to death but I'm hoping the form experts will bear with me with my questions about converting my mill to CNC. I actually posted on the Practical Machinist forum and was told this forum is better for what I am doing. I've read many posts and have been able to digest only a fraction of the technical details. With that said let me begin with where I'm at and see if folks can help with the barrage of questions.

Requirements:
1. Low budget hobbyist interest.
2. Maximize existing hardware which is an Enco tabletop mill.
3. Maximize existing software and knowledge of such software. I have TurboCAD and just recently purchased TurboCAD Pro V12 and the TurboCNC plugin. I think I will still need to purchase a controller such as Mach 3 if I'm understanding this part of the equation.
4. Simple CNC needs such as crossing out gear blanks for grandfather clocks.

Current Configuration Plan:
1. Enco tabletop mill.
2. Nema 34 740oz stepper motor from HomeShopCNC. I have only purchased one so that I can begin fabricating the motor mounts.
3. Rolled ballscrews .631 x .2 pitch HomeShopCNC with preloaded ballnut. I have clearance problems so this is probably the maximum size I can work with.
4. Geko 201 drivers. Here again, I purchased one to begin researching and setup of the case.
5. 48V/20A unregulated power supply.
6. Timing pulleys and belts. I will be retaining the handwheels for manual operation so will need to use belts. I also plan to use a 1:1 drive.
7. 7201 40 deg. Contact angle, dual-Load Angular-Contact Steel Ball Bearings—ABEC-3. I realize these are not optimum but fall into the low budget part of the equation.

Immediate work to be performed:
1. Design and build motor mounts. I have purchased .5 and .25 inch aluminum and will begin this as soon as the steppers and aluminum arrive.
2. Design and build thrust bearing housing. I’m not sure if I will use the existing ballscrew supports or fabricate an entirely new setup. Suggestions?
3. Determine how to attach ballnuts. For the X axis, I will have plenty of room but for the Y axis, I will need something creative as I have very little room. See attached photo. Suggestions welcome!

That’s certainly enough for now and hope folks will have some suggestions.

Best Regards.

Carl

[Bubba]

OK,
as the saying goes, been there done that, and I offer the following:
1. Loose the hand wheels! I did this based on many posts in various forums and haven't looked back since.
2. I use Turbocnc and works great for me.
3. I used the existing bearing mounts for the right side of the X and on the y axis and should have on the left side of the X axis.
4. I made new mounts for the ballscrew nuts out of aluminum and am now replacing the y axis with one of steel (my fault for several crashes)
5. Look at my web page (tag line) for some of the ideas.
6. I made a mistake in the way I did the drive for the X axis and lost some travel. should have made an extension for the drive and used the orignal bearing mount (see 3 above)

contact me if you need additional info or help.

Bubba

http://bellsouthpwp.net/A/r/Arts_home_page/cnc/

[cmnewcomer]

Bubba,

Thanks for the feedback as it certainly helps to clarify some of the things that have been puzzeling me. I was thinking about boring the rear of the Y axis block to insert the bearings recessing them an extra 0.25 in order to insert a spacer which would be larger than the outer diameter of the bearings to provide a way to load the outer race. In addition, I believe the bearings may be smaller than the current hole in the mill base. With the outer race held captive, I could then have a threaded section on the front of the ballscrew to preload them?! I realize this is not optimal from reading the posts but it seems it would work for light duty work.

Now that I see the ballnut supports you fabricated, I feel better in doing it myself. I was curious about using aluminum for these supports especially the Y axis which has a fairly long lever arm to cause failure. I think I may use cold rolled steel for that support and aluminum for the X axis. I'll need to get the ballnut thread size and pitch to begin working on that immediately.

Best Regards.

Carl

[Bubba]

Carl,
If your using the "standard" 5/8 (.631) type of ball screw then, the thread is 15/16 -16. I also got a tap from MSC to do the final chase of the threads in the mounts after I had started the threads on the lathe.

I agree with you on the Y mount and that is why I am making one out of steel. I have this gut feeling that is the problem. I had several hard crashes with the aluminum one. Also, be careful on the orientation of the return tube on the nut as there is not much clearance under the base. While it is not good practice, I had to turn the return tube so it is 90 degrees left or right from verticle. I attempted to hold the original with a 6-32 setscrew and locktite and the nut was not actually "seated" on the mount. This time, I will take the time to do it right and tighten the nut in the holder. If necessary, I will scrape the back side of the holder and this time, the set screw is going to be 1/4" with a brass button under it (along with the locktite) Hopefully this sucker won't move! This time the raw block is bigger in cross section also to hopefully give more seating area on the bottom of the saddle (block is 1 3/4 square) In order to maintain y travel, I am going to have to trim the slot in the base some (square it up and take out about an additional 1/4"). I use the entire 7" of travel quite often and don't want to loose any if I can help it!

The plan is to finish the new holder up this weekend and then start the teardown

Later and good luck on yours.
Bubba

[cmnewcomer]

Bubba,

Thanks for the information on the ballnut thread size. This will let me get started on the mounts.

I have purchased one Nema 34 740oz stepper and was going to use a 1:1 drive ratio. However, in re-reading some of the feedback I got from HomeShopCNC, I just noticed that they recommend 60v to 68v which I assume is the power supply output. I just purchased a 48v 20a power supply so probably have already screwed this up a little. Does this mean I will need to drive this using a 1:2 ratio? What other options would be recommended?

Any feedback would be greatly appreciated.

Best Regards.

Carl

[bluechips]

Carl,
My conversion is very different than yours, due to budget constraints, the requirement to swap back to manual within 15 minutes, and a servo-biased mindset, however, I was wondering if you had given consideration to the problem (in my enco machine, anyway) of the gibs on X and Y?

I may be the only person that has had any problem with the gibs on the enco mill drill, since I haven't heard any mention of it on the 'web.

My Y axis tapered gib was never completely controlled by the adjuster screw, as it came from enco. a combination of the adjuster screw to gib fit, the adjuster screw rocking in it's threads, and the expected play in these threads created a very noticeable difference in the drag (gib pre-load) when changing directions.
I finally ended up making a "pacman" shaped spacer to go under the gib adjuster screw head so that the movement caused by the play in the adjuster screw threads was eliminated.

[bluechips]

Carl,
I also noticed an issue with the quill (Z) feed on the enco. My Enco mill/drill exhibits somewhat odd behavior when changing directions, etc. It's not just predictable backlash, and it doesn't smell like errors with the worm wheel or worm (I'm assuming you'll be using the stock Z feed, if not then ignore). I am currently leaning towards the theory that the 6mm key which attaches the tapered clutch/spider handle unit to the quill feed pinion/shaft has play (it must have some clearance, since the tapered clutch/spider has to slide in "normal" operation).
The odd behavior exibited is that the Z axis does not respond to the motors actions as would be expected.
I added a dial indicator to the Z axis (quill) 10 years before adding the servos, since I had problems with the quill feed from the get-go. This is why the problem with the Z response was immediately apparent when I was testing the servo set-up.
I am planning to build a replacement tapered clutch piece with a set screw to bear on the 6mm key , and no spider handles. I am hoping this will eliminate this source of unpredictable "play" in the z axis, and should only add a couple of minutes to the manual to CNC swap over time.

[Bubba]

Carl,
I don't work with steppers, but from what I remember reading, the lower voltage will affect the maximum speeds available more than anything else. Based on this, I would probably run the 1:1 ratio and see what happens. If you try increasing the speed by a 1:2 ratio, I would worry about the torque available at speed. Torque falls off as speed increases in a stepper and you might not have enough for your low speed work. NOTE: Just a guess on my part.

Bubba

[cmnewcomer]

Bluechips,

I've never been satisfied with the X/Y axis on my Enco mill but not coming from a machinist background did not realize this was not normal. I have tightened the gibbs to what I would think is too tight to eliminate table movement and have noticed differences in drag when changing directions too. I may look into your recommendation during this conversion to try and improve the movement and drag. Thanks for the information.

As for the Z axis, I suspect I will encounter the same problems as you so will look into this now and watch for suggestions from you and/or the forum if they become available.

Bubba,

I was actually thinking, but probably referenced it wrong, of make the motor side the smaller pulley assuming this would allow for more torque also realizing that I would loose some speed. I will need to research this more but I like your idea of just setting it up 1:1 and testing as it should not be a problem to change ratio's especiallly if I plan for it now.

Best Regards.

Carl

[Bubba]

Carl,
If your are talking a reduction ratio, then you will compound your problems. Best bet like you say is to do the 1:1 and see what happens!

I agree with you on the gib situation. Am in the process of rebuilding my Y axis (long story), but have been trying to think of ways to "lock" the gibs in one place. Some mills have a locking screw on the opposite end to do just that. BUT, making one to fit similar to what is on the adjusting end will be a royal PITA to try and do in my shop as it would have to be done with hand tools! Probably the "shim washer" idea will be the best compromise.

Bubba

[bluechips]

Okay, I've attempted to attach crude renderings of my tapered gib "quick fix" for the enco mill/drill. The gib adjuster screw is a fairly straight forward replacement for the original unit, but it is two pieces. An allen bolt (or differrent head type if you're so inclined) threaded right up to the head, plus a threaded spacer to match the slot in the tapered gib. Assemble the spacer and allen screw assembly (to each other) "good and tight" . This unit, alone, will take up the slop introduced back in China between the tapered gib, and its adjuster screw. But, what I've found, is that the adjuster screw (even the "new improved" version I've just tried to describe) STILL allows significant play in the tapered gib.

I feel this is due mostly to the gib adjuster screw "rocking" in its threads.
Watch it some time and see if you can see it move with relation to the rest of the saddle. Or just notice the change in "drag" when changing directions.

The "pacman" shaped spacer I've attempted to attach is what I came up with as a quick and dirty solution for this problem that, so far , "works for me".
it is installed between the gib adjuster screw and the saddle. It is intended to limit the lateral movement of the tapered gib to the clearance between the "new and improved" adjuster screw, and the gib, which is determined by how close you can fit the two pieces.
Unfortunately, this is a "cut and try" process. It took me two trys to get an acceptable thickness for the "pacman" spacer.
You can (and probably should) test the "gib drag" manually, until you're happy with it, before firing up the steppers.

I haven't included any dimensions, since I can't bring my self to believe that anyone else recieved a chinese mill/drill with 80 to 90% american threads (but with metric heads?!) and my gib slot dimensions have been "tinkered with" since the first bush was in office.

[Bubba]

bluechips,
Thanks for the info, will have to give it try and it has to be better than what I have now. There are times that simpler is better.

Thanks,
Bubba