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Bubba
10-06-2005, 05:01 PM
Vibration is your enemy!

I am writing this little epistle in an effort to help some of the newer people and stop them from making the mistakes that I have made.

As many know, I have converted a mill/drill to cnc. This has included servos, gecko drives and ball screws which is the primary topic at hand. I have had this conversion working for about a year now and lately have found that things weren’t working quite as they should and did originally. Namely, I was hearing some strange noises from the Y axis and on occasion and the drive would fault out when homing or getting near the maximum limit and at times, there was a “ticking” noise in the X axis. This is not a good sign, so I figured out (after a few weeks of procrastination) it was time to tear into the machine and have a look see at the problem(s).

Being a noob myself, there have been many times that I have not used proper speeds, feeds etc and my machine has complained, groaned, snapped bits and generally vibrated like crazy. Well, when I started to dig into things, I found several problems:

1. I had forgotten to “lock-tite” a couple of the “set screws” for the ball nuts in their holders.
2. I had used “set screws” to lock down the ball nuts in their holders.
3. It is either possible that I had failed to tighten a screw (or vibration had loosened it).
4. I found the Y nut had actually rotated and was hitting the base casting (this was the “strange” sound).

Lessons Learned:

1. When contemplating your assembly, be like an aircraft pilot, set down and WRITE out a check list of what you think will be needed (AND FOLLOW IT).
2. Vibration is your enemy! (Can’t say this one enough). If a process if vibrating, find out why and fix it!
3. Lock-Tite is your friend. Use it liberally.
4. Double check your work (and checklist). It is easy to see the end of the assembly and the desire hurry up and try it!
5. If this is a re-assembly, manually check your limits before you try a power slam into them. (Don’t even ask:{(
6. Did I mention, Lock-Tite is your friend?
7. While allen head set-screws may look nice, use socket head screws when you can. I used 10-24 set-screws originally and now have 10-24 screws. You can tork down a whole lot more with a 5/16 allen wrench than you can with a 5/32!

While I am on the subject of setting up ball screws, there is/was an excellent tutorial on the http://www.industrialhobbies.com/ site on how to line up the ball screws and the bearings on the end of the axis. I highly recommend you find this and use the principals.

Oh, by the way; vibration is your ENEMY:}) and so is getting in a hurry so you can see it run!

Hope this helps someone :cheers:

ViperTX
10-06-2005, 09:44 PM
Well I had an experience today with my Jet 18MD mill. I'm making the ballnut support block from 7075 AL and I had drilled a 1/2 inch hole and was going to open it up to 0.8750 for the 15/16-16 Tap. Installed the boring head....had just started the boring process....which "is very boring" when I noticed that the mount was moving up and down in the machinist screwless vise....so, I stopped and changed to some lower height parallels so that the vise would have a better grip.....well, didn't get it quite centered...but it was close....."figured no problem" the hole will be a little oblong for a bit.....well a credit to my clamping because when I was backing out the carbide bit....all of a sudden there is all this noise and vibration....I noticed that the mill table which was locked down was moving back on forth in the y-direction....geesch talking about scary.....I finally got it out...checked everything and it was allright...ran to Lowe's and picked up a 3/4 inch Deming bit.....I have no idea why it's called that....anyway drilled out the hole and made it round again.....back to the boring head and everything came out just fine.....