Lead screw whip

[spalm]

I know this subject has been covered a lot, but I am still really confused. I was hoping some of you elders could help me out.

I built a JRGO type machine and have been having a blast with it. But the X-axis (the long one) lead screw is whipping like crazy. I really notice this during rapids, but am pretty sure it influences my slower movements. I am using 3/8” 12 pitch ACME screw, 200 oz steppers, and LoveJoy couplers to go from 3/8 to the 1/4 motor shaft. The lead screw nut is a home made Delrin type. On the far end I am using a ball bearing with a nut on each side captured in two pieces of MDF.

I can think of at least four things wrong;
The lead screw is only supported at one end, causing the motor bearings to take a beating.
The lead screw is in compression, so any tendency to whip is encouraged.
The ball bearing is taking lateral thrust (which I don’t think it is built for).
The LoveJoy coupler allows the lead screw to “pull out” again encouraging whipping.

So if I want to fix this right, I am thinking about changing to a 1/2 inch screw to make it more ridged and mounting bearings on both ends.

Now the questions:
1) What is the maximum rpm for a particular lead screw? (I am doing 60 ipm rapids)
2) Is 60 ipm to fast for a MDF/gas pipe design or a 3/8 rod?
3) Are different kinds of ACME rod stiffer than others? (3/8 rod is MSC 01205897)
4) Can someone point me to mountable end bearing supports that would be more professional than my captured roller bearing? (Or even an end bearing support that requires some aluminum tooling on my part.)
5) How do these bearing supports work? Do they have a set screw or C-clip or require nuts?
6) Do I need to have the ends turned down and tapped? (I will if that is what I should do, but I’m not sure how to get it done right now.)

I have been studying the catalogs and can not seem to understand all the varieties. I don’t mind spending some money on the problem if it will yield something that I can transport to my next machine.

Thanks in advance,
Steve

[HacknHew]

Steve,
I can tell you about the bearings....what you need are angular contact bearings, preferably mounted at the same end as the motor is located. Not only will they bear a radial load, they can also tolerate an axial thrust load. It takes two bearings facing one another, separated by approx. 0.100" (think of a bearing block with a 0.750 thru hole, with 1.00" counterbores on each side that the bearings lightly press into but bottom out before butting up against each other.) The block is rigidly mounted to your frame, the screw passes through each bearing, and is retained by a nut/jam nut arrangement. Tighten down the first nut to remove any backlash, then run the jam nut tight up against the first nut. This requires that the screw be machined to fit the bearings and to have a threaded end. Once this assembly is set up, the far end of the screw can ride in a simple radial ball bearing (the screw end again machined for fit). Here's a link to a source for angular contact bearings:
http://www.bearingsdirect.com/produc...=category&id=4

For some reason I've only been able to find them in metric sizes, and the local machine shop guy says that's the only way he's ever known them to be sized.

[HacknHew]

Ooop.....disregard that link for the bearings. Those are HIGH-dollar!!
Do this one instead....same supplier, but a little less precision.
http://bearingsdirect.com/products/i...&id=4&subid=78

[spalm]

Thank you so much, that was exactly the kind of response I was hoping for.

I went off to Nook Industries to see what they had if I wanted to buy something off the shelf and discovered a great document on lead screws called "Technical Introduction - PowerAc" with charts for max speed, max length, types of bearings, etc. Good stuff.
http://www.nookindustries.com/acme/AcmeCatalog.cfm

Now I need to figure out how to get the ends machined.

Steve