I'm getting ready to buy some acme thread and want to know if I should go with 3/8-12 that I saw Ger21 suggest to someone on another thread or 1/2-10? I'm concerned about the whipping of it since it will be about 4-5 feet long. I'm not so much concerned about speed - I just want it stable.

Thanks!

Warren

-For all this help from the board, maybe I'll become a gold contributor! :)

Even 1/2" may whip at 4-5ft, depending how fast you want to spin it. But there are a lot of factors involved. If you go to 3/4", it will take a lot more power just to spin the screw. Using a higher lead screw, like 2 start 1/2-8 will let you spin it slower, but again, you may need bigger motors because it doesn't give as much mechanical advantage. You could also mount the screw under tension, which will help to minimize whipping.

I think I suggested 3/8 acme as a replacement for allthread. I personally would use no smaller than 1/2" for any size machine. There's really no price advantage for using 3/8".

4 or 5 feet? I would go 1/2 inch, anything to help with the deflection over such a length.
Is it possible to make mounting blocks for the ends?

The X axis on the machine that I'm building is close to 4'.
http://www.logantele.com/~jhonaker/cnc/router/cncrouter.htm

I decided to use 3/4" ACME for all of the rod.
I got a pretty good deal here: http://dependableacme.com/
They also sell the nuts.

I"m planning on using 3/8 standard threade rod for the jgro machine, using 127oz/in steepers what kind of speed can i expect??

mrbaseball....count the threads per inch....that will give you the basic number of revolutions to travel one inch....if you have 10 threads per inch then it takes 10 revolutions to travel one inch.....if the motor does 100 RPM then theoretically you could travel 10 inches per minute.