acme thread combos and thread mixing

[calaber40]

im having some problems with my acme screws being to long and getting some whipping as they turn. what i have now are 10 turn 1/2'' 60'' long for x and y .if i go to 5/8''acme 8 turn for more speed ,it will not have to turn as fast. do i have to change the z as well , and can i program my software to accommade for the difference .i guess ill be using mach 3 as im just cutting foam and 1/2'' mdf. another question is that i have managed to get rid of my backlash on my screws by fitting them perfectly to the end bearing blocks, but will the back and forth motion eventally blow out the bearings, should i be doing something else as well. this is my first build ,and would like to see it run for a while before i need to do repairs on it, do to wear and tear.replies greatly appreciated . ps i wish i was a master at cnc like you pros here .my hat goes off to you. cheers.

[BillTodd]

How difficult would it be to fix the lead screw and rotate the nut. (i.e. mount the motor and rotating nut onto the gantry )

[calaber40]

not sure how to do that , is there a picture of one i can see here

[calaber40]

i also have acetal nuts , can you put some type of lub on the thread ,like oil .will it hurt the nuts

[ahren]

For a screw that long, you really want multi-start ACME. A 5 start ACME screw will cut the rotational speed by a factor of 5 for the same linear speed, drastically decreasing whip. This will let you work with your existing bearing blocks as well. Another benefit of 5 start nuts (besides reducing whip) is that they are more efficient. Furthermore, they keep your steppers running at lower RPMs, where they have more torque -- it's a win/win/win situation. They cost a little more, but it's definitely worth the upgrade.

If you're worried about your bearing blocks, you might try a sandwich of thrust bearings. Check out the "parts" page on my site for an example of how to do this. With this setup, you have thrust bearings taking the thrust load, and leave the radial bearings to handle only radial loads.

Finally, for lubricant, a silicone lubricant works OK for Delrin (acetal), but for the most part you shouldn't need any if the nuts fit properly.

Best regards,

Ahren
www.cncrouterparts.com

[cheetahcnc]

Originally Posted by calaber40 not sure how to do that , is there a picture of one i can see here

This setup is pictured here on CNC Zone. It is a very impressive design.

http://www.cnczone.com/gallery/showp...0/ppuser/93736




Jim