Replacing the lead screw and nut on a mill.

Obviously...

VERY well done, both in the machine work and the documentation. It occurs to me to wonder if this method would work well on heavier machinery? I wonder because I feel that cutting threads is going well beyond my pay grade for the foreseeable future, if not till the end of time! This appears to be a great solution for one so machining illiterate. I have a US Machine Tools vertical mill (sized as a Bridgeport) that is pretty loose on the X, and this sounds somewhat doable, even for me!

Thanks for sharing your work!!
 
Hello Redlineman:

There are many mills and lathes out there, large and small, that use Delrin for the lead screw nut. You can thank Evan Williams for the idea. He is one of the most competent and innovative machinist that I have run across. His original post can be found here:

http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way

I took his concept and adapted it to my machines. As shown in my original post a holder of some type is need to support and position the nut. Sometimes this is the more difficult step in the process since obtaining accurate measurements is sometimes difficult. But once you have the holder replacing the enclosed nut is very easy. I have never had to replace one yet, the cross slide on my lathe has been in over two years and the backlash is now up to 0.0015".

Regards,
Jim
 
Question Jim --- I see how the threads are formed but at what point do both halves fuse together again? Maybe I missed something?

"Billy G"
 
Hello Bill: If my memory serves me correctly Delrin (acetal) begins to heat flow at just over 400 degrees Fahrenheit. When the process ends the two halves are fused together in a single piece that you will not be able to separate. One area to be careful of when heat flowing this material is too much heat. The process of heating the screw and allowing that to in turn heat Delrin takes 10-15 minutes. Some folks want to hurry this along so they apply more heat to shorten the process time. This results in the screw becoming the source of too much heat and the Delrin softens to the point where it oozes out of the form.

Regards,
Jim
 
JimSchroeder said:
Hello Bill: If my memory serves me correctly Delrin (acetal) begins to heat flow at just over 400 degrees Fahrenheit. When the process ends the two halves are fused together in a single piece that you will not be able to separate. One area to be careful of when heat flowing this material is too much heat. The process of heating the screw and allowing that to in turn heat Delrin takes 10-15 minutes. Some folks want to hurry this along so they apply more heat to shorten the process time. This results in the screw becoming the source of too much heat and the Delrin softens to the point where it oozes out of the form.

Regards,
Jim
Click to expand...


Just a wild thought: What do you think of the idea to use a buzz-box or better welder to resistance heat the acme screw ? It might work nicely to ease up on the temp curve & give a more consistent heat. I might be overestimating the current capabilities of a buzz box. Just sayin'.
 
-->Bill G. I can t find it at the moment, but a while ago when I was looking into this process, someone, it may have been Evan, tried pulling a fused piece apart. It proved extremely difficult and the plastic tended to tear rather than separate on the fuse line.

Cheers Phil
 
All I can say is WOW! Nice work and a nice write up too. What really caught my attention is how neat and clean your shop is. Very nice!
 
Hello Uncleharry, I do not know anything about buzz boxes so I have no idea if that would work. Even heat is what is required, once you reach the temperature where flow begins you will see a small amount of excess begin to exit at the ends. That is the time to remove the heat. It helps if the shaft is supported in the correct position so that it does not sag at this point.

Regards,
Jim

PS - The clean shop is a phenom that comes and goes.
 
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