Delrin Cross Slide Nut

ddickey said:
Would I need to make a new lead screw or just mold the nut onto my current one?
Click to expand...
There are some You tube clips showing how a guy heats the screw to the plastic soft melt temp & then uses a shaped heated split form to to clamp in to two halves ..one either side of the rod & squash them on to it .
I think he had three cheap digital thermometers onn the pieces to ensure he got his heating temps just right .
He managed to thermo form a a reasonable sized block of Delrin & then transfer it to his mill to get a true copy of the dimension

. I can see that that could also be done on a lathe with a four jaw chuck & a bit of ingenuity b
There can be the problem of it being a tad too tight ... I suggested to some guys thinking of copying it that perhaps they could used one of the aerosol sprays of stove coating to add a clearance coating to the thread . Then using a bar cutting tool & carefully ground cutter tip to clean out the paint using the lathe to give the acme thread requirements of speed & travel rate .
Once the thread is thermoformed the rest of the " Blob of plastic" can be shaped up drilled & tapped with ease to get it close to the original shape .

One word of warning keep it as thick /meaty as you can , but not so meaty that it catches up on things & prevents you getting the normal range of movements on your lathe.

Try looking for " Delrin Hot thread forming " or " Thermo forming threads in Delrin " on the You Tube index list or similar .

I'll see if I can find some of the ones I viewed as well..... a few minutes later ...
youtube.com/watch?v=rBIf_d_pAhQ
This was one of the early un heated methods . he's used tube

The heated version I saw was using angle iron to get th sides of the outer faces reasonably square .

youtube.com/watch?v=EVW7Q469RnA

Similar to this one but the rod is gently & evenly heated to the ideal softening temp at both ends with a gas torch , so are the two angle iron clamping lengths .
The angle iron clamp is clamped up in a 6 inch bench vice


This one may also be helpful for it shows where a source of excessive back lash can also be found on the cross slide shaft nut . .
youtube.com/watch?v=NqF_ETWvBCA
 
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I made one for 7/16 x 10 acme (southbend 9A cross slide) and had extra length of acme rod, so knurled the end of the rod and threaded the delrin nut on a few times and cleaned the threads up nicely so it was a smooth fit.
 
DuPont recently produced a series of videos showing Delrin outperforming generic acetal at least in every test they chose to include. But they are also interesting just for seeing how the two materials perform in a variety of applications. Here is one example, and you can see the rest by clicking through to their channel:

 
4gsr said:
As much time and expense put into trying to heat and form a plastic around a thread, I can single point a thread on a piece of Delrin quicker and cheaper.
Click to expand...

The point of this method, though, is that it produces an *exact* fit. Practically zero backlash. That is an incredible feat with any method of thread cutting.
 
I had a similar problem on my small Flexispeed lathe, where the main nut had worn and had a lot of lash. I moulded Polymorph around the leadscrew and then cut it into a block. I then attached this block to the existing nut. It has removed all of the lash, is still light enough and smooth enough to use and, so far, is lasting well.

James.
 
Jon,
I know you said "practically zero backlash" but you cannot also, have an "exact" fit on a thread. It will not work. And even if you have created your "practically zero backlash threaded nut", you still need to wind out past the backlash and back in again to avoid take up problems.
Granted Delrin is a great product. And I do have a Delrin evanut on my mill. But you cannot, (on a home scale), eliminate backlash and dodge basic machining practice. One of the 1st things we learned in machine shop was wind out, then wind back in to zero.

Cheers Phil
 
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