Zero Backlash LH Trapezoidal Thread Cross Slide Nut, From Delrin

[Ulma Doctor]

My good ol' Shenwai SW900B is showing signs of excessive slop at the dial.


excessive slop for me is right around .050"

after pondering materials to construct a new nut from, delrin was immediately apparent.
its tough and structurally sound, it's easy to get and cheaper than other materials too.
so delrin it is!!!

i procured some 1-1/4" black delrin and planed the billet to usable dimensions on my Ammco 7" shaper

here is video of the planing operation:

after planing the billet,
i cut off a slightly larger than necessary piece and reduced it to final dimensions on the shaper, using a simple round nose grind.

the OEM nut is constructed from bronze ans is very rectangular in shape, with rounded corners.
i copied the dimensions to the millimeter and transposed the centerlines of the longitudinal axis and a transverse drilling for the nut retaining bolt

i special ground a HSS bit for the corner rounding operation and went to town on the nut



after cutting the profile on one side to satisfaction, i flipped the part in the vise and reacquired zero,
then matched the radius with the cut before


after i finished the blank, i punched and drilled the blank- then tapped the left hand trapezoidal threads.
there is zero backlash between the leadscrew and the delrin nut, but the leadscrew can be turned with very little effort- YIPPEEE!!!!!

i then drilled and tapped the retainer bolt to M6, to reuse the OEM bolt.

Only after completing the nut, did i transpose the dimensions to paper.
without further adieu, my version of the LH trapezoidal thread cross slide nut!




i'll be installing soon!

stand by-
same bat station, different bat time!

 

[mikey]

Great job, Mike. It will be interesting to see how well it holds up. Thanks for sharing.

 

[C-Bag]

I've always wanted to see how Delrin would do in crosslide or any lead screw nut. Especially how an adjustable one would hold up. Isn't Delrin tougher than brass?

I need a new X nut on my Enco RF30 and a new crosslide nut in my Atlas 7b shaper and probably screw too.

 

[Cadillac]

I’ll be curious to see how long delrin last. I use splined couplers at work that are a plastic combination. The oem ones from the dealer look alittle different and feal harder. They look like they have a fiber reinforcing it. Where as the aftermarket ones which are half the price look like a shiny delrin material. Well the aftermarket ones strip right out on the splines if jammed the slightest or overloaded. The oem ones last for years. I would think brass is more durable. On the other hand I would rather replace just the nut than both screw and nut??

 

[C-Bag]

I got onto Delrin over 20yrs ago when our leased box machine kept going down. The main ram pin that first formed the box would break over time. It was steel and looked beefy. They went to a hardened pin and it didn't last as long. One day the service man came in and I saw him whacking away and looked in and he's driving this piece of black plastic in the hole! He said it was Delrin. I was shocked and thought how could this be? He told me the secret was it was a little oversized and would actually peel the extra material off as he drove it in. It never went down again.

Plastics are even more crazy than metal designations. I've run into those parts that seem to be fibrous and they do feel hard. Wonder if the aftermarket is truly Delrin or? PETE, UHMW or some other alphabet soup designation? How do you even tell if there's no marking? It isn't like you can do a spark test

 

[Cadillac]

I saw a YouTuber name AVE. He is very knowledgeable about plastics. He does a lot of tool tear downs and reviews. He always seems to know the material just by markings or simple heat test or by scratching the material.
I’ve also seen precision lead screws with a zero backlash plastic type nut so they must be up for the job just what exactly is the material idk. Good luck.

 

[kb58]

I recently replaced the cross feed lead screw and nuts on a Takisawa TSL-800 lathe, and went with bronze. The reasoning is that it was used daily for 40 years in the machine shop it came from. It's in my garage now, used once or twice a week, and I just turned 60. The math says I won't have to mess with it again. With plastic, it's more of an unknown.

 

[RJSakowski]

I got onto Delrin over 20yrs ago when our leased box machine kept going down. The main ram pin that first formed the box would break over time. It was steel and looked beefy. They went to a hardened pin and it didn't last as long. One day the service man came in and I saw him whacking away and looked in and he's driving this piece of black plastic in the hole! He said it was Delrin. I was shocked and thought how could this be? He told me the secret was it was a little oversized and would actually peel the extra material off as he drove it in. It never went down again.

Plastics are even more crazy than metal designations. I've run into those parts that seem to be fibrous and they do feel hard. Wonder if the aftermarket is truly Delrin or? PETE, UHMW or some other alphabet soup designation? How do you even tell if there's no marking? It isn't like you can do a spark test

Delrin has a very characteristic odor when it burns. UHMW will smell more like candle wax. Ultem and PEEK have very little odor although Iltem is a characteristic transparent amber color and PEEK is an opaque beige color. Another plastic which has better mechanical properties compared to Delrin is Ertalyte (PET-P).

I find a burn test to be one of the best ways to identify plastics. Rather than an open flame, I use a soldering iron. It helps to build up a library of known samples to test against.

 

[machPete99]

In a recent post on PracticalMachinist someone said they replaced crossfeed nut with delrin and fount that knurling operations did not work as good:

Which method to reduce cross-slide backlash?

About 1/2 turn (60 thou) backlash on a Sheldon I've just brought "online". The screw shows light/reasonable wear on visual inspection, and backlash is about the same even at the far end of travel where there would be zero wear; so the bulk is in the nut. Machine a new bronze nut? No acme...

www.practicalmachinist.com

 

[chips&more]

UD, if there is a problem, I know you can fix it!