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Delrin leadscrew nuts?

DocsMachine

Titanium
Joined
Jan 8, 2005
Location
Southcentral, AK
I'm in the middle of a fairly straightforward refresh of a Spanish-made Anayak Exacto vertical mill. Can't really call it a proper rebuild, I'm not scraping anything, and surprisingly little needs to be fixed. With only a few exceptions, it's really just a clean-and-paint. :D

You can read about my progress so far, by clicking here.

exacto96.jpg


Now then, the one problem with this machine when I got it, was all three (!) of the leadscrew nuts were either badly worn, or just stripped outright. The screw itself, however, was still in surprisingly good condition- there's some minor wear, of course, but nowhere near what you'd think with the nuts being that bad.

The machine comes with a hugely overpowered power feed- it weighs about 100+ pounds, and has a 3/4HP (!) 3-phase motor. I strongly suspect some inattentive operator let the feed go past its stops, and let it keep trying to pull the leadscrew through the nuts.

As I was cleaning things out of the saddle, I kept finding half-circles of yellow metal that looked sort of like snap rings- debris of the nuts being stripped, not worn out.

Anyway, as I'm reassembling it, I decided to make a pair of new leadscrew nuts... out of black Delrin.

exacto87.jpg


The nuts are fairly big- about 3" of contact to the screw, each- and adjustable:

exacto94.jpg


The screw is smooth, with no appreciable galls or burrs. It does have a keyway, for the front-mounted third handwheel, but hopefully that won't be an issue.

Now, the question is, how well do you gents think those will hold up? I know people have tried Delrin nuts before, and I know injectable epoxies like Moglice are used even on big industrial machines.

I'm fairly easy on my machines, with workpieces rarely exceeding 10lb (not counting the vise or rotary table) and largely in aluminum. I expect the nuts will hold up well, with a presumed lifespan of at least a couple of years.

But, I've also never used them myself, before, and I'm curious if anyone has more direct experience concerning how long they might last. In other words, should I start shopping for some chunks of bronze right away, or can I maybe wait a while. :D

Doc.
 
I'm in the middle of a fairly straightforward refresh of a Spanish-made Anayak Exacto vertical mill. Can't really call it a proper rebuild, I'm not scraping anything, and surprisingly little needs to be fixed. With only a few exceptions, it's really just a clean-and-paint. :D

You can read about my progress so far, by clicking here.

exacto96.jpg


Now then, the one problem with this machine when I got it, was all three (!) of the leadscrew nuts were either badly worn, or just stripped outright. The screw itself, however, was still in surprisingly good condition- there's some minor wear, of course, but nowhere near what you'd think with the nuts being that bad.

The machine comes with a hugely overpowered power feed- it weighs about 100+ pounds, and has a 3/4HP (!) 3-phase motor. I strongly suspect some inattentive operator let the feed go past its stops, and let it keep trying to pull the leadscrew through the nuts.

As I was cleaning things out of the saddle, I kept finding half-circles of yellow metal that looked sort of like snap rings- debris of the nuts being stripped, not worn out.

Anyway, as I'm reassembling it, I decided to make a pair of new leadscrew nuts... out of black Delrin.

exacto87.jpg


The nuts are fairly big- about 3" of contact to the screw, each- and adjustable:

exacto94.jpg


The screw is smooth, with no appreciable galls or burrs. It does have a keyway, for the front-mounted third handwheel, but hopefully that won't be an issue.

Now, the question is, how well do you gents think those will hold up? I know people have tried Delrin nuts before, and I know injectable epoxies like Moglice are used even on big industrial machines.

I'm fairly easy on my machines, with workpieces rarely exceeding 10lb (not counting the vise or rotary table) and largely in aluminum. I expect the nuts will hold up well, with a presumed lifespan of at least a couple of years.

But, I've also never used them myself, before, and I'm curious if anyone has more direct experience concerning how long they might last. In other words, should I start shopping for some chunks of bronze right away, or can I maybe wait a while. :D

Doc.

Find a way to 'see' in there periodically.

Black shreds of evidence should start showing up early-on if the keyway is going to make a meal of them. Scout for Bronze if so.

Otherwise, they are so looong they might last a very, very long time.

But you knew that..

Bill
 
I don't have experience of Delrin nuts, yet... But if you go shopping in the future, you'll probably find that cast iron will do at least as good a job as bronze. Moreso if the feedscrew wasn't hardened.
 
If not damaged then im willing to bet they will outlast bronze. IMHO bronze is not as good as a lot of the modern plastics for stuff like this if the contact areas are large enough to keep the surface pressures in a range the given polymers happy with.
 
Quite so- I've encountered an Ormerod shaper where the cross feed nut was nylon and seemed to be doing OK. I seem to remember the newish DSGs having Dural cross feed nuts.
 
Probably last as long as the originals.I made some devices that used a tripple lead acme screw with Torlon nuts.That was 12 years ago and are still tight(not any where near the same load as your screws).Much as I like Delrin I would have used Nylatron(Nylon with graphite) or better yet Nyloil with MDS.The only draw back with the plastics is that they cut easily so the screw needs to be as smooth as possible.
 
The only reason I might expect less rigidity is because you didn't wrap it all in a retaining metal of some sort. When I see this type of thing installed on a "professional" machine, it's usually encased in steel, just as a backer. You still get the wear properties of the acetal, but you then get the strength of the steel.
 
In the process of trying to get a cross slide nut for my lathe, I did some searching and found that people have used Delrin for nuts with success. Those did not have the length of contact with the screw and apparently held up well, so yours should be fine even for a long term fix. I've cut both acetal and brass nuts and will be using them to see if there's a difference. My guess is that with the limited use the lathe will have, no differences will be found.
 
The only draw back with the plastics is that they cut easily so the screw needs to be as smooth as possible.

That's my only real concern, that the keyway in the leadscrew will act as a slow reamer, perhaps wearing out the nut sooner than it otherwise might.

Time, apparently, will tell. :)

Did you cut the threads or just bore a hole and heat press it together to form threads?

-There's a brief series of photos on the linked pages. Nothing special, I turned a couple of blanks from a bar of 3" round, bored them to size, and threaded them with a simple homebrew boring bar. Straight up machining 101. :)

I'd considered the heat/press thing, but the leadscrew has a keyway. A molded nut, wether by heat or epoxy/Moglice, would be locked in place and unremovable.

Doc.
 
Probably wouldn't hurt to work the potential cutting edges of the keyway ( tedious ) to chamfer the thread profile. Then no cutting potential to the nut.
joe

Just what I was going to suggest. Should be good for several hours of fun and games. On the more general topic of Delrin vs. "real" material, it probably wouldn't have been my first choice as a replacement at this level of rebuild, but the plastic should work well for quite some time as long as the loads aren't too high, and there are no sharp edges to accelerate internal wear.
 
Probably wouldn't hurt to work the potential cutting edges of the keyway ( tedious ) to chamfer the thread profile. Then no cutting potential to the nut.
joe

I would have thought the bronze nuts would have long worn off any burs on the steel screw, .....FWIW deburring a keywayed lead screw with a swiss file, isn't too bad, ;- I use a 1/2 round, ................the trick is to use an US end mill to hog the slot, then change to a new one of the same size and open to width one side at a time.
 
IMO, if there are no sharp edges cutting the Delrin, it should last a very long time. There may be better bearing plastics, but not at the price and easy availability of Delrin. There's also Delrin AF, but I've never been convinced it was that much better than the regular black stuff.
 
Any cutting edge requires a relief angle to cut. The leadscrew doesn't,of course. I would not say that under a lot of pressure,the leadscrew keyway could not begin to scratch away some delrin. But,you say you're easy on your machines,so all should be well for a long time.
 
How would it work to make a poured in place Babbitt filling of the nut. I have to think that Babbitt is too soft and would wear away quickly. Yes I know it would not work for this job with a keyway unless you make a keyless short piece just for the pour.
Bill D.
 
Bill babits just like bronzes, lubed they were very slowly, slightest hickup on the lube and they wear even faster, most plastics won't wear that fast even dry if the bearings surface is reasonably smooth!
 
I've gotten the table mounted and set, and had a chance to wind it back and forth a couple of times- albeit with no real load.

exacto117.jpg


I'm not seeing any black chips or swarf coming out either end, so it's at least not immediately destroying itself. :)

As soon as I can get the head finished, I'll give it a good college try and let you know what I come up with.

Doc.
 
It's been 11 months, is there an update to the nuts. I'm thinking of replacing my x and y nuts on my Bridgeport with some UHMW plastic. If it doesn't work, oh well. I've got lots of material to work with and I'll only be out my time.
 
Six of those months were spent with the project on hold, waiting to have a set of head-rotation gears made, since the originals were either missing or badly damaged.

Two more of those months were spent reassembling the head in my limited spare time, and another couple were spent tinkering with things like a bent spindle, bad spindle bearings, a damaged drive pulley, a broken back-gear lever, and other tidbits.

All more or less detailed on my build pages, with the head rebuild starting about here.

I only finally got it fully straightened out, wired, and VFD'ed maybe a month ago. I have since only used it for a few small pieces, as there's still some niggly bits to sort out- one of which is the knee crank is badly rounded out, so raising or lowering the table is a major pain in the ass at the moment. :)

Since finding a factory replacement is going to be virtually impossible, I'll likely have to make one, or try to modify a Bridgeport or clone crank.

Doc.
 








 
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