lead screw nut making ?

i have a very nice scew with 4 starts, the problem is that i dont have a nut for it, some people here here made a nut out of derlin or similar plastic product, i tried to make the screw go inside the delrin but its not cutting anything at all even after i made a pilot hole.
i tride to heat a part of the screw then forced to enter the derlin, and it did and worked but it was so firm and not running freely
any suggestions ?

You have to cut or grind flutes into the screw to cut the threads, so it looks like a tap. Like this.
http://www.factorydaily.com/forums/attach...achmentid=1039

any idea how can i cut these flutes ?

When I made my tap I used a dremel with a cutoff/grinding wheel to put the flutes into the threaded rod.

I used a dremel as well, first cutting a slot with a cutoff wheel and then enlarging it with a chainsaw sharpening stone. It takes a little while, so be patient.

Has anyone ever tried casting a nut around the acme thread. Babbit bearings can be cast around the shaft that will run in them. It should be possible to do the same for a nut; and get very little backlash. An alternative could be something like graphite filled epoxy but making sure it did not stick to the metal, as it is designed to do, could be a bit tricky.

Has anyone ever tried casting a nut around the acme thread. Babbit bearings can be cast around the shaft that will run in them. It should be possible to do the same for a nut; and get very little backlash. An alternative could be something like graphite filled epoxy but making sure it did not stick to the metal, as it is designed to do, could be a bit tricky.

Yes, it's been done. This is what's usually used.
http://www.moglice.com/

actually i have also made it, using alumilite, polyester and epoxy, the problem is that these all has a shrinkage factor after beeing cured , so they become so so tight on the screw.

I've heard you need to lap the nut on the screw to relieve some of the tightness. And try to put a couple heavy coats of release agent on the screw too.

i tried something similar once, and used a few coats of car wax as a space filling release agent. I might have just gotten lucky, but the resulting epoxy filled nut worked really smoothly on the threads.
ed

What kind of epoxy are you talking about and where can one get it?

fibreglass body filler makes pretty sweet molds , strong easy to find and cheap ,just use a thin film of axle greese

actually the car fillers are polyester resin, which you can buy it cheaper

actually i am talking about fibreglass body filler . polyester filler is softer and not nearly as strong and absorbs moisture , so tolerancing it may be a problem , you will find fibreglass filler right the next polyester resin in any auto store , if youve used fillers before this stuff is the same to work with but much stronger

Bondo is polyester, as is the fiberglass resin you find at an auto parts store. It's all polyester.

Has anyone tried casting it in brass? Would the brass stick to the steel?

Has anyone tried casting it in brass? Would the brass stick to the steel?

It is possible to coat the steel so the brass will not stick but you are dealing with high temperatures and would probably create a severely heat affected zone on the screw. Also thermal shrinkage would probably result in the cast brass nut being immovable.

actually i have some friend who cast it in teflon and it worked just fine (according to his words), but the best thing is to get a part and make it as a taper, i just did it and it works great for cutting derlin nuts, if you must have it in aluminum or brass you can make a mold for the derlin nut and then cast it, but i dont know what will catch the small details of the nut, lost wax maybe, i dont know

Hey, thanks for the good tips. I am going to have to rethink a method of making a new leadscrew nut. The metal filled epoxy method looks the most promising. I don't want to think of how I could have screwed up the temper on my lead screw or having to melt off an aborted attemp of casting a nut on it.

I've used alumilite which really does not shrink, however it is pretty tight. To gain the proper space, I wrapped my lead screw with Teflon tape first. Put the screw in a pvc pipe, filled it up. Alumilite has a 90 sec POT life so you need to be ready when its mixed. I've made the travelers using this method and I've also made some end nuts with the same method with the exception of using less Teflon so that they are tighter. I drill and tap these end nuts and thread a set screw in them. Alumilite is stable up to 250 degres F. The Teflon melts and becomes hard inside the thread. Most of the teflon comes out once you remove the part from the thread and then thread it back onto the lead screw. This material is very easy to work with and making the parts is pretty quick. We can make replacement parts and replace them on the machine in a couple hours when needed. We are currently working on building some split nuts which have an aluminum casing made from 3/4" square tubing to hold them in place. This way we can change the nut out without taking the end of the lead screw assembly apart. You just slide the square tubing off the split nut, take the old split nut off, put on a new set and slide the casing back into place. We will probably use a rectangular tube so we have plenty of header to put a bolt clear threw the casing and split nut for mounting. But the prototype idea worked really well.
Lunar Draco

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