Hello.
Is it possible to cast a brass nut just around the leadscrew to save up on the threading?
Doable?


Konstantin.

I don't think this will work - the casting will shrink as it cools

I think you should be able to use a piece of threaded rod as a core in a sand mold and cast threads out of aluminum (Not sure about brass). This is Gingery's method of producing a split nut for his lathe. Have a look at this link:
http://www.backyardmetalcasting.com/lathe3.html
You still need a tap to cleanup the threads.

knonstantin....sure it's possible.....but as others have informed you casting do shink about 10 percent or so......is you want to take that approach it's fine....then use moglice on the casting.....

This thread discusses making a leadscrew nut by casting something around the thread. http://www.cnczone.com/forums/showthread.php?t=15973

It is very unlikely you would be able to cast a brass nut directly and use it in place because of shrinkage. The shrinkage might cause the brass to crack and it would make the nut too tight to move. Also the heat of the molten brass would probably warp the screw.

However, if you cut off a small length of the lead screw slightly longer than you want the nut to be and drilled a hole through it about 0.10" smaller than the root diameter of the thread you may be able to cast a useable nut around this. Removing most of the material by drilling the hole means that the lead screw material would heat up quickly to the temperature of the molten brass and then everything would cool and contract together so the brass would not crack also because the nut material was well expanded by the heat when the brass solidified the shrinkage would come back closer to the correct size of the screw. Then if you cut the whole thing exactly in half lengthwise you should be able to peel the screw material out of the brass to get two good half nuts. If you turned the outside of the cast nut to a smooth finish first you would then be able to mount the half nuts in a slightly oversize housing to compensate for the shrinkage.

I have not tried doing this but it seems a plausible approach.

Just change the material. Epoxi doesn't shrink. :)

I want to try this to re babit the thread's in the split nut's on a old lathe I need to repair oil or neverseese on the screw and a brass or aluminum shim between the two halves any help Thank's Kevin

svenakela
Epoxy shrinks! Trust me - I've proved it - bummer. BUT you can minimize the shrinkage - add fillers - max 50%, slow the hardening process - cool the mix or use slow hardener, etc. will bring some of the shrinkage back to zero - but still may get some. Cheers - Jim
I suppose in Sweden cooling is easy!

I want to try this to re babit the thread's in the split nut's on a old lathe I need to repair oil or neverseese on the screw and a brass or aluminum shim between the two halves any help Thank's Kevin

My recollection from a long time back doing babitting (is that a real word) is that oil or never seize is not what you want. The heat vaporizes these and you get cavities in the babitt. We painted the shaft with a suspension of graphite in water and dried it to leave a thin film of graphite which formed the separator between the steel shaft and the babitt; it also left a non seize surface.

Sounds like an old Atlas. I had the same problem with my half nuts almost wore out. I cleaned the old nuts with a degreaser and cleaned and light oiled the shaft. I used JB weld(epoxy) on the half nuts with a couple of pieces of wax paper between the flanges. Let setup then split. Used them for over a year before buying new. They are expensive to replace on mine for a piece of casting.
John

Couldn't you simply coat the screw with a thin layer of furnace cement or plaster of paris first, which could then be broken afterward to make room..

You might want to try a zinc/aluminum alloy: ZA12 or ZA27. The casting temps are MUCH lower, 450-550 C, and the alloy is supposed to have strenght and bearing properties similar to cast iron.

Konstantin why not use SKC anti-friction coating, its made for the purpose. It can be sprayed, injected or applied by spatula. Doesn,t shrink, reduces stick slip etc. You can use it to build up existing worn components etc. ame.com sells it.
RZ
edit
I checked ame.com site, no mention of SKC
another name "Moglice" @ RGB Industries
RZ

You could try spraying the short peice of thread with a ceramic coating like HTC100 first, or make a steel die mold to hold the treaded rod, this way you could preheat the mold to the same temp as the brass, then it's just down to the coefficient of expansion of steel and brass, one problem may be that cooling brass too slowly would affect the metallurgy. Whatever you do the threaded rod will be a verry tight fit ( not sliding ) and would need further work to clean it up to provide a sliding fit. Making a tap out of some spare leadscrew is probably 'easier'.

svenakela
Epoxy shrinks! Trust me - I've proved it - bummer. BUT you can minimize the shrinkage - add fillers - max 50%, slow the hardening process - cool the mix or use slow hardener, etc. will bring some of the shrinkage back to zero - but still may get some. Cheers - Jim
I suppose in Sweden cooling is easy!

It really depends on what kind of Epoxi you use. I'm using "low weight" resin with no fillers for laminating and to create threads directly in the composite. :)