Cast leadscrew nuts vs. machined

S

smarrocco

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I've read a lot of information on cast leadscrew nuts (moglice, various epoxy/teflon/magic dust recipes). Many people have made their own to what sounds like great success, with little or no backlash because of the casting directly to the leadscrew itself. After doing the math, substances like Moglice, while expensive, amount to very little actual cost per nut. I can find no obvious issues with wear. I'm well aware of the issues with machines solutions such as anti-backlash assemblies machines from various brass pieces that can manually tightened and calibrated. I've done plenty of casting of resin, various epoxies before and it is hardly difficult for a hobbiest with some patience. I currently abuse Sherline equipment and deal with the anti-backlash solutions for that often My system runs manual and under custom CNC control and I have plenty of correction for backlash. It brings to mind a question:

If cast leadscrew nuts work so well, and are not that expensive, why aren't they more common or standard issue?
 
I personally would never use a polymer for my half nuts. In my mind it is an uncertainty. I have an old worn out set for my Clausing. When I get to it, I will make up a threaded mandrel, tin the half nuts up and pour them in babbitt. Reading an old article, many outfits noticed that iron and bronze half nuts always shed some powder, and wear the leadscrew in the process. When they went to babbitt half nuts, the half nuts lasted a very long time, and wear on the screw stopped. Good enough for me.
 
Moglice in the putty form would be the only one I would use. I used it to bring back the saddle height on my L & S lathe. Its tough! Now the issue to me would be using it in a set of half nuts on a lathe that has a lead screw with a keyway cut down the length of the lead screw. I think it would crap out over a short period of time. Next thing, regardless what polymer you selected, it has to be lubricated with lots of oil while in use. Just my gut feel from actual use of Moglice.
Now, having said that, what would be a good metallic bearing material to use? Bearing bronze, cast iron, or babbitt?
 
I think you mean feed screw and not lead screw, correct? You are talking about the screws that drive the table in X & Y. The cast material is porous so it can retain oil/lubricant and extend life. But has less surface area so I suppose it could not last as long but would be easy on the feed screw. And then on the other side of the coin. Something like aluminum bronze is very tuff and will probably wear out the feed screw first. It’s a coin toss on what you want to replace in the future. A feed screw or a feed nut depending on which one is cheaper and easier to replace I quess…Dave
 
The cast in place Moglice is not porous. That's why I say you have to keep it lubricated. 660 bearing bronze and 454 navel bronze makes the best nuts and give you better wear properites against a steel leadscrew or feed screw. I also like to make my feed screws from either 1144 T,P,& G, or drill rod.
 
I have also read quite a bit of the Evanut postings on the web and have them book marked I think.
 
This is something I thought to try next time mine gets loose.

For the cross slide, use the old nut.
Bore it out as much as possible.
Drill a hole thru to the bore on a side.
Make a end-cap for each end to fit over the screw.
Blacken the screw, place inside the bored out nut with end-caps holding it in center.
Preheat nut.
Pour Babbitt in thru drilled hole and now I have new very tight tolerance nut.
 
Jimsehr said:
Have you looked at evanut ? Lots of info there.
Jimsehr
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Yes. The evanut seems like a nice experiment to be sure. Like a lot of forum threads, the evanut discussions seemed to end soon with 'it is wonderful' but have no long term follow up that I could find. Hence my concern of "if it is so great why doesn't everyone use it?"
 
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