Cast leadscrew nuts vs. machined

Thinking I read a follow up after a year on a cnc mini mill and the user was still satisfied. The only question in my mind about them
 
Wow that went badly, the last post wouldn't post. Any how to continue/ finish the post again, The only question in my mind about them is wouldn't they trap grit and wear the lead screw?
 
tweinke said:
Wow that went badly, the last post wouldn't post. Any how to continue/ finish the post again, The only question in my mind about them is wouldn't they trap grit and wear the lead screw?
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Funny, tweinke, I thought for a minute that you were about to reveal a big secret when all of a sudden someone snuck up and gagged you at the big moment! ;) shades of the castle Camarrrrg from Monty Python.

The grit issue seems to come up in discussion, but I can't imagine it would be any worse than a tight backlash nut system pressing grit against the screw threads. I do wonder if it would merit something like a 'slot' cut across the length of the moglice nut for lubricant access.
 
I have made Evanuts from Delrin for the y axis of my mini mill and the cross slide of my 12" Craftsman lathe. The one on the mill was done about 2 years ago. It had almost no backlash when I first did the mod and now has about .005". The lathe nut was done about 6 months ago and has about .003".
 
Nice to hear from someone who has actually done it. Any comments on the process and procedures that you used? I ask because my Shoptask 1720xmtc could use a new nut for the lead screw due to backlash getting bigger then I would like.
 
tweinke said:
Nice to hear from someone who has actually done it. Any comments on the process and procedures that you used? I ask because my Shoptask 1720xmtc could use a new nut for the lead screw due to backlash getting bigger then I would like.
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I used the same procedure as described in http://bbs.homeshopmachinist.net/th...-leadscrew-nuts-the-easy-way?highlight=evanut.

In a nutshell, you take a piece of Acetal/Delrin bore it to the minor thread diameter you need, slit it in half, clamp it over the lead screw you are using, apply heat to the screw, then apply more clamping force when the Acetal begins to melt, allow to cool, machine the piece to the required shape. Evan goes in the details much better than I can explain and there have been many follow on threads, some using different types of Acetal, different methods of heating and such. It really is fairly easy to do and I will probably be doing a couple more in the future. The biggest problem I had was with the first one in that it was very tight on the screw and I had to work it quite a bit to get it to to spin free. This problem was addressed in some of the follow on threads, with various methods to alleviate it. Bill
 
Thanks for the reply, When it warms up out in the shop will do a test nut and see how that goes. Thanks again!
 
smarrocco said:
If cast leadscrew nuts work so well, and are not that expensive, why aren't they more common or standard issue?
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I've wondered the same thing myself and I bet a cast Zamack nut on a Sherline leadscrew would work well. My Emco lathe uses Zamack leadscrew nuts with the typical slotted backlash adjustment feature. An Emco lathe has zero backlash on both the cross slide and compound and is smooth as silk. Moreover, the nuts can last for decades. I suspect Emco used Zamack because it casts very precisely and has properties suitable for the application. Currently, Zinc-based alloys (probably some Zamack alloy) are often used to cast nuts for precision leadscrew applications and the reasons stated for using this material is precision in casting and accuracy in use. If I were going to attempt to cast a leadscrew nut, I would use Zamack and cast it in a block around the leadscrew and then machine it to the dimensions I needed.
 
I needed to make some plastic disks for a guy and for material I went to Walmart and bought 20 of their white plastic cutting boards. Then I cut the disks out of them. So I had the left over pieces in the scrap bin and just to see what would happen I took a few pieces out of the scrap bin and made an evanut out of the scrap. I just put the 2
Pieces over the threads on a bolt and heated the bolt. I had a hard time unscrewing the bolt. But it worked good enough for me to try it on a leadscrew when I get around to it.
Ps Walmart must have thought I had a hell of a kitchen.
Jimsehr
 
mikey said:
I've wondered the same thing myself and I bet a cast Zamack nut on a Sherline leadscrew would work well. My Emco lathe uses Zamack leadscrew nuts with the typical slotted backlash adjustment feature. An Emco lathe has zero backlash on both the cross slide and compound and is smooth as silk. Moreover, the nuts can last for decades. I suspect Emco used Zamack because it casts very precisely and has properties suitable for the application. Currently, Zinc-based alloys (probably some Zamack alloy) are often used to cast nuts for precision leadscrew applications and the reasons stated for using this material is precision in casting and accuracy in use. If I were going to attempt to cast a leadscrew nut, I would use Zamack and cast it in a block around the leadscrew and then machine it to the dimensions I needed.
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I like Zamak too. It is pretty fabulous bearing material. Same reasons as for my appreciation for babbit.
 
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