View Full Version : Half nut lapping?

Bob Quale
09-27-2002, 02:02 PM
I recut a half nut. I then lapped it in against a new screw with lapping compound. In service it will be used with a new screw. The nut is brass.

I saw in a previous thread that the lapping compound will get into the brass and keep cutting the screw.

Well I guess that wasn't the best idea I've ever had, but I did it, so now what should I do? Just use it? Will it wear out the screw in short order? any ideas will be helpfull.


09-27-2002, 03:10 PM
If you have an Ultrasonic cleaner put it in there for a spell or clean it well with a toothbrush. It won't be that big of a deal.

09-27-2002, 03:53 PM
Ultarsonic cleaning sounds good. You didn't say what kind of lapping compound you were using Bob. If it's aluminum oxide it will wear down soon even if you don't remove it all. If it's a diamond paste you may have a problem. That stuff doesn't wear hardly at all.

Bob Quale
09-27-2002, 05:23 PM
I lapped it with auto lap grinding compound. I'm not sure what it is made of, but will check tonight. Also, I do not have an altrasonic cleaner. Will just a tooth brush do?

Thanks Bob

09-27-2002, 06:15 PM
yeah - a toothbrush & acetone or metho, or even petrol should do the trick for you. Don't have a smoke while you're doin' it tho'

09-28-2002, 12:44 AM
Bob: If you used what I call valve grinding compound just wash off with hot soapy water until a clean white rag or paper comes away unstained. Most lapping compounds get rounded pretty fast, Clover (best in my experience) lasts a longtime, others break up quickly,

this is pure speculation but I suspect your wear (if it occurrs) will be on the flanks, not the OD. still might be a good idea to measure the screw and remeasure after some operating hours. record the measurements and measure agian after time. if it is wearing fast then junk the nuts and buy nuts before you have to buy nuts & screw.

From experience: I use lapping compound often on a nut/screw. A few passes up and down and they spin like velvet. I have done this with brass nuts and steel nuts. I always wash them down with brake cleaner, water and I have never noticed any wear. But I was not looking for wear so I may have missed something.

Bob Quale
09-28-2002, 09:10 AM
The valve grinding compound is made by NAPA. It does not say what is in it, only that it will not cut your rings and contains no glass. I would have to think it would dull down quickly or it would work its way into your engine?

The nut is not a replacable item. I had to make it, so replacement would not be a quick thing. The screw is an acme 1X10 which I bought and made fit.

Maybe I'll take it apart again, and clean it, one more time just to be sure it's good. I just hate re-doing my work, it seams I get so little time in the shop.


09-28-2002, 10:58 AM
There is an outfit, Green Bay Mfg. in Two Rivers, WI, Ph 920-793-4848 that makes acme
nuts and leadscrews, 3/6-12 to 2.0-4 sizes.
You might try them for nuts.
Jack C.

09-28-2002, 11:33 AM
BOB: Your logic is impeccable, your facts are faulty http://bbs.homeshopmachinist.net//smile.gif.

Valve grinding compound used to be left on valve (by slopply or unknowledgeable workers). It got into valve guides and the valve job did n't last long. Grit from honing does the same. You assumed most re-build jobs last there fore the compound can't do much damage. Fact is most first time rebuild jobs are unintentionaly built to fail (burn oil, knock etc). "soft bearings ( crankshaft bearings for example) havethe ability to "absorb" grit, embed it deep enough to keep the wearing to a minimum. Hard bearing surfaces (valve grinds) hold the grit to the surface and s continue toi wear till clearances take care of the problem or the item wears out or the grit becomes non cutting.

All the theroy aside,You have an interesting problem but not many solutions available: you can clean it up as best you can or you can declare it a failure and do it all overagain. I would suggest you clean it up, put it into service and see what happens. You are probably going to see improvements you would make next time anyway, so use it, wear it out and do it again with a better idea of how to do it next time. Doesn't progress really come about when and idea almost succeeds, and is improved next time its built? If you decalre it a failure now, you will never know how these parts will work- cuase I bet you will make some changes next time any way. You can call this one "establishing a base line" http://bbs.homeshopmachinist.net//smile.gif to which to next job can be compared.

Bob Quale
09-28-2002, 03:34 PM

I don't like it, but I guess that is the reality. This half nut is actually a brass casting about 2x3x1-1/2, with a one inch diamiter shaft out the bottom. It then slides up and down in order to initiate the screw. It also slides up and down on the casting of the machine itself in order to keep it located. I have alot of time into this part starting with making the casting. The half nut is for a Do-all surface grinder. The part new was $3500.00 so even if I have to make it twice I am still way ahead of the game.

I'll log this one into the learning curve.

Thanks Bob

09-28-2002, 06:32 PM
You will propbably get more wear from actually using the grinder and grit getting into the works (it always does eventually). I would not worry too much about it - should work fine.

One way you can keep grit out is a low positive pressure system encasing the screw mechanism. This can be fairly effective even under very adverse conditions but requires full encasement of your screws in a bellows and the geardrive or half nut as well.

09-28-2002, 09:19 PM
Bob: I've not done this one myself. I have heard of lathe half nuts being drilled and a new set of threads soldered in with keys etc. I bet a beer we have men who have really done it> Does it work? would that make a good back up plan?

Comments? Steve

09-28-2002, 10:46 PM
Heck, that has been written up in the very mag that hosts this site...........

That would be my very first choice of approaches, faced with that $3500, although I have not had to do it.

Bob Quale
09-29-2002, 08:50 AM
This half nut is really a 1/2 of a nut, about a three pound chunk of brass. My new one works great. I just went too far by lapping it in. I took the whole works apart last night and cleaned it. It seems better. Perhaps I haden't cleaned it as well as I thought the first time. The approach I took is different then any I have seen in the mags, and the nut is different. Maybe I'll put together an article and see if HSM is interested. I took photos as I went along.

Is an electronic relay a full wave triac? If not what is a electronic relay? I beleve a SCR gives half the wave? Please enlighten me. Ok to e-mail as opposed to boring everyone else.


[This message has been edited by Bob Quale (edited 09-29-2002).]