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Dimensions of 10L small dial compound screw?

StrayAlien

Cast Iron
Joined
Aug 18, 2014
Location
Melbourne, Australia
As part of this rebuild thread:

http://www.practicalmachinist.com/vb/south-bend-lathes/early-10l-rebuild-teardown-inspection-290320/

I bought a new compound nut and the compound screw I have doesn't fit in it.

P1110584_zpss59siafg.jpg


And I am pretty sure an SB compound screw is not faced like this:

P1110585_zpsxlfziwbc.jpg


That could mean (I guess) that:

a) the size changes over the years and my 1941 is not the same as the year of my new nut
b) my screw and nut are shop made - which is a possibility as the tail stock quill is, and maybe also the screw and nut there.

So ... before I go and buy a new compound screw I'd best make certain that the bore through my compound rest bushing and (small) dial has not been messed with.

Anybody got a 10L small dial compound screw handy to measure the diameter of the non threaded section?

Many thanks.

Greg.
 
I may be wrong but that looks like a cross feed nut, which is threaded left hand.
IIRC the compound nut looks the same but is shorter and is right hand threaded.

Bet your cross feed screw fits it.
 
Heya. No so I am afraid - I checked. The CF nut is much larger (I bought a new one of those as well, and it does fit the CF screw). You can tell the diff as the CF nut has a oil hole in the bottom of its mount screw hole while the compound nut has none (it is mounted 'upside down').
 
The compound feed dial/mount bushing shaft is .3745 (+0, -.0005)
regrind or turn the 15 degree angle at end of the threads in your photo to a length of .2500,(the 3rd thread) clean up that start thread.

Steve Wells
 
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Thanks Steve,

Appreciated. It is the nut you supplied and I figure you know what you are talking about .. hence me verifying whether my screw was stock!

Btw, the taper CF nut and screw you supplied is beautiful and just amazing. I would not have realised how **really** bad mine was (and it *looks* bad!) until I received the one you supplied and felt just how little play a new one is supposed to have. Wow. I think I get about 30-30 thou play on mine. The sleeve it goes into on the taper is bored, so .. before I can use it, I have to make me one of those. I'll get there!

So, if my compound bushing (etc) has not been bored then I'll likely be hunting a new compound screw as well. It is test assembled at the moment so I'll check in the next night or two when I get it apart.

And .. while I have your attention, I must say, that the amount of times I have visited your web site and thought I should buy you a (cross out as required) beer/bourbon/orange juice/martini-shaken-not-stirred I have lost count of. Well done and thank you. Very much appreciated. <glass being raised>
 
So, if my compound bushing (etc) has not been bored then I'll likely be hunting a new compound screw as well.

I believe Steve was suggesting the threads on the end of the screw are likely damaged and that by filing or grinding them you may find that the rest of the screw is fine.

Teryk
 
Thanks Teryk. I got that and I'll give it a go. :-) What I meant was that I had tasted the sweet waters of a new (even if as-yet-uninstalled) CF screw / nut and if the compound doesn't match up then I might just have to get a new one. :-)
 
We need to make sure it's not the nut too, Tom Ross made the last batch of 10L compound nuts I have and I did find one that something is wrong with the threads, albeit just one...but I didn't test every one, let me know if after the thread clean up, it still presents a problem, I'll send another one that I test fit. Tom's work is really good, so I think it's in the start thread, I'll take another look at the one I have and make a cleanup tap in 3/8 10 to see what it is.
Keep me posted. Is it stamped "made in USA" ?

Steve Wells
 
Just a quick test. I didn't make 15 degree taper but I did clean up the end of the screw and it would happily turn into the new nut about 4 threads before it stops. It is bind, not an awkard spot on the thread or something.

My screw is .377 and the bore through the bushing is .379-.380 so I am guessing the screw is shop made (with a not as accurate 10 tpi as the nut) and the bushing has been bored out ever so slightly to suit, and my existing nut may be shop made as well. I guess that answers that .. and we're not comparing apples with apples. The new nut may well be fine but my screw may not be.

Rather than bore everybody here with details of what happens next I'll email you. Thanks all. Appreciated.

Greg.
 








 
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