Inserted cross slide feed nuts

It did cross my mind that a twin start thread of two 24tpi either Whitworth or 60 degree form would be easier to produce a in the limited space. Of course, a new leadscrew would also have to be made at the same time. Just making a new nut will highlight the uneven wear on your leadscrew.

Doing the maths, I was surprised to find that for 12tpi, the dials would have to have 83.3333 divisions per turn, that is total madness if thousandths of an inch were needed.

Yes 12 TPI is an odd number when you put a dial on it but I dont think that the Faircuts were the only lathes to use 12TPI.

The usual fudge is a dial with 80 graduations... which is what my lathe has. It seems pretty well made (and resettable) but some of the graduations are a bit wonky so maybe not a factory item. Anyway, whatever its origins, I like it.

I say the 'usual fudge' but in practice most 12 TPI lathes probably had no dial at all. If one is resorting to chalk marks on the handwheels or whatever then 12 TPI is probably not a big issue.

If you splash out for a bigger bit of brass and make the nut a loose fit and secured by holes in a flange projecting to the front you only lose 1/10 inch on cross slide travel and maybe make a modified front plate or spacer to get that back. When you do make a new screw make it longer and remake the front plate etc to incorporate taper roller thrust bearings.

If you are prepared to depart from absolute prototype, for a closer approximation to a thou per division, then the dial needs 83 divisions. This makes each division 0.001004 inch.

4 millionths of an inch is probably an acceptable error, in an non temperature and humidity controlled environment!

The Myford ML1,2, 3 and 4 also used 12 tpi leadscrews on Cross and Topslide, again with 80 divisions on the dials, giving an error of 0.0004" per division..

Howard

I want to keep the existing dial so I will live with the 80 division oddity (if I can manage to make a new 12TPI nut anyway)

TBH it is not a big issue for me. If I want to know how much cut I am putting on it is perfectly fine for that. If I want to turn down to a size then I get the mike out anyway. Quite often the job is metric in any case.

@Bazyle: the order for some LG2 has gone in already so the first attempt will be a fairly like for like replacement. If the new one lasts 80 years then I won't be very worried when it wears out.

I made a new nut for my M type lathe and made a finish tap from silver steel. I roughed out the thread by screw cutting and used the tap to Finnish it.

Have a go.

David

If 80 divisions is required, then make a leadscrew and nut of 12.5 tpi, it will be perfect. To do that, you need a lathe which will do 25 tpi, and double the leadscrew speed.

For a 1/8-inch lead-screw, I work out 12.5 tpi being feasible with a 32T change-wheel. Pair it with a 50T wheel. (Or 64 / 50 with 1/2 compounding.)

Note you might need keep the half-nuts engaged the whole time unless the lathe has a thread-dial indicator.

I have a small Denbigh horizontal mill, not yet back in service, and one of the screws on that is 6TPI. I forget which but I think it is the long-travel lead-screw!

@David: thanks - good to see someone who has actually done it. I was thinking along similar lines. Making one tap seems less hassle than making three.

Did you screw cut a square thread or a pointy one?

Looks like you heat treated your tap - did you just harden it or did you harden and temper?

12.5 TPI... an interesting idea thanks but I probably lack the gears to do that. The Faircut has 2 off 20T and then goes up in 5T steps to 65T. I suspect this is the full original set. It would also mean making the screw and nut at the same time.

FYI the Faircut has a permanently engaged leadscrew..

Cutting a feed screw length thread brings some additional challenges that I'd rather save until another occasion.

For now I'm going to go with 12 TPI and see if I can actually make a nut that works. At least the gearing is straightforward.

8 / 40 x 25 x 50 / 20 .= 12.5

Probably impossible to set up like that but that's as far as my brain wants to go just now.

Andy - that lathe sounds similar to my EW, with that change-wheel range and permanently-engaged lead-screw; 1/8 inch lead on the EW.

I once cut a non-standard metric thread on it, and working out the gear train to give minimum pitch error took some doing!

I did those sums by multiplying 8/12.5 to the lowest multiple of 8 for integers and a feasible pinion size; hence 32/50.

I must have missed the Howard Lewis post mentioning the Myford leadscrew pitch. There is your answer, Myford spares are far easier to get hold of than any other make, and the modifying them to fit is by far the easiest option.

Now if anyone makes feed screws for the ML1-4 then that would really save me some effort. I haven't found any though.

I suspect the nut design is... err... unique... to Faircut so I'm getting started on making one to see if I can do it.

Andy, if there's a particular gear you need for your setup to get you 12.5TPI I could probably make it for you.

Thanks for the offer Pete but at the moment I'm going with 12.

Well that went better than expected...

A long way from the finished article but the approach shows promise. I had a think and remembered 'The Squire' which came with the lathe when I bought it. I wondered if he could help...

I dug out some cheapo chinese 3mm HSS milling cutters and ground up a couple of inserts. Not easy and they both ended up a bit under the correct width but they are not too bad.

The job on the lathe...

I've made a bush to hold the new cross feed nut in the 3 jaw for drilling, boring and threading. I could have used the 4 jaw but didn't want to squash the job, plus if I'm making several then this way will be less hassle in the long term.

The idea was to swap from the short insert to the longer one part way through. The shank on 'The Squire' is 6.9mm and the minor thread diameter about 7.4mm, which means I can only have half the 'stick out' that I need to fully cut the thread.

I stopped the job after bottoming out the shorter insert. I've now decided that changing inserts mid-job was a bad idea and I need to make a 'mini squire' that will allow the full thread depth of 'stick out'. I also need to make a proper mandrel handle but turning the countershaft by hand is definitely the way to go.

Hi Andy I screw cut the thread with a square bit the same size as the thread. The tap was cut to same pitch with same gears and after milling with a ball end slot drill to give the cutting clearance I hardened it and then tempered it back to dark straw on the cutting part and let the shank down to blue. the internal thread cutter was just ground from a piece of HSS.

if you need any help just drop me a message.

David

Cheers David. I'm still waiting for a the materials to do the 'proper job' (including silver steel for a tap) but practicing with what I have is teaching me a lot. I was aiming for the correct width on the tools... but found it was all too easy to end up under size. Still... I have another 9 chinese 3mm end mills still available for upcycling. They arent much use for milling.

This is definitely a learning experience...

Got myself a little more 'tooled up' yesterday by making a mini 'Squire' from 6mm silver steel on the Cowells. This fits into the Arc Euro holder that is intended for their HSS boring tool.

I also made a handle for the countershaft (which is effective but looks awful so no photos!) and a couple of little gauges from 15 thou brass, one to check the thread width and the other to check the depth.

Tonight I had another go at the same cross slide feed nut and proved to myself that I couldn't 'pick up' the thread. No matter... this is a test... I pressed on to the point where the depth gauge just about fitted and the smaller bar and countershaft handle both proved their worth. Then on the final cut the cutting insert came loose from the bar (doh... should have tightened the screw again once it was held in the toolpost).

I'd 'lost' the thread again but it was near enough to try. It just about goes on to a not too worn thread but is very stiff. Making a finishing tap should help (still waiting for the silver steel). I also discovered that I'd made a howling error. Can you spot it?

I can't say what your howling error is, but hold fire on getting the thread in the nut any looser. The most used part of the leadscrew will be much looser on the nut, assuming that it can be screwed right on to find out.