Corbetts Little Jim Lathe restoration - newbie needs advice

I've made my own in the past Andy - I bored out some steel bar to take the bearings and welded feet on the bottom. Then you can clamp the two housings together (with the shaft slid through the bearings) and mill the feet flat/level. The old way to make plummer blocks was to clamp the bearings between hardwood 'halves' bored to take the shaft (or bearings).

We are a bit spoilt these days but people often had to 'make do' in the past, so I'm sure you will manage to figure something out!

Regards,

IanT

Andy,

The fixed dovetail will be pulled up snug to the bed by the wedge action which ensures the tailstock bore is also parallel to the bed.

I would make your 12mm plate at least 2" long and tap it for a stud, the stud position will be critical.

The pin doesn't look long enough to do anything.

3 step pulley.

tIAAOSw0lVgykFK">countershaft link sounds like a 5/8 shaft + blocks

10" pulley  just need to sleeve it

Edited By Dave Halford on 06/07/2021 19:27:42

Thanks Dave, Ian, and others. 

I think I have a plan for the motor and a new countershaft. Will order a pulley and some bearings and take a picture when done.

If you have the time and interest I would also appreciate any get any ideas on my next problem. The picture shows the crossslide.  The thread in the brass insert is knackered.  The screw looks like a 0.35" 10tpi square.  Any suggideasestiocrossslidens how to fix?

Maybe
- how to drillout the brass without damaging slide.
- where could I find someone to make me a new insert.
- how would I fit such an insert - interference fit or would glue work.

Are there any sort of insert threads that might work at least until I learn enough to make such an insert myself. I had thought of tapping some metric thread but there is not really enough meat left.

Any other ideas. 

Edited By Andy Thompson 3 on 06/07/2021 21:51:15

Because your cross slide handle moves with te slide that makes it a RH thread. I would get a 7/16" x 10TPI ACME tap and run it straight through that nut then make or buy a new cross slide screw. If you need help making the screw then several people here myself included could do that.

I may be wrong but it looks like the slide is designed to ride on the top flat ways rather than the bottom dovetail ways. If it is then those ways need attention. If it isn't then they need taking down a bit so that the slide isn't riding on a part that it's not supposed to.

It could be a 3/8th 10 TPI ACME thread Andy - so you can get a tap to do that.

Unless the threaded part is 'pinned' in someway, you should be able to pull it out using a simple puller. So with a bit of planning, you could make a replacement part (and the puller) before you take the original nut out. Normally, the feed nut (being softer) will wear a bit more than the threaded steel rod - so you might be lucky and find that a new feed nut will be good enough...

Regards,

IanT

Looking at the cross slide photo, there seems to be a lighter spot on the flat surface above and just to the right of the brass feed nut. It may just be discolouration, but is it a retaining pin? I doubt whether the nut is just pressed in.

Edited By Redsetter on 07/07/2021 07:15:12

Hi Andy,

I've been following this thread over the past couple of days. Looks like you are getting some good advice.

On the subject of the cross slide nut, I replaced the one on my Faircut lathe last year. Mine looks like a very similar design to yours. With the Faircut I did find it necessary to finish the job by tapping in situ.

Mine was a square thread which made life more tricky - I had to do most of the cutting with a single point tool on the lathe and also make my own tap to do the finishing cut. If you don't have a working lathe you will need a different approach to mine but if you intend to replace the feed screw too then you can pick whatever thread you like so that should help.

It was a fairly long job with a lot of uncertainty along the way. The words are on a couple of threads on here...

https://www.model-engineer.co.uk/forums/postings.asp?th=166091
https://www.model-engineer.co.uk/forums/postings.asp?th=144221&p=5#2638709

Good luck!

Thanks guys

Pete - not really enough meat left for a new thread plus must be a stepped hole as little brass showing on inside.

Ian - not acme but square thread and I don't think you can get taps for that see pic. But moving to a 3/8 acme thread may be the solution. There are taps and dies in RDG tools for £20 each. Would a hand die cut such a long screw from scratch.

Red - you have eagle eyes and I have been blind. See pic. There is indeed a pin. Do you foresee any issues with drilling this out? Need to make sure new pin is below level.

Andy - that very similar to my problem. I need through through your thread again. I know I don't have your skill and tools to repair in the same way

Andy, the pin is probably parallel and goes right through the casting. If so, it can be persuaded out with a light hammer and a suitably sized pin punch. It should not be too tight.  Can you see the other end?

Edited By Redsetter on 07/07/2021 12:20:34

That does look like a pin to hold the feed screw in place Andy, in which case it would need to be drilled out to remove the nut. However, this would probably be easier than working on the nut in-situ I think.

A 'square' lead screw of that length really needs to be screw-cut and would not be something I'd recommend you try at this (or any) point in your hobby machinist career!

You can however purchase ACME threaded rod and also a matching nut - although it may have to come from the US. Over here a similar (metric) thread is called a 'trapezoidal' thread and might be easier/cheaper to come by. It should be a much simpler job to modify commercial threaded parts (to fit your lathe) rather than making them from scratch...

Regards,

IanT

Edited By IanT on 07/07/2021 12:30:37

Redsetter - you are a star. Knocked the pin out. Tapped a dodgy M10 thread and used large socket a puller. So the sucker is out.

Now - any idea where I could get a nut 3/8 -10 nut made. O.D. from my vernier is 12.8mm. Don't think I need huge accuracy, just something to get me going. The hole is off centre slightly but I think centred would be fine - surely I could just drill the faceplate hole larger if necessary. Happy to pay!

Ian - I hear what you say and will look at this if I cannot get something made.

Hi Andy,

I would not suggest that you go down the same route as me - I had a working lathe to make the nut and tap and it was still a lengthy job that took multiple attempts. Square threads are a pain to get right. Hopefully some of my posts will still help you though.

Another option you could consider would be to use a vee thread form. If your feed screw is 3/8 diameter then you could use 3/8 BSF which has 20 TPI so every turn would be 50 thou. That might make it easier/cheaper to source threaded rod - GWR Fasteners do it in mild steel for example. Going metric would expand your options further but you may wish to keep things Imperial.

Some folks have approached this job by making a flanged nut and drilling and tapping a couple of holes on either side of the nut to hold it in place - this will allow you to side step any questions of press fit tolerances and that retaining pin. The downside is that you will lose a little cross slide travel to accommodate the flange thickness.

Glad you have the nut out.

I'd be a bit cautious - the cutout for the retaining pin has broken through into the bore so you may not have much room to play with if you want to carry on using the pin to secure the new nut.

I'm sure there are plenty of folks on here willing to help once you know for certain what you are going to do with both the nut and the feed screw.

Whereabouts are you located BTW?

If the OD of the Leadscrew is 12.8 mm, it is a 1/2"

For a machine of that age, I would expect everythging to be Imperial, so securing threads are likely to be Whit form, BSW for Coarse, and BSF for the fine ones, possibly with BA for the gib adjusters.

You mentioned damaged gears. Most likely caused by engaging Backgear with the pulley locked to the mandrel, to lock it while a stuck chuck was freed.

Moral DON'T DO IT!

There are methods of unsticking a chuck without endangering the gears.

When you bare looking for replacements (possibly from another machine, and require modification - boring or bushing )

The gears need to be the same DP and pressure angle.

Count the teeth on one gear, and measure the OD in INCHES. (Teeth + 2 ) / OD = DP. For a machine of that age, the Pressure Angle is likely to be 14.5 degrees.

Modern gears are almost invariably 20 degrees, so will not match..

If you cannot adjust out the end float, while the lathe is functioning, you should, be able to produce a solution.

measure the end float and turn up a washer, (Ideally phosphor bronze, or brass ) to fill the gap,

Then remove the mandrel and reassemble so that end float is eliminated.

HTH

Howard

Thanks Andy. Not sure the best way to go.

The simplest for me would be get someone to make a nut, I could send them the rod. 10 tpi does sound like quite coarse contol - 3.6 deg for a thou

I like the idea of 20tpi but can the slide be driven by any thread form. I thought square or ACME was necessary.

Could I use an M10 rod. I see GWR have M10 stud connectors - apparently with an OD of 13mm? Perhaps I could file/turn this down to fit 1/2" hole. I think it is still OK to use the pin. Need to drill through with insert in (or maybe mark insert take it out and file a groove. I think the pin penetrated the bore because of my mangling - even if it does then just run a tap through it. Perhaps a grub screw would be better?

Thanks Howard. I measure the screw at .35" with vernier so presumably 3/8" with clearance. The nut is 12.8mm so as you say 1/2".

Since you bring up the backgears let me add that story.

The driven pully on the spindle has a grub screw to secure it to the spindle. The lathe has an eccentric lever to engage the backgears. The grub screw in the spindle pulley would then be moved to the big backgear bullwheel.

See picture of the large backgear. The hole for the grub screw is broken. I think you have explained how this happened. It was like this when I got it and yes the chuck is stuck. How can I fix this.
- mount wheel at angle on my pillar drill and drill opposite to the break. Would this be safe?
- find someone to braze up the broken bit? (Is gear bronze?).

And how do I free the stuck chuck - how do I grip the spindle.

Cheers

Hi AT3!

Yes, you could well set up the gear and drill and tap another hole in the boss. As close as possible to square to the bore, would be my advice.

You will have lost a little bit of bearing are when using Back Gear, but probably not enough to cause any disasters

You are in the "Chickem and Egg" dilemms. The really nice thing to do would turn away the boss where it bis broken and then to make up a Top hat bush, ready drilled and tapped for the grubscrew, and Loctite that into a slightly enlarged bore in the gear. But for that you need the facility of another lathe! Or someone nearby who can do those jobs for you.

As to removing a stuck chuck, there are are various slight variations on a theme.

Firstly, tighten the belts for motor and countershaft, setting up for maximum Chuck speed.

1 Grip a piece of hexagon bar in the chuck.Choose a sensible size, and for which you have a 1/2" drive socket.

(3/8 might do but 1/2 will ,be stronger )

2 Put a long power bar into the socket.

3 Hit the end of the power bar, HARD, with a mallet.

4 Alternatively, Apply an Impact wrench to socket, in the hope that it will hammer the chuck free.

or

A Grip a piece of sturdy bar (preferable to wood ) through the chuck jaws.

B Whack end HARD

Either way it might need more that one bash to free the chuck.

You may find that warming the body of the chuck with a heat gun will help it to unstick

In either case, hopefully, the inertia of the motor will be such that the chuck unsticks. Once it has moved a few degrees, the grip should decrease dramatically.

Place a board across the lathe bed, in case it fall!

For the future:

You already know not to engage Back Gear to lock the mandrel

Clean both internal and external threads.

DON'T run the chuck on under power, it will tighten under cutting loads.

HTH

Howard

Take your time, applying additional coats of thinking is usually a good plan.

No particular thread form is necessary provided that the screw and nut match. Each form has its pros and cons of course but a new thread of any form will work better than what you have now. Plenty of lathes are designed with vee form cross slide screws - the Stringer/EW 2 1/2 inch for example.

Both square and ACME tend to be quite a coarse pitch in order to achieve a sensible thread depth. All types will work... you just need more turns on the handle with a finer pitched thread.

M10 would work but the usual pitch for M10 is 1.5mm which would be less convenient for mental arithmetic when using the lathe. You can get finer pitches (i.e. 1mm) but they are less common (and probably more expensive). It's also 0.5mm bigger diameter than 3/8 inch so you will be losing some wall thickness on your nut... plus it will be 0.25mm more likely to foul the retaining pin. On balance sticking to 3/8 might be better. I've been trying to remember where I saw someone who had metricated their (worn out) cross slide screw but I can't find it now... probably one of the many lathe restoration videos on YouTube.

Can you turn something (anything) yourself ? Maybe... it depends on whether you can get this lathe working at least in a basic way so that it can mend itself. You could perhaps lock the cross slide by tightening the gib screws and then set the compound to 90 degrees and use that to put the cut on... just while you get the cross slide screw fixed up.

Thanks Howard, Andy,

You have given me plenty to think about and a few more coats of thinking is better than stripping back. I will order up some stuff and experiment and get back to you.

Andy - a while ago I bolted up the cross slide and used the top slide to turn some wood and a brass ferrule. So I could try again, however this is the thread that keeps on giving. I just checked the top slide thread and eek - see picture.

This is the same 3/8x10 screw but this time the casting is threaded. And the casting is cracked and the threads are nearly gone. I guess I can try the same approach for the topslide, maybe turn down a M6 stud connector and make a new screw.

I guess I may need a new topslide. The slots in cross slide appear to be 57mm or 2 1/4" apart. Is this fairly standard and will it be easy to find. I don't really understand this top slide anyway. There is only one bolt to hold it down and this bolt is on the right. Given the downward force from turning surely it would be better on the left?

I am thinking that a Myford ML7 feed screw and nut might be adaptable to the cross slide. The nut has a flange with two screws so it should be attachable, and the hole can be opened out if necessary to clear the body of the nut. Not sure about other dimensions, but they can't be far off, as it is doing much the same job. Maybe not the cheapest solution but they are readily available.