Advice on lathe Threading tools

Just a comment regarding thread cutting, this process really does benefit from a quality thread cutting oil. I use a small paintbrush and Rocol RTD oil but others are available.

The other thing I have done is an aluminium dummy spindle nose (not bored) to check the threading progress in backplates as is cut. Before you start on an actual backplate this would make a good project to practice threading on. I'll dig out either the dummy or an existing photo.

Martin C

Edited By Martin Connelly on 22/05/2020 11:47:35

Hi Martin.
Great minds actually. It was also my intention to make a dummy spindle nose to check the threads, plus it’s going to be simpler for me to start with the external I think. I’ve got some MS steel blanks of the right size in order too.
move got some Moly cutting grease. Maybe that’ll work.

By all means use lubricant on steel when you cut threads, I always use a little CT90 spray. When you cut cast iron, do it dry, and a vacuum cleaner and magnets help to reduce the mess of CI powder, and take care to remove all the dust from the lathe afterwards. I made a dummy spindle nose for the Model A, the difficulty is getting it exactly the same size. As I mentioned before, when your insert just makes a mark on the 1.750"/1.751" register, the thread size is exactly right. These large 8 tpi threads have a lot of leeway in the size, going a bit loose is much preferable to tight.

You haven't mentioned how you intend to hold the plate as you machine it.

Hi old Mart.

I have a 3 jaw with reversible jaws that I hope will be big enough to hold the boss.
That makes me thing though - which side should I be cutting the thread from. Using your method I would need to be seeing the inside of the boss register, so that wont work too well.

Perhaps the outside of a 5" plate will fit into the reversed jaws of my 6" 4 jaw?

In the end, I guess I could reverse it and bolt it to the 3 or 4 jaw plate with some temp holes?

As you don't have a faceplate, holding a blank will be difficult. Therefore, I would tend to go for a part machined, one with a 1 1/2" Boxford thread. It will be easier for you to hold and there is enough meat in the bore to go to 1 3/4" S&B. Being machined will enable you to attach it to one of your chuck backing plates by drilling and tapping it. A four jaw independent chuck can be used as a faceplate if tee nuts are made to fit in the jaw slots. You could also drill and tap the four jaw between the jaws, I have done this mod on both the chucks at the museum to attach balance weights. Chronos have a 6" one that would suit.

**LINK**

It's a while since I did mine but I think I held mine in my 4 jaw. I can turn an 8" diameter so a plate at 6" or a little more could be held with clearance between the lathe and the jaw protrusions. I can't remember taking any photos of the job but I know that I unscrewed the chuck and backplate to check against the spindle then remounted it to take a bit more off without taking the backplate out of the chuck. I think towards the end I was hand chasing it, polishing it with a small stiff wire brush and scotchbrite to get a smooth fit on the thread rather than use the threading cutter driven by the lathe. It took time but did the job.

Martin C

I have just worked out that I have done this job 4 times now. The first was to make a faceplate that could also be used as a catch plate for turning between centres. This was bought as one for another machine that was then modified to suit much as old mart is suggesting with the Boxford backplate. I ended up with a ragged thread which is why I ended up with the hand chasing and polishing on the rest. The next one was for a 100mm chuck then one for a spare 6" chuck and finally for an ER32 chuck, pictured below. You can see the thread witness mark on the register that old mart mentioned somewhere.

Martin C

That Chronos 6" plate was the only one that I could see that had a decent diameter boss for increasing the thread diameter, and the price increase over an unmachined blank is well worth the reduction of CI mess. The 160mm od could be reduced to 5" if that was the size required using the boss to chuck up on normally, and then the four jaw could hold it easily boss to the right. The advantage of using the four jaw is that the plate will then stand off the chuck face, giving a little runout when threading. Boring the register and the thread bore and threading should be done together to ensure perfect concentricity. To check the thread, which will be fine, the cheat is to unscrew the chuck, and try out the thread on the spindle without taking the plate out of the chuck. Screw it back on only if the backplate needs another pass or two of threading.

Edited By old mart on 22/05/2020 17:03:49

To check the thread, which will be fine, the cheat is to unscrew the chuck, and try out the thread on the spindle without taking the plate out of the chuck. Screw it back on only if the backplate needs another pass or two of threading.

Ha - cunning!

I very much appreciate all these tips and advice. I know you guys must have answered these questions before, so its doubly appreciated. I have just ordered the 6" semi machined boxford plate from Chronos.

Any clever solutions for knocking up a manual winding handle?

Can't find a picture unfortunately but I made one for my mini-lathe based on the mechanism used to adjust bicycle handlebars.

Turn about 75mm of aluminium rod so the diameter just fits in the spindle. Drill a 9 or 10mm hole through the rod to comfortably pass a long M8 bolt. Then saw the rod at a 45 degree angle across the middle and fix a crank handle to one of the pair.

No need for any precision.

Assemble so the head of the bolt is inside the spindle and supported by a large washer on the flat end. With the bolt loose, insert the two parts into the spindle and tighten the nut. Tightening causes the two angled surfaces to slide and expand to grip the inside of the spindle. Undoing the nut releases the grip allowing the winder to be removed.

Dave

What is the slowest speed on your lathe? Mine is nominally 66 rpm which is close to 1 rev per second. If you have a lower slowest speed then it should be possible to use power for threading. One thing to be wary of with a manual winding handle is that if you are using carbide tooling then any reverse rotation of the spindle with the tool in contact with the workpiece runs the risk of breaking the carbide. It's great in compression being pushed down onto its seat but hopeless in tension which applies when the tip is pushed away from its seat.

Martin C

The winding handle I made to do the first 1 3/4 8 W backing plate thread was super crude. Whatever materials came to hand. The end in the spindle had a simple expander and the winding handle was just a bit of scrap iron, nothing like those very nice Myford winders.

As mentioned by Martin Connelly, you must back off the tooling each time you reverse to the start point. Earlier I mentioned zeroing the cross slide dial before starting. Because this is a bore you are threading after practicing on external threads, you should just touch the bore first and then dial in the total depth of cut expected (0.080". Remember, you are cutting backwards like when boring. So you should return each time to 80, or a bit more or the insert will probably break. Having the intended cuts written on a sheet of paper and crossing them off as you go is a help also. So the cuts would be as follows:

80, 68, 58, 48, 40, 32, 25, 19, 14, 10, 7, 5, 4, 3, 2, 1 until the first marks show on the register.

By hand has another advantage, it will be obvious when you run off the end of the thread at each cut. You will feel and probably hear the cut in progress, and if you count the turns from first contact to running out of thread, you can then reverse a couple of turns more backing out. This will take care of any backlash when going into the cut.

Making a practice dummy out of aluminium first before committing to the backplate would be a good idea, but you must use AC90, or WD40 to lubricate it when you are machining it. And it should be set in the chuck with the same gap between it and the face of the chuck as the real thing would have.

Hi Guys,

I made my lathe winding handle from a scrap plastic drum pulley from a old front loading washing machine. I made a revolving handle and screwed it into one of the spokes to make it easy to turn.

The collet is similar to the one in the drawing above.

There are other pictures in my album.

That handle will make all the other Myford people green with envy. You will never get me to post a photo of the one I made.

Oh go on ! It can't be that bad if you still have and use it.

That wheel came from a scrap yard just for the price of taking a bolt out of the hub and I kept the belt. Handy keeping a mover in the boot.

Myford gears are a coarser pitch than S&B ones. A shame as they are plentiful.

There is info available from lathes UK on the Sabel:

https://store.lathes.co.uk/print/ms580c

Edited By old mart on 23/05/2020 14:43:21

One thing I forgot to mention is that while you are winding the spindle by hand, is to keep the leadscrew nuts engaged throughout. Reversing the spindle at the end of each cut will automatically move the saddle to the starting position. It doesn't matter how far you go back, but two extra turns will take care of any backlash in the gearing.

None of the backplate stuff arrived for the weekend to I made a spindle handle instead. Thanks for the inspiration.

Hi Jim, Guys,

Not bad, not bad at all ! I've seen far worse.

I put a collar on mine to stop the winding wheel from fouling the change gear cover. You can't see it in my pictures above. But it was too easy to put the handle in and then find that you couldn't turn the handle because it was pressed up against the cover.