Thank you for the promise, Ian!

And interesting progress report.

Tracy Tools list ACME taps up to 3/4" . £40. They say other sizes are available but, no, they won't be cheap.

I've still the problem with my mill of the very stiff quill, so much so that sensitive drilling is a gamble. Unfortunately I can't see how to gain access to the rack and pinion, which might simply be bunged up with congealed grease, and I don't have the tools for handling the spring safely.

There's also a curiou spot on the long travel where the handwheel seems to suddenly jump ahead of itself, but I have not been able to establish exactly where and in what circumstanes this happens.

Funny you should mention 1" x 5 ACME, I have just made a tool to hold the er22 5tpi Acme lay down insert. The tool will pass into the 0.800" start bore for that size. You will never be able to buy one as tooling for that size would need a start hole more than 1 1/4 " diameter. The tool is right hand and will be used away from the chuck for a LH thread. I will have to measure the working length, maybe 2 1/2". The knee of the Tom Senior could do with a new nut.

I would be willing to lend you the tool, if your lathe can manage it.

Edited By old mart on 10/06/2021 17:38:12

Edited By old mart on 10/06/2021 17:39:31

You could grind an HSS boring-tool, alterntively use the steel-insert type boring-bar in which the cutting tip itself is a small piece of HSS round.

As it happens this is a problem I have to solve for myself, not for a machine-tool but the steering-gear for my steam-wagon. I have worked out it should be a long-lead so 2-start thread, square or ACME – probably 3/4" dia X 1/4" lead – to give about 4 steering-wheel turns lock-to-lock. My thought is either a steel-insert boring-bar, or to turn what is effectively a single-tooth tap in silver-steel.

For the latter, screw-cut enough of the silver-steel to pass right through the nut, then either machine grooves in it to create a machine-tap that will be driven by the change-wheel train, or neck the material behind the last turn down to leave just a single cutting-tooth.

'

Just a thought… there are internal tools that use a circular insert screwed onto the end face of the boring-bar. These are typically for cutting O-ring and circlip grooves, but I wonder if there are thread-cutters made for these. If so ones of appropriate size may be available.

I looked on the Cutwel (one 'L' ) site, and though they do stock such tools they do not include ACME cutters. They do though sell the more conventional flat-mounted inserts and holders for ACME internal threads.. .but apparently not 5TPI

'

Thank you for the offer! Yes, if you can find it I will appreciate it. I am very wary of clock-type springs, from near-misses many years ago and warnings published for those making clocks – and using special tools for that.

From what I can see, one end of the quill spring is clipped into the cover, the other to the shaft, but I can't see how in detail, nor how to release all the tension safely. I don 't think simply unwinding the cover is enough to slacken it fully.

Edited By Nigel Graham 2 on 10/06/2021 22:53:46

Looks like a lovely job, is that made from silver steel, will you harden it? I'm a bit hazy about insert codes but does er22 denote an external thread insert intended for a 22mm bar, if so why not an internal NR type?

William.

I had a bit of a snigger when I read the comments about the tool I had made to hold the 22 size insert and still pass into a hole of 0.800". I have to confess two points regarding that tool. It is made of a bit of steel that was laying around, and I strongly suspect it is a bit of stainless steel. The photo is the only one taken of it and as soon as I fitted the insert, I realised my mistake. The insert housing is much too near the end of the tool and the insert overhangs the end dangerously. The entire end has now been remachined to give the best support that I could manage.

Regarding lending the tool, The chance of damaging it is remote if careful attention to the actual thread cutting is adhered to. With a 5 ACME, the actual depth of thread is 0.1" deep from the start bore of 0.8", resulting in a finished diameter of 1". This might have to be increased very slightly if the leadscrew is used as the go gauge.

To use the leadscrew as a gauge, you would have to remove the tailstock.

If the thread is produced in multiple passes normally, from first touch in the bore, depths of +0.015",(twice) + 0.014", +0.012", +0.010", +0.008", +0.006", +0.005",(twice) +0.004, +0.003", +0.002", +0.001", which make the total 0.1" deep cut. Any further passes to get the leadscrew just fitting to be made at 0.001" or less. The reduction in depth of cut as the threading gets deeper is because the ammount cut is getting bigger each time.

I can make another tool any time and your only requirement would be to buy me another insert if you broke it which is very unlikely, so the offer stands.

I'm back at the museum tommorrow and will be able to measure the working length of the tool, which will have to be longer than your nuts if the thread is right hand to give you time to disengage the leadscrew nuts after each pass.

Edited By old mart on 11/06/2021 18:49:30

I remembered to check out the ACME threading bar when I was at the museum today, and have brought it home with me.

After a bit of a struggle, I managed to find your address and the tool will be in the post Monday.

If you are careful and take the cuts that I recommended in my post of the 11th, there is no danger of a crash. The hard thing I find is remembering to go back to the zero on the cross slide every time before withdrawing the tool. It helps to have the settings on a piece of paper and tick them off as you go. I would try out the leadscrew for fit during the last few cuts.

Edited By old mart on 12/06/2021 19:16:02

Edited By old mart on 12/06/2021 19:23:25

Edited By old mart on 12/06/2021 19:30:38

Those figures I put down would be easier to manage in a slightly different form. Starting by just touching in the 0.800" bore and setting 100 on the cross slide, using thousandths of an inch numbers and working back towards zero.

100 – 85 – 70 – 57 – 47 – 39 – 32 – 26 – 21 – 16 – 12 – 9 – 6 – 4 – 3 – 2 – 1

Start checking the fit at 3. There is a possibility that you might reach 1 and still not be able to get the leadscrew to go in. You would have to creep up slowly in that case. Also worth checking if things were tighter than expected, would be the core diameter of the male thread. I have machined this gunmetal dry, and if you have an airline, blow the swarf out every pass.

Glad you have got it, now for some very careful setting up. I would shim the tip height about 0.005" above centre. I hope the tool is long enough for you to comfortably disengage the nuts, I made it just long enough for the nut length I wanted, but I have the easier left hand threading away from the chuck. I have relieved the lower part of the insert because the helix angle is greater with that small diameter to pitch ratio. If you need to turn the insert, you shouild also use a diamond file to relieve the lower edges of the next edge. There is very little chance of blunting the insert cutting bronze. Make as many nuts as you like. You could even produce a test nut made from a bit of aluminium, if you do, use WD40 or equivalent to lubricate things.

I have checked out HPC gears and have bookmarked them in my favorites, they could be very useful.

Edited By old mart on 16/06/2021 18:31:11

The threading bar arrived back safe and sound along with a nice letter and some money, which was unexpected, but much appreciated. I will spend the money on tooling for the museum. Now I will have to get on with using the bar myself, very easy as the thread on the Tom Senior's knee is anticlockwise. Keep us updated with the mill repairs.

It's a good job you mentioned the insert, I have been transfering rubbish from the bin into a bin bag, searching, and found it after 1/4 hour. I now have 5, 6 and 8 tpi ACME inserts. I would like to make a better nut for the drill mill X leadscrew, but have not been able to find 2.5mm trapezoidal inserts.