Acme thread

[Anonymous]

I made these square thread serial taps:

to make the nuts for the brake shafts on my traction engines:

After I'd made them I cut a trial thread in brass which was easy. In contrast the bronze I used for the actual nuts was a total PITA.

Andrew

Edited By Andrew Johnston on 27/11/2019 22:22:12

[egaParticipant @ega]

The comparisons of ease of tapping suggest one possible advantage of the reviled standard Myford nuts; better to have to replace a relatively cheap component than the expensive leadscrew?

[Shaun BelcherParticipant @shaunbelcher81617]

Posted by Andrew Johnston on 27/11/2019 22:21:29:

I made these square thread serial taps:

to make the nuts for the brake shafts on my traction engines:

After I'd made them I cut a trial thread in brass which was easy. In contrast the bronze I used for the actual nuts was a total PITA.

Andrew

Edited By Andrew Johnston on 27/11/2019 22:22:12

Wow, thats impressive! I dont think that grinding HSS to make taps would be an overly easy job.

Anyway, ive been looking at different taps on the market and they appear to be fairly tapered and long so should in theory make it very simple to cut the thread without a sequential series of taps.

[HopperParticipant @hopper]

I wouldnt use stainless. Can be a right PITA to machine and no great advantage in this application. Mild steel works just fine, especially with brass nuts. Most of the commercially available threaded bar will have a rolled thread which is left in a work-hardened condition.

If you do use bronze for the nut, make it leaded bronze and not phosphor bronze as the latter will wear non-hardened steel faster. The idea of brass nuts is the same as Myford's orginal Zamak, the nut is sacrificial and wears faster than the leadscrew. So you replace the inexpensive nut, not the expensive leadscrew. Plus its easier to machine.

Don't suppliers of trapezoidal threaded rod also usually supply brass nuts to match? Would be easier, and probably cheaper, to buy the nuts even if you have to machine them down to a sleeve then bore out the original nut and Loctite and pin the sleeve in place.

Edited By Hopper on 28/11/2019 01:04:09

Edited By Hopper on 28/11/2019 01:22:27

[HopperParticipant @hopper]

Posted by Shaun Belcher on 27/11/2019 10:36:41:

Posted by mark smith 20 on 27/11/2019 09:37:14:

Shaun , a slightly larger diameter screw would still work the same in regard to the dials if the pitch TPI is the same .(as long as everything else is machined to fit (the nut, dials ,handles etc…)

Edited By mark smith 20 on 27/11/2019 09:37:59

Thanks, thats all I need to know.

I would hate to find the dials were not accurate if i used this feedscrew.

Im actually considering making my own resettable dials anyway, but would need to CNC engrave the markings on the outside accurate enough

Dials will still be accurate. The imperial dials you have have are graduated in 100 graduations. This becomes then 1/100th of the 2mm pitch of your feedscrew or .02mm. Diameter of screw makes no difference.

Model engineers were engraving dials long long long before CNC was invented. You engrave the lines with a sharp lathe tool mounted sideways in the tool post that is racked back and forth by the carriage handwheel, using a carriage stop to control length of the line.

Position of the lines is controlled by a pointer or similar engaging with the correctly set up change gears on the headstock quadrant. To get 100 graduations, you use a 50 tooth gear meshing with a 25 on the spindle, or some similar 2:1 reduction combination of gears such as 20 on the spindle meshing with a 40 which has the 50 tooth gear on the same stud.

You then stamp the numbers on using number stamps and a hammer. A simple jig to hold the dial and punch in the right positions helps make a tidy job.

Many of the old ME books by G H Thomas, LH Sparey, Ian Bradley etc cover the technique. Thomas in the most detail. His "Model Engineers Workshop Manual" includes the drwaings and instructions to make resettable dials for a Myford.

Edited By Hopper on 28/11/2019 01:24:27

[Shaun BelcherParticipant @shaunbelcher81617]

Posted by Hopper on 28/11/2019 00:59:16:

I wouldnt use stainless. Can be a right PITA to machine and no great advantage in this application. Mild steel works just fine, especially with brass nuts. Most of the commercially available threaded bar will have a rolled thread which is left in a work-hardened condition.

If you do use bronze for the nut, make it leaded bronze and not phosphor bronze as the latter will wear non-hardened steel faster. The idea of brass nuts is the same as Myford's orginal Zamak, the nut is sacrificial and wears faster than the leadscrew. So you replace the inexpensive nut, not the expensive leadscrew. Plus its easier to machine.

Don't suppliers of trapezoidal threaded rod also usually supply brass nuts to match? Would be easier, and probably cheaper, to buy the nuts even if you have to machine them down to a sleeve then bore out the original nut and Loctite and pin the sleeve in place.

Edited By Hopper on 28/11/2019 01:04:09

Edited By Hopper on 28/11/2019 01:22:27

The supplier sells the nuts but they dont have the correct flange, I would have to machine them down as you say, plus they are expensive, although I can find the same ones overseas for a fraction of the price.

Yes ive seen a youtube video of someone engraving dials in a similar fashion. I just dont have any of the correct gears for my lathe at the moment.

Im still in the process of getting my lathe up to scratch and getting tooling etc.

[HopperParticipant @hopper]

Buy the overseas ones – that's what your local supplier does these days!

[BaldricParticipant @baldric]

Like Andrew I have made my own taps for a 3/8", 2 start square thread, made from silver steel, then hardened and tempered, the thread was milled using a 1/16" cutter rather than done on the lathe as there was no run out to go in to on the part, the taps made with the same set-up. Using the taps in brass was fairly easy, about 1 turn, then remove to clear the swarf.

Baldric.

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