How to identify a thread, ACME vs TR

[Michael Gilligan]

On Michael Gilligan Said:

On David George 1 Said:

Just checked the Z axis leadscrew and it is 5/8″ diamiter […]

That’s uncannily strange … exactly 2mm bigger than moonman measured his

MichaelG.

Moonman measured his X axis as that is what failed, hence David’s offer of his Z axis screw being of no use.

[Michael GilliganParticipant @michaelgilligan61133]

Doh !

MichaelG.

[JasonBModerator @jasonb]

I was just looking and TR14x2 taps are available both left and right hand delivered for less than the cost of a piece of 14mm silver steel excluding delivery. So unless you can’t wait a couple of weeks it is hardly worth making your own.

The only advantage of screwcutting it would be that you could probably get a closer fit right from the off then any antibacklash slots & screws have less work to do.

[old martParticipant @oldmart]

I would bet on the 2mm pitch TR thread, I have not come across 13tpi ACME.

I had wanted to make antibacklash nuts for the museums round column mill which has 2.5 pitch TR leadscrews which are somewhere about 22mm diameter. It was several years before a Chinese ebay seller suddenly offered  threading inserts in that pitch and I bought a box immediately. Now we have 9 unused inserts and one pristine one after using it for both RH and LH nuts in gunmetal.

[Martin Johnson 1Participant @martinjohnson1]

Just to bring the topic out of orbit – if you cut an Acme and it should have been a trapezoidal, how would an ameteur tell it was wrong?  I know several ways it can be done in industry but for the average home workshop???

You are looking for an odd thou or so on the form, most of us would covet a T& C grinder that could produce the tool tip to that accuracy.

I have cut several square or acme nuts and it is a tricky job, mostly in the tool making.

On Delrin nuts, I had a set of compasses with Delrin nuts which served me through school, apprenticeship, drawing office and chief designer roles.  They are still in use for marking out wood.  That’s a life of 50 years and counting!

Martin

[old martParticipant @oldmart]

That is true, the differences are minimal, and if you use two in tanden for antibacklash, then the biggest problem would be caused by uneven wear in the length of the leadscrew.

[JasonBModerator @jasonb]

I think I would just buy an insert rather than covert a T&C grinder.

[JasonB]

On JasonB Said:

I think I would just buy an insert rather than covert a T&C grinder.

………That just happens to fit in a boring bar that just happens to go down the root diameter with room to spare and sufficiently rigid to cut an Acme or trapezoid thread.  Aye right?……..

Actually some of us get more pleasure out of making things than buying things.  Either way, my main point still stands.

Martin

[JasonBModerator @jasonb]

Wouldn’t that also apply to a tool you ground yourself?

I’ve a bar that takes the size 11 inserts which would fit, if It were smaller could always go down the Carmex tinytool route. Though these days may even be easier to thread mill but not everyone has the machines for that.

Should not need that much rigidity. What’s a 2.0TR cutter going to be about 1mm wide on average and cut 1mm deep into bronze? Not a lot different to what I was cutting this afternoon a 1mm wide by 1mm deep groove, the reduced shank after the head on that cutter is about 4mm dia, cut like butter.

[moonmanParticipant @moonman]

Well chaps I’ve got an email back from Chester and a new crossnut is nearly £100, it has to come from China and most of that is postage and VAT. Fair play to them though for finding a solution to an older model machine, if I do ever upgrade I’ll be sticking to that brand as they have been very help.

I did decline though as I’d rather spend an afternoon making one and then take the £100 to the pub.

While I was waiting I knocked up a little internal threading bar and have made a working replacement from some Brass scrap I had so the mill is back and limping along but I think I need a better more permanent solution.

The ball screw solution does interest me, is that a big improvement? I thought this was more of a CNC conversion thing.

I’ve also read a few posts about people creating “evan nuts” out of delrin. There shouldn’t really be any real load on that nut so I think this would also work. I know you can also get impregnated plastic so it would self lubricate like bronze.

And of course I could use a nut and make a housing for it, or even make my own tap at this stage now my mill is back online.

It’s been a good opportunity to clean my mill though, it’s been completely degreased and is now back together with fresh oil and it’s running the best it has in my ownership.

[David George 1Participant @davidgeorge1]

This is my 1/2″ x 0.1 pitch square thread internal screw cutting tool.

David

[David George 1]

On David George 1 Said:

This is my 1/2″ x 0.1 pitch square thread internal screw cutting tool.

David

That’s very similar to the one I ended up making, the only difference is I used a 01 tool steel shaft and cross drilled it for a bit of HSS (a dead endmill).

It worked nicely, I’ve got some Bronze on the way for the “final” attempt at it.

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