2 pitch acme threading inserts

anyone know where i could get some 2-pitch acme threading inserts. i need to do an id thread with a 1.250 minor dia. it is a 2- pitch , 8 start thread. thanks in advance for any information.

On the really big (course) stuff like that - I think Greenleaf is a good souurce.


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I am Ox and I approve this here post!

The lead angle on that sucker is 40.425 degrees!

mrainey said:

The lead angle on that sucker is 40.425 degrees!

Click to expand...

My first thought was ''That's gonna be one hell of a helix angle, sooner them than me'' but 40 odd deg?.......... surely that'll be special tooling or technique?

mrainey said:

The lead angle on that sucker is 40.425 degrees!

Click to expand...

I didn't catch the 8 start part the first time!

That's gunna be a trip!

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Think Snow Eh!
Ox

Holy Yikes!!! That's some thread!

The only insert I've found for 2 pitch is a topnotch style, and that sucker is BIIIGGGGGG!!!
Size 6!!!

You'll need a left hand insert, J&L catalog# KTN-15227E
And then some internal holder, but here is the kicker. J&L - for your convenience - doesn't even list it.
That's OK though as it would not fit into your 1.25 bore anyway.

My suggestion: Have one ground out of a solid carbide bar.
I once purchased some lista cabinets at an auction, loaded with custom tooling.
There were quite a few acme looking internal tools in there. They were brazed carbide tip with a wicked chipbreaker, curling towards the front.
These were production looking thingys as they had the part# engraved on them, and there was a bunch.
I think grinding it out of solid for 1 or 2 piece would be cheaper.
OR
Make a steel holder and braze the topnotch onto it.

How about 2" lead, 8 start? That I can imagine.....almost

I think the only realistic approach to this (assuming there is some depth to an 8 start thread?) would be to cast it to a threaded mold somehow...


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I am Ox and I approve this here post!

Without doing any calculations I'd bet 8 starts with a 2 pitch acme will leave nothing but a bore equal to the major diameter. Is it really a 2 pitch or is the lead 2"?

Geeze,
The Manual Guys could do it ..

By Internal Thread milling..

Multi Start and Thread Mills seem to go together...

ASARGENT

We Make a screw 7ft long X 3.5" dia. with 6ft of acme 2TPI single start as well as the aluminium bronze nut bushing. We use Kennametal top notch. If you require any further info feel free to ask. Just realize that your not talking about a 2TPI lead forget about that. With such a lead 4" you would be better to mill it or the piece better be short.

Robert

we do actually have the gage already. we had it custom made and my dumba## didnt look for inserts to do it first. i will look the gage over closely. maybe there is something more to it. it really doesnt look that bad. i will let you know.

No way out of it. That tool is gonna have to be a special. An insert will not work for high helix angles. For one thing an Acme thread flank angle is always taken from the radial plane. If you tip a 14 1/2 degree insert 40 degrees it throws the pressure angle off by an amount you'd have to work the solid trig to get. Too early for fancy math for me. Anyway the tool's top plane has to be normal to the helix angle but the profile ground on the tool has to produce a thread that's 14 1/2 degrees when cut through with a radial plane.

Incidentally, that=s the big difference between worm threads and Acme threads. The pressure angle of an Acme thread is taken from an axial plane and that of a worm thread is taken normal to the helix angle at the pitch line.

A garden variety threading insert will cut an OK thread for most single start Acme threads because the effect of a 5 degree helix angle isn't much. The same insert if used to cut a thread on a 40 degree helix angle will result in consideerable error. Crafty old rebuild machinists who cut lots of lead screw nuts will try the threading tool in the new (or re-cut) screw with the shank correctly oriented before they start boring threads in the nut. See, the lead screw may not be accurate in its flank angles either. No problem, so long as the flanks of the thread and nut mate properly.

Then there is the minor diameter. Subtract the whole depth from the major diameter and another 0.020" for clearance and your boring bar gets real skinny. Consider downwards tool deflection and its effect on the axial lead error; it may be pronounced. I strongly suggest you approach this thread with two tools. One a grooving tool to hog out the meat and a narrow singlle sided threading tool to cut the flanks individually.

One last thing is tool force when machinig the trailing flank may be enough to drag the carriage away from bearing on the half nut. You may need some pull-back to keep the carriage in contact with the driving flank of the lead screw.

This is not a usual machine shop problem. If the nut is to bear correctly on its screw and if it's to run efficiently and wear slowly the flank angles of the nut and screw have to match. A little care and preparation will go a long way to secure good results. You can't just throw in an insert and take good results for granted. It's not uncommon for a good repair machinist to blue up the first threads of the lead screw and try the new nut on it. If the thread shows bearing only on the major diameter crest or the root you may have to make him a new nut for free.

Lead angle

mrainey said:

The lead angle on that sucker is 40.425 degrees!

Click to expand...

What exactly is the lead angle and how do you calculate it? I'm working on a 9mm lead, 3 start OD thread. The insert has to be ground for relief. It's a sandvik trigon insert. They make a seat with an inclination angle of 4 degrees but that's not enough. I'm not sure exactly what the relief angle needs to be. Any insight is appreciated.

An Idea:

Use the formula for square threads to arrive at a roughing tool and finishing tools.

Should give you a clearance angles and tool inclination angles.

Just dont use a square threading tool....

such threads take at least two cutting tools. (if you draw out the geometry you will see)

One for the leading edge, and one for the trailing edge.

Efficiency would suggest a third tool to "rough" out the thread, but that can be almost anything.

An 8 start acme, that does seem to crowd the available real estate...

At that lead, you might consider driving the lead screw rather than the spindle.

Agree with Calc on this one. If you draw it out either CAD or with a pencil and paper you will realise that it is an insane angle (Ask me how I know when it came to doing some fly press spindles). Maybe rough with a square tool on all the starts, remember you going to need your relief on that tool too, and then put in a tool that only cuts the front flank and then another for the back.

Then once that is all done you put in a finisher that is ground to the correct profile to finish the form so that all of the starts are correct. Once drawn out I surface ground tools to the correct profile, I actually used HSS which was a pain but worked. You could get a specialised tooling guy to make them for you in a way that to get sharpened you just have to give the top of the tool a lick on the grinder.

But take my advice and draw it out, the helix on it will scare you.

Oh crap... Sorry didnt see that the thread is so old.