turning a 5/8-18 unjf 3A p/p single point

[Brandhoff1234]

i've cut threads before but i'm useing an old johnson gage with two measurements on it. one measures pitch dia on one dial, and the other measures the thread form on another dial.

i get the pitch...thats obvious but i'm not understanding the other(the form).

im on a cnc lathe and not understanding what i can do to better control the form.

i'm cutting in a canned cycle, using the proper insert to do a j-thread, i am NOT using a full profile insert. i did not have luck with that.

i've tried adjusting the feedrate of my thread cycle...it seemed to change it a little but not enough. i've moved the major around but it doesn't seem to change it much.

maybe i'm just not understanding what the second gage is measuring.

any and all help would be great.

[PixMan]

There will be a specific insert set for that Johnson gauge that has the specific UNJ form. And for that form, there will be a specific UNJ setting plug. Do you have these?

I'm just confused about one thing: If you are doing a 5/8-18 UNJF 3A, why wouldn't a full-form insert work better for you? I've always had MUCH better results with them than the partial profile types.

BTW, why would you change the feedrate? Wouldn't that result in a pitch error?

[Brandhoff1234]

I checked today and i've got the correct inserts in my johnson Gage.
I'm using a partial insert because
the full profile I was using was leaving my thread engagement too high as far as the Gage was concerned even when my pitch was riding the bottom. Once I switched to the partial, the engagement dropped closer the the pitch. I will have to try and snap off a picture at work. Maybe that will help me a little better.

[PixMan]

And you're certain you've used the corresponding setting plug for the Johnson gauge and have the right anvil under the threading insert?

[Brandhoff1234]

I actually went with a kennametal TopNotch insert as to eliminate the possibility of the seat rubbing. And I ground clearence on the previous holder's seat because of that concern. As of right now my pitch is .0005" lower than my thread form at all times...according to the Johnson gages. I would like to get them closer. That's my real issue. Everytime I offset the thread tool + or - the thread form and pitch move evenly but I don't know what to move to get them closer. Keep in mind I'm not on an amaIng machine. It's an old miyano that only reads 4 decimal places. The machine might not be accuate enough to perform what I want. For now it seems to be good enough. I've ran about 150 pcs of 320 and it's holding within tolerance.

[PixMan]

Sorry, but I'll tell you I despise Kennametal Top Notch for threading because you have zero control over the helix angle clearance on the insert. And I've found increasingly poor quality control on those inserts. It's Vardex full profile for me. I've collected all of the anvil options and have started the collection of as many ER and IR styles and pitches as I can swing. A couple here, a couple there.

Respectfully, you may have a bit more to learn about full and partial profile insert threading if you feel it's necessary to grind a carbide seat. The whole reason that lay-down threading is more precise is those seats that can be changed to accommodate the range of lead angles in normal threading. Grinding away the seat does nothing to affect the clearance issue of the insert. For an 18 pitch UNJ in a 5/8" O.D., the anvil used would be the normal YE3.

What about using a full profile insert didn't work for you? If you can't accurately diagnose what the failure of that was, don't be surprised if things aren't coming out much better with a Top Notch. I think the Top Notch are OK for grooving, but I refrain from using them for threading in deference to the higher-quality threads I get with the full-profile lay-down inserts.

[dwolfhope]

For external UNJF 5/8 18 threads can be cut with the top notch insert you have to use a NJF3009r18 insert, because on a UNJF external thread the thread from has a controled root radius call out on it . That must be held in a UNJ thread from.