Threading on a Lathe

[gerritv]

The number of passes doesn't change, regardless of straight in or (thread angle - .5dg) . The reason we never learned any other way in NA is because every single text says the same thing. The WWW just makes it worse because finding links from the rest of the world is difficult due to the algorithms and built in bias in search results. As I said earlier, for anything finer than 18-20 there is really no point to the offset at all. On large lathes probably much coarser. The threading tool is a form tool, meant to cut on both sides.

 

[Susquatch]

Sandvik don't make it easy to link :-( Go to this page, in the box on left select Technical Information and then Apply. Traingin Handbook, Turning Handbook and Threading Application Guide are there.
And I know you didn't want a YT link but this is as clean an example as I can find at the moment: (No compound)

Note the tool shape, no top rake at all, ground from 6 or 8mm round HSS.

View attachment 24395

Thanks for the links @gerritv . I think I have them now. I will confirm later.

The video was interesting. Especially making custom new change gears from linen laminate. That's a trick I never imagined but it makes a lot of sense. One of the things I discovered long ago is that most lathes will cut more threads than their charts suggest. Furthermore, some of these can be quite popular threads that make one wonder what the lathe manufacturing people were smoking..... I find it's worthwhile to step back and make your own charts using every gear combination you have.

Regarding the threading, it's more or less what I expected. I noticed he changed the threading tool part way through the job but didn't mention it. I can't help but wonder why. I suspected a clearance issue but a closer look said otherwise. I'm thinking he wasn't happy with the cut quality and sharpened the tool off camera and ground a side relief at the same time.

I like that he used HSS. But I didn't like his depth of cut. Looked like an awful big chip for that tiny little thread. But who am I to criticize.....

 

[Susquatch]

The number of passes doesn't change, regardless of straight in or (thread angle - .5dg) . The reason we never learned any other way in NA is because every single text says the same thing. The WWW just makes it worse because finding links from the rest of the world is difficult due to the algorithms and built in bias in search results. As I said earlier, for anything finer than 18-20 there is really no point to the offset at all. On large lathes probably much coarser. The threading tool is a form tool, meant to cut on both sides.

As you might know by now, I started another thread dedicated to the 30/29.5 vs 90 degree thread cutting.

Thread 'Threading - 29.5/30 vs 90' https://canadianhobbymetalworkers.com/threads/threading-29-5-30-vs-90.5411/

You may be right about why things are different. Yours is as good an explanation as any. But I'd like to see what other members think as I suspect there might be more to it than that.

Regardless, I'm sure I'll learn something! You and the other members here are a wealth of knowledge!

 

[gerritv]

He ground the tool's left side to give clearance to the shoulder. Normally you would grind the v to the left of centre of the tool for this reason.

 

[VicHobbyGuy]

Here you go @thestelster. Affordable and plenty accurate enough for any threading job I do. Free shipping too!

Accusize Industrial Tools 0-1'' by 0.001'' Screw Thread Micrometer with 5 Anvil in Fitted Box, S916-C750 https://www.amazon.ca/dp/B0189RHDWS/ref=cm_sw_r_apan_i_KY35B39PGXBA8QFZP8G7?_encoding=UTF8&psc=1

Turns out that's what I have. But I got mine in a two micrometer set about 5 years ago - maybe more..... Mine are also only 1 thou mics. But that's plenty for the threading I do.

Thanks for that link. My thread micrometer is on its way to me!
Anybody want to buy a nice set of thread wires, used once?

 

[Susquatch]

Thanks for that link. My thread micrometer is on its way to me!
Anybody want to buy a nice set of thread wires, used once?

Keep them. You will need them for other thread types like ACME, etc.

 

[Susquatch]

He ground the tool's left side to give clearance to the shoulder. Normally you would grind the v to the left of centre of the tool for this reason.

I thought that too. But a closeup of the video showed otherwise. There was lots of clearance there before the huge grinding job.

 

[Dabbler]

Being late to the discussion - I first learned to correctly set the toolpost at -exactly- 30 degrees, by indicating it in... I've never used the 29.5, nor could I find a "rational" reason for 29.5. (My apologies in advance to those that have always used 29.5. I never do things without a cogent reason as to why)

Used it that way for over 30 years, and then converted to plunge cutting like the Europeans. I'm now a *total* convert!

I am a big fan of thread micrometers. I don't like the fussiness of thread wires, and I always do 60 degree threads.

 

[Susquatch]

Being late to the discussion - I first learned to correctly set the toolpost at -exactly- 30 degrees, by indicating it in... I've never used the 29.5, nor could I find a "rational" reason for 29.5. (My apologies in advance to those that have always used 29.5. I never do things without a cogent reason as to why)

Used it that way for over 30 years, and then converted to plunge cutting like the Europeans. I'm now a *total* convert!

I am a big fan of thread micrometers. I don't like the fussiness of thread wires, and I always do 60 degree threads.

I tested 30 vs 29.5 a long time ago because I couldn't see why it was necessary either. I became a convert shortly thereafter and almost never do it any other way now.

You will enjoy my thread on threading and I will enjoy your input.

The rationale for the 29.5 is fairly well explained in the paper that Brent provided in that thread.

Post in thread 'Threading - 29.5/30 vs 90' https://canadianhobbymetalworkers.com/threads/threading-29-5-30-vs-90.5411/post-78489

Threading at 90 as a habit is new to me. I've done it from time to time for various reasons but never really fell in love with it. That could change from the discussion.

See you over at the other thread.

 

[Susquatch]

I first learned to correctly set the toolpost at -exactly- 30 degrees, by indicating it in.

Btw, this is yet another reason for doing 29.5. It's not necessary to dial it in. The 29.5 isn't critical. It's only critical that it be a little LESS than 30. NEVER MORE. Again, Brent's paper does a good job of explaining that.

That said, I may become a 90 convert - we shall see.

 

[ducdon]

Being late to the discussion - I first learned to correctly set the toolpost at -exactly- 30 degrees, by indicating it in... I've never used the 29.5, nor could I find a "rational" reason for 29.5. (My apologies in advance to those that have always used 29.5. I never do things without a cogent reason as to why)

Used it that way for over 30 years, and then converted to plunge cutting like the Europeans. I'm now a *total* convert!

I am a big fan of thread micrometers. I don't like the fussiness of thread wires, and I always do 60 degree threads.

I'm from the old fart squad that was taught and do the 29.5 slant depth method. Were the cross slide is used to control tool position and the compound to control depth of cut. I think it's a carry over from the days of lantern tool posts and fish tail gages. If you follow guys like Robin Rensetti and Stefan Gottswinter they have borrowed technology from the CNC world. They replace the compound with a fixed block that insures all their quick change tooling is square to the lathe axis. A multi program DRO is used to control tool position and depth of cut. Their machines are really a hybrid. Just mount the tool touch off, zero the DRO and plunge. ManualNC, MeNC ?