Threading away from shoulder

[carlsbad]

WHo threads away from the shoulder and what kind of setup do you use? Do you have a setup that reverses the helix angle on your cutter to match the threads from the opposite angle?

-Jerry

 

[boltfluter]

Jerry,

Seems like I tried it once. If memory serves, I believe I ran the lathe in reverse with the threading tool upside down.

Or maybe not. Lol.

Paul

www.boltfluting.com

 

[Danny1788]

Ive done it with an internal threading bar, setup on the backside of the tenon, run the lathe in reserve and then its normal threading. I used a carbide threading insert and ran the lathe at around 280RPM

 

[Ggmac]

Still early and sipping coffee , but , upside down and reversed . Sounds like my usual day !
I just used a 60 deg

 

[carlsbad]

Thanks for the replies.

Thinking about the helix of the thread, it seems to me when you go upside down you need a left handed insert to match the progression of the thread. Same for the boring bar in the back. I tried the boring bar in the back and got very nice results, but the insert appeared to be leaning the wrong way which bothered me.

--Jerry

 

[ridgeway]

I believe the method is called reverse helix method. As long as you have your 60 degree bit centered just like top threading and not cocked...60 degree is the same upside down. Tool height might be little harder to set being upside down.

 

[carlsbad]

Here is a good reference from Sandvick.

So at least Sandvicks toolholders are shimmed to tilt the insert about 1 degree in the direction of the threads.


Here is a photo of my test threads:


Not bad but I guess it's my OC that makes me not like threading with the wrong relief on the insert.

-Jerrry

 

[Alex Wheeler]

So long as there is enough relief thats all that really matters. I think you will only run into an issue if you use a full profile insert with minimum relief for a specific pitch. That NT should have enough relief that you wont rub.

 

[Erik Cortina]

Don't do it!!! Learn to do it properly. Learn to thread towards the shoulder without a thread relief, that is the best way to do it, it's faster, and looks better. Not to mention, that is you ever need to set a barrel back 1/2" or so, there is not a thread relief right in the middle of your tenon.

I have threaded in reverse when I had no choice, I used an inside boring bar on backside of thread and ran lathe in reverse.

It's good to know different ways to do things, but the basics must still be mastered.

 

[carlsbad]

Eric,
Thanks. I have been threading for years in the conventional "right" direction with good results.

However, if you're not learning and getting better, you're going backwards. Advantages of threading away from the shoulder include better surface finish from higher speeds.

---Jerry

 

[carlsbad]

OK Guys. I found a left handed toolholder and I also think I determined that the kennametal threading insert doesn't have the 1 degree lead angle that the Sandvick reference says theirs has. So as Alex says above, I think I'll be good with it. Lets take it for a spin.

--Jerry

 

[Bigguy1951]

Here is a good video from a very good machinist, 13 minutes. Give it a look.

 

[carlsbad]

Thanks. I found that. He doesn't tell you but I've concluded his upside down tool is indeed left hand. He implies that you don't need to buy anything, just turn your tool over but it won't work that way. A lot of the youtube videos are done on plastic, brass or aluminum to demonstrate something and they cheat and work around problems that you would have to solve if it were real work. I do like him though. His advice is good. Not everyone would like the huge plunge cut he makes on that brass thread. --Jerry

 

[gat]

Here is a good video from a very good machinist, 13 minutes. Give it a look.

He uses a relief cut in this technique. Whats the big deal about a relief cut?

 

[carlsbad]

You have to use a relief cut to thread from the shoulder because you have to be able to put your tool in the starting position. Now you can make it smaller or even make it the same size and shape as the tool bit. Pull the bit into the work and engage the half nut. He used a huge relief cut, much more than required. Like I say, you tube videos for demonstration take some liberties.

The big deal with a relief cut is that not using one is an advanced technique so people like to be able to say they don't need one. Eric pointed out that if you want to set your barrel back a half inch and not cut off the tenon, you can pick the thread up (another advanced technique) and continue it. With a relief cut, you'd lose the threads where the relief cut is. I recently set a barrel back 1" by cutting it off at the point where the relief cut was...didn't help to set it back, it still shot like crap....

The relief cut, if it is the same depth as the root of the threads, does not weaken the joint, in fact, it might make it better if it give the tenon a bit of stretch (on the order of .0001 inch). When you torque a joint, you are stretching the material. A joint up against a 1/4" lug only has 1/4" to stretch and it is approximately the major diameter. No stretching really available to maintain tightness. So the strain takes place in the threads. It obviously works but isn't optimal joint design. For example, the 8" diameter studs that hold the head on the reactor vesssel of a nuclear power plant are 5' long and stretch about .025".

--Jerry

 

[boiler_house7]

PM sent.

 

[gat]

You have to use a relief cut to thread from the shoulder because you have to be able to put your tool in the starting position. Now you can make it smaller or even make it the same size and shape as the tool bit. Pull the bit into the work and engage the half nut. He used a huge relief cut, much more than required. Like I say, you tube videos for demonstration take some liberties.

The big deal with a relief cut is that not using one is an advanced technique so people like to be able to say they don't need one. Eric pointed out that if you want to set your barrel back a half inch and not cut off the tenon, you can pick the thread up (another advanced technique) and continue it. With a relief cut, you'd lose the threads where the relief cut is. I recently set a barrel back 1" by cutting it off at the point where the relief cut was...didn't help to set it back, it still shot like crap....

The relief cut, if it is the same depth as the root of the threads, does not weaken the joint, in fact, it might make it better if it give the tenon a bit of stretch (on the order of .0001 inch). When you torque a joint, you are stretching the material. A joint up against a 1/4" lug only has 1/4" to stretch and it is approximately the major diameter. No stretching really available to maintain tightness. So the strain takes place in the threads. It obviously works but isn't optimal joint design. For example, the 8" diameter studs that hold the head on the reactor vesssel of a nuclear power plant are 5' long and stretch about .025".

--Jerry

I normally use a relief cut. I cut the relief the same depth as I expect my thread to finish at. I have set back literally hundreds of barrels and have never noticed any problems cosmetically or mechanically so long as the relief was cut with the same degree tool as the thread. Picking up the thread is a must for anyone who wishes to do barrel work as sooner rather than later you will need to. I have been barreling for 26 years or so and have threaded in reverse with an upside down tool etc. and know there are fads (many of which work but often just as well as the norm i.e. bedded barrel blocks) that tear through the barreling world the same as any other industry. Do I see the fads stay, not typically. Master the basics, watch what works and be willing to change if you see marked improvements in the way others do it! Great Luck to you!

 

[jfseaman]

Here is a good reference from Sandvick.

So at least Sandvicks toolholders are shimmed to tilt the insert about 1 degree in the direction of the threads.


Here is a photo of my test threads:

Not bad but I guess it's my OC that makes me not like threading with the wrong relief on the insert.

-Jerrry

Nice threads

 

[TAJ45]

Just a hint for those who want to start learning the skill of picking up threads :
Take your clip board with a white sheet of paper and place under it when setting up the tool. Also consider making dry passes while adjusting the compound and cross slide minutely till you get a "rub". Our apprentice instructor told us he would ask for our hand ground threading tool, mid cut would "touch it up" for us, usually blunting it and hand it back. All in a learning day's work. Once you do it with maybe .002" pd to work with a few times, it ain't nuttin' but a thang.
To preserve an especially good performing threading tool, I often would do the healthy plunge thing with an average tool then swap out to finish.

 

[Jay Christopherson]

I suppose that using this method, if you are attempting to thread at a higher speed using it, you better be right when you engage the half-nut... Threading towards the shoulder, I at least have a short "runway" to disengage if I miss the mark.