Threading a barrel question.

[swampers]

How many passes does it take to get to your final depth of threads.

 

[STS]

That depends on the thread pitch. I've never counted but I would guess 12 to 15 on a 16 pitch Remington depending on how many .001 passes near the end I have to make to get the fit I'm looking for.

 

[jscandale]

On a 16 tpi thread, I normally take about 7 or 8 passes with a carbide insert at about 400 rpm.
A 28 tpi, it's about 4.
I will say that I do it so often that I've got it down to a science. If I was unfamiliar with the machine or didn't do it very often, I guess it would take about 10-12 passes.

JS

 

[X Ring Accuracy]

Depends on depth of cut. Some smiths cut .005 .010 per pass. They are nuts. If you don't know what depth you are cutting then it can be 1 pass if hogging it or 16 passes if .001 per cut. I suggest not hogging it

 

[Preacher]

Thats a good suggestion....

 

[jscandale]

A lot has to do with if you are going straight in or on the 30° angle. I am one of those nuts that takes .020" per pass for the first 2, the .010" per pass for the next 4, then .005, then .002, or maybe no advance at all when approaching full depth. Works quite well for me, but who knows, I'm nuts.

Here's another thing to prove I'm nuts. I thread moving away from the chuck, and go straight in. The threads look like they are ground when they are done. Told ya I was nuts.

JS

 

[swampers]

I was just curious. I have been making any where from 15 to 20. It just seem like a lot.

 

[STS]

A lot has to do with if you are going straight in or on the 30° angle. I am one of those nuts that takes .020" per pass for the first 2, the .010" per pass for the next 4, then .005, then .002, or maybe no advance at all when approaching full depth. Works quite well for me, but who knows, I'm nuts.

Here's another thing to prove I'm nuts. I thread moving away from the chuck, and go straight in. The threads look like they are ground when they are done. Told ya I was nuts.

JS

;D If my math is correct that adds up to .087 of tool advancement. What would be barreling that has a thread depth of .087?

 

[jscandale]

Sorry, that woud be on the diameter rather than on the radius. My cross slide dial measures on the diameter. Not all lathes do. Sorry for the confusion.

I machine a lot of AR15 barrels. The threaded tenon is .812-16 tpi. In order to get the barrel extension to about a class 3 fit (depending on the manufacturer of the extension), the depth of the thread is about .043"

JS

 

[STS]

Js, I figured out what you were working off diameter after I asked the question. ;D You are doing pretty much what I'm doing except I feed the tool advance with the compound until the last couple of thousandths then I crossfeed straight in to make sure both faces of the thread are all pretty. I usually go .010 x2, .005 x2, ..003 x3 then measure with my thread mic and start thinking about getting a good fit at .001 per pass. If I do good I treat myself to a Dr. Pepper.

 

[jscandale]

Ya know, I always though that feeding with the compound was the only way people did it. Some guys set the compound to 29°-30° or anywhere in between. I have a good friend in MN who is a long time machinist (about 52 years) and mold maker who I trust very much. He told me that he goes straight in, so I tried it and ended up liking it very much. It is faster, but certainly no better or worse in my opinion. I set my compound at 30° and only use it to pick up a thread or cut a very deep course thread to lessen the tool pressure, but for threads under about 10 tpi, I still go straight in. Try it once.

JS

 

[STS]

I've tried it more than once. It works just fine and can yield just as nice a set of threads as any other method. There's more than one way to skin this cat. Gotta go to work, the ER says HELP!

 

[X Ring Accuracy]

Ya know, I always though that feeding with the compound was the only way people did it. Some guys set the compound to 29°-30° or anywhere in between. I have a good friend in MN who is a long time machinist (about 52 years) and mold maker who I trust very much. He told me that he goes straight in, so I tried it and ended up liking it very much. It is faster, but certainly no better or worse in my opinion. I set my compound at 30° and only use it to pick up a thread or cut a very deep course thread to lessen the tool pressure, but for threads under about 10 tpi, I still go straight in. Try it once.

JS

Under meaning more threads per inch than 10 or under meaning say 8 TPI down. I am asking because when I first taught myself plunging the cross slide seemed the way to go. I went to conventional thinking but ALWAYS looking to do things better. I am self taught so go easy on me. Been doing it for too many years but like fresh / new / old but new ideas

 

[Preacher]

I always go straight in with only .001 advancement per time, but I do have a lot of time to devote to it, so thats never been a problem..
I use carbide at 160 RPM's, on some jobs, and HS steel on others, but always straight in......

 

[jscandale]

Both ways get you to the same result quite well. I don't really have the cause to cut anything less than 12 tpi very often, however the reason that I say I would use the compound for very course threads relates to the root depth. The deeper the root, the more tool pressure on both sides of the cutter there is. I this case, I would start to use the compound after getting pretty deep in the thread by which I would only use one side of the cutter. I guess it would be a "feel" kinda thing.

I always take heavy cuts for the first 2 passes because there is relatively light tool pressure because of the small contact at such a shallow depth. The deeper I go, the less I advance. You should just try it on a scrap piece sometiime.

I really like the indexable carbide inserts a great deal. They last forever and never change shape. If for some reason, the point chips, just index it and it's dead on. I can cut a ton of threaded tenons with one insert before I ever have to change it and never have to sharpen. I even got my friend in MN (the long time mold maker from the previous posing) and he really likes it. Go figure.

JS

 

[GabbyJs]

Here's another thing to prove I'm nuts. I thread moving away from the chuck, and go straight in. The threads look like they are ground when they are done. Told ya I was nuts.

JS

jscandale- Sounds like you have a lot of threading experience. How do you set up to cut a left hand thread?

 

[jscandale]

I don't actually cut a left hand thread. I cut a standard right hand thread at higher speeds. What I do is use a 1" internal threading bar and cut on the backside of the work piece while running the lathe in reverse. It allows me to start the tool in the reliefe area and run the lathe at a higher speed away from the chuck never having to worry about disengageing the half nut in time. Using carbide and a high speed produces excellent surface finish in 4150 and 416 stainless. Here is a pic while making a die out of 1144.
If the goal is to cut a left handed thread, all you have to do is use a standard outside threading tool, run the lathe forward and run away from the chuck.

JS

 

[Rustystud]

It is interesting to hear different folks speak of their different ways to cut threads. We all strive to acheive the same goal a good quality 60* V thread. I personally have only used the straight in approach with achme and square threads. I guess that I will have to get a piece of stock and experiment a little. There are other factors to consider with the improvments in tooling ie: HSS, Alloy, Coated, carbide and ceramic, lubricants and collants and CNC operation.
The reason I enjoy this and other forums as we all learn from each other. We all may not agree on the process but we all agree on the outcome.
Nat Lambeth

 

[swampers]

A lot of different ways but they all get the job done. What speed do you use, I was cutting mine at 70 but was getting a little chatter marks. I speeded up to 190 and now they look perfect. I'm using a A.R Warner HSS tool.

 

[STS]

I don't actually cut a left hand thread. I cut a standard right hand thread at higher speeds. What I do is use a 1" internal threading bar and cut on the backside of the work piece while running the lathe in reverse. It allows me to start the tool in the reliefe area and run the lathe at a higher speed away from the chuck never having to worry about disengageing the half nut in time. Using carbide and a high speed produces excellent surface finish in 4150 and 416 stainless. Here is a pic while making a die out of 1144.
If the goal is to cut a left handed thread, all you have to do is use a standard outside threading tool, run the lathe forward and run away from the chuck.

JS

Chicken! ;D ;D Just jiggling your cage a little. That's a valuable technique if you need/want to use it. I thread without a relief cut because I want to be able to go back later and pick up an existing thread and set the barrel back if necessary.