Multiple entry threads on a barrel

C

cloudrepair

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I'm new to rifle barrel fitting. And this forum. I have been a machinist for 20 years or so and have been thinking about something for a while. I read somewhere about barrel indexing and thought a multiple an try thread may be helpful? like a 32 thread 4 entry. Do you guys know of anyone that may have tried this.
 
Good thinking but don't do it!

cloudrepair said:
I'm new to rifle barrel fitting. And this forum. I have been a machinist for 20 years or so and have been thinking about something for a while. I read somewhere about barrel indexing and thought a multiple an try thread may be helpful? like a 32 thread 4 entry. Do you guys know of anyone that may have tried this.
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Several years ago, I began experimenting with barrel indexing and stumbled on a way to do it without affecting headspace by placing a differential threaded bushing between the receiver threads and barrel tenon. It enabled me to orient the barrel in any position by simply rotating the internal bushing and temporarily holding it in position with a setscrew while I reinstalled the barrel. WOW! I really thought I had something! :cool: I had something alright; a solution to a problem that does not exist. :p

Yep, I had a lot of fun with it but finally abandoned the idea concluding that unless a barrel was unusually crooked, nothing could be gained by indexing. :p If a barrel is that crooked, I'll simply return it to the manufacturer for a replacement.

Gene Bukys has a recent thread that you should read on indexing/chambering. He came to the same conclusion that I did; barrel indexing is a waste of time. :p

Oh and BTW, you would not want a multi-start thread on a barrel tenon because, as you know, it advances a whole lot quicker per revolution than a single start even with a fine thread. I don't believe you could get a solid lockup between the tenon and receiver threads. Know what I mean Vern? :p

And BTW, welcome to BR Central. Here you will find a treasure trove of information about extreme rifle accuracy and all the machining and technology that goes with it. Enjoy the journey!:D

Later,

Gene Beggs
 
have you looked at receivers yet ??

cloudrepair said:
I'm new to rifle barrel fitting. And this forum. I have been a machinist for 20 years or so and have been thinking about something for a while. I read somewhere about barrel indexing and thought a multiple an try thread may be helpful? like a 32 thread 4 entry. Do you guys know of anyone that may have tried this.
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Thanks Gene. It was your thread that got me thinking about this. the threaded union with two different threads for setting the head space.
I was thinking with an Ackley cartridge it would work but yes 8 threads per inch may be a little steep then it would be waist of an action if it wasn't suitable. I have chambered a few barrels the last one was a remington 700 barrel i had sitting and a browning abolt action and a savage barrel nut. So the barrel has two threads for setting the headspace. about .800 of 1x32 and .825 of 1.055x20
Maybe not the best idea but It works fine. I only experiment with my own stuff.
 
cloudrepair said:
I'm new to rifle barrel fitting. And this forum. I have been a machinist for 20 years or so and have been thinking about something for a while. I read somewhere about barrel indexing and thought a multiple an try thread may be helpful? like a 32 thread 4 entry. Do you guys know of anyone that may have tried this.
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32tpi and a 7 or 8?in pitch???

I think you'd be stripping threads off long before you achieved a meaningful tenon stretch....

I see no reason anyone would try it :)

JMO

Also, indexing in quarter-turns doesn't really give you the ability to gain anything. I personally work within about a 30* window, of which there would be three in every quadrant in your scenario!

I index in degrees, using maybe 20-25 of them. A specific 25 of the 360 available.



al
 
I appreciate all replies. I only work for myself and my boys hunting rifles , I don't plan on competing but I do want and expect the best .and my experience tells me the people here are some of the best so the reason I'm here.
 
Allinwa
I've cut many multiple entry threads and the more I thought about it it would be a pain for just four testing points. Yes maybe not suitable.
 
As a Machinist, I can only amagine what stacking four different 18 TPI on a 1 inch long barrel tenon would look like.

You mentioned you are new to barrel threading and tenon fitting. The best piece of advice I can give you is avoid solutions to non existing problems.

A lot of what you read is just that.
 
The problem with multiple entry threads is that for a given TPI, every additional start multiplies the lead angle of the thread equivalent to the number of starts. So if 18 TPI at a specific diameter has a lead angle of 1 degree, 4 thread entries will increase the lead angle to 4 degrees, and you will no longer be able to screw the barrel into the action.

You can counteract this by increasing the TPI. So if you increase the TPI to 72 (18*4=72), you would have a lead angle that's close, but not exact. The minor diameter of the threads on the tenon would be too large and would interfere with the major diameter of the threads in the action. To get the lead angle at the pitch diameter to match up exactly, you would have to thread the tenon at 72 TPI, with 4 starts, and a major diameter of 1.029". I'm not sure if there would be thread interference at this diameter. I'm also not sure if you'd get enough thread engagement at that diameter to have a secure fit. I suspect this number is close but not perfect, some trials in scrap pieces would be necessary to see if this is feasible. The threads would not engage at the pitch diameters on both parts. I'm pretty sure you could get something that will screw together, but strength would probably be considerably compromised. The considerable length of the barrel tenon would probably give you enough of a safety margin that it would still be functional.

It's an interesting machining puzzle, and it would be cool to see. But it seems like the consensus is that indexing is a waste of time. Solving unique problems like this is never a waste of time, in my opinion.

Math skills are not my strong point, I used this thread calculator to cheat and generate some of the above numbers. I probably made some mistakes.

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx
 
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James Lederer said:
The problem with multiple entry threads is that for a given TPI, every additional start multiplies the lead angle of the thread equivalent to the number of starts. So if 18 TPI at a specific diameter has a lead angle of 1 degree, 4 thread entries will increase the lead angle to 4 degrees, and you will no longer be able to screw the barrel into the action.

You can counteract this by increasing the TPI. So if you increase the TPI to 72 (18*4=72), you would have a lead angle that's close, but not exact. The minor diameter of the threads on the tenon would be too large and would interfere with the major diameter of the threads in the action. To get the lead angle at the pitch diameter to match up exactly, you would have to thread the tenon at 72 TPI, with 4 starts, and a major diameter of 1.029". I'm not sure if there would be thread interference at this diameter. I'm also not sure if you'd get enough thread engagement at that diameter to have a secure fit. I suspect this number is close but not perfect, some trials in scrap pieces would be necessary to see if this is feasible. The threads would not engage at the pitch diameters on both parts. I'm pretty sure you could get something that will screw together, but strength would probably be considerably compromised. The considerable length of the barrel tenon would probably give you enough of a safety margin that it would still be functional.

It's an interesting machining puzzle, and it would be cool to see. But it seems like the consensus is that indexing is a waste of time. Solving unique problems like this is never a waste of time, in my opinion.

Math skills are not my strong point, I used this thread calculator to cheat and generate some of the above numbers. I probably made some mistakes.

http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx
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I thought he was talking about was not a true multiple lead, but simply cutting a 18 pitch thread to fit, then moving the compound, ( which would be straight with the bed), exactly 13.88 inch, cut another 18 pitch thread, do it again, and then again. You would be splitting the lead by 1/4 each time.

If you left the lathe in 18 pitch, there would't be much left. Of course, this would not be a true multiple lead thread, it would just be a 4 times cross thread.

A true multiple lead would have to have a multiple lead in the action to match.

Two entry points might be feasible, 180 degrees apart. Cut one, then move the compound 27.77 inch, cut another. It would screw into the receiver, and be " clocked" 1/2 turn according to which lead you started in.

I think you would still have 1/2 of the original thread left on each lead.
 
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jackie schmidt said:
I thought he was talking about was not a true multiple lead, but simply cutting a 18 pitch thread to fit, then moving the compound, ( which would be straight with the bed), exactly 13.88 inch, cut another 18 pitch thread, do it again, and then again. You would be splitting the lead by 1/4 each time.

If you left the lathe in 18 pitch, there would't be much left. Of course, this would not be a true multiple lead thread, it would just be a 4 times cross thread.

A true multiple lead would have to have a multiple lead in the action to match.

Two entry points might be feasible, 180 degrees apart. Cut one, then move the compound 27.77 inch, cut another. It would screw into the receiver, and be " clocked" 1/2 turn according to which lead you started in.

I think you would still have 1/2 of the original thread left on each lead.
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If indexing was a benefit I was thinking of trying a 32 tpi pitch with 4 lead or entry with 8 threads per inch on the tennon and in the reciever so you would have 4 points to time the barrel.. every 90 deg.
Interesting thought Jackie I like your thinking it would work better if all we needed were two indexing points 180 apart. If indexing was a benefit?
 
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It may well be a non existent problem, but that's also how we discover new things and creative minds can not stop thinking.
 
ranch23 said:
It may well be a non existent problem, but that's also how we discover new things and creative minds can not stop thinking.
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Thanks for the positive feedback that is the way I try to look at things.
 
I don't know what Y'all are talking about here...

And...not sure I want to know. The deal I've gathered over the years is keep it simple - the barrel is either going to shoot well or it's not going to shoot well. I don't believe chambering differently will cause a "not" barrel to shoot well.

I could be wrong...very likely to be wrong...but I could just as easily be right. Conversely, if it doesn't work you can cut it off and try something else. I can't do that!! I can get somebody else to do it but not cheaply.

I just love talking about stuff I know absolutely nothing about!
 
Wilbur, the reason many of us do the things we do is because we already know how to fix it if what we had in mind doesn't work out.

My off the wall projects usually fall into 3 categories. Those that work out quite well, those that are abject failures, and those that while being successful prove to be way too much of a hassle to mess with.
 
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