So I have a question. I have a machinist friend that when he builds a rifle he cuts his tenon threads away from the recoil lug with his lathe in reverse. I have never seen it done this way before? He said it avoids the problem of going too far when threading and avoids messing up the area that has been cut for the recoil lug. Anyone else cutting their threads this way?
Gunsmithing Cutting Barrel TenonThreads
- Thread starter dakor
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Re: Cutting Barrel TenonThreads
Sure you could do that, but youd need to set up special tooling either behind the barrel or upside down.
Also, tenon threading is the easiest to not screw up, you dont have to thread all the way to the shoulder, only within. 300 or however thick your lug is.
I also prefer not to cut relief grooves at shoulders, which reverse threading 100% requires it.
Sure you could do that, but youd need to set up special tooling either behind the barrel or upside down.
Also, tenon threading is the easiest to not screw up, you dont have to thread all the way to the shoulder, only within. 300 or however thick your lug is.
I also prefer not to cut relief grooves at shoulders, which reverse threading 100% requires it.
Re: Cutting Barrel TenonThreads
No need for special tooling - a standard right-hand internal threading tool works just fine:
Sorry for the poor photo quality (cell phone in a poorly-lit shop), but it should convey the concept.
This works well for inexperienced operators when cutting relatively coarse threads at high speeds.
No need for special tooling - a standard right-hand internal threading tool works just fine:
Sorry for the poor photo quality (cell phone in a poorly-lit shop), but it should convey the concept.
This works well for inexperienced operators when cutting relatively coarse threads at high speeds.
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">
I also prefer not to cut relief grooves at shoulders, which reverse threading 100% requires it. </div></div>
So, do you just pull the cross slide out of the work when you hit the end of your threads? Depending on speed that is hard for me to hit everytime, dead on.
G
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">
I also prefer not to cut relief grooves at shoulders, which reverse threading 100% requires it. </div></div>
So, do you just pull the cross slide out of the work when you hit the end of your threads? Depending on speed that is hard for me to hit everytime, dead on.
G
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body">No need for special tooling - a standard right-hand internal threading tool works just fine:
Sorry for the poor photo quality (cell phone in a poorly-lit shop), but it should convey the concept.
This works well for inexperienced operators when cutting relatively coarse threads at high speeds. </div></div>
In your second pic...are u cutting those threads dead on or at a angle (29 degrees)??? looks like dead on.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body">No need for special tooling - a standard right-hand internal threading tool works just fine:
Sorry for the poor photo quality (cell phone in a poorly-lit shop), but it should convey the concept.
This works well for inexperienced operators when cutting relatively coarse threads at high speeds. </div></div>
In your second pic...are u cutting those threads dead on or at a angle (29 degrees)??? looks like dead on.
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body">No need for special tooling - a standard right-hand internal threading tool works just fine: </div></div>
You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.
How do those threads actually look? If not so good that insert is scrubbing because the helix angle is wrong.
If you're scratching your head and asking what the hell is the helix angle then you need to read pages 123 & 126 in the Vardex catalog http://www.vardexusa.com/vardex-pdf/thread_turning_products.pdf
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body">No need for special tooling - a standard right-hand internal threading tool works just fine: </div></div>
You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.
How do those threads actually look? If not so good that insert is scrubbing because the helix angle is wrong.
If you're scratching your head and asking what the hell is the helix angle then you need to read pages 123 & 126 in the Vardex catalog http://www.vardexusa.com/vardex-pdf/thread_turning_products.pdf
Re: Cutting Barrel TenonThreads
in theory you want the tool pressure to go on the side of the saddle with the guide V on the bed, how important that is would depend on the size of your lathe,(saddle weight) and the surface finish you could obtain in reverse.
With any type of experience you should have no problem threading in forward. I thread at 280 rpm and can thread to within .080" of the shoulder, with-out worries of crashing the shoulder. That close is really only necessary with actions that have integral lug or no lugs. (591, bats ect.)
in theory you want the tool pressure to go on the side of the saddle with the guide V on the bed, how important that is would depend on the size of your lathe,(saddle weight) and the surface finish you could obtain in reverse.
With any type of experience you should have no problem threading in forward. I thread at 280 rpm and can thread to within .080" of the shoulder, with-out worries of crashing the shoulder. That close is really only necessary with actions that have integral lug or no lugs. (591, bats ect.)
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: avidflyer</div><div class="ubbcode-body">In your second pic...are u cutting those threads dead on or at a angle (29 degrees)??? looks like dead on. </div></div>
Are you asking if the insert is setup @ 29° or if the compound of the lathe is setup for a 29° infeed? Since we cannot see the lathe compound in his pictures I'm assuming you're asking if the insert is indexed @ 29°. If so that would be incorrect. You would index the insert "dead on" with the thread form at a right angle to the workpiece. It is common to set the compound of the lathe to use a 29° infeed but many use the cross slide for a straight in (radial) infeed. Neither is more or less correct it's what works for you or the material, TPI, thread type, etc...that you are working with. On page 125 in the Vardex catalog I referenced shows different recommended infeeds and when you might use them.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: avidflyer</div><div class="ubbcode-body">In your second pic...are u cutting those threads dead on or at a angle (29 degrees)??? looks like dead on. </div></div>
Are you asking if the insert is setup @ 29° or if the compound of the lathe is setup for a 29° infeed? Since we cannot see the lathe compound in his pictures I'm assuming you're asking if the insert is indexed @ 29°. If so that would be incorrect. You would index the insert "dead on" with the thread form at a right angle to the workpiece. It is common to set the compound of the lathe to use a 29° infeed but many use the cross slide for a straight in (radial) infeed. Neither is more or less correct it's what works for you or the material, TPI, thread type, etc...that you are working with. On page 125 in the Vardex catalog I referenced shows different recommended infeeds and when you might use them.
Re: Cutting Barrel TenonThreads
I thread that way with the tool flipped upside down and run in reverse. I don't have any issue threading toward the shoulder, but when running in reverse I can thread at 600 RPM and get a cleaner finish.
I thread that way with the tool flipped upside down and run in reverse. I don't have any issue threading toward the shoulder, but when running in reverse I can thread at 600 RPM and get a cleaner finish.
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.</div></div>
Good observation. You are correct in that the helix angle will be wrong when using an internal threading toolholder in this fashion. However, because of the increased relief angle, there really isn't any substantial "scrubbing".
While we're looking at the details, it should also be noted that most internal threading inserts have a larger radius at the nose and cut slightly shallower threads than their external counterparts.
This certainly is not the end-all-be-all of threading setups, but for an inexperienced operator, the above issues are pretty minor compared to some of the other problems that can arise. If these issues are bothersome, than the use of an external toolholder with negative-helix anvils would be preferable to the setup I showed.
Of course, one can also either learn how to run a "normal" setup at the speeds required to get carbide to cut correctly, or use HSS tooling.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.</div></div>
Good observation. You are correct in that the helix angle will be wrong when using an internal threading toolholder in this fashion. However, because of the increased relief angle, there really isn't any substantial "scrubbing".
While we're looking at the details, it should also be noted that most internal threading inserts have a larger radius at the nose and cut slightly shallower threads than their external counterparts.
This certainly is not the end-all-be-all of threading setups, but for an inexperienced operator, the above issues are pretty minor compared to some of the other problems that can arise. If these issues are bothersome, than the use of an external toolholder with negative-helix anvils would be preferable to the setup I showed.
Of course, one can also either learn how to run a "normal" setup at the speeds required to get carbide to cut correctly, or use HSS tooling.
Re: Cutting Barrel TenonThreads
No need to hit it dead nuts the same spot every time, as long as you dont go over. I usually end up around 080 off like the other guy said which is plenty for anything with a decent counterbore. Id rather cut a deeper counterbore in something than cut a relief at the shoulder. Just personal preference though, I think it looks a little better and technically stronger even though that probably doesnt play a part ever for our purposes.
Other problem with an internal threading tool is they are not near as rigid as an external tool so you end up having to take probably twice as many passes to do the same work. I know when cleaning up receiver threads, even with my Kennametal Carbide bar I can run at the same depth 3 or 4 times and still cut material. With an external, normally only 2 at the most until its done cutting material with a much deeper cut also.
No need to hit it dead nuts the same spot every time, as long as you dont go over. I usually end up around 080 off like the other guy said which is plenty for anything with a decent counterbore. Id rather cut a deeper counterbore in something than cut a relief at the shoulder. Just personal preference though, I think it looks a little better and technically stronger even though that probably doesnt play a part ever for our purposes.
Other problem with an internal threading tool is they are not near as rigid as an external tool so you end up having to take probably twice as many passes to do the same work. I know when cleaning up receiver threads, even with my Kennametal Carbide bar I can run at the same depth 3 or 4 times and still cut material. With an external, normally only 2 at the most until its done cutting material with a much deeper cut also.
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.</div></div>
Good observation. You are correct in that the helix angle will be wrong when using an internal threading toolholder in this fashion. However, because of the increased relief angle, there really isn't any substantial "scrubbing".
While we're looking at the details, it should also be noted that most internal threading inserts have a larger radius at the nose and cut slightly shallower threads than their external counterparts.
This certainly is not the end-all-be-all of threading setups, but for an inexperienced operator, the above issues are pretty minor compared to some of the other problems that can arise. If these issues are bothersome, than the use of an external toolholder with negative-helix anvils would be preferable to the setup I showed.
Of course, one can also either learn how to run a "normal" setup at the speeds required to get carbide to cut correctly, or use HSS tooling. </div></div>
While pondering the use of that toolholder in that position I was wondering if the extra relief on an internal insert might let one get away with it. I hear and read of people using a toolholder all the time in what is technically the wrong position and have wondered if they are really doing it and getting away with it. I'm fortunate to have a variety of toolholders and anvils available for most any threading operation needed.
Good you brought up the difference between internal to external threadforms. Using an insert for the wrong application could cause an issue for someone down the road. It may not be so bad if a partial profile is being used but there may be more potential for trouble if full profiles are mis-applied. I've been on the receiving end of a non-standard threadform before. It can make a person a bit grumpy and not fun to be around in the shop.
I agree, once you practice cutting towards a shoulder it isn't that big of a deal, could be a bit intimidating at first though. Get the right setup, learn your equipment and it's pretty amazing how many rpm you can get used to.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">You sure about that? Isn't the helix angle of the insert positive with that setup? Wouldn't you need a negative helix for that toolholder in that position? Most internal tools don't have changeable anvils (most RH internal toolholders that size are a fixed +1.5°) so correct me if I'm mistaken on your setup.</div></div>
Good observation. You are correct in that the helix angle will be wrong when using an internal threading toolholder in this fashion. However, because of the increased relief angle, there really isn't any substantial "scrubbing".
While we're looking at the details, it should also be noted that most internal threading inserts have a larger radius at the nose and cut slightly shallower threads than their external counterparts.
This certainly is not the end-all-be-all of threading setups, but for an inexperienced operator, the above issues are pretty minor compared to some of the other problems that can arise. If these issues are bothersome, than the use of an external toolholder with negative-helix anvils would be preferable to the setup I showed.
Of course, one can also either learn how to run a "normal" setup at the speeds required to get carbide to cut correctly, or use HSS tooling. </div></div>
While pondering the use of that toolholder in that position I was wondering if the extra relief on an internal insert might let one get away with it. I hear and read of people using a toolholder all the time in what is technically the wrong position and have wondered if they are really doing it and getting away with it. I'm fortunate to have a variety of toolholders and anvils available for most any threading operation needed.
Good you brought up the difference between internal to external threadforms. Using an insert for the wrong application could cause an issue for someone down the road. It may not be so bad if a partial profile is being used but there may be more potential for trouble if full profiles are mis-applied. I've been on the receiving end of a non-standard threadform before. It can make a person a bit grumpy and not fun to be around in the shop.
I agree, once you practice cutting towards a shoulder it isn't that big of a deal, could be a bit intimidating at first though. Get the right setup, learn your equipment and it's pretty amazing how many rpm you can get used to.
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">
I agree, once you practice cutting towards a shoulder it isn't that big of a deal, could be a bit intimidating at first though. Get the right setup, learn your equipment and it's pretty amazing how many rpm you can get used to. </div></div>
300 is my best on muzzle threads to get within ~.080 of the shoulder. 450 is pretty easy on tenon threads or wherever there isnt a need to get tight to a shoulder.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WCS</div><div class="ubbcode-body">
I agree, once you practice cutting towards a shoulder it isn't that big of a deal, could be a bit intimidating at first though. Get the right setup, learn your equipment and it's pretty amazing how many rpm you can get used to. </div></div>
300 is my best on muzzle threads to get within ~.080 of the shoulder. 450 is pretty easy on tenon threads or wherever there isnt a need to get tight to a shoulder.
Re: Cutting Barrel TenonThreads
yup.....a lota guys do it that way.....when they are worried about crashing the tool into the shoulder.
The reason I don`t like it..... you must have an undercut for your tool to start.....
I believe causing a weaker joint....
bill larson
yup.....a lota guys do it that way.....when they are worried about crashing the tool into the shoulder.
The reason I don`t like it..... you must have an undercut for your tool to start.....
I believe causing a weaker joint....
bill larson
Re: Cutting Barrel TenonThreads
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bill Larson</div><div class="ubbcode-body">you must have an undercut for your tool to start.....
I believe causing a weaker joint....
bill larson </div></div>
Go do the calculations on the reduction in ultimate tensile strength that is caused by a thread undercut, and you'll quickly realize that this is a purely semantic argument. If we were talking about a fastener that is much more highly stressed (say, an automotive wheel stud or rod bolt), then it'd be a much larger problem.
Regardless, the finished tenon looks nicer without an undercut, and I realize that may be important to many people (pride in one's workmanship generally being a very healthy thing).
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bill Larson</div><div class="ubbcode-body">you must have an undercut for your tool to start.....
I believe causing a weaker joint....
bill larson </div></div>
Go do the calculations on the reduction in ultimate tensile strength that is caused by a thread undercut, and you'll quickly realize that this is a purely semantic argument. If we were talking about a fastener that is much more highly stressed (say, an automotive wheel stud or rod bolt), then it'd be a much larger problem.
Regardless, the finished tenon looks nicer without an undercut, and I realize that may be important to many people (pride in one's workmanship generally being a very healthy thing).
