Chambering question on worn lathe

One thing that hasn't been brought up is work piece deflection. Over the last several years I've chambered literally thousands of barrels just using drawings. No action in hand. You tend to pay attention to a few things that you wouldn't with the action in hand. I measure the pitch diameter of every barrel after threading. One day I decided to measure it on each end of threads instead of midway. These barrels have a 1.5" long threaded tenon held in a spider. It wasn't a big surprise but there was a measurable difference in the PD. I don't mean to open up a can of worms but what the hell. I'm assuming my headstock is aligned with the ways. Is yours?

Dave
 
Dave Tooley said:
One thing that hasn't been brought up is work piece deflection. Over the last several years I've chambered literally thousands of barrels just using drawings. No action in hand. You tend to pay attention to a few things that you wouldn't with the action in hand. I measure the pitch diameter of every barrel after threading. One day I decided to measure it on each end of threads instead of midway. These barrels have a 1.5" long threaded tenon held in a spider. It wasn't a big surprise but there was a measurable difference in the PD. I don't mean to open up a can of worms but what the hell. I'm assuming my headstock is aligned with the ways. Is yours?

Dave
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Hey T, personally I like the idea of a tapered thread if we only had a method of getting it to fit perfectly. Remember when one of the major benchrest action builders had tapered threads and they called it a "feature"?

.
 
Jerry I do remember that and have two actions made that way. Can I tell a difference? No. It's something that gets lost in all the noise.
 
Dave Tooley said:
Jerry I do remember that and have two actions made that way. Can I tell a difference? No. It's something that gets lost in all the noise.
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Did you remachine the threads or just thread a barrel to fit? I bought a 1-1/16 18 bottom tap but never used it. Its on loan.
 
I just fitted the barrels as I always would. Knowing there's taper and matching a taper is two entirely different things. I can program any taper I want but because of the flexibility in our setups I would have to whittle on several barrels to get close to matching the action.
 
Dave Tooley said:
One thing that hasn't been brought up is work piece deflection. Over the last several years I've chambered literally thousands of barrels just using drawings. No action in hand. You tend to pay attention to a few things that you wouldn't with the action in hand. I measure the pitch diameter of every barrel after threading. One day I decided to measure it on each end of threads instead of midway. These barrels have a 1.5" long threaded tenon held in a spider. It wasn't a big surprise but there was a measurable difference in the PD. I don't mean to open up a can of worms but what the hell. I'm assuming my headstock is aligned with the ways. Is yours?

Dave
Click to expand...

One thing you have an advantage of being able to do is program that taper out of the threads, if necessary.
 
JerrySharrett said:
Hey T, personally I like the idea of a tapered thread if we only had a method of getting it to fit perfectly. Remember when one of the major benchrest action builders had tapered threads and they called it a "feature"?

.
Click to expand...

Was this to more evenly distribute the tension in the tenon?
 
Dave Tooley said:
One thing that hasn't been brought up is work piece deflection. Over the last several years I've chambered literally thousands of barrels just using drawings. No action in hand. You tend to pay attention to a few things that you wouldn't with the action in hand. I measure the pitch diameter of every barrel after threading. One day I decided to measure it on each end of threads instead of midway. These barrels have a 1.5" long threaded tenon held in a spider. It wasn't a big surprise but there was a measurable difference in the PD. I don't mean to open up a can of worms but what the hell. I'm assuming my headstock is aligned with the ways. Is yours?

Dave
Click to expand...

Dave,

My old lathe and my current lathe both have adjustable headstocks via an opposing bolts type of affair. A lot of people don't realize that their headstocks can be adjusted and instead play with a level to try and get them to cut straight.

Take the cover off of the outboard side of your headstock and look for two bolts situated horizontally, with the ends resting against a solid piece of the bed. They're usually down towards the bottom of the headstock, tucked behind the gears. If you see something similar, they're probably your adjustment screws. If anybody cares, I'll post a picture of mine when I get home tonight.

It is scary how straight you can get them to cut by this adjustment.

You'd think the headstock would be aligned with the ways and I think they are...to an extent. I think there is an industry tolerance for straightness, i.e., 5 thou a foot or something like that. I'll see if I can find it when I get home.

Justin
 
The trouble here Justin is even if you get the spindle and tailstock in perfect alignment it will change since your platform, floor, constantly moves. Plus most tool room lathes and practly none of bigger lathes have adjustable head stocks. Don't know about these commy tin lizzies!!!
 
conrad said:
The trouble here Justin is even if you get the spindle and tailstock in perfect alignment it will change since your platform, floor, constantly moves. Plus most tool room lathes and practly none of bigger lathes have adjustable head stocks. Don't know about these commy tin lizzies!!!
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Conrad,

I'm not talking about getting the spindle and tailstock lined up. I'm talking about the spindle running true with the bed/ways. Getting a true cut with a tailstock is another can of worms...

Tell me about ground movement! I live about 45 minutes from the San Andreas Fault...things are constantly moving. But with the adjustment, you can turn something pretty close to dead nuts straight if you want/have to. May not stay that way for long, but it can be done.

I straightened mine out last weekend. If I get a chance I'll check it this weekend.

I've never messed with tool room or bigger lathes, but I believe you. I don't know your definition of "big" but my buddy has a couple of Mori Seikis which are 17x40's or so. I THINK they have the adjustment feature. My old lathe was a Mori clone and it had it.

Justin
 
mks said:
Was this to more evenly distribute the tension in the tenon?
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Yes. Years ago Stiller did the calcs as to what the optimal taper would be in his action and put it into his action. Some complained with the difference in fitting barrels so he stopped using that feature.
 
Rubicon Prec. said:
Having a perfectly aligned headstock isn't going to help with a tapered thread pitch diameter due to work piece deflection.
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Rubicon,

True...but you'll have less taper. Gotta be better than having a mis-aligned headstock. Unless you can mis-align it to take the taper out of your threads....and I'm not that good!

Where is Greenwood?

Justin
 
How about tapersd shoulders ?

Has anyone tried using tapered shoulders on barrels? I believe one of the well known Rimfire Smiths tapers his shoulders now. Apparently the reason is to align the barrel to the action face more completely.

Pete
 
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