Straight tapered bbl

[boltman223]

If I were figuring this, I would take half the reduction from the shank diameter as the side opposite which would be .175. Then I would take the length of the tapered portion (parallel with the bore, as the side adjacent. The tangent of an angle is defined as opposite over adjacent, which would be .175/18 = .00972 (with the 2 repeating). To get the angle I would need to take the arctan, which by my inexpensive calculator (pushing the 2nd and then the TAN buttons) results in an angle of .5570 degree.

http://www.coolmath.com/reference/triangles-trigonmetry

Is that taking the full length of the barrel in consideration?

 

[boltman223]

We all should probably just say, thank you WSnyder and move on.

 

[boltman223]

Essentially you want 15" of tapered barrel from 1.350" dia to 1" dia in that length. That's a half angle of .670°. Your offset at the tail stock on the full 24" blank between centers should be .280". Your total depth of cut should be ~.210". Put the barrel in the lathe with that offset, run an indicator along side the barrel and see if the dimensions work before you cut. You should see .175" in 15" of travel. Adjust accordingly if needed.

For him to make sure, couldn't he offset his tailstock until his indicator reads zero at his desired length?

Ie where the indicator looses Contact with the barrel.

Or put indicator at the 2.5-3.0 mark and offset tailstock until indicator reads .175 at muzzle end?

 

[boltman223]

Or just buy a real lathe with a taper attachment. Sorry couldn't resist.

Actually hats off to ya for coming up with the boring head idea. There's something to be said for the guy who makes do with what he has.

 

[BoydAllen]

The shank has nothing to do with calculating the angle. You could have no shank or a foot, the angle would be the same. I figured the angle relative to the CL of the barrel.
My answer has nothing to do with lathe operation, only calculating the angle from the information that was given. Trig. can come in handy sometimes.

If you calculate (or measure) the circumference of a circle that has a radius of 18" it will come out to 113.097". Dividing that by 360 tells you that a degree is .314", measured along the arc. I mention this to give a ballpark reference to use for evaluating some of the other answers.

 

[WSnyder]

Or put indicator at the 2.5-3.0 mark and offset tailstock until indicator reads .175 at muzzle end?

If I read you correct then yes if what you call the muzzle end is at the 15" mark from the 2.5-3" mark. The offset needed will change depending on the length of the blank, if you figure the angle you can do the trig to figure the offset need for whatever the blank length may be. The angle of the taper is the key.

He could just put his blank in the lathe no matter what the length, put two sharpie marks on the barrel 15" apart and start cranking in some offset. Keep checking with the indicator until he gets .175" change between the marks. No trig or mind bending needed that way.

 

[boltman223]

The shank has nothing to do with calculating the angle. You could have no shank or a foot, the angle would be the same. I figured the angle relative to the CL of the barrel.
My answer has nothing to do with lathe operation, only calculating the angle from the information that was given. Trig. can come in handy sometimes.

If you calculate (or measure) the circumference of a circle that has a radius of 18" it will come out to 113.097". Dividing that by 360 tells you that a degree is .314", measured along the arc. I mention this to give a ballpark reference to use for evaluating some of the other answers.

Yeah, but he's not using degrees he's using a boring head which has .001 increments(not in degrees, in linear movements).

 

[boltman223]

He could just put his blank in the lathe no matter what the length, put two sharpie marks on the barrel 15" apart and start cranking in some offset. Keep checking with the indicator until he gets .175" change between the marks. No trig or mind bending needed that way.

Yes, this is exactly what I was saying in post #23. I should have elaborated. No math no guessing just wam bam thank you ma'am.

And like I said in post #11 you'd be able to sneak up on your deminsions if you didn't have an indicator. Just keep bringing your tool back to the same spot then adjust your/his boring head.

Or do the math and if you have a taper attachment you could use degrees or taper per foot.

 

[boltman223]

What do you guys think of this formula? Large diameter minus small diameter then multiply by 28. then devide answer by length of taper. Should equal taper in degrees.

 

[DaveTooley]

Tail stock offset method with the taper rate known

T X L divided by 2
where T= taper rate per foot
L=total length in feet
To calculate the taper rate
D-d divide by the length of the taper in feet

Great idea using the boring head. I question the rigidity but that's what steady rests are for.

 

[Nvreloader]

Thanks guys,

I am more confused by this degree stuff.......
and this mind bending math stuff, hurts my head,
TOO old to remember from school, etc.

I do not have a taper attachment on this lathe, so I can't figure the degrees out.

I have a dial indicators and a boring bar head, which measures in .001" increments,
for off setting the muzzle end, to get it as close as possible, etc.

Wsynder post,
Makes the most sense to me so far,
I have already put sharpie marks on the bbl, 15" apart,
of where I want this taper to start and end at.

I'll make a couple of light passes to see the results.....

DT,
I have had no problems so far with chatter, with no steady use so far,
as I only make light cuts, .005 to .020" per pass with a fast feed rate.
These cuts depths will be reduced in amount, the closer I get to the final end.

Tia,
Don

 

[Riesel]

Essentially you want 15" of tapered barrel from 1.350" dia to 1" dia in that length. That's a half angle of .670°. Your offset at the tail stock on the full 24" blank between centers should be .280" (edit .330"). Your total depth of cut should be ~.210". Put the barrel in the lathe with that offset, run an indicator along side the barrel and see if the dimensions work before you cut. You should see .175" in 15" of travel. Adjust accordingly if needed.

I run it very much like this using a steady rest on the breech end offset enough for the taper. Run tool from headstock to steady rest.