math help, cone thickness please

[Investigator]

As a matter of fact, math is not my strong suit. I bet this is likely very simple but apparently so am I.
I'm building a suppressor for a rifle and am trying to figure how to make the cone baffle. All legal paperwork and stamps in hand.

I'm trying to make a 60* cone baffle. I will need several, some with a wall thickness of .100" and some with a wall thickness of .065".

What I need to figure out is how much to move the saddle, or compound if that is a better way to do it, in order to make a baffle with a specific thickness.

For instance, I have a piece of 17-4 in the lathe. I have drilled the center hole and used boring bars to cut the inner surface of the baffle. I have a little chatter, but overall looks pretty good, a nice 60* cone. Now I need to work on shaping the outside of the baffle. So I need to figure out how much to move the carriage in order to make the wall thickness .100". This will be the blast baffle for a direct thread can.

Is there a formula for figuring this? I bet there is and I bet it involves trig. I never had trig, only algebra and geometry.

 

[magicniner]

You can solve it with scale drawing if you don't want to use trig, if you use a 10x scale drawing (1" = 0.1") then you will be able to measure it at least as accurately as you can machine it,
Regards,
Nick

 

[Wreck™Wreck]

I dislike helping a gun person, however since you have numbers for the finished tapered bore the OD taper would be, shake the magic ball, +.200".

 

[Bill Gruby]

If I am reading this correctly you have an angled bore that you cut. The wall thickness is the same the full length. This says the outside angle is the same as the inside angle. This translates to you don't change it. Outside angle equals inside angle, or did I miss something??? As Wreck said just move .200 and you are there.

"Billy G"

 

[MarkM]

Does the o.d match the internal taper. Taper formula is big diameter minus small diameter divided by the taper length. Once the number is figured out the angle is the tangent of this number. Set up your compund to match this angle using trig. Your compound stroke becomes your hypotenuse. Using say a two inch stroke on your compound. Set an indicator on your crosslide. Work out this length using trig. Sine of the angle times your two inch from your compound stroke gives you the distance you set your crosslide from your work. Trial and error using your compound only with a two inch stroke you should hit zero after your two inches with the compound on your indicator if it s exact. If you don t hit zero tap your compund a bit to change the angle and dial it in. Really cant picture what your doing but here are some good formulas to work with.

 

[Dave Paine]

Sounds like you need sine or cosine. I am not following how the piece is mounted without a picture. Try this site.

Sine and cosine calculator

If the compound is already at the 60 deg angle, then I think you need to move the carriage back (1/sin 60) = 100 / 0.866 = 115.473in - if I have the correct interpretation.

 

[gjmontll]

I hope I correctly interpreted your project description. If so, here is my formula and results.

The adjacent side is your desired thickness and the hypotenuse is the carriage crossfeed amount. My diagram uses the half angle, 30°, and its cosine is 0.6. The formula is crossfeed = desired thickness / 0.6.

Using the formula, I arrive at 0.167" for the 0.100 wall, and 0.108" for the 0.065" wall.

Greg

 

[whitmore]

I'm building a suppressor for a rifle and am trying to figure how to make the cone baffle. ...
What I need to figure out is how ... to make a baffle with a specific thickness.
... I have drilled the center hole and used boring bars to cut the inner surface of the baffle.

So, you have the outer surface of a cone to cut... with a different tool from the boring of the inner,
you'll start with a trial cut (making a too-thick cone) and measure the thickness. Then, because
the cone side is 30 degrees off-axis, each 0.001" of carriage travel lessens the cone thickness
by 0.001 * cos(30 °) = 0.000866"

The 60 degree cone has a benefit; after cutting the inside, you can pull up the tailstock and crank
a center into it, for extra support. Stability is a good thing.

 

[rock_breaker]

I am not sure if I understand your question but I agree that you can scale it out. I used my trusty slide rule (can't find my calculator) and come up with 0.167" for 0.1000" thick and 0.108" for 0.065". This was arrived at the trig formula Cos 60` = side opposite/hypotenuse. The side opposite being the thickness of your baffle and the hypotenuse is a line parallel to your lathe ways.

To answer your question I would set the compound at 60` then move the saddle the required distance using a dial indicator then cut the second side of the baffle with the compound. Hopefully a real lathe operator will get involved here.
Ray

 

[HBilly1022]

Assuming the 60 degree angle is measured from the spindle centerline and using the calculator Dave Paine provided, the cosine is what you want for this operation. Therefore the saddle should be moved exactly twice the distance of the desired thickness, ie for the 0.100 thickness move the saddle 0.200 and for the 0.065 thickness move it 0.130.