ratio to angle math question

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Hi all, I'm building a Reil burner for a small foundry and it calls for the end of the burner tube to flair at 1:12. I plan to drill out and then bore the taper with a boring bar in my 9A South Bend. Trouble is, the markings on the compound are in degrees and I'm at a loss on how to do the math.

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Extra question: This isn't something I need to know for a project but I've always wondered about if you had a pentagon 5 sided or a 7 sided rod, but only a 3 and 4-jaw chuck, how you would hold it. If the rod were long and it needed to go thru a steady rest, how would that work.

There must be a better way to hold it (other than driving between centers) with the chuck and steady. My guess is for the steady, mill out a sleeve that's round on the outside and same for the chuck.

Thanks
 
Tan[SUP]-1[/SUP](1/12) = 4.76°
 
as far as holding odd work with 5 or 7 sides,
you could make a tube fixture that fit's into the chuck that is larger than the intended work,
you'd then drill and tap a series of holes in the tube's end that sticks out of the chuck for adjustment bolts.
lightly tighten the bolts to the work you need to hold.
you'll need at least three bolts in contact with the work.
then you can indicate the work in the fixture and adjust the bolts as necessary to run concentrically.
this method will work for other odd shapes other than a 5 or 7 sided pieces.

like this: your fixture may look different but the principle is the same- click links below

http://www.google.com/imgres?imgurl...iact=rc&uact=3&dur=832&page=1&start=0&ndsp=20

http://www.google.com/imgres?imgurl...ct=rc&uact=3&dur=691&page=7&start=152&ndsp=28

i hope the info is helpful
mike:))
 
wow, thanks for such a quick response; I don't know trig, so keep that formula handy and then plug it into an online calculator whenever I need to know such things

thanks on the holding device question as well! I don't think it's too often you run into 5 and 7 sided rods thank goodness!
 
If you are stuck without a calculator Ratios can also be converted using pencil and paper. 1/12 just means a rise of 1 (unit of measurement) along a line of 12 (units of measurement) So draw a straight line 12" long, at one end measure up 1", then draw a line from there back to the start point of the first 12" line. Now you have a long narrow triangle that you can measure with a protractor. Works the same in feet, yards, miles, heck even in metric, if you americans ever drag yourself out of the middle ages ;)

Cheers Phil
 
12bolts said:
Works the same in feet, yards, miles, heck even in metric, if you americans ever drag yourself out of the middle ages ;)

Cheers Phil
Click to expand...

Yeah, but I hate working in metric radians. :biggrin:
 
Playing Devil's Advocate here...
I've usually read taper as being a change in diameter for a given distance of axial length. Since diameter changes twice as fast as the change relative to the axis, to which the cross slide angle is relative, wouldn't the cross slide be set to 2.38 degrees to get an overall 1:12 conical flare of 4.76 degrees?

I was taught the sleeve for holding odd shaped/sized work is called a "Cathead". I have several of them floating around for holding non-round stuff in my steady rest.

Them thar metric Volts and Amps still confuse me :)
 
The dark ages? hummm We have a saying here, "If it ain't broke, dont fix it."
 
eightball said:
The dark ages? hummm We have a saying here, "If it ain't broke, dont fix it."
Click to expand...

Agreed. Feet, inches, pound and pints were used by the working man because the units of measure were found to be useful. Metric was invented by some French scientist guy with the express purpose of screwing up the Brits:)) and it eventually worked.
 
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