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Old 11-13-2017, 08:44 AM   #1
Naiveambition
 
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Default How to find a taper amount?

The project I'm working on now requires a internal taper or "bored taper". Don't know how to find my compound degrees. Will be done on my lathe.

My part will be 1 inch long.
Starting bore is .741
End of bore ..710

Hopin someone can help me out


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Old 11-13-2017, 09:12 AM   #2
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Somehow I doubt that that just altering the top slide by what degrees will work.
Un less you have a very very good machine, you are chucking snowballs at the moon!

All that you are doing is removing a 1/64th of an inch from a cylinder an inch long??

I would make a male 'dummy' with a 1"round blank with the two sizes machined at each end and waisted in between.

Leaving the dummy piece in the lathe, I would knock the top slide over to touch both rings that you have machined( by trial and error)

Once the top slide is fixed, then change the lathe tool to a boring bar and whilst not disturbing anything other than the feed screw, bore the taper in the bit that you want.

That, roughly, is how Myfords suggest you make a test bar for tailstock alignment! I have one!

Not how you have phrased the problem but that is my solution


Norm


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Old 11-13-2017, 09:49 AM   #3
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If you already have the mating part you can use a dial gauge to set the topslide to the correct angle. If not you can put an accurate bar between centres, or take a skim off an inaccurate bar in the chuck, and set the topslide round until you get
a dial gauge movement of 0.0155" over an inch of travel as measured on the topside dial.
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Old 11-13-2017, 11:11 AM   #4
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If you have a sine bar set and lock it to the needed angle. The hold the base of the bar against the ways and turn the compound so that the tool is aligned with the angled top.
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Old 11-13-2017, 11:07 PM   #5
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Here is a general approach to cutting odd angle tapers. Sketch shows your example with big bore = 0.741”, small bore = 0.710”, center distance = 1.000”. This is everything we need to calculate the compound set angle.

- Angle = ArcTan [ (0.741-0.710) * .5 / 1.000 ] = 0.88801 degrees

- Now how to accurately set the lathe compound to this tiny, oddball angle?

- Chuck a nicely ground accurate test bar extending out

- Using compound leadscrew, feed down the test bar with indicator mounted. We want no needle deflection meaning the compound is now initially referenced at same zero degrees (=parallel to spindle axis)

- Now mount a lobed sine bar into toolpost such that both lobes contact the test bar. Only adjust the sine bar, not the compound swivel. Sine bars come in different lengths, Imperial, Metric etc. Let’s use a 5” center-to-center in this example.

- Make up a gage block stack (or an accurate cut-off) to this thickness
Thickness = 5.00 * Tan (0.88801) = 0.0775”

- Now with sine bar attached, loosen & swivel the compound. Insert the 0.0775” spacer under one of the lobes (depending on which direction you are cutting taper). So one lobe is resting on the test bar, the other lobe is trapping the 0.0775” spacer block. Lock down the compound in this position & you are ready to cut.

Methodology similarly applies to making tapered ‘male’ parts. 1” is short traverse & likely within range of your compound travel. But once this range is exceeded, we typically revert to conventional taper turning methods using displaced tailstock, taper attachments etc.
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Last edited by petertha; 11-13-2017 at 11:11 PM.
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Old 11-13-2017, 11:36 PM   #6
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Since describing the ways to do this can easily take a thousand words I offer this suggest, check out the OXTOOL videos on Youtube. He recently went through setup of a compound and also various ways to measure an unknown taper. Lucid well done videos is I do say so.
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Old 11-14-2017, 02:10 AM   #7
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I use a piece of bar that I turned between centres to be parallel and true. It's about six inches long and 5/8" diameter.
With that bar set between centres in the lathe, I use a dial indicator to measure the amount of movement from parallel while winding the carriage along by one inch according to the graduated dial on its handle. So as long as you know how many thou taper over one inch, as you do, you just set the topslide angle to get the desired amount of taper indicated on the dial indicator.
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Old 11-14-2017, 05:01 AM   #8
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Quote:
Originally Posted by Naiveambition View Post
The project I'm working on now requires a internal taper or "bored taper". Don't know how to find my compound degrees. Will be done on my lathe.



My part will be 1 inch long.

Starting bore is .741

End of bore ..710



Hopin someone can help me out


I would machine a male taper gauge to suit.
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Old 11-14-2017, 05:09 AM   #9
bazmak
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If you can set up the compound to machine a male taper then you
have already setup to do a female .For the simple home machinist
i would trial and error with a dial indicator to cut a male taper small end to the chuck.Simple to mike up then you have the setting for boring the female
and a test gauge to blue up.No need to get complicated
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Old 11-16-2017, 03:11 AM   #10
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Default How to find taper amount

Awesome guys. Just what I needed. Will cut my part in the next couple days so will let you know how it turns out. The bad part is I have to do all the other operations before I taper, So really hoping I don't muck it up then.


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