Measuring Tapers with Combination Square

grungymachinist · Sep 12, 2019

On Instagram (@grungymachinist), I share tool tips from old machinist books in my personal library every Thursday among the old machinery pictures I typically share. Today I posted the following tool tip on measuring tapers with a combination square, and I was surprised by the reaction it received. So I thought many people on here would find this tip useful as well.

I'm interested to hear if you have ever heard of this technique before, or if this is news to you.

Grungymachinst

Grungy Machinist (@grungymachinist) • Instagram photos and videos

johnoder · Sep 12, 2019

Good luck in determining the difference between Morse and Jarno. (2.974 degrees and 2.864 degrees)

Toms Wheels · Sep 12, 2019

That looks like a poor way to check tapers. Hows this, put a 5" sine plate on the surface plate, place gage block of correct size for desired angle, place work on since plate, using height gage measure across top of work, should be same end to end.

EPAIII · Sep 12, 2019

Yes, the protractor head for the square is not accurate to better than about 1/4 or 1/5 degree. I have two of them, a B&S and a Starrett and neither of them will give you any better than that. This method will just leave you in doubt.

Even with a Vernier scale that reads to 1/10th (6 minutes) or 1/12th (5 minutes) of a degree you are still going to be guessing.

If you are measuring a taper, you need sine bar type techniques.

johnoder said:
Good luck in determining the difference between Morse and Jarno. (2.974 degrees and 2.864 degrees)

Cole2534 · Sep 12, 2019

Horses for courses- this seems like a good spot check for....something?

scraper · Sep 12, 2019

To use a sine bar you have to know what the angle is. If someone just walks up to you and hands you this part and says make one of these, you have no idea what this angle is, a guess (if you are really good) might get you within maybe 5 degrees. That’s a whole lot of trial and error in stacking gauge blocks. This method ought to easily get you within maybe 5 to 10 minutes. From there it’s a pretty easy adjustment to get the exact angle.

Cole2534 · Sep 12, 2019

scraper said:
To use a sine bar you have to know what the angle is. If someone just walks up to you and hands you this part and says make one of these, you have no idea what this angle is, a guess (if you are really good) might get you within maybe 5 degrees. That’s a whole lot of trial and error in stacking gauge blocks. This method ought to easily get you within maybe 5 to 10 minutes. From there it’s a pretty easy adjustment to get the exact angle.

No. Mark two spots 1" apart, measure big end, measure small end, 2.5x (or whatever your sine bar dictates) that difference is your beginning gage stack. Dial it in, or use measuring tools, and calc your angle.

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Measuring Tapers with Combination Square

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