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Re: Measuring a diameter without a caliper

Posted: Wed Apr 10, 2019 9:23 pm
by Rich_Carlstedt
whateg0 wrote:
Wed Apr 10, 2019 3:57 pm
Rich,
Your instructions made no sense to me.
..........
Dave
Dave, Here is a picture.
Very simple solution, no welding , no oversize instruments
Just use shop calipers (with a sharp point(s) and measure the depth of the beam.
In the attached picture, my Beam is 1.548 deep and with a .869 (Precision block), it's effective depth is .679"
and the span ( CHORD ) is 3.219

Marv, lots of guys do not like math like we do, so links seem to be easier solutions
Rich
P4100020 For Chaski.gif
measure Chord on any diameter ..Note, must be level !

Re: Measuring a diameter without a caliper

Posted: Wed Apr 10, 2019 9:40 pm
by Rich_Carlstedt
Applying the numbers I got from the above quick test . I get a result of 4.494" and I then miked the round with a 5 inch mike and got 4.496 which shows a accuracy of 99.9589 %
Rich

Re: Measuring a diameter without a caliper

Posted: Thu Apr 11, 2019 8:19 am
by John Hasler
This is the elegant solution. Note that accuracy is highly sensitive to the ratio of chord to radius.

Re: Measuring a diameter without a caliper

Posted: Thu Apr 11, 2019 10:14 am
by earlgo
Very nice solution Mr. Carlstedt. Nice math calculation Mr. Klotz
This is worth keeping in the 'notebook'.
--earlgo

Re: Measuring a diameter without a caliper

Posted: Thu Apr 11, 2019 5:03 pm
by whateg0
Rich_Carlstedt wrote:
Wed Apr 10, 2019 9:23 pm
Dave, Here is a picture.
Very simple solution, no welding , no oversize instruments
Just use shop calipers (with a sharp point(s) and measure the depth of the beam.
In the attached picture, my Beam is 1.548 deep and with a .869 (Precision block), it's effective depth is .679"
and the span ( CHORD ) is 3.219

Marv, lots of guys do not like math like we do, so links seem to be easier solutions
RichP4100020 For Chaski.gif
Man, that sure made a lot more sense to me than the words did! Thanks! I designed a radius gauge that uses a fixed chord length and a DI for measuring what you've identified as the beam depth. Just didn't make sense when I read it.

Dave

Re: Measuring a diameter without a caliper

Posted: Thu Apr 11, 2019 5:35 pm
by RSG
Thanks for the tutorial Rich! So will this method be as accurate as your test piece since I will only have 6" calipers available and the dia. of the cylinder is roughly 11.65"?

Re: Measuring a diameter without a caliper

Posted: Thu Apr 11, 2019 7:34 pm
by Rich_Carlstedt
Accuracy is dependent on several things .
1. Have a sharp point on both legs of the caliper. You might want to even stone or file them parallel to the beam . this would also ensure they are the same length and have a sharp 90 degree corner ( only a few thou is needed !)
CHECK your clamp screw . On some calipers , tightening the screw changes the leg length ?? Make sure the leg doesn't cock and leave the screw alone once you know the legs are equal.
2. Keep the jaws level ! consider putting a cord or strap or hose clamp around the subject part so you can lay the jaws on the strap if you will, or use a V Block strapped to the round and the end of the block will be square for the caliper.
3. Do several measurements at different points and change the depth of the beam block
4. The bigger the jaw opening ( Like 5.5" versus 2.7") the more accurate your reading because the the round surface is less acute and more positive . The most accurate point (least error) is at 45 degrees on each side ---that means on a clock face , the 7:30 to 4:30 Chord is the best point , but most likely not available to you - if that clock face was 12 inches in diameter, that distance would be ( 12 x .707) 8.404"
5. surface finish can have a big impact

6 Lastly , all , I mean ALL , instructions for using calipers are in error- do not use the thumb wheel for precision measuring --please !
It cocks the legs because the moving reading head is spring loaded. Always use your finger tips ( or finger and thumb on short measurements) and push the legs close at the point you are measuring at to get accurate readings

I have to ask How accurate does it have to be and why ?

Hope this helps

Rich

Re: Measuring a diameter without a caliper

Posted: Fri Apr 12, 2019 7:57 am
by RSG
Thanks Rich!

I'll try to give that a go! It's for a riser I recently cast for my mill. I have to machine the mating components so I'd imagine even a few thou more will work fine (unless it needs a friction fit?) as the bolts will tighten things up. I'll post my success when complete!