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Low profile boss measurement weapons of choice

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petertha

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#1
I'll try & describe a situation I keep running into with words, but if that doesn't work I'll take a pic. Basically I am turning parts that have an extending boss off the end. They need to be accurate but I'm having a tough time getting conventional micrometer anvils over the boss diameter because the part of the mic where anvils come out of actually bump up against the material behind it. Even now I can only get half the anvil on so always conscious of proper contact & perpendicular to the surface. I can get conventional caliper jaws across it because the jaws are thin & flat, but they aren't really that great for accuracy compared to a mike. So to put numbers to a part, say the base stock diameter is 3" with a 1" diameter boss extending of this, but only sticks out 0.100".

I was thinking this style with the extended anvil might be better. But I think I'll run into the same issue where the anvil area material conflicts. https://www.itm.com/product/mitutoyo-117-107-micrometer-unimike-0-1in-0001in

I used my 2" mike with a gage block in between. It somewhat worked because the fixed end is smaller. But its fiddly & error prone. There has to be a better way?
 

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benmychree

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#2
You might consider a vernier caliper as opposed to a dial caliper, which I do not trust for accurate measurements, and besides, they are cheap on e bay, generally; they will read to .001" accurately.
 

mmcmdl

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#3
You need flange mics , or set 2 adjustable parallels ( to a known dimension ) , set over the boss and measure over them and subtract the 2 parallel dimensions ,
 
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kd4gij

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#4
v anvil micrometer but they aren't cheep
 

Tony Wells

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#5
Disc micrometer. Used to run thousands of parts with a shallow boss and a bearing fit bore. IIRC they were pump covers and the boss was to locate the cover in the housing. Tolerance was +0.000/-0.002. This pain of a part also had a full radius groove in the bore so had to buy a groove-gun too.
 
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f350ca

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#6
Bit of a waste of material, but, make the boss long enough to measure then face it off to length.

Greg
 

mzayd3

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#7
Make a GO-NOGO gage?


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T Bredehoft

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#8
Tell us what tolerances are acceptable? If you have as much as ±.0025 a dial or vernier caliper will do the job.
 

petertha

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#9
I'm having to measure & machine within 0.0005" specifically for bearings & similar fits. I have good quality calipers (Mitutoyo Digimatic) as well as verniers 'with a dial on' them :) Actually my little 4" Starrett gave me the best consistency but the bigger bodied 6" travel just vary by a thou or so in this particular application because of the orientation & contact area.

Disc micrometer - now that looks very promising!
 

petertha

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#10
...assume like these? Looks like discs give overhang so the mike body (where the anvil comes out) wont interfere
 

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mmcmdl

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#11
That's them ! ;) Flange or disc mics .
 

Tony Wells

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#12
Yes, that's the one. This is one of the main applications for this instrument. They work nicely. The discs to clear the body, just like you need for this job.
 

MSD0

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#13
Make a GO-NOGO gage?


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That’s a pretty good idea, especially if you have a lot of parts. Question is, how accurate can you make the gage?
 
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