Proper Measuring Techniques

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EdK
Posts: 688
Joined: Tue Apr 13, 2010 6:20 am
Location: Minnesota

Proper Measuring Techniques

Post by EdK » Fri Jul 30, 2010 12:32 pm

I need to measure the width of the groove down the center of this jaw and was wondering what the proper tool and technique is to use for such a task? I'm measuring for making soft jaws but let's assume I want to get a precise measurement of that groove for whatever reason. In the past I would use my dial caliper but I can't seem to get a consistent measurement with it. In our previous discussion about gauge blocks I was told they're not used for such measuring tasks. I want to take my projects to the next level and need to learn how to make accurate measurements so that's the reason for this post. Not how to make soft jaws.

Thanks,
Ed
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Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

randyc
Posts: 497
Joined: Sun Jun 13, 2010 10:46 pm
Location: Eureka, California

Re: Proper Measuring Techniques

Post by randyc » Fri Jul 30, 2010 12:55 pm

Ed, there are many ways to make a measurement like yours. Frankly, I find calipers to be very useful for small slots and that would be my first choice when measuring the width. However, I'd also make sure that the caliper jaws are perpendicular to the part being measured.

Image

I've supported the calipers and the part with 1-2-3 blocks on a surface plate so that the measurement is made at a right angle. After measuring a couple of times, I'd double check the fit by inserting a piece of slightly thinner stock into the stock and then make up the difference with automotive feeler gages until the fit is as you desire. Then use your micrometer to measure the thickness of the stack-up.

If the slot was wider, an adjustable parallel could be tweaked to obtain the desired fit, miking the parallel to obtain exact distance. For critical applications, you might make the part .001 - .002 oversize and then lap to fit with 220 grit paper temporarily taped to the surface plate.

In principal, I agree that gage blocks shouldn't be used in this manner but for a critical application I might relax that rule ...

Best wishes,
Randy C

ieezitin
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Joined: Sun Jul 04, 2010 4:13 pm

Re: Proper Measuring Techniques

Post by ieezitin » Fri Jul 30, 2010 1:41 pm

EDK.

What randy said is good advice. I would add that is a tricky thing to measure, not deep enough to get a pair of outside calipers in, no real defined corner edges, no real machined surfaces to get a datum point from, if it had you could use the vernier height gage on the surface table.

I would do as suggested slip an adjustable parallel in shy of around .010 and use feeler gages. Then over size the part and hone in to suit.

Vernier / digital calipers are not really a measuring device I only use mine for reference only, the digitals drive me mad with the fluctuation of the readings.

123 blocks are apart of your tool inventory, they should be used anytime necessary, treated with care like all precision tooling they will last you a lifetime.

Have fun. Anthony.

EdK
Posts: 688
Joined: Tue Apr 13, 2010 6:20 am
Location: Minnesota

Re: Proper Measuring Techniques

Post by EdK » Fri Jul 30, 2010 4:32 pm

Randy,

That looks like a good solution. I have two sets of 123 blocks and a set of 246 blocks so I have the necessary tools to use your method. Thanks for the suggestion :!:

Ed
Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

EdK
Posts: 688
Joined: Tue Apr 13, 2010 6:20 am
Location: Minnesota

Re: Proper Measuring Techniques

Post by EdK » Fri Jul 30, 2010 4:40 pm

ieezitin wrote: no real machined surfaces to get a datum point from, if it had you could use the vernier height gage on the surface table.
Actually the sides of the slot are machined, it's just the bottom that looks crappy.
ieezitin wrote: I would do as suggested slip an adjustable parallel in shy of around .010 and use feeler gages.
The slot is too narrow for adjustable parallels.
ieezitin wrote: Vernier / digital calipers are not really a measuring device I only use mine for reference only, the digitals drive me mad with the fluctuation of the readings.
Those are my thoughts also. I don't own digital measuring devices.
ieezitin wrote: 123 blocks are apart of your tool inventory, they should be used anytime necessary, treated with care like all precision tooling they will last you a lifetime.
I have 123 & 246 blocks and they are indispensable. I just need to learn more about the uses for them like Randy suggested.

Thanks Anthony :!:

Ed
Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

John Evans
Posts: 1989
Joined: Tue Jan 20, 2009 9:33 pm
Location: Phoenix ,AZ

Re: Proper Measuring Techniques

Post by John Evans » Fri Jul 30, 2010 5:29 pm

As I recall the dimensions for American std. chuck jaws are in Machinery's handbook.
www.chaski.com

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