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SMALL HOLE / SLOT MEASURMENTS - HOW DO YOU GUYS DO IT?

Rcgiovannani

Aluminum
Joined
Apr 6, 2015
Hi guys,

I keep running into this problem - how do I measure an internal feature that is less than about 0.100" when I have to hold less than 0.0005" total tolerance? Whether it be a slot or a hole.

I'm aware that there are bore gages like this (but they always seem to be crazy expensive and have a minimum measurement of about 0.1000"):


Is the only economical option to buy a range of deltronic pins for each specific hole / slot I am working on? I bought a smaller probe tip (2MM) for my Renishaw probe and now I can measure down to like 0.150". I'd really like some hard gaging for this, though.

Any suggestions?
 
I have an 82AZ and would be surprised if Starrett couldn't probably make a little smaller split ball probe for it. Other than that, an air gage could surely be made that would work, though they are pretty size specific and don't have much range.
 
An air gauge would certainly do what you want, but not necessarily for jobs where you are looking for an "economical option". Have a look at Western Gauge.

-Marty-
 
A simple machine like a Brown & Sharpe 13 grinder or other decent OD grinder would do. It would soon pay for itself by making gauges. A dial indicator micrometer would prove gauges to about 25 millionths. likely 10,000 would make a decent gauge-making setup.
Go No gauges would be made, Agree gauge pins are handy buy they don't come in every half-tenths size.
 
Mitutoyo Series 526 split-ball dial bore gages come in sizes down to .037 inch. Look at models 526-176 (range .037-.061) and 526-166 (range .060-.157). They can be ordered less dial indicator and will work with electronic digital indicators. Price for the 526-166 is something over $3000, depending on the retailer and whether you want the setting ring set.

Larry
 
Where I'm at, with the parts we make, holes too small to take a precision bore gage (e.g. Sunnen) are inspected with Go / No Go Gage Pins (Class X minimum):

Example:

DIM: .0982 +0 / -.0002

Go Pin: .0981
No Go Pin: .0985

Note: The ID has to be CLEAN for this to work. At these tolerances if there is anything left on the ID surface the Go Pin may very well jam/seize giving you a false No Go. I've got a set of pipe-cleaner plastic brushes, some very small. Quick dunk in a bucket of Mineral spirits with one in/out of the brush, compressed air blowout, and suddenly the Go pin slips through just fine.
 
All good suggestions.

I feel like somewhere I saw a gage that has a series of dowel holes and a dovetail on one end for a test indicator (like interapid) that can be mastered on gage blocks. Does that sound familiar to anybody? Maybe I could make one with a 1/16" dowel pin.
 
I used to make odd special gauges with a surface grinder and a B&S 13 grinder. Most I had a tenths or two, some down to 6 to 12 millionths.
Sometimes, I would make one with "No detectable error" with a top-grade CCM..(just to get a dig on the inspectors.)
Usually, anything less than a tenth, or half-tenth was engineering overkill.
Every half-tenth to one inch would cost a fortune in a pin set and 95% would never get used.
*I guess it depends on how much you are spending on special gauges and if you can make other use of a high-grade grinder.

 
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why not use gage blocks for the slot?
Slot size less than 0.100. A standard 81 block set starts with 0.1001, and wear slips/blocks are typically 0.100 each. Strike that, a standard set goes down to 0.050, but the next step is 0.050. You only get tenths resolution higher above 0.100

Could make use of the smallest standard pin gage set, though, but not with resolution to tenths. And as mentioned above, Delco size+- sets are spendy and most pins don't get used.
 
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With my old indicator micrometer, I can get way down to almost zero with comparing to my master set of JoBlocks.
I don't think there is any measuring device that can measure accuractly off the dial without having a gauge such as a good JoBlock.
Getting down to a half tenth is pretty tricky..and then there is out of round, A special No Go with only perhaps 30% gauge at each 180* makes a good out-of-round checker. That boils down to In House making the gauge,
Re; most below .0005 TIR is engineering overkill, but you have to do the drill.


Yes, the thimble is just the rapid feed, you never gauge off the numbers, Only off the three times feel off the JoBlock.

These mics are so close that when you clean them with 20 wt spindle oil it takes 10 minutes for the pointer to get back to normal speed.
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Hi guys,

I keep running into this problem - how do I measure an internal feature that is less than about 0.100" when I have to hold less than 0.0005" total tolerance? Whether it be a slot or a hole.

I'm aware that there are bore gages like this (but they always seem to be crazy expensive and have a minimum measurement of about 0.1000"):


Is the only economical option to buy a range of deltronic pins for each specific hole / slot I am working on? I bought a smaller probe tip (2MM) for my Renishaw probe and now I can measure down to like 0.150". I'd really like some hard gaging for this, though.

Any suggestions?
 
Slot size less than 0.100. A standard 81 block set starts with 0.1001, and wear slips/blocks are typically 0.100 each. Strike that, a standard set goes down to 0.050, but the next step is 0.050. You only get tenths resolution higher above 0.100

Could make use of the smallest standard pin gage set, though, but not with resolution to tenths. And as mentioned above, Delco size+- sets are spendy and most pins don't get used.
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with these find a stack having a medium slip fit, add 2µ and thats your dimension.

as to the pins, i wonder what the tolerance on straightness and parallelism might be (unless you just want to stick them in vertically). surface roughness makes a difference also.
 
How do you stack up gauge blocks to an exact size that is less than 0.100"? The blocks with the smaller increments usually have that amount as the starting point. So even just two blocks would be over 0.200" just to start.



why not use gage blocks for the slot?
 
They make probes that can determine coordinates of parts when used in a CNC device. Such a probe could be mounted horizontally in an attachment designed to reach down into the interior of the of the part. Then all you need is the software to do the measuring.

If you do not have such CNC software or a CNC device to hold such a probe, all of the above could be done with some or all of the above being shop made. A horizontal wire could be the probe. Music wire would probably work, just check it's size with a micrometer. Or solder a small bearing ball to the end of a smaller diameter wire. Connect a continuity detection circuit to it and the part. When it touches the upper and lower surfaces of the slot or hole you get a light. A good height gauge used on the shop's surface plate would provide the readings. And some kind of arm could be fabricated to allow the arm of the height gauge to reach into the interior of the part.

But before doing any of the above I would talk to the customer and find out just how they will check those dimensions. And just how much they will pay for a guarantee of that tolerance. You may just find out that they only need +/-0.005" instead of +/-0.0005".
 








 
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