# Measuring the diameter of shallow holes



## DMS (May 31, 2014)

I am making some parts in delrin that involve a shallow hole 0.118" deep (3mm). The diameter is 0.866" (22mm). It's also a bearing fit (a pair of these parts fit over a 608 bearing), so I need to be pretty consistent. I am going for a fairly heavy press, as friction is all that will be holding these in place. My problem right now is measurement. I have been using telescoping guages, but the hole is so shallow, and the plastic is so forgiving, it is hard to get a consistent measurement. I'm thinking somebody out there has to have a better way. 

One other thing; this is a test batch (6 pieces). If it works out, I need to make another 12. It took me about 2 hours to make 3, mainly because I was measuring 3 times after every pass before I was sure I was really "there".


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## Tony Wells (May 31, 2014)

Indical. High resolution DTI on it.


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## JimDawson (May 31, 2014)

This is a bit difficult in a soft material.

This is one of those times that I would 'trust the dials' on my machine.  Once you find the the number that gives you the diameter you want, just come back to the same spot for each part.  Do everything the same way each time.

Calipers do work pretty well for measuring shallow pockets.  You should be able to measure to about 0.001 or better.  You could also make a set of go-no go plug gauges.

I'm sure somebody will have a much better idea.


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## DMS (May 31, 2014)

Tony Wells said:


> Indical. High resolution DTI on it.



Not sure how this would work. Unless you are talking about the depth. I guess my original question was not clear. I am trying to measure the diameter. I have a depth mic, but the depth is less critical, though my repeatability is pretty good. I do have a a couple decent indicators, a 0.0005" DTI, and a 0.001mm DI, I'm just not sure how I would configure them to measure an absolute dimension (I have only used them to measure relative dimensions)

Jim, you may be right that I should just trust my dials. I have been doing a bunch of tool changes (well, 3, face, bore, part), and have been leery of doing that. I'll give that a try.


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## Tony Wells (May 31, 2014)

The Indical is ideal for soft materials. Low measuring pressure. Don't confuse it with an Indicol. Different animal. Useful for measuring ID's, ID grooves, relief diameters, etc. I works very well for a shallow bore gage.


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## NightWing (May 31, 2014)

http://www.flexbar.com/PDF/General/130- split ball large bore type.pdf


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## mikey (May 31, 2014)

I'd use a inside micrometer for this but if I didn't have one I'd probably use either my dial calipers or make a plug gage 0.0002" undersize.


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## DMS (May 31, 2014)

Tony Wells said:


> The Indical is ideal for soft materials. Low measuring pressure. Don't confuse it with an Indicol. Different animal. Useful for measuring ID's, ID grooves, relief diameters, etc. I works very well for a shallow bore gage.



AAAAAH Gotcha. That looks like it would work well (I have seen those before, but the name didn't jog my memory). 

NightWing, I was looking for something like that first gauge in the linked pdf, but nothing like it showed up in my google searches other than hole gauges, which seem to max out at 0.5". The Indical may be more versatile overall. 

I think i will press forward on the first set with Jim's suggestion. If it works out, it may be worth investing in an indial or large bore gauge for the remaining 12. Any excuse for more tools


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## TOOLMASTER (May 31, 2014)

no go/go pins


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## swatson144 (May 31, 2014)

I have something like this http://www.globalindustrial.com/p/t...gclid=CPyB67Pv1r4CFRRbfgod50MAeg&gclsrc=aw.ds that is of a different make It is my go to measuring tool for the kind of measuring you mentioned. For harder material I use pins or small hole gauges. http://www.amazonsupply.com/starrett-s830fz-small-3-2mm-12-7mm/dp/B0006J4QM8

The links are simply to the 1st site I found and no recommendation.

Steve


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## fixit (May 31, 2014)

DMS said:


> I am making some parts in delrin that involve a shallow hole 0.118" deep (3mm). The diameter is 0.866" (22mm). It's also a bearing fit (a pair of these parts fit over a 608 bearing), so I need to be pretty consistent. I am going for a fairly heavy press, as friction is all that will be holding these in place. My problem right now is measurement. I have been using telescoping guages, but the hole is so shallow, and the plastic is so forgiving, it is hard to get a consistent measurement. I'm thinking somebody out there has to have a better way.
> 
> One other thing; this is a test batch (6 pieces). If it works out, I need to make another 12. It took me about 2 hours to make 3, mainly because I was measuring 3 times after every pass before I was sure I was really "there".





Make up a SPADE DRILL BIT of the correct diameter, or modify a store bought one. Your only cutting plastic.

fixit


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## elf (May 31, 2014)

Wouldn't a Go-No Go gauge work well for this?


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## DMS (May 31, 2014)

fixit said:


> Make up a SPADE DRILL BIT of the correct diameter, or modify a store bought one. Your only cutting plastic.
> 
> fixit



I'm sure I can cut it, but would that be accurate enough? I tend to think of drills as being ballpark sort of things.

- - - Updated - - -



elf said:


> Wouldn't a Go-No Go gauge work well for this?



A go/no go gauge would let me check pass/fail. I suppose if I had a full set of pins in that size range I could make it work. Unfortunately pins in that range seem to be pricey. I think the other methods posted would get more use in my shop. I do want to pick up a set of pins at some point, but just not sure if I need anything greater than 0.5"


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## JimDawson (May 31, 2014)

I had another thought after reading about spade drills.  How about a 22mm, center cutting, end mill, Enco has them for $22.  With a good set up it should give you pretty much a reamed hole, and will be sharp enough to cut Delrin just fine.


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## Andre (May 31, 2014)

Use a gauge pin or mushroom hole gauges.


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## elf (Jun 1, 2014)

DMS said:


> I'm sure I can cut it, but would that be accurate enough? I tend to think of drills as being ballpark sort of things.
> 
> - - - Updated - - -
> 
> ...



I was expecting you to just make the gauge


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## DMS (Jun 1, 2014)

elf said:


> I was expecting you to just make the gauge



I can make the gauges, but unless I am missing something, they just tell me if I am pass fail. I would need a series of gauges to see what size I was at before my finish pass to see how big that final pass needs to be right? Am I missing something here? Or is the plan just to sneak up on it till the "go" side just fits? That doesn't seem like it would be much faster than my current method...though maybe more consistent and accurate...

After that little bit of musing, seems like it may be a good thing to do to dial things in, and then I think I could use the method Jim suggested. I made a boring bar holder last night to help things along; I'll try things out today.


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## mikey (Jun 1, 2014)

DMS said:


> I can make the gauges, but unless I am missing something, they just tell me if I am pass fail. I would need a series of gauges to see what size I was at before my finish pass to see how big that final pass needs to be right? Am I missing something here? Or is the plan just to sneak up on it till the "go" side just fits? That doesn't seem like it would be much faster than my current method...though maybe more consistent and accurate...



You might want to make a stepped plug gage with 2 steps. When I use these I machine the smallest step 0.0100' larger than the target bore; when it slips in I know I am close. The next step depends on which insert I am using. If my nose radius calls for a finish depth of cut of 0.003" then I make the next step 0.006" larger than the target bore. When that slips in I dial in my finish cut and will usually come in on size, or very close to it.


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## xalky (Jun 1, 2014)

What about buying a 7/8" (.875")forstner drill bit for wood and grinding the OD down to the exact size that you need. It's only .009" to grind off the OD. Chuck it up in a hand drill and spin it as you touch it off on a grinding wheel. A little at a time, checking and touching up as necessary. It shouldn't take very long at all to dnce the drill bit is made and set  , you wouldn't even have to check your holes anymore. 



http://www.harborfreight.com/http-w...tride-coated-forstner-bit-set-39812-html.html

That's a whole set in the link, but I'm sure you could buy just the size you need at Home Depot or some other place that sells wood working tools.

Marcel


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## DMS (Jun 2, 2014)

I tried just trusting my dials, and was able to turn 5 out in about 30 minutes, fit was much better too.

My main issue it turns out, was stubbornness. I was using as small HSS boring bar. Too small for my quick change holder to repeat accurately. I made a boring bar holder to bring it up so that it repeats. I'll post some pics of the parts I am making later, pretty pleased with how they turned out. 

I'm still glad I asked the question, I at least, have learned a lot here


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## JimDawson (Jun 2, 2014)

DMS said:


> I tried just trusting my dials, and was able to turn 5 out in about 30 minutes, fit was much better too.
> 
> My main issue it turns out, was stubbornness. I was using as small HSS boring bar. Too small for my quick change holder to repeat accurately. I made a boring bar holder to bring it up so that it repeats. I'll post some pics of the parts I am making later, pretty pleased with how they turned out.
> 
> I'm still glad I asked the question, I at least, have learned a lot here



I'm happy that worked out for you.


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## retmac (Jun 3, 2014)

JimDawson said:


> I'm happy that worked out for you.



How about old stile inside calipers .
I know I'm showing my age.
RETMAC


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## papermaker (Jul 7, 2014)

Can you turn a plug gauge that is the correct diameter. Kind of like your own go/no go gauge


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