# #87 in a series of dumb questions



## Johnturner (Aug 7, 2018)

When measuring a drill bit to determine its size I usually measure right below the flukes. Above any square or smaller shank. I have found that sometimes my measurements don't read the same as the numbers on the hole I just took it out of?


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## dehn0045 (Aug 7, 2018)

Not sure what you're drilling, but my experience is with pens. Is the hole bigger or smaller? I find it rather difficult to get accurate measurement of a hole, whereas measuring a bit is pretty easy. By definition, the minimum diameter of the hole is equal to the diameter of the bit, but it can be larger for various reasons.

Runout on the DP can be a problem. There are good youtube videos on how to check runout. I usually drill on the lathe, so mounting the blank in the chuck can cause problems if it isn't perfectly square to the bit. Also, if the tailstock is not accurately aligned then you can have problems. I find that these problems will cause a larger hole at the initial entry point, with a more accurate hole size at the exit. Also excess heat is a problem (the following is mostly speculation) - I think heat can cause the bit to wander, also I think the it can release stesses in the wood doing funny things (warping, rapid drying, etc). Lastly, allowing the flutes to clog up will both add heat and cause the hole to enlarge from added friction. Like I said, just my experience, so take with a grain of salt...

Reactions: Agree 1 | Informative 1


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## kweinert (Aug 8, 2018)

How securely are you holding the blank when you drill? (I think we're all presuming that your hole is larger than expected.) Any blank movement will make the hole bigger, of course. I agree with what @dehn0045 already said.

The other question is this - does it really matter? Is the hole too large for the tube (presuming you're using tubes) to fit properly? Most folks are using some sort of gap filling glue (epoxy, gorilla) to put the tube in which means that any little extra space isn't an issue (unless, for some reason, your blanks are really marginal compared to the final pen size.)

Just a couple of random thoughts, hope it helps.

Reactions: Agree 1


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## Karl_TN (Aug 8, 2018)

There can be a lot of variance in bit sizing between different manufacturers (and sometimes within ). This is especially true for cheaper bits made in China, but it can even be true for well known brands. It's been my experience size variance with Forstner bits is worse than standard twist bits.

Here's a handy chart showing decimal sizes for fractions down to 64ths for anyone with a good micrometer:
https://en.wikipedia.org/wiki/File:Decimal-fraction_equivalents--v0006.svg

Reactions: Agree 1


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## Johnturner (Aug 8, 2018)

That is all good info and I appreciate it - but I my question relates to the actual sizing of the bits not the hole created. 
I have a recent set of DeWalt brad pointed bits. There is a number in front of each bit, 3/8, 5/64 etc. Say I take 3 out at the same time. All 3 are next to each other. When measuring each bit to put it in the appropriate hole, sometimes the number I get from the digital caliper on the bit just measured will not fit in the same numbered hole. It's not a matter of putting it in a hole where it fits because usually there is a bit in that hole. So back to the question - is there a specific place on the bit where you get the correct measurement? 
I think I'm making it more complicated than it has to be.
John

Reactions: Informative 1


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## gman2431 (Aug 8, 2018)

As stated there will be a tolerance in the bits from manufacturer. When I need a true sized bit I buy from a local place that also does sharpening. It will be exactly what I ask for since they will take off any extra. But these bits are meant to be sharpened so after one sharpening they will never measure the same again. 

What exactly are you drilling?


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## dehn0045 (Aug 8, 2018)

The hole you are talking about is the manufacturers (dewalt) container? 

This is what I understand is happening: you take 3 bits out of the container, do whatever it is you do with them, then you are returning the bits to the container, you do this by measuring the bits with a digital caliper, two of them are returned to the container just fine but the third doesn't fit in the last remaining slot. Therefore one of the bits is in the wrong slot.

The diameter of the bit should be measured at the shank. Measure perpendicular to the bit, this will give the widest measurement. Possibly the caliper's zero is drifting or inaccurate. Rather than get an accurate measurement of each, just get a relative measurement (in thousands of an inch, rather than fraction), put the biggest one in the biggest slot and smallest in the smallest.... Another alternative is using a drill bit gauge like this: www.amazon.com/Irwin-12092-2-Inch-29-Hole-Steel/dp/B000CFNHX0/ref=sr_1_3?ie=UTF8&qid=1533762635&sr=8-3&keywords=drill+bit+gauge

Reactions: Agree 1


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## gman2431 (Aug 8, 2018)

I guess I was way off on what this is about...


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## rocky1 (Aug 8, 2018)

Speaking from experience, I believe I probably have the same set of Dewalt Brad Point bits, picked it up at Lowes, metal case, runs up to 1/2" Bits numbered stupidly on the front of the three rows except for the back row. The holes in the bit container are plenty flippin tight! Very close tolerances. If you have any nature of bur on the shank, it ain't goin back in the box!! 

As for the numbers not matching... I'd have to guess that related to tolerances and discrepancies in the digital caliper. Or, in manufacture of the bit. Or, both. But given the task you are looking at here, as Sam suggested, measuring at the shank would be appropriate, and that's where I always measure mine.

Reactions: Like 1


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## Karl_TN (Aug 8, 2018)

John, many machinists would probably use a micrometer for this task since the pads help them measure flutes at their widest points. Nonetheless, good micrometers can be pricey so maybe the simplest answer is the Drill Bit Gauge that Sam linked above.

Reactions: Like 1


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## Johnturner (Aug 8, 2018)

Sam
That drill bit gauge looks like exactly what I need.

Thanks all for your input - You guys are the best!
John

Reactions: Like 2


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## Tony (Aug 9, 2018)

When I put my bits back in the rack I insert them in upside down, that way if there is a burr on the shank it still goes in. Just a tip! Tony

Reactions: Like 3


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## Steve in VA (Aug 9, 2018)

Take one bit out of the case at a time. Put it back in the same hole you took it out of. Repeat for the next bit you need.

Sorry, I couldn't help myself....

Reactions: Like 1 | Funny 2


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