Measuring TIR, which measurement do I believe?

[WobblyHand]

Think of it this way, for every .001 the center is off, the hole will be .002 larger. Any number of very small differences can cause one flute to cut more than the other. An optical comparator is probably the only practical way to measure drills precisely. You can't be certain what size the hole will be without drilling it. That's why there are still reamers, and even a reamer can be made to cut oversize.

Here's something dealing with the subject:

View attachment 326084
View attachment 326085

Machinist Drilling Mechanical Tolerance Capabilities Chart - ANSI Size Drilled Hole Tolerance, ISO Metric Drill Sizes

This chart defines drill manufacturing process capabilities for ANSI size machinist drills. Drilled hole locations and size variations are cumulative of several manufacturing variables. Tool sharpness, accuracy, tool and machine rigidity, machine spindle bearings wear, general quality of...

www.engineersedge.com

Perfection is impossible, that's why we have tolerances.

Thanks, this was helpful!

Someone could probably make a lot of money by inventing better drill bits. I'd imagine it would reduce machining costs quite a lot. (I had to resist saying it would reduce machine costs quite a bit.)

 

[Janderso]

Using reamers kind of limits one to few standard sizes, just to protect your wallet. Boring sounds like the way to go, but is darn difficult for smaller sizes. Above 3/8" seems to be doable, at least for "not too deep" holes.

Agreed, The , Micro 100 line has some really cool super sharp small boring bars. You can make the holders that fit into your QCTP.

 

[GunsOfNavarone]

AND.. when you sharpen a reamer it loses diameter, cutting smaller. I'm gonna make a laser hole cutter. Easy, peasy, lemon squeezy.

 

[Diecutter]

What about adjustable reamers? Each one is supposed to be adjustable within a small range and they come in sets covering all sizes within a max and min. sort of like ER collet sets do. I'm curious whether anyone has experience whether they work well or not? I often thought of buying a set.

 

[Bob Korves]

What about adjustable reamers? Each one is supposed to be adjustable within a small range and they come in sets covering all sizes within a max and min. sort of like ER collet sets do. I'm curious whether anyone has experience whether they work well or not? I often thought of buying a set.

Adjustable reamers, by the way they are designed, are not strong or robust. They must be kept sharp, carefully used, and never forced or they can easily be tweaked, ruining them. They are definitely not bulk removal tools in stronger metals like steel or similar. I only use one on ferrous metals when it is the only solution at hand, and then with a gentle and careful touch, no hogging. They work pretty well when used correctly on brass, bronze, and aluminum bushings...

 

[Diecutter]

Adjustable reamers, by the way they are designed, are not strong or robust. They must be kept sharp, carefully used, and never forced or they can easily be tweaked, ruining them. They are definitely not bulk removal tools in stronger metals like steel or similar. I only use one on ferrous metals when it is the only solution at hand, and then with a gentle and careful touch, no hogging. They work pretty well when used correctly on brass, bronze, and aluminum bushings...

Thanks for the explanation, Bob. I never fail to learn useful information when visiting this site.