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how much bigger does a drill bit drill?

Rcdizy

Steel
Registered Member
#1
If I want to drill a hole in stainless, and press fit a 3/16, O1 drill rod (.1875) into it....

What drill size? numbered, lettered, decimal?
 

Bob Korves

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#4
Drills do not make holes to an accurate size. Drills do not make round holes. Drills do not make straight holes. All that said, the #13 might do it for you, depending. It also might end up too tight, or might possibly end up loose, depending... A drill one size smaller, #14, followed by an appropriate reamer for the desired press fit, would make for a lot less guesswork and a lot more confidence in a good outcome. You should also carefully measure the O-1 rod diameter with a trusted micrometer or compare it with a 3/16" dowel pin. O1 is usually within .001" of nominal size, but is definitely worth checking, especially at the end of the rod. Check it at several clock positions, too. In a hole of that small size, there is less room for tolerance stack up if you want a specific fit.
 

Rcdizy

Steel
Registered Member
#6
The #13 was too loose still, Size smaller too tight.

The rod is excactly .1875

So in a perfect world, what reamer?

Would locktight work in this type of application?
 

RJSakowski

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#9
In my experience, drill rod is often slightly smaller than nominal size. How much oversize a drilled hole is depends a lot on the condition of the drill. +1 on the undersized hole followed with a reamer. The size depends on the class of fit you require. Are you going for a tight slip fit, light press fit, or heavy press fit?
 

Bob Korves

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#11
Read your original post. We have no idea what you are making or what it will be used for. Only a rod to push into a 3/16" hole. Some things want to be put together pretty much permanently and resist becoming loose. Others want to be relatively easy to take apart. We need at least a feel for what you are making, even if the actual intended use is highly classified... ;)
 

Bob Korves

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#14
I am sure I could bore a small hole with a small boring bar in a small lathe or mill, but the real question is if I could get the press fit right...

Edit: Just need a Moore jig borer... or jig grinder... :cool:
 

Desolus

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#15
I am sure I could bore a small hole with a small boring bar in a small lathe or mill, but the real question is if I could get the press fit right...

Edit: Just need a Moore jig borer... or jig grinder... :cool:
I just turned a shank for a tool I'm making on my sherline lathe to .3750 on the dot, over the entire length of the shank... seeing as how boring is exactly the same operation im going to go ahead and say that you could in fact get the press fit right...
 

mikey

Active User
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#16
I am sure I could bore a small hole with a small boring bar in a small lathe or mill, but the real question is if I could get the press fit right...

Edit: Just need a Moore jig borer... or jig grinder... :cool:
A Sherline lathe has very precise leadscrews and their handwheels are very accurate. Dial in half a thou, take a thou off the diameter. With the right tools, cutting to tight tolerances on a Sherline is pretty simple because what you dial in is pretty much what you get.
 

Dr_Romeo_Chaire

Ears got caught in a rice picker
Registered Member
#17
Boring comments aside, maybe the OP needs some guidance on what constitutes a light/medium/heavy press fit? (probably depends on materials involved also, right?)

I seem to recall pressing 0.125" dia steel dowel pins into 0.250" aluminum plate and using a reamer that was 0.005" undersize for a heavy press fit. It's been decades though and I've forgotten, plus I might've just been guessing back then -- so it would be good to know for future projects!
 

Tozguy

Active User
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#18
The #13 was too loose still, Size smaller too tight.

The rod is excactly .1875

So in a perfect world, what reamer?

Would locktight work in this type of application?
Reamer size already suggested in this post.

Excellent question Dr. Suess, .1865
The lock tight (or super glue) should salvage the situation, choose the right one.
 

mikey

Active User
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#19
Boring comments aside, maybe the OP needs some guidance on what constitutes a light/medium/heavy press fit? (probably depends on materials involved also, right?)

I seem to recall pressing 0.125" dia steel dowel pins into 0.250" aluminum plate and using a reamer that was 0.005" undersize for a heavy press fit. It's been decades though and I've forgotten, plus I might've just been guessing back then -- so it would be good to know for future projects!
Fits are a huge discussion that cannot even begin until the OP gives us an idea of what the application is.
 

Tozguy

Active User
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#20
To respond to the title question, how a drilled hole turns out is a function of several factors not the least of which is the quality and grind on the drill bit. It is not predictable. It might even be possible to end up with a hole smaller than the drill.
 

BGHansen

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#22
Like mentioned above (so not adding any help here), I'd spot drill for starters, then drill undersized by 0.010" - 0.015". Then use an undersized or oversized (+/- 0.001" from 3/16") ream. The oversize will give you a slip fit for separating the parts. I've had very good success with my over/under set from Shars off eBay for a touch over $70 delivered. The set includes reams from 1/8" - 1/2" by 1/16", probably the only reams you'll ever use.

Bruce

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Bob Korves

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#23
I just turned a shank for a tool I'm making on my sherline lathe to .3750 on the dot, over the entire length of the shank... seeing as how boring is exactly the same operation im going to go ahead and say that you could in fact get the press fit right...
Internal cuts are more difficult to hit accurately than external cuts. They can be more difficult to measure accurately and the tooling is much less rigid, at least for small holes. They are of course totally doable.
 

Desolus

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#24
Given that the smallest cut you can take is directly proportional to the surface finish of your cutting tool (I took mine to a mirror finish for the last cut on that shank which was 0.007mm or about 0.00027 inch) the largest factor in how well you can finish a part out is machine repeat-ability, with a highly polished cutting tool you can take multiple 'spring passes' to virtually eliminate any deviations in diameter caused by a lack of tool rigidity. I'm learning that working on a small lathe on small parts is entirely different than forcing your way through material on a large heavy rigid lathe using rigid tools... I honestly didn't know what to do when I got my sherline, started cutting and realized just how floppy everything was... I don't have anything to accurately measure an run-out on an ID so I can't compare but I have bored small holes in watch parts using tools that I ground and polished on my faceting machine and the holes preformed as designed.
 

Bob Korves

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#25
Given that the smallest cut you can take is directly proportional to the surface finish of your cutting tool (I took mine to a mirror finish for the last cut on that shank which was 0.007mm or about 0.00027 inch) the largest factor in how well you can finish a part out is machine repeat-ability, with a highly polished cutting tool you can take multiple 'spring passes' to virtually eliminate any deviations in diameter caused by a lack of tool rigidity. I'm learning that working on a small lathe on small parts is entirely different than forcing your way through material on a large heavy rigid lathe using rigid tools... I honestly didn't know what to do when I got my sherline, started cutting and realized just how floppy everything was... I don't have anything to accurately measure an run-out on an ID so I can't compare but I have bored small holes in watch parts using tools that I ground and polished on my faceting machine and the holes preformed as designed.
I don't see what "polish" has to do with it. If you are speaking of honing the cutting edge, then yes, a sharp tool deflects less. The amount of shininess has little to do with it. At some point, mirror polishing will make the edge less sharp, and sharp is what is needed. A shiny and dull tool will just rub.
 

Desolus

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#26
polishing and honing describe an almost identical process, the use of abrasive to produce a precision surface. Polishing is typically only about making something shiny, and also typically to tighter surface tolerance. But in gem cutting which is my default when talking about making precision surfaces, polishing is about surface finish (100k - 200k grit typical) AND producing that finish on a very sharp edge consisting of two or more very very flat planes. I've been cut by many a sapphire... So I agree with you that typical polishing won't produce a cutting tool and instead a rubomax, but if done correctly you can get an incredibly sharp cutter that will cut shallow with no problem... you just can't take a deep cut with it or you ruin all your hard work...
 

RJSakowski

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#27
A lot of information is missing here. Is the a hole in the end of a piece of round, in a flat plate, or in an irregularly shaped part. What is the machine; lathe, mill, drill press? What class of fit? How deep is the desired hole? There is a big difference on boring a 1/8" deep hole through a piece of plate and boring a 1" deep hole.

As to boring and turning being equivalent operations, I would say only on the condition that you were boring a fairly shallow hole. For a hole where the depth greatly exceeds the diameter, the boring bar will be relatively flexible and subject to deflection. Measuring the diameter of a hole is problematic as well. A pin gage will only tell you what the smallest diameter is. It conveys no information regarding roundness, cylindricity, surface finish, etc. Determining the true state of a hole requires the use of something like an air gage.
 

Bob Korves

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#28
polishing and honing describe an almost identical process, the use of abrasive to produce a precision surface. Polishing is typically only about making something shiny, and also typically to tighter surface tolerance. But in gem cutting which is my default when talking about making precision surfaces, polishing is about surface finish (100k - 200k grit typical) AND producing that finish on a very sharp edge consisting of two or more very very flat planes. I've been cut by many a sapphire... So I agree with you that typical polishing won't produce a cutting tool and instead a rubomax, but if done correctly you can get an incredibly sharp cutter that will cut shallow with no problem... you just can't take a deep cut with it or you ruin all your hard work...
The first thing that comes to my mind with polishing is a buffing wheel on a motor shaft and a stick of rouge. That is not going to make something sharp, just shiny. Thanks for the clarification of what you meant and how you achieve it.
 

benmychree

John York
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#29
I quite agree with the earlier writer who suggests the over/under reamers; I had a set at my shop (left them there) and every time I used them to fit holes for dowel pins, they made the proper fits; force fit for the part the pin is pushed into, and a snug fit for the other part. Drills have no place in this sort of work, other than to make a hole for the reamer to enlarge.
 

Bob Korves

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#30
I quite agree with the earlier writer who suggests the over/under reamers;
I have lots of nice previously owned reamers from many sources, and usually have the one I need for a job, but it can take time to find it. They are sorted by nominal size, but many are really difficult to read, and I never know if they have been previously sharpened, so I have to measure or test them, and also pick one the right style for the hole type as well. Sometimes have to hone it sharp, too. That all takes time, lots of it. I have to admit that a set of over/under reamers in basic fractional sizes like Bruce posted sure sounds quick and easy for lots of work.