If you're trying to get a good fit out of your drill bits, they almost always cut oversized. Were that me trying to do this the hard way (You have good advice so far on the right way...). I keep a card with drill bit dimensions handy for dumb stuff like this. You're looking for 6mm, which is (about) 236 thousandths of an inch. A letter A at 235 thousandths is sure to be sloppy after it gets done oversizing the hole. The next two down, numbers 1 and 2 are 228 thousandths and 221 thousandths respectively. That's way too small, except all that is relative. "Way too small" in this case entails is eight or fifteen thousandths of an inch. a 0.228 drill bit that's cutting oversized (as it probably will) doesn't have to be out by much to be in the ballpark. I assume it's not "that" deep? Slip fit with a set screw? So drilled accuracy is fine? If you feel like playing with it, try drilling a test hole in a piece of similar material. Drill without oil. That tends to enlarge a hole "slightly". Or take one flute of a slightly undersized drill and just dust it ever so slightly on a fine stone to offset the point just a whisker. Not so much in the bigger sizes (although they can be adjusted), but in the smaller drills, with a bit of practice, you can really fill in the gaps if you put your mind to it. Assuming of course you need drilled hole accuracy. If you need better, reaming or boring is gonna be your best bet. It might or might not be a solution for this project, but it's a great thing to pay attention to, as every now and then it can bail you out of a pinch.
-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Making and measuring small holes (<8mm)
- Thread starter rronald
- Start date
If you're trying to get a good fit out of your drill bits, they almost always cut oversized. Were that me trying to do this the hard way (You have good advice so far on the right way...). I keep a card with drill bit dimensions handy for dumb stuff like this. You're looking for 6mm, which is (about) 236 thousandths of an inch. A letter A at 235 thousandths is sure to be sloppy after it gets done oversizing the hole. The next two down, numbers 1 and 2 are 228 thousandths and 221 thousandths respectively. That's way too small, except all that is relative. "Way too small" in this case entails is eight or fifteen thousandths of an inch. a 0.228 drill bit that's cutting oversized (as it probably will) doesn't have to be out by much to be in the ballpark. I assume it's not "that" deep? Slip fit with a set screw? So drilled accuracy is fine? If you feel like playing with it, try drilling a test hole in a piece of similar material. Drill without oil. That tends to enlarge a hole "slightly". Or take one flute of a slightly undersized drill and just dust it ever so slightly on a fine stone to offset the point just a whisker. Not so much in the bigger sizes (although they can be adjusted), but in the smaller drills, with a bit of practice, you can really fill in the gaps if you put your mind to it. Assuming of course you need drilled hole accuracy. If you need better, reaming or boring is gonna be your best bet. It might or might not be a solution for this project, but it's a great thing to pay attention to, as every now and then it can bail you out of a pinch.
- Joined
- Mar 26, 2018
- Messages
- 8,407
The shipping has got to be more than the sale items.
It's OK though They can make it up in volume
That's helpful.
Long ago (about 50 years back), I was a machinist apprentice at GE Evendale for 18 months or so. We had 13-14000 employees making roughly one product (a jet engine) per day. Huge facility. There were several tool cribs where one could go sign out any tools needed for a job. So, if I need a reamer of any size....they had it. But I'm never going to have hundreds or thousands of reamers on hand in my workshed for all the possible dimensions below 1/2 inch or so (above that size a boring bit can be used).
Making an appropriate holder to fit a single flute mill into the toolpost should allow me to bore down to ~1/4" or perhaps .2". I'll be on the lookout for some reamers below that size....for common sizes and a few ticks smaller/larger.
Oh great then. I'm pretty sure that I've just thoroughly and completely offended whoever it was that taught you to use a drill bit properly.
I excel at forgetting things from that long ago. The only thing I remember well is that I was pretty good at grinding tool bits. Not that I remember how to grind them (which would be much more valuable). I'll get back there eventually.Oh great then. I'm pretty sure that I've just thoroughly and completely offended whoever it was that taught you to use a drill bit properly.
- Joined
- Feb 28, 2019
- Messages
- 499
The shipping has got to be more than the sale items.
It's OK though They can make it up in volume
- Joined
- Jun 20, 2022
- Messages
- 204
Don't know whether it's "right" but since I have neither pin gauges nor small hole gauges I have at times made my own from drill rod. Say if I wanted a press fit on a shaft I might turn a bit of drill rod .002" smaller (or whatever), figuring that if I sneak up on it I will end up with a .001" press fit.
- Joined
- Sep 3, 2023
- Messages
- 218
Great, more tools that I didn’t realize that I should have on hand for that time in the future I might actually need it.
Then do I get two sets, one for my home shop toolbox, and one for my work tool box. Decisions, decisions…
Unfortunately, the four pack was $9.89 in my cart. Guess they know that they have me on the hook already, and do not need to entice me with the super cheap intro deals.
But, I’ll probably go with the 10 piece set for $24 anyways.
One thing nice about building up my home retirement shop, while still working, is my budget is a bit more flexible now. When I retire, if I ever do, ( hopefully slow down quite a bit at least, I figure I will work til the day I die) my budget will be going on a huge diet.
Sent from my iPhone using Tapatalk
- Joined
- Apr 8, 2013
- Messages
- 1,980
I have pin gauges that go from tiny to 1/2 inch by .001's. I fly radio controlled aircraft and I'm often dealing with small weird holes. The pin gauges have been a Godsend. Drill bits are a crapshoot. You really need to make or buy a small boring bar.
- Joined
- Apr 8, 2013
- Messages
- 1,980
Reamers are good for their intended purpose but they have two limitations. First; They will only create the size hole they were made to create. And more importantly, they will follow the hole. Ream a crooked drilled hole and you'll get a crooked reamed hole. Only by boring can you make straight concentric hole that is any size you need it to be.
Last edited: