Drill bits and tolerances

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mrfeeney

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Good day everyone, I'm hoping some here can help me understand drill bits and how they are sold.

Documented below is my recent experience in case it might help someone else, also please note this it the first time I have ever bought a set that included anything except the standard fractional bits.

I recently purchased a 115 piece drill index, it was cheap so I assumed the quality wouldn't be great but hoped it would get me by for awhile. On inspection several things jumped out right away as I could not pivot all the trays to access the bits which it turns out was because only one tray on the "letter" side was attached to the pivot point, the next thing I found after getting it unbound and opened was the tray for A through K was inverted to the markings, ie. K was the smallest and A the largest bit in the tray.

Next one of the numbered bits stood out because it was shorter than its neighbors on either side, the number 5 hole was occupied by a clearly marked 13/64 bit, and almost none of the (smaller diameter) larger numbered bits were within a thousandth of what they were supposed to be and several were the same diameter and some were ground so poorly the chisel point was off center by 1/3 of the diameter or worse.

While waiting for a reply from the vendor which sold me this set I bit the bullet and purchased a brand name USA set, (at six times the cost) which is a vast improvement, however I still found a few bits (four in the numbered set) that were a thousandths or more different than what they were supposed to be. To be fair I must admit I have always used USA manufactured bits and have always taken the diameter on faith and never checked them with a mic.

So the question -
1. Is this normal? (example the 1/4" bit has a diameter of .2485) or have I managed to get a sub standard USA manufactured set as well?
2. If you really need an accurate hole you ream it, so is a bit within a thou or two common and acceptable?

Thanks
 
When I buy import drill bit sets, I have no expectation that they will be sharpened correctly or on size. My experience is with the HF bits. The TiN sets seem to be the worst, and normally require sharpening before use. The sizes generally bear little resemblance to the real world. But, they do poke holes in metal, and are therefore useful, as well as cheap.

The HF black oxide sets seem to be better than the TiN sets as far as quality control. The HF cobalt sets seem to be pretty good, but I haven't really checked the sizes.

All of the HF drill indexes seem to be junk.

An undersize 1/4 bit may actually cut over size anyway, I don't know what the tolerance is on a drill bit. I measure mine at the cutting edge, rather than the shank. I don't know where you are measuring at, but it's not unusual for the shank to be a bit undersize.

As you stated, if an accurate hole is needed, drill then ream, or bore.
 
I bought a cheap Chinese number set but made sure to open in the store and check them out. I got one of each size but some of the sets had doubles and some had defective drills. drills often vary a little bit in size usually not more then .0005 in good drills. It can also be a little difficult to get an accurate reading on the widest part of the drill. My good USA made set is more accurate then my Chinese but it does not make a difference to me in a hobby setting. Drills rarely make a hole the same size as the drill anyway unless you have a very accurate chuck etc. In my work I often have to make parts with holes +- .001 dia and can use drills without finishing afterwards but it requires some attention to the setup. And sometimes a certain drill just won't work.
 
You need to bite the bullet and buy USA made drill sets. And never buy the sets with all 3 sets of drills in them.

Even USA made drills can be out of tolerance,or even have a curve in them. If it is possible,buy them in person. Check each drill for straightness by running them back and forth across a counter top,and look for wobbling while you roll them. Check the tips to make sure they are visibly ground ON CENTER. Some may not be. Hardware stores usually sell CARBON steel taps,but they sell HSS drills normally.

Some Chinese drill bit sets are only hardened in the common fractional sizes,like 1/8,1/4",etc. They think the average household user will only use these common sizes,and will try to get by without hardening all of the bits. I can't really blame them because the American public demands the moon for a pittance. You get what you pay for in drills,taps,and reamers. Personally,I don't see how the Chinese manage to make things so cheaply as they do. When I was young,everything was so expensive in relation to my pay,because everything was made in USA or Western Europe. You'd be lucky to have an Atlas lathe back then. A 9" South Bend would really be for those with good incomes!

Personally,I buy bright drills(as opposed to black oxide coated ones). Putting on that nitride coating takes the sharp edge right off of drills and rotary files. I got so disgusted back in the 60's,when I ordered a new set of rotary files from Sears. The old ones were bright,and felt like they could cut your fingerprints. The new ones were black,and DULLER than the bright ones I had discarded as too dull,and burning the wood I was cutting with them.

I buy drill sets made in USA from MSC co. You can get similar ones from Enco(I think). Just be sure that they are USA made ones. Cobalt drills cost a lot more. I have just used regular HSS myself,but I know how to sharpen drills. It's your call. Cobalt will last a little longer,but will need to be sharpened at some point. Be sure to not breathe the cobalt dust. Or the HSS,or ANY metal dust,for that matter. Cobalt is not good for you.
 
mrfeeney said:
Good day everyone, I'm hoping some here can help me understand drill bits and how they are sold.

Documented below is my recent experience in case it might help someone else, also please note this it the first time I have ever bought a set that included anything except the standard fractional bits.

I recently purchased a 115 piece drill index, it was cheap so I assumed the quality wouldn't be great but hoped it would get me by for awhile. On inspection several things jumped out right away as I could not pivot all the trays to access the bits which it turns out was because only one tray on the "letter" side was attached to the pivot point, the next thing I found after getting it unbound and opened was the tray for A through K was inverted to the markings, ie. K was the smallest and A the largest bit in the tray.

Next one of the numbered bits stood out because it was shorter than its neighbors on either side, the number 5 hole was occupied by a clearly marked 13/64 bit, and almost none of the (smaller diameter) larger numbered bits were within a thousandth of what they were supposed to be and several were the same diameter and some were ground so poorly the chisel point was off center by 1/3 of the diameter or worse.

While waiting for a reply from the vendor which sold me this set I bit the bullet and purchased a brand name USA set, (at six times the cost) which is a vast improvement, however I still found a few bits (four in the numbered set) that were a thousandths or more different than what they were supposed to be. To be fair I must admit I have always used USA manufactured bits and have always taken the diameter on faith and never checked them with a mic.

So the question -
1. Is this normal? (example the 1/4" bit has a diameter of .2485) or have I managed to get a sub standard USA manufactured set as well?
2. If you really need an accurate hole you ream it, so is a bit within a thou or two common and acceptable?

Thanks
Click to expand...

On the 1/4" dia., I don't know if that is acceptable these days. sounds more like a size used to ream a .250 dia. hole.
 
I will buy the cheap hardware store drill bits from time to time and run them through my Leslie 91000 drill bit sharpener before putting them in use.
I have ran into some of those cut rate tool supply places and grabbed a few bits and got back to the jobsite only to find out that the cheap bits didn't have relief angle and would not cut, and I had to touch them up on the side of a carbide cutoff wheel to get them to work.
Now when I pick up a bit I will rotate the point on my thumb to feel if it has a sharp point.
Going into the shop on the weekend to do that clean and reorganize will include sharpening drill bits. They are a tool that gets used daily and is often in need of a dressing.

Joe
 
JimDawson said:
When I buy import drill bit sets, I have no expectation that they will be sharpened correctly or on size. My experience is with the HF bits. The TiN sets seem to be the worst, and normally require sharpening before use. The sizes generally bear little resemblance to the real world. But, they do poke holes in metal, and are therefore useful, as well as cheap.

The HF black oxide sets seem to be better than the TiN sets as far as quality control. The HF cobalt sets seem to be pretty good, but I haven't really checked the sizes.

All of the HF drill indexes seem to be junk.

An undersize 1/4 bit may actually cut over size anyway, I don't know what the tolerance is on a drill bit. I measure mine at the cutting edge, rather than the shank. I don't know where you are measuring at, but it's not unusual for the shank to be a bit undersize.

As you stated, if an accurate hole is needed, drill then ream, or bore.
Click to expand...

It would seem to me that the cheaper TIN coated drill manufacturers use the coating as an excuse to use much poorer grades of tool steel to make the drill; they do not hold up as well as the bright finish HSS drills made in USA, at least those made by well known brand manufacturers; the biggest secret, if a secret it be, is that slopwer speeds and heavier feeds are what make drills stay sharp longer and preform better, and coolant / lubricant adds to the equation.
 
mrfeeney said:
So the question -
1. Is this normal? (example the 1/4" bit has a diameter of .2485) or have I managed to get a sub standard USA manufactured set as well?
2. If you really need an accurate hole you ream it, so is a bit within a thou or two common and acceptable?
Click to expand...

1. Without knowing where AND how you measured the bits, 0.0015 undersize may be correct. You need to measure the working end of the bit, and ensure you are getting the max dia across the cutting edges and not the flutes. A mic can be difficult to use on larger, (relatively) drill bits because the anvils arent large enough to span several twists. I prefer to use a dial caliper for measuring drill bits.
2. Bits often drill under or over sized holes. Yes you need to ream for an accurate hole.

mrfeeney said:
one of the numbered bits stood out because it was shorter than its neighbors on either side
Click to expand...
Number drills are usually shorter than compartive fractional/metric bits, so if you had a # drill flanked by 2 fractional drills it would appear shorter.
But all said and done it sounds like you got a lemon

Cheers Phil
 
george wilson said:
You need to bite the bullet and buy USA made drill sets. And never buy the sets with all 3 sets of drills in them.

Ok, I had never heard there is a difference in the quality of an index with numbered, lettered and fractional inches.

Are you saying that you get better quality bits if you purchase numbered, lettered and fractional indexes separately instead of a complete package?
Click to expand...
 
There may be mixed sets that contain high quality drills. I just haven't noticed any. If they did have letter,fractional,and number drills in the same index,they'd cost a LOT. Usually too much for the average guy to hand out at once. I just have bought them 1 set at a time. And,don't forget,for those in between sizes,there are metric sets too! But,we get into the realm of reaming to get really precise holes,or single point boring.

I don't feel like poring through my 4" thick MSC catalog. This is research others can do for themselves.

I was just thinking about those mixed Chinese sets that are commonly sold every where. Those should be avoided.

BTW: The Tin coating on some of those Chinese drills and end mills are so thin you can just about see through them. Does this coating really stay on the sharp cutting edges? I doubt it. The coatings mostly serve to avoid galling and metal sticking to the flutes of tools.

If I'm wrong about the coatings NOT sticking to the teeny actual cutting edges,let me know. And,what happens at the first sharpening?
 
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