Drill Bits Bending

Although a bit off topic but related to drill bit runout. I purchased a 29pc M42 cobalt drill set some time ago. It came in a nice Huot case but the larger bits have the 3 flats on the shanks. Well the flats are poorly ground & when using them there is a lot of runout. I clock the drills so the jaws grip on the full shank & there is minimal runout but it's annoying. Other than that they're fine but I'll never buy drills with 3 flat shanks ever again, US made or not. I don't trust them.
 
I'll see your 3 flat shanks and raise you this. A local manufacturer here makes some nice looking HSS bits with a single flat in the shank. Not a small flat like you see on some end mills but a flat running pretty much the length of the shank. I can't see how a drill chuck is going to grab that with no runout.
 
Drill bits with three flats from a reputable manufacturer are no problem. For larger sizes, the three flats prevent the slippage which tends to chew up the shanks. On the other hand, some of the junk bits out there will have the runout without the flats.
I once bought a full set of numbers, letters, and fractional for work. We used them only occasionally but when we needed a particular size, we would have it. The first use was drilling a a piece of steel channel. The bit was thrashed after two holes. At a later time, when using some of the smaller number bits, we found that several bits were the same size. The bits also tended to break easily when pushed.
 
Still on drill bits - What gets my goat is all the manufacturers that place the drill size right where the chuck grips the bit and only uses a light etch so it wears off almost in the first use.
I have a very old set of imperial bits where the sizes are engraved on a reduced band just above the twist. never wear off
 
Bits are dull/sharpened wrong. or steel is harden have you tried the bits on different steel? Some thing like a piece of angle. Could also be you are feeding to hard for the speed of the drill. Like the spindle speed is to slow or you are forcing the bit to hard. Looking back at it being a 5/16 I would bet for sure you are feeding to hard. What is your spindle speed set at for the 5/16 bit?
 
savarin said:
Still on drill bits - What gets my goat is all the manufacturers that place the drill size right where the chuck grips the bit and only uses a light etch so it wears off almost in the first use.
I have a very old set of imperial bits where the sizes are engraved on a reduced band just above the twist. never wear off
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Yeah what Savarin Said! and could they make the number a little bigger. the type on everything is so small these days. :grin big:
 
Last year I bought a drill set from a major US vendor, with lettered/fraction/numbered drills. Many have snapped, many were never properly sharpened (no relief), and many were bent right out of the box. I could get angry about it, but I see it as educational: 1. Never buy an "affordable" large set of drills, 2. Learn how to properly sharpen drills, 3. Roll every drill bit before use to determine if it is bent, 4. Measure every small bit to make certain it's the size the box says it is. I've found several that are the same size.

Agree with the size stamp issue. I now use a lighted magnifying lamp on all very small things. Dang small numbers - what were they thinking? :calm:

Tom
 
If your drill bits are bending in those larger sizes,like 5/16",you need to buy some better drill bits.

Will carbide bend? Probably a microscopic amount only. HSS can bend SOME,but should only be seen in the smallest size bits. I expect to see some flexing in a 1/16" bit,maybe a 1/8" bit.

I would NEVER,EVER buy Chinese drill bits. You are going to get what you pay for. And,some of those sets of bits only have the common fractional sizes hardened at all. They think the average American user,repairing some household item,will only ever use the common fractional sizes,like 1/4",etc.. So,they only harden those. Machinists need EVERY size hardened.
 
george wilson said:
If your drill bits are bending in those larger sizes,like 5/16",you need to buy some better drill bits.

Will carbide bend? Probably a microscopic amount only. HSS can bend SOME,but should only be seen in the smallest size bits. I expect to see some flexing in a 1/16" bit,maybe a 1/8" bit.

I would NEVER,EVER buy Chinese drill bits. You are going to get what you pay for. And,some of those sets of bits only have the common fractional sizes hardened at all. They think the average American user,repairing some household item,will only ever use the common fractional sizes,like 1/4",etc.. So,they only harden those. Machinists need EVERY size hardened.
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Carbide bits do bend quite a lot actually. I work with a lot of small sizes (.014 -.060"). If drilling a hole with the lathe that was not accurately centered, you can watch the drill tip precess around the lathe center. These bit have 1/8" shanks and a working length of about 3/8" and I would guess the amount of bend in some cases exceeded .020". If the drilling was continued, it invariably would break the drill since the amount of bend got worse as the depth increased. I would view the start with a 20x magnifier and if I saw any wobble at all, it indicated a need to recenter the hole. I would expect the same amount of bending with larger bits assuming the deflecting force was scaled as well.
In my experience, Chinese drill sets need to be avoided. I would buy a house (= Chinese?) brand from a major machine tool supplier before I would buy a name brand from the local DIY or hardware store. I can't imagine that MSC or TTC would knowingly sell junk. Ditto for taps and dies. I never ever buy cutting tools from HF.
 
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