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Cobalt Drill Bits \ What to expect when buying a full Drill Index

richlando

Plastic
Joined
Mar 6, 2020
As this is my first post here I'll start with thank you to all the knowledgeable folks here. I have been lurking for years and learned some ways to accomplish tasks with the tools I have on hand and better ways to approach my projects.

I recently bought a Chinesium (Accusize) drill bit set from Amazon in fractional, letter and number sizes as a backup set to the few good bits I already have. I do understand if you want good bits the best option is to buy the good ones as you need them. They were listed as 5% Cobalt (M35) 135° split point. First thing that jumped out, after the number bit rack fell off one side, was the gold coating. Then out of 20 I measured not one was 135° and many were 15-20° off with most at 120° or so. All of the smaller number sizes (#32+) and fractional smaller than 1\8" were nearly 1/3 off center and nothing smaller than 1/8" was split. Most bits were a tad undersized, which I think is good? but the 17\32 I miked was + 0.009, yikes. At least they were mostly round. I am pretty sure real M35 bits are not coated. I know you get what you pay for, most of the time, but that Mophorn Dividing Head with a 5" 3 Jaw Chuck I bought for less than $300 with 0.00025 TIR got my guard down. :-)

The questions...
What is the smallest size you can expect to be split in a 115 piece index? I have split 1\16" bits with a jig and a magnifier.

Would a 5% Cobalt bit be coated with a gold coating?

Is there any 115 drill piece index worth buying?

I really just wanted to have all the bits I need for my tap set which is almost every size up to 5\8" and up 13 mm.

Thanks,
Rich L. in Florida
 

robbar10

Plastic
Joined
Nov 17, 2017
All of the cobalt bits I have bought have been some sort of gold coating.

The two brands I tend to buy are Precision Twist and Hertel. I dont recall bits being split under 1/8 an inch nor would I think it would make much of a difference.

I may forget the 115 pcs set, buy a decent brand 29 pieces fractional set and add in whatever number/letter sizes you need for your tap set.
 

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
I did it this way.

Get number and letter drill sets from Precision.

Buy high performance taps as needed. Eventually the collection is custom populated for myself.

No regrets.
 
G

Guest

Guest
About a dozen years ago I had a friend restoring a vintage 73 Corvette, more like destroying it. I let him use my garage, he had a pretty complete set of HF tools. He was not to touch mine unless he asked and he usually did not want to put up with my verbal abuse. I had to get even for him bragging about the bargains he gets on tools and how I always over pay. He never bought into my disgust with HF tools and never understood how something could be brand new and still useless trash.

Anyway he needed to drill out some aluminum rivets I think it was to dissemble the back braking system. He is cussing up a storm saying his cordless drill must not be working right as none of the drills will cut the aluminum.

I remember them as those fancy gold colored ones in an index box. Of course I asked him what he paid, he said like $50 for over 100. I told him he got ripped off, even if they paid him to take them. All the ones I looked at had the direction of the cutting angle clearance proper for a left handed drill, unfortunately the flute twist was right handed.
 

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
Buy a medium priced set. Full sets like that are almost to the same spec as as other drills. Lip clearance, lands, etc. But full set bits also have legs and a cloaking function. They can hide in plain site. You will start to notice empty slots in your index. Those bits walked out and you will never find them if you need them.
You will buy that set with the intention of replacing any broken bits. Yeah, sure you will.
 

EPAIII

Diamond
Joined
Nov 23, 2003
Location
Beaumont, TX, USA
First, I would not expect any drill bit set on Amazon to be worth the free shipping, much less even a $0.01 price. There is a lot of competition for low priced drill sets and the Chinese have stepped up with increasing low quality. On the retail market, drill sets have become a "commodity" item, made to a price point and not a quality level. Some years ago I made the mistake of buying a fraction-number-letter set for less than $50 from Enco. I knew it was cheap, but I hoped that, as a machinist supplier it would at least be usable. It was total trash. Bits sharpened backwards (left hand cutting?), off sized, and some were completely unhardened. I was lucky, they took them back with credit towards a good set.

Most drill bits are just a bit under size, one or two thousandths, depending on size. This is normal. I would think that better quality ones are closer to the indicated size. I have never seen one that was 0.009" over sized. Know this: some drill bit manufacturers will deliberately make the shank a bit smaller than the tip. For an accurate reading you need to carefully mike the tip, not the shank. This, in the other direction, could explain your 0.009" over sized bit.

Split point: Generally speaking, 1/8" is the smallest that most drill bit makers are willing to grind a split point on. I have seen smaller ones from some of the better makers, perhaps down to 1/16" but I haven't searched for smaller ones so I can't say if that is the limit.

"Is there any 115 drill piece index worth buying?" Of course there are. Just look for brand names that are known to make good quality bits. You can expect good to excellent quality levels from many suppliers to the trade. McMaster is one place where you can expect that any set they sell will be good to excellent quality. Others, like MSC also sell good quality drill sets. For a 115 piece set, fraction-number-letter, I would be suspicious of any price that is less than $150 in today's world.

I can understand the desire to have a full set in the shop. It is irritating in a home shop and can cost dollars in a commercial shop if a project or job needs to wait for the proper sized drill bit to arrive. BUT, I can also tell you that I got along for years, DECADES even with a full set of fractional bits (1/16" to 1/2") and a number size index that I purchased empty and filled with only the tap drill sizes plus one higher and one lower than each of them. I still have that index and it is still half empty. I have never had any real need to completely fill it up. As for letter sized bits, there is very little need for them other than tap drills. I literally had only one or two letter sized bits for many decades and never had a need for others.



As this is my first post here I'll start with thank you to all the knowledgeable folks here. I have been lurking for years and learned some ways to accomplish tasks with the tools I have on hand and better ways to approach my projects.

I recently bought a Chinesium (Accusize) drill bit set from Amazon in fractional, letter and number sizes as a backup set to the few good bits I already have. I do understand if you want good bits the best option is to buy the good ones as you need them. They were listed as 5% Cobalt (M35) 135° split point. First thing that jumped out, after the number bit rack fell off one side, was the gold coating. Then out of 20 I measured not one was 135° and many were 15-20° off with most at 120° or so. All of the smaller number sizes (#32+) and fractional smaller than 1\8" were nearly 1/3 off center and nothing smaller than 1/8" was split. Most bits were a tad undersized, which I think is good? but the 17\32 I miked was + 0.009, yikes. At least they were mostly round. I am pretty sure real M35 bits are not coated. I know you get what you pay for, most of the time, but that Mophorn Dividing Head with a 5" 3 Jaw Chuck I bought for less than $300 with 0.00025 TIR got my guard down. :-)

The questions...
What is the smallest size you can expect to be split in a 115 piece index? I have split 1\16" bits with a jig and a magnifier.

Would a 5% Cobalt bit be coated with a gold coating?

Is there any 115 drill piece index worth buying?

I really just wanted to have all the bits I need for my tap set which is almost every size up to 5\8" and up 13 mm.

Thanks,
Rich L. in Florida
 

Bondo

Hot Rolled
Joined
May 14, 2011
Location
Bridgeton NJ
I have had good luck with cobalt norseman bits. Made in USA but I drill mostly by hand in stainless.

Sent from my SM-G960U using Tapatalk
 

Forestgnome

Stainless
Joined
Aug 2, 2008
Location
Californeeeah
I never had cobalt drills that were coated. Most cheap cobalt sets are coated (cobalt-coated?), but aren't made of cobalt steel. Cobalt steel has a slightly gold tint to it, but it's a slight tint. If the name brand cobalt bits are coated I imagine they're truly cobalt with a nitride or some other high quality coating. Real cobalt drills aren't cheap, so you won't find cheap cobalt drills.
 

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
More than 25 years ago I bought a 20 dollar fractional set from MSC. I still have it, or what is left of it. Tried to buy another shorty after, same part number, crap. Random grind angles, some positive some negative rake.....
 








 
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