What type of drill bits are these?

Question

https://drive.google.com/file/d/1JPV6dRqB6f__N1eCcmn6QkOStLpVdc-U/view?usp=drivesdk

Here's an image for bits Head.

https://photos.app.goo.gl/HS8hFqLeWn8jecka7

In the image above (Google Images & Drive) a bunch of drill bits I found in my father's house. How do I know what are they used for? Wood, metal or multipurpose? I did some research online but couldn't find answers for a lot of questions I have. If you view the image above you can see that bit #7 and #8 have the same size but with different body shape. Why? Can you drill both wood and metal using the same bit if it's multipurpose? Does bits color has anything to tell about its type? Please be easy on me, I'm trying to learn.

Answer 1

They look like standard twist bits in relatively good shape (good cutting ends). Very likely High Speed Steel ("HSS"), doesn't make a difference which HSS for a homeowner. Presume they were properly heat-treated as any test other than hardness would cost more than the value of the whole set. And for the homeowner it does not make much difference if the hardness is HRc (Rockwell hardness scale C) 62 or 65. They were intended for cutting ordinary steels, cold rolled and hot rolled, but will cut anything up to about hardness HRc 40. NO ceramics or masonry. Different manufacturers may use different spirals on the flutes ( 7/8 difference ) but no real difference. Easily cut wood, plastic, aluminum, copper alloys, etc. Manufacturers of products like plastics where they cut many thousands of holes a day may get special design bits that clean the hole and break chips and have a clean breakout, but again, no interest to the homeowner. Color of gold is a VERY thin layer of titanium nitride. I think black is normal heat-treat oxide, silver flutes and point are cleaned by grinding after Heat Treatment. All-black could be a thin nitride layer (no titanium). I don't pay any attention to color when I use them.

Answer 2

If you want to keep them for personal reasons, their condition and quality doesn't matter.

If you actually want to use them, there are a few "warning flags". First, apparently they were not in any sort of packaging. Somebody who knew the value of good quality tools wouldn't keep them loose in a box or whatever.

Judging from the sizes and shank lengths, they are part of a set but with several bits missing. Murphy's law says that the first time you want to drill a hole, it will be one of the missing sizes.

The USSR used the metric system in the 1980s but there is no easy way to tell exactly what size the bits are, and whether they will be the correct match for modern screws, bolts, etc. Measuring drill bit sizes (or the size of hole they drill) is not trivial even if you have a set of calipers - another reason why the lack of packaging is a warning flag. Bear in mind that modern drill bits are easy to buy in size increments of 0.1mm, and there is a reason why there are so many different sizes avaiable.

Finally, even if they were originally high quality, you can ruin any drill bit in 30 seconds if you use it incorrectly, and you have no idea how these have been used in the past.

Personally, if I was considering using these bits I would first try them on some scrap aluminum or brass. If they didn't cut it like butter I would throw them away. Blunt drills are more trouble than they are worth, and if you had the tools and knowledge to sharpen and re-harden them, you probably wouldn't be asking the question!

Note, I'm not "against old tools" as a matter of principle. I regularly use some hand tools that are more than 100 years old, but I know their history, I know why modern replacements of the same quality would be very expensive, and I know how to look after them so they will last another 100 years or more.