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Thread: Feeling the pain of HF tin coated drills

  1. #1
    BillH Guest

    Post Feeling the pain of HF tin coated drills

    Well, I started drilling holes and making brackets to mount my 8" HF scale to my micro mill. Made a really nice aluminum block that has a 3 hole drilling pattern which will offset the calipers to the column. Well I ended up going with a 2.5 hole pattern, as my drill bit decided that it wanted to break away and make itself home deep in my .640" thick bracket.

    Now drilling holes into the stainless Steel of the calipers to mount them, used my high quality cobalt 90 deg spotting drill, absolutely no problems anywhere, then to use my tin coated HF drill. Drilled 1 hole just fine but at the very end it got very loud, and I was using lubricant, tapmagic. Needless to say its dull as heck now.
    Im now thinking of buying replacement cobalt drills for the ones im wearing out from the set.
    Cobalt is much heavier than HSS, which means its more dense, which I assume means the cutting edge on Cobalt tools will last longer?
    Another question, how did others go about drilling into this Stainless Steel on their calipers?

  2. #2

    Post


    You're burn up your bits almost instantly if your RPM is too high.. Try drilling at 1/2 the RPM you're drilling now and see if they last longer.. Keep reducing the RPM and I think you'll get a lot more life out of them.. I used to burn up my bits all the time until I learned the correct speeds and feeds..

    -3Ph
    When in doubt, doubt your doubt.
    www.metalillness.com

  3. #3
    Join Date
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    Post

    Ditto what 3Ph says. The only ones I've broken from the HF Tin set are a couple of the tiny ones(#42, 1/16, 3/64) and that was my fault. The plain black one's are another story though. I wouldn't use those in anything but wood.

  4. #4
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    Heavy feed, slow speed.

  5. #5
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    I don't think density has much to do with what cobalt does for HSS. Actually, cobalt is about the same density as iron (atomic weight of Fe=55.847, Co=58.9332). Cobalt added to HSS increases its red hardness which can result in longer life under conditons in which M2 HSS might not withstand the higher heat.

  6. #6

    Post

    I guess I'll sound off on this one. I ran a radial drill in a production shop for about 2 years. I have used virtually any kind of drill you can immagine. I have drilled, reamed, tapped, counterbored, and countersunk more holes that the average machinist will in two life times. DON'T WASTE YOUR MONEY ON M42 COBALT! I can tell you from experience they only last about 10 to 15 % longer than a good HSS drill bit will. Only difference is that cobalt are 135 split point and HSS are 118 standard point. I can sharpen good standard point bits in my sleep. 135 split point are much harder to resharpen by hand. Just use regular bits and resharpen as nessary. If you need real drilling power get carbide one by one as you need them. Trust me a good quality HSS set is all you need.

  7. #7
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    And the stuff about cobalt drilling hard material is BS, IMO.

    I've tried it, and got nowhere except a dull drill. Carbide drilled the hole fine.

    Cobalt drills also seem to break or twist off easily. This just was mentioned elsewhere, I think on PM.

    BTW, the HF TIN coated drills ought to be called "tin" drills. Either they are made of tin, or that's all they will drill.....they dull, break, split, and in one case, unwound the spiral and re-wound the other way.

    Total crap, tempered cold-rolled with a TIN coating.....or worse.

    Buy a good set of HSS and never look back. Get them at garage sales and sharpen yourself. I have lots of good brand drills from garage sales and estate sales.
    1601 2045 1412 2321

    Keep eye on ball.
    Hashim Khan

  8. #8
    Join Date
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    Yep,there really isn't a need for cobalt drills unless you are drilling a lot of stainless,even then they don't offer much advantage.

    A good HSS drill will drill nearly anything that is drillable.

    For all the stuff that doesn't drill to good,I buy carbide masonary bits and sharpen them on a green or diamond wheel so the cutting edge resembles that of a 135* drill.

    With a slow speed and water based coolant they will drill leafsprings,insert toolholders and even some bearing races.

    Just be aware that they are not sized and will only produce an approximate hole.If you need anything of any aaccuracy then you will need to grind the sides for the proper diameter.

    I have had excellent results from the following brands Bosch,Dewalt,Hilti and Hitachi.

    I just need one more tool,just one!

  9. #9
    Join Date
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    I, too, broke a drill bit while drilling a hole in calipers. It wasn't a HF bit, either.

    I don't know what kind of steel is used for calipers but it work hardens very easil. The work hardening was the problem, not the bit.

  10. #10
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    Most calipers I have seen are a hardened stainless. I don't know what specific alloy most are made from though.
    Paying Attention Is Not That Expensive.

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