PDA

View Full Version : Feeling the pain of HF tin coated drills



BillH
03-29-2005, 11:01 PM
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?

3 Phase Lightbulb
03-29-2005, 11:32 PM
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

Joel
03-29-2005, 11:43 PM
Heavy feed, slow speed.

CCWKen
03-29-2005, 11:43 PM
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.

sidneyt
03-29-2005, 11:47 PM
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.

jimfun
03-30-2005, 12:05 AM
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.

J Tiers
03-30-2005, 12:37 AM
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.

wierdscience
03-30-2005, 08:07 AM
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.

MTNGUN
03-30-2005, 09:10 AM
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.

ERBenoit
03-30-2005, 09:40 AM
Most calipers I have seen are a hardened stainless. I don't know what specific alloy most are made from though.

sidneyt
03-30-2005, 01:21 PM
From some of the discussion I have read about M42 cobalt drills, endmills, etc from users who claim they use nothing else you might think M42 was some "magic" metal. I will never drill even a fraction of the holes that JimFun has, but I have come to realize that for drilling Al, CRS, CI and Brass that I usually work with, 118 degree M2 drills seem to work fine. I have also found that M2 end mills also work fine for the same type of material. I am sure are circumstances in which M42 might be a better choice, but it is not always so obvious when.

BillH
03-30-2005, 01:37 PM
Thanks guys for the suggestions, I guess my new question would be how to get past the work hardened dimples I have now? Diamond burs in a dremel? then continue drilling?
Hell, maybe I should just develop a clamping system instead of drilling holes.

ahidley
03-30-2005, 02:41 PM
SS is a bitch.. It hardens from the heat of the drill bit. So:
1- use LOW RPMs
2- bear down on the bit forcing it to cut. If it spins and does not remove chips it will heat up, even with oil. THE CHIP COMMING OUT HAS HEAT IN IT, THUS REMOVING THE HEAT WITH IT
3- use plenty of coolant

3 Phase Lightbulb
03-30-2005, 02:55 PM
<font face="Verdana, Arial" size="2">Originally posted by BillH:

Feeling the pain of HF tin coated drills
</font>

Trust me, you haven't felt pain until you drill into the palm of your hand.. http://bbs.homeshopmachinist.net//wink.gif

-3Ph

Your Old Dog
03-30-2005, 06:45 PM
BillH, If you're open to thinking out of the box why not try making a mount of 5 minute epoxy. Needless to say, just clean it first with alcohol. Easy enough to do a simple test with some other stainless but it might work. When I made custom hunting knives I used to grind a few notches into the tangs before sliding them into the handle material and it worked really well.

Let me know how you make out, I might do it the same way when I'm ready!

Paul Alciatore
03-30-2005, 08:31 PM
I wouldn't drill holes in the calipers to mount then. Just use a clamp action to hold them in place. It may even be best to put a flexable element in line with one mount to allow for any slight misalignment.

Paul A.

mochinist
03-30-2005, 08:49 PM
Like others have said "low rpm's and high pressure". Well this becomes tough when your using a little drill, like I suppose your using on your caliper's. You put to much pressure on the drill and you can see it bend and then break if you get too heavy with it. Make sure the drill is sharp, I don't care if it is a brand new drill they do not always grind them right(specially chinese cheapos from harbor freight, why do you think they were such a good price). If you do work harden the stainless you can get under it with a small carbide endmill if you have any small enough, or turn the part over and drill from the other side. I like a nice heavy cutting oil over waterbased coolant for stainless it seems to work better for me. good luck

wierdscience
03-30-2005, 09:39 PM
<font face="Verdana, Arial" size="2">Originally posted by BillH:
Thanks guys for the suggestions, I guess my new question would be how to get past the work hardened dimples I have now? Diamond burs in a dremel? then continue drilling?
Hell, maybe I should just develop a clamping system instead of drilling holes.</font>

Like I said,cheap masonary bit,they have small ones for drilling screw holes in block walls.

George Hodge
03-30-2005, 09:52 PM
I've had good results with really small drill bits by having only a small amount of the drill extended out of the chuck.My chuck has a small hole drilled in the back.Shove the bit in and leave only a 1/2inch or less extended.

BillH
03-30-2005, 10:33 PM
Wierd, im using 3-48 screws to bolt it to the mill, I wasn't aware they got mason bits that small.
Ah Geez, it seams like its time for me to learn how to resharpen my own drill bits!