Machinists: Carbide Drill Question

[MattGreen]

Like any salt-water O/B mechanics, we often need to drill out broken stainless bolts. While it isn't a major problem to do once you know the tricks and have appropriate tools, I would like to be able to do it FASTER. What do you guys think about using "hardened steel" carbide drills to allow a faster feed rate, taking advantage of the carbide's hardness and wear resistance to overcome the work-hardening of the stainless ? I'm worried about breaking the brazing and having a carbide tip stuck in the hole. I have lots of experience with carbide woodworking tooling, but have never used carbide metalworking tools. Comments from machinists would be appreciated.

Regards,
Matt Green :)

[WATERWINGS]

Solid carbide drills are very expensive, they will chip easily, and if you drop it it will break.

How about a cobalt drill, it is very hard, cheaper, and it will not chip or break if it is dropped.

[MattGreen]

John,
I'm talking about carbide-tipped drills. They are expensive, but not horrible. You only need a few sizes for drill out bolts. We have used cobalt, and they work fine, but we've had even bettter success with Norseman "Super-Premium" HSS drills and surplus HSS drills from Boeing (I have no idea who makes them). My idea was to use such a wear-resistent drill that you could bring the speed up and not fight the stainless so much.

Matt

[LaveyT]

On a drill press or Bridgeport carbide is fine.Free hand held drill a carbide tip might work.A solid carbide Never.

[RichS]

If you're using a press or mill carbide is the best, but you have to be able to control the feed and keep pressure on it. and, Keep the workpiece solid. If you're hand feeding use cobalt. but it will still chip if you're not steady. Carbide tips are ok if ya get good ones.
Tooling Eng. for 25 years.

[Bill Rogers]

A continous supply of high-quality coolant/lubricant will let you increase speed/feed substantially and make the bits last a lot longer. The coolant needs to be directed in such a way that it completely washes the chips out of the hole. The ideal setup would use drill bits with coolant feed holes.

I wouldn't risk using a drill with a brazed-on carbide-tip.

[rookieflyer]

I would forget about brazed tips unless you are talking about some kind of specialty tool. I have owned & run machine shops and also have been involved with lots of field service repair work on large machinery, and I would suggest sticking with cobalt. Yes, they do come apart inhigh-stress situations and worse, they fracture horribly when drilling by hand.

It sounds like you appreciate the need for good tools, so keep in mind that there is a *BIG* difference in the quality of drills from one manufacturer to another.
Always use american made jobbers drills or short-shanks - and always pass on bargains from home centers and hardware stores. Even when these handle cobalt drills, they are so horribly ground - they are an accident waiting to happen.

I agree wholeheartedly with the comment on coolants. Use one especially made for drilling stainless. A good coolant will take 1/2 the time off the job of drilling out a broken bolt or stud.

Try MSC, or even Wholesale Tool for bargains on some decent stuff (but beware of their chinese drills!). You didn't mention extractors, but good spiral ones also work much better than the common square ones.

I also realize that it's not often a good practice to apply heat, but when a stainless part is stuck in a cast housing, or any aluminum part for that matter, the thermal coefficients for expansion are so grealy different between the two materials that something almost always has to move instead of breaking. This is a super way to not have to work so hard - when you can. Even a small hand-held map-gas torch works wonders.

[skidoo29]

I agree with rookieflyer completely, you get nwhat you pay for.
also carbide tipped drills are a waste of time unless you are drilling something hard, concrete or steel that is at least 40 rc.(stainless isn't hard enough) otherwise the tips will just grab and chip off, if you are using the tipped drills ,when you are sharpening remember to put a little angle on the cutting edge, this will allow the drill to scrape instead of taking a full cut like a normal dril, and will make your drill last longer

warren

[Stv Euro]

I have had experience in cobalt jobbers. Cobalt is great when heat and speed is a factor. The stainless does not have enough carbon in it to make it hard enough for the carbide to work well. So I would try the cobalt with a good manufacture and put your bolts back with silver antisize or the copper for heat. This should help with the sticking ang breaking of S/S in other metals. Good Luck!

[MattGreen]

Thanks everybody. I should have specified that generally we are hand-drilling these out. If it's possible to effectively clamp the parts we do it in the press, otherwise by hand. Based on the responses about the carbide, I might experiment a little with the carbide-tipped ones on some junk parts, but you guys reinforced my suspicions about breaking off a brazed tip.

Rookie-flyer: I'm WELL aware of the benefits of using heat to free stuck SS bolts in aluminum - that is the mantra for saltwater O/B mechanics. We have over a 95% success rate getting stuff apart without broken bolts, but you break one every now and again. We use oxy-acetylene and a full-scale cutting tip - not for the faint-of-heart, but it works well.

Most of the "drilling projects" are actually on Billy Bayliner's engine that he and his buddy were going to fix themselves. Then the bolt is likely to have some Home-Depot drills broken off in the bolt as well....... :rolleyes:

Like I said, I like the Norseman "Super-Premium" bits (www.norsemandrill.com), some kind of exotic HSS; they have out-performed cobalt on stainless and I've yet to break one. The coolant is a good idea, what do you guys reccomend specifically for stainless ? I've just been using regular Rapid-Tap (I know, not the best choice). Would this still be beneficial in a hand-drilling situation (i.e. not a continuous flood of fresh coolant) ?

And to STV Euro: silver/graphite/copper (worst!) anti-seize compounds are a no-no in saltwater applications: you are adding ANOTHER metal to the little galvanic cell and will actually make the problem worse. The ultimate solution is Tef-Gel non-metallic anti-seize (expensive). OMC/BOMB "elephant snot" gasket sealer also works pretty good (Merc makes a similar product). You'd also be surproised how well a heavy grease, like Triple-Guard, works on preventing stuck bolts. It won't alleviate the corrosion, but does a surprisingly good job of keeping the bolt shanks from getting seized in the aluminum.

Fun stuff, crusty motors......
Matt Green

[rookieflyer]

But I have to share this one -
A local shop that is touted as having a super mechanic for older O/B's actually snapped more than a handful of head bolts on one of my V6 Merc's. (That's just aboutthe time I started doing ALL the work myself) He then tried everything he could come up with, including asking his welder to try to weld tabs onto the broken bolts that he might grab with a vice-grip or some such thing.
I tried to tell him that it would be a waste of time, but he insisted - and got nowhere.
He put a chunk of unpaid hours into all his attempts.

So now I have a 2.0 powerhead with a bunch of broken head bolts to drill out.

Forgive the simplicity of my comments - I have no idea of the working background someone has from these short forum postings.
I can comment on the general aspects of machining with various materials and tools, but I need to rely on folks with hands-on experience with these motors in a working shop environment for application help at times.

So, while I go look up the cutting fluids that work well with various stainless materials, maybe you can teach me some technique in removal of these snapped bolts...pleeeeeze!

Oh, BTW, the coolant in any volume is especially helpful with many stainless bolts and studs because I believe they are all, (or almost all) work hardening to an extent.

C

[Bill Rogers]

For me, the key to removing wrung-off bolts is to use left-handed drill bits.

If you're lucky enough to have your work properly fixtured in a mill or drilling machine, choose a bit just under the root diameter of the bolt. Just before it cuts through the bottom of the bolt, slow the cutting speed way on down. As it tries to cut through, the bit will grab what's left of the bolt and literally unscrew it - with no damage at all to the inside threads. (I was most impressed first time I saw this done)

Hand drilling is another matter. You can't drill perfectly straight and on-center by hand. I like to start with a bit about 2/3 of the root diameter of the bolt. If it cuts all the way through without grabbing and unscrewing the bolt, I'll just keep going up in size until it does.

Rookieflyer, you said you used to have a machine shop - do you still have access to a milling machine? Since your block has "bunches" of broken off bolts (that's a sad story - hard to believe any mechanic would just twist em off one right after another!), you really ought to use a mill, a radial drill, or a hefty drill press. The right setup with a left-handed bit and plenty of coolant will make that job easy.

By the way, I use Syn Kool on both the lathe and mill mixed 1 part to 10 with water. It works good with stainless and aluminum. For hand drilling you might want to try one of those mist systems.

[MattGreen]

Rookieflyer:
Thanks for your input - it seems our respective experiences complement each other - my knowledge of tooling is limited.

There was a thread on drilling bolts a few weeks ago on this forum, with lots of good ideas; anybody embarking on such a "fun" project should dig it up.

Bill Rodgers made some good points about using "lefties". They can be helpful in certain situations, BUT let me add a few cautions. Obviously, you have to have them to use them. Good-quality left-hand drills are not a common stocking item for most suppliers (at least in my area), so be forewarned you may have to special order them. Snap-On and MAC both sell small sets for <$50, that may be the best route.

My main reservation is that in the situation when the bolt is hopelessly seized in the Al casting to the point where heat, carefully applied impact, copious cursing, et cetera has been applied, and yet the head still broke off. The lefties aren't going to help you in this case; nothing will thread it out, it must be entirely drilled out.

FOR SALTWATER BOATERS FIXING THEIR OWN ENGINES: LOTS OF HEAT WILL PREVENT THIS FROM HAPPENING 90% OF THE TIME.

Matt Green:D

[Bill Rogers]

Matt, I found and read the thread on broken bolt removal. Looks like all the bases have already been covered. I was gone earlier this year and missed a lot of good discussion. The last thing I want to do is come on here and sound like a know-it-all.

Most of my experience is with machinery. I really had no business commenting on hand removal. I will say this though: No matter how bad it's stuck, if I can use the mill, I'll get them out 99 times out of 100, without heat, and without thread damage.

MSC stocks left-hand bits by Chicago-Latrobe and Precision Twist Drill, but like you say, they ain't cheap.

[rookieflyer]

Matt sent me some super advice off-list. Thanks.
I am a little confoosed....
Am I being anal when thinking that using a heli-coil = repair failure, or at least translates to a hack-job?
My experience is also mostly with machinery and jet aircraft, and inserts were a last resort...

[MattGreen]

Hey Bill,
Don't worry, I'm always open to learning new (and better) ways of solving tricky problems. I'd really like to watch you go at one with the mill. I'm not a machinist, but your way, and rookieflyers, sounds the best if you have the tools and time. In the marine business, often we have limited amounts of both.

Matt :)

[Bill Rogers]

Next time I do one I'll take a series of photos.

I'd like to learn more about hand removal - especially the judicious use of heat. I'd love to see what you sent to rookieflyer...

[Superdave]

Left handed drill with extractor. I removed 5 broken turbo exhaust screws with zero problems. The first one took longer than the other 5. That's when I bought theses.