Drilling and Tapping Up

[Lonsdale73]

What's the secret to successful drilling and tapping?

I have a Pesto M8x1.25 Tap set, bought on a forum member's recomendation a few years ago and a 12" length of bar, the remains of an Irwin One Hand Clamp, which fits nicely into the t-track slot and already has a hole of around 6mm at one end. It took forever to get a threaded hole in that.

Then I tried to put one in the opposite end. Perhaps stating the obvious but I don't do a great deal of metalwork and right or wrong, I approached it in similar way to I would drilling in wood or masonry by starting with a smaller drill to create a small pilot hole. Except, several hours later all I have is a slightly lighter patch in the surface of the bar where the HSS drill bit simply danced around without ever actually penetrating the bar. What am I doing wrong? Or maybe not doing at all?

 

[sunnybob]

many things.... :shock:
Mark the centre of the hole carefully.
Use a punch and hammer to put a dimple exactly where you want the drill to start.
Unless you have super hard steel you would not need a pilot hole for an M8.
You need a 6.7 mm drill, which is the correct drill size for m8 threads.
ideally you would be using a bench drill on a medium slow speed. If youre using a hand drill try to keep it below top speed (slow speed is good, even though it says HSS on the tin) keep steady pressure but DO NOT try to force the drill in. It will just discolur and then youve made the end soft and its only fit for the bin.

When the hole is drilled, start the tap slowly making sure it is vertical to the hole. Go no more than one turn before backing up a quarter turn to clear the threads. keep doing this, 1 turn in and a 1/4 turn out. After three or four turns, back it out a couple again to clear the threads. use a small amount of lubrication, wd 40 if nothing else is available.

 

[CHJ]

….. Except, several hours later all I have is a slightly lighter patch in the surface of the bar where the HSS drill bit simply danced around without ever actually penetrating the bar. ..

The 'silly one' but it's not unknown, drill rotating in reverse if you are using a powered hand drill.

You say you had difficulty tapping the other end, apart from the pilot hole being undersize (6mm?) it could indicate that the steel bar is hardened & tempered.

If this is the case then any approach of the drilling without optimum drill sharpness and cutting force will rapidly heat the surface and work harden the metal further, even to the point of matching the hardness of the drill.

 

[Lonsdale73]

I have been known to attempt to drill in reverse but this was with a bench drill, probably not a very good one but I don't want to lay all the blame at it's door. There have been times when a reverse on that would have been most useful!

I used the bench drill to tap, thinking it would be more likely to drill perpindicular - was this the wrong thing to do?

I considered asking suggestions for a replacement drill press but I've neither the budget nor restoration skills required for the usual responses of Meddings / Fobco / Startrite.

 

[Setch]

The bar is case hardened, so the outer surface is extremely hard to drill. Try using a Bosch multipurpose drill bit, which is a TCT bit like a masonry bit, but sharp, and drill a shallow, oversize hole on each side of the bar.

You should then be able to drill through the bar with a normal twist bit of the appropriate size, and tap your thread. The oversize hole in the case hardened outer is important, as trying to tap a thread in the hard material is a sure fire way to break a tap.

 

[Trevanion]

If you're drilling hard material, HSS doesn't really do it that well. Ideally, you will want something like a HSS-Co (High Speed Steel - Cobalt) drill bit which is hard enough to put holes in very hard steels. To identify whether you have hardened steel or not try to file it with a regular metal file, if it just skates off or barely bites into the material, unlike how it would bite into softer steel, that would indicate a hardened steel.

Edit: Setch is probably right on the money with case hardened bar! Hadn't even thought of that.

 

[CHJ]

I have been known to attempt to drill in reverse but this was with a bench drill, ...

Then I would stick by my suggestion of

..
If this is the case then any approach of the drilling without optimum drill sharpness and cutting force will rapidly heat the surface and work harden the metal further, even to the point of matching the hardness of the drill.

If the drill cutting edge skids for just a few seconds without biting into the material and advancing because of lack of sharpness (incorrect clearance rake etc.) the work hardening can be almost instantaneous.

+1 for the case hardened skin.
You could always try heating the bar to red heat and allowing it to cool slowly to anneal it.

 

[Bm101]

If the drill cutting edge skids for just a few seconds without biting into the material and advancing because of lack of sharpness (incorrect clearance rake etc.) the work hardening can be almost instantaneous.
+1 for the case hardened skin.
You could always try heating the bar to red heat and allowing it to cool slowly to anneal it.

I had no idea work hardening could occur so quickly. That's a good bit of knowledge shared, thanks.
Out of interest wonder if its worth heating the oven up to top heat, put your mapp torch etc on your track to cherry red then chucking it in the oven and turning oven off. Will cool really slowly with oven in the enclosed space.
Is that overkill? Asking from a general perspective on annealing really.
Thread strictly on track!
Cheers
Chris

 

[CHJ]

For something as basic as your bar just heat to cherry/ bright red and let it air cool.

 

[Lonsdale73]

Thanks chaps but all way above my skill level!

What it was, I bought some "T-track, T-slot hold down clamps" however, as you can perhaps see from the photo in the initial post, the supplied nuts are sized for for 3/4" mitre track rather than 1/2" T-track. I did have some lozenge type flat nuts that came with Incra hardware, 1/4" thread I think and I did manage to drill out and tap those. They work after a fashion nut they're so thin there's only about a single thread holding them in.

 

[Bm101]

Why?
If you have a plumbing torch. Get the metal red. Turn off and annealing should make it drillable.
It's Magic, not science.
Anyone can do it. Even Paul Daniels.

 

[Lonsdale73]

I don't have a plumbing torch and I can buy some M8 t-bolts from Axminster that will do the trick which was what I planned to do eventually. I was just trying to improvise to press the clamps ito immediate service.

My other idea was to buy a length of aluminium and a carbide spiral bit to mill it size and shape but not sure I want to subject my router to that.

 

[TFrench]

Surely you've got a hacksaw? And a file? AES has written some great articles on here about what you're looking for in both cases. Bill Carter can make works-of-art planes with a hacksaw and files, so cutting a square bit of aluminium, filing it smooth and tapping a hole in the middle is certainly within the realms of possibility for mere mortals.

 

[Steve Maskery]

Trigger clamps are hard. Really hard.
I once needed a couple of short ones, I can't remember why. The very helpful guy in the shop sold me a couple that were too long and said I should just shorten them. Ha! A hacksaw didn't even scratch them. I ended up using an angle grinder and even that took a while. So I'm not the least bit surprised you couldn't drill and tap.

When you do finally get in a position where you can tap your hole, use a bit of thread-cutting compound such as Trefolex or CT-90, it will give you noticeably cleaner threads.

 

[Lonsdale73]

Surely you've got a hacksaw? And a file? AES has written some great articles on here about what you're looking for in both cases. Bill Carter can make works-of-art planes with a hacksaw and files, so cutting a square bit of aluminium, filing it smooth and tapping a hole in the middle is certainly within the realms of possibility for mere mortals.

Oops, no hacksaw either. I do have a set of draper files, think they cost about £3 from Wilko many years ago. I do have an angle grinder which meets my few metal cutting/grinding needs. Would you have a link to one of AES' articles on the subject?

 

[AES]

I've missed all this, sorry (too much to do on my pedal car). My articles (VERY long) are both stickies right at the top of this Metal Working section. One's called "Files , blah, blah" (I forget exactly, sorry!) and the other "Hack Saws, blah blah"!

But in short just buy an ordinary 12 inch hack saw frame and a packet of bi-metal 24 TPI blades by a known manufacturer ("Eclipse", "Starrett", "Sandvik/Bahco", are the best names - don't bother with cheapo no name blades). As said 24 TPI will cover general work, 18 TPI for thicker work, 32 TPI for thin sheet. Above article shows how to identify bi-metal blades but these days you'll find little else unless searching hard I think. Small outlay for a set of tools that will cover most things.

+1 for "removing case hardening" - just heat until red then wait until you can touch it again. That's it.

Some great help been offered by everyone so far, hope the above helps too.

 

[disco_monkey79]

I had to drill out some hardened steel bolts (seized suspension components on an old truck). HSS wouldn't touch it. but cobalt bits sailed through.

I've bought both decent branded ones, and the cheap ones from Toolstation, and been happy with both.

 

[Lonsdale73]

Read through both of AES' comprehensive posts, brain now well and truly fried.

Draft shopping list so far:

1 x engineering vice

1 x 12" Hacksaw

1 x Selection of each blade mentioned

1 x Drawer full of quality files in flat, half round, round, triangular and special ali-file

1 x Cutting Compound

1 x Stash of aluminium from which to cut two t-shaped nuts

Should maybe have just bought Incra versions and paid the postage!

 

[AES]

Sorry about brain fry Lonsdale 73!

Yup, a lot of info, but take it easy, LOTS of practice, and you can't go far wrong (if those apprentice teachers could knock it into me, then anyone can do it)!

Have fun (as always)

 

[Lonsdale73]

Sorry about brain fry Lonsdale 73!

Yup, a lot of info, but take it easy, LOTS of practice, and you can't go far wrong (if those apprentice teachers could knock it into me, then anyone can do it)!

Have fun (as always)

You made it a lot more interesting than my old metalwork teacher. Mr Shillito was his name and even he didn't sound all that interested in the subject. Still, I suppose years and years of teaching hundreds upon hundreds of snotty nosed, useless kids like me would have that affect, He also had the unusal habit of hissing out any word that ended with an "s" and then he'd repeat it. Eleven years of age and after one brief, equally disinterested demo, they let us lose with the braising torch. I recall it had two levers for mixing gas and air, thing used to feel it had a life of it's own? And we braised against a sheet of asbestos! One term of that was more than enough for me.

The woodwork studio was right next dor and they really were night and day. Woodwork area looked all bright and shiny and new and had a nice woody smell to it whereas was as dark as hell, everything was black and there was always a greasy, oily aroma mixed in with the smell of burnt children and their excrement, courtesy of that damned braising torch!