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By Lonsdale73
#1291252
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?
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By sunnybob
#1291258
many things.... :shock: :D
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.
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By CHJ
#1291261
Lonsdale73 wrote:….. 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.
By Lonsdale73
#1291263
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.
By Setch
#1291264
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.
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By Trevanion
#1291265
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.
Last edited by Trevanion on 25 Jun 2019, 20:47, edited 1 time in total.
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By CHJ
#1291266
Lonsdale73 wrote: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
CHJ wrote:..
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.
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By Bm101
#1291403
CHJ wrote: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! :D
Cheers
Chris
By Lonsdale73
#1291435
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.
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By Bm101
#1291437
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.
By Lonsdale73
#1291440
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.
By TFrench
#1291688
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.
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By Steve Maskery
#1291691
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.
By Lonsdale73
#1291707
TFrench wrote: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?