How to drill through a hardened tang?

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Laurentius

Bushcrafter (boy, I've got a lot to say!)
Aug 13, 2009
2,422
614
Knowhere
I need to make holes for rivets in a tang hardened to about 50 -52 rockwell, I have tried so far with my standard Bosch power drill and an HSS bit from Wilco without making much of an impact, I destroyed one bit and am scarcely making a mark with another.

It is fairly clear I am using the wrong tools here, short of finding a friendly engineering shop with a pillar drill, what can I do?
 

stone monkey

Tenderfoot
Jun 2, 2015
84
0
east yorkshire
Hi, if you have access to a welding torch or small blowlamp, heat just the spot you need to drill to cherry red and drill through it then. Not ideal but a method i have used on hardened steel before, but not a knife:)
 

Fraxinus

Settler
Oct 26, 2008
935
31
Canterbury
I would ask why the tang is hardened as the blade is usually the part that is and if the blank is going into a kiln then the holes are predrilled.
As to the remedy, then my option would be to cover the blade with wet sand and keep it wet to act as a heat sink then heat the tang as mentioned in the previous post #2.
Sometimes drilling with progressively larger bits will work in hard steels when lubricated with an oil and water emulsion or washing up liquid but slow speed and steady pressure help.

Rob.
 

Janne

Sent off - Not allowed to play
Feb 10, 2016
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Cobalt steel.
Start very gently ( low pressure and medium speed) and with oil lubrication with the smallest diameter bit, then work up in size.
You need to be able to hold the blade and drillbit in exactly the same position or the thinnest bits will snap.

Pesonally I would not touch the hardening as I for sure would ruin the blade.
 

Laurentius

Bushcrafter (boy, I've got a lot to say!)
Aug 13, 2009
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I would ask why the tang is hardened as the blade is usually the part that is and if the blank is going into a kiln then the holes are predrilled.
As to the remedy, then my option would be to cover the blade with wet sand and keep it wet to act as a heat sink then heat the tang as mentioned in the previous post #2.
Sometimes drilling with progressively larger bits will work in hard steels when lubricated with an oil and water emulsion or washing up liquid but slow speed and steady pressure help.

Rob.

Well whatever, it does seem to be hardened considering the impossibility I have found in drilling it.
 

Laurentius

Bushcrafter (boy, I've got a lot to say!)
Aug 13, 2009
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- solid carbide bit

- masonry bit can work sometimes.

- centre punch with a square pyramid profile can also help.

I have tried with a masonry bit, I think it will be off to machine mart tomorrow to find the hardest bit going.
 

Laurentius

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Aug 13, 2009
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Well if I could just get a pilot hole through I dare say I could do the rest with a file, trouble is failing to make progress with the right sized bit for the hole, I tried a smaller bit and promptly broke it.
 

Laurentius

Bushcrafter (boy, I've got a lot to say!)
Aug 13, 2009
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Well if I could just get a pilot hole through I dare say I could do the rest with a file, trouble is failing to make progress with the right sized bit for the hole, I tried a smaller bit and promptly broke it.
 

Janne

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Feb 10, 2016
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Well if I could just get a pilot hole through I dare say I could do the rest with a file, trouble is failing to make progress with the right sized bit for the hole, I tried a smaller bit and promptly broke it.

You applied too much pressure, the bit bent and broke.
Do you have a stand you put the Bosch in or did you work freehand?
I tend to break the smallest bits working freehand.

52 Rockwell is much softer than HSS.
 
Jul 30, 2012
3,570
224
westmidlands
A masonry bit isnt sharp enough, so you need to sharpen the edges, and carbite being very hard its unlikely a stone or file will yeild results in sharpening it, but you may be lucky enough.

The allround drill bits come sharp thoes that drill metal and stone, they are essentially masonary bits.

Once you have a sharp one run the drill fast and the heat softens the steel enough to gain a small indent, as the reason drilling doesnt work on hard steel is that you cannot deform the surface enough to gain purchace, let alone the hardness of the steel to be cut.

The carbide does not succumb to the heat unlike the steel so the carbide tip scrapes the surface away as it heats and softens the steel, rather than cutting like a conventional drill bit. It is also slower by a factor of five +.
 

Laurentius

Bushcrafter (boy, I've got a lot to say!)
Aug 13, 2009
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You applied too much pressure, the bit bent and broke.
Do you have a stand you put the Bosch in or did you work freehand?
I tend to break the smallest bits working freehand.

52 Rockwell is much softer than HSS.

Working freehand, I do not have a drill stand, maybe the bits are too blunt, or just not high enough quality, standard fare from Wilco or Homebase.
 

Janne

Sent off - Not allowed to play
Feb 10, 2016
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Working freehand, I do not have a drill stand, maybe the bits are too blunt, or just not high enough quality, standard fare from Wilco or Homebase.

I must have broken enough bits working freehand to fill a wheelbarrow.
Fix the sword to your worktabke with a wood block underneath, work with holding Bisch using both hands and elbows supported.
Good luck!
 

santaman2000

M.A.B (Mad About Bushcraft)
Jan 15, 2011
16,909
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Florida
Soft metal means faster speed and lighter pressure. Harder steel means slower speed and heavier pressure. However as Janne said, with a small drill bit too much pressure will easily break said bit. A high speed bit will work if you're practiced at drilling but cobalt is better. Lubricating oil or beeswax is a plus. Make sure your bits are sharp.
 

C_Claycomb

Moderator staff
Mod
Oct 6, 2003
7,353
2,363
Bedfordshire
Bosch Multi Material Drill bits, available from Screwfix.
http://www.screwfix.com/c/tools/drilling/cat5920002#category=cat5920044&brand=bosch
Don't waste your money on solid carbide, without a drill press you will break bits. Even with a press you may break bits. Don't waste your time and money searching for Cobalt. The Cobalt HSS is only slightly better than regular HSS and whatever bit you get needs to be well ground. Unless you are shopping at Cromwell or similar industrial supply place, chances are the drill bits won't be all that well ground. I have used Cobalt on both hard and soft steel and didn't find it was worth it on the hard stuff. The Universal bits scrape with a sharp edge, rather than cut, but they are tough, cheap, and forgiving if you don't hold them dead straight since they are carbide brazed to a slightly smaller steel body. They won't be dead accurate, but good enough and better than some ways.

Interestingly, this thing, a spade type solid carbide for hard steel has a cutting edge a lot like those universal drills. http://www.drill-service.co.uk/Product.asp?Parent=020480020000&Tool=355 Good source for drills, but overkill for this job.

Whatever you do, do not drill pilot holes and then chase down them with larger drills trying to enlarge the hole. This is often repeated advice, and sort of works, but it makes for inaccurate holes and tends to trash the drill. Twist drills require the centre of the hole they are creating to keep them centred. Drill in a pilot hole and get shake and vibration and out of round hole. If the difference between pilot and final hole is too small, the bigger drill won't cut and just rubs its way down, then breaks. If you drill into a pilot hole the bigger drill encounters a sharp corner at the pilot hole edge and chances are it will chip. I have broken and damaged too many solid carbide twist drills, while in a press, attempting to enlarge holes in harden tangs to think its even remotely a good idea.

Filing will be painful. You can try a chainsaw file, but its not going to be fun and won't do the file much good. The only way I have found to do this for a nearly right size hole is a 1/8" solid carbide burr in a rotary tool (Dremel), running fast. Carbide burrs likes speed. Unless the hole being enlarged is only slightly too small its hard to keep it round with this.

Use a chunk of steel underneath the tang, clamp it so that you can lean on your drill, drill through into the support block. The block will help cool the work. The only thing that drills hot is Stellite, everything else is better cool. That's why industry spends so much on spray cooling and cutting fluids. The support block also helps control break out and gives a cleaner hole. Does not need to be hard steel, some mild will do. Aluminium will too, but steel would be better in this case.

The local softening method with a torch can work, depends what the blade is made from. Not too much danger to the blade temper if you keep the blade wet. However it is possible for steel to be soft and still be horrible because of how the carbides are distributed, and the torch is only going to temper the steel, not take it back to full soft. Can be worth trying, but if it doesn't work, there are always those Universal bits

Good luck!
 
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