What would be the right tool to make a 1/2" hole in a piece of heat treated AUS-8? The steel is 3/16" thick. I tried a standard carbide drill bit in a bench vise, but it barely did anything. I don't have any titanium or diamond-bonded bits on hand, and was hoping for some advice before I go out and buy something that won't work. I don't need the bit to be durable; good enough for one or two uses is good enough for me.
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Making Holes?
- Thread starter JNieporte
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A Hi-Roc bit is probably what you'd be after... Definitely need a drill press or a mill I would think, and they are NOT cheap.
I suspect someone can come up with a better answer than that. Does the hole need to be to finish, or is it a clearance hole that will be covered by something?
I suspect someone can come up with a better answer than that. Does the hole need to be to finish, or is it a clearance hole that will be covered by something?
It will be an opening hole for my new XL Voyager. Spyderco-style hole.
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Hmm, ok, then finish is going to be quite important, obviously. A rather ghetto-rigged method that might be sucessful would be using a powdered abrasive and a consumable brass/steel tube as your drill. I've used that in glass a number of times, I'd think it would work on hardened steel as well. It will take time, and you have to have your knife very solidly mounted to your drill press. If it slides, it's not good.
Chuck the tube in the press, add a touch of water and the powdered abrasive on the side of the blade where the hole will be, set the drill for low RPM, and lower it into light contact. Periodically retract the tube and rub the slurry into the abraded channel, adding more abrasive from time to time. Note, LIGHT contact is the trick here, you want to rub the abrasive against the steel, not smash your tube. I'm SURE there's a better way, but that'd probably get you a nice-looking hole without the ~$80 investment for the RIGHT tool for a single hole.
Chuck the tube in the press, add a touch of water and the powdered abrasive on the side of the blade where the hole will be, set the drill for low RPM, and lower it into light contact. Periodically retract the tube and rub the slurry into the abraded channel, adding more abrasive from time to time. Note, LIGHT contact is the trick here, you want to rub the abrasive against the steel, not smash your tube. I'm SURE there's a better way, but that'd probably get you a nice-looking hole without the ~$80 investment for the RIGHT tool for a single hole.
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I'm _not_ a machinist, so I'm really just _guessing_....
But if I had to drill a 1/2 inch hole in hardened knife steel, then I would buy a grinding bit for a drill. For example, a cubic-boron-nitride (CBN) grinding bit. Some of these are specifically designed for grinding hardened steels.
http://www.mcmaster.com/#grinding-bits/=dw5kqh
http://www.mcmaster.com/#grinding-bits/=dw5nis
Also be sure to buy cutting fluid. Grinding will generate a ton of heat, which can be bad for your knife's heat-treatment, and also possibly bad for your drill bit (can damage HT of the drill bit). The cutting fluid will reduce unnecessary friction (reduce heat generated), and also conduct heat away from the drill-bit and grinding area.
Then I would drill/grind, but very _very_ slowly. And I would also closely watch how hot it got... They say if it gets too hot to touch, then it's too hot. Go more slowly, add cutting fluid, and/or cool the part off (just wait, or maybe a bucket of water? I'm not sure).
I'm waiting for a real machinist to us an answer in this thread!
If you're a machinist, please chime in
Sincerely,
--Lagrangian
But if I had to drill a 1/2 inch hole in hardened knife steel, then I would buy a grinding bit for a drill. For example, a cubic-boron-nitride (CBN) grinding bit. Some of these are specifically designed for grinding hardened steels.
http://www.mcmaster.com/#grinding-bits/=dw5kqh
http://www.mcmaster.com/#grinding-bits/=dw5nis
Also be sure to buy cutting fluid. Grinding will generate a ton of heat, which can be bad for your knife's heat-treatment, and also possibly bad for your drill bit (can damage HT of the drill bit). The cutting fluid will reduce unnecessary friction (reduce heat generated), and also conduct heat away from the drill-bit and grinding area.
Then I would drill/grind, but very _very_ slowly. And I would also closely watch how hot it got... They say if it gets too hot to touch, then it's too hot. Go more slowly, add cutting fluid, and/or cool the part off (just wait, or maybe a bucket of water? I'm not sure).
I'm waiting for a real machinist to us an answer in this thread!
If you're a machinist, please chime in
Sincerely,
--Lagrangian
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- Jun 25, 2011
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- 400
You might post your question to the knife-making/makers sub-forum; hopefully the knifemakers probably can give you good advice.
Ok, machinist here, chiming in. What you want to drill with is a carbide spade drill. It is of critical importance that you use proper speed, or RPM when drilling. Too fast will burn up the edge, and too slow will fracture/crumble it. This is probably what happened with your initial carbide drill. For a 1/2" carbide drill in 60rc steel, shoot for 600-800 rpm. The drill and the workpiece must be rigidly held, so use a mill or drill press and a vise. The CBN grinding bits mentioned above are not designed to make a through hole!! You will most likely destroy one if you attempt to do so. They are made to take light cuts (in the range of ten-thousandths to a few thousandths of an inch at a time) on the periphery only.
The method outlined above with the brass tube and abrasive will also work but will take a very long time. To keep the abrasive slurry in place you should build a dam around the desired hole location with plumber's putty and fill it with the abrasive slurry, then commence with abrading the hole. You want the slurry mix to be fairly thin, slightly thinner than a milkshake. It should poor pretty freely. The advice about light pressure is spot on. Use light pressure on the down stroke and you should be constantly moving the tube up and down to keep fresh abrasive flowing into the interface between tube and workpiece.
For both of these methods you should be using a drill press or small milling machine and have the workpiece solidly clamped in a vise with the vise clamped to the drill press or mill table. Anything less is going to be mostly an exercise in frustration.
The method outlined above with the brass tube and abrasive will also work but will take a very long time. To keep the abrasive slurry in place you should build a dam around the desired hole location with plumber's putty and fill it with the abrasive slurry, then commence with abrading the hole. You want the slurry mix to be fairly thin, slightly thinner than a milkshake. It should poor pretty freely. The advice about light pressure is spot on. Use light pressure on the down stroke and you should be constantly moving the tube up and down to keep fresh abrasive flowing into the interface between tube and workpiece.
For both of these methods you should be using a drill press or small milling machine and have the workpiece solidly clamped in a vise with the vise clamped to the drill press or mill table. Anything less is going to be mostly an exercise in frustration.
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Dang, now that's a good thought with the plumber's putty dam, I'm going to use that. Typically I've just depended more or less on the surface tension to hold it in place, and made a huge mess. That'd be a LOT cleaner.
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@eKretz:
Thanks for your advice!
I'll keep in mind that CBN grinding bits are not designed for making holes.
Sincerely,
--Lagrangian
Thanks for your advice!
I'll keep in mind that CBN grinding bits are not designed for making holes.
Sincerely,
--Lagrangian
- Joined
- Jun 25, 2011
- Messages
- 400
@eKretz:
Quick question: Would you recommend using cutting fluid? If so, would any cutting fluid be okay, or is there a particular one you like?
Sincerely,
--Lagrangian
Quick question: Would you recommend using cutting fluid? If so, would any cutting fluid be okay, or is there a particular one you like?
Sincerely,
--Lagrangian
@Lagrangian:
No coolant is needed if you keep the tool cutting. In fact, it's a bad idea to use anything unless you plan to douse it. Hitting a hot carbide cutting edge with a fluid will often cause such a thermal shock that the carbide will crack on a microscopic level, causing the cutting edge to crumble away. So, the rule is: if you can't keep the tool cool enough to touch at all times, don't use a coolant.
@tinbasher:
A masonry bit can be made to do the job, but it is unlikely to produce a cosmetically nice looking hole. Also, most common folk will be unable to sharpen carbide since to do it properly requires a diamond grinding wheel. A green silicon carbide wheel can be used to roughly shape carbide, but the finish at the cutting edge leaves much to be desired, and when drilling hardened steel, an edge ground with a SiC wheel will not last very long unless after grinding it is hand-honed with a diamond hone. It's a bit of a bodge, basically. For our non-UK folks, you could say it's the Shade Tree Mechanic method; it could work, but isn't the right way.
@db:
A carbide spade bit can be had for around $20 or less if you look in the right places.
No coolant is needed if you keep the tool cutting. In fact, it's a bad idea to use anything unless you plan to douse it. Hitting a hot carbide cutting edge with a fluid will often cause such a thermal shock that the carbide will crack on a microscopic level, causing the cutting edge to crumble away. So, the rule is: if you can't keep the tool cool enough to touch at all times, don't use a coolant.
@tinbasher:
A masonry bit can be made to do the job, but it is unlikely to produce a cosmetically nice looking hole. Also, most common folk will be unable to sharpen carbide since to do it properly requires a diamond grinding wheel. A green silicon carbide wheel can be used to roughly shape carbide, but the finish at the cutting edge leaves much to be desired, and when drilling hardened steel, an edge ground with a SiC wheel will not last very long unless after grinding it is hand-honed with a diamond hone. It's a bit of a bodge, basically. For our non-UK folks, you could say it's the Shade Tree Mechanic method; it could work, but isn't the right way.
@db:
A carbide spade bit can be had for around $20 or less if you look in the right places.