Help grinding a scraper

[Mike Peace]

I have an extra HF 1/4"x1/2" scraper I want to regrind into the profile below. It is HSS. How is the best way to accomplish this? I have Dremel cutoff tool, a WC slowspeed 8" grinder, an old Crafsman 6" with the old gray wheels and a 6" belt sander. I have not done much in the way of making tools.

[David Walser]

Mike,

If it were me, I'd use a permanent marker to outline your desired shape and then take it to your high-speed grinder to grind close to the line. Then, I'd use a combination of the belt sander, the slow speed grinder, and the dremel to finish the job. With HSS, you shouldn't need to worry about overheating the steel and destroying the temper.

[Steve Schlumpf]

Mike - I agree with David in that I would mark it with a permanent marker first, then high speed grinder - then I would finish it on the slow speed grinder. Figure whatever profile you end up with has to be sharpened on the slow speed anyway - so no sense making details you can't get to with the slow speed anyway!

Good luck with it!

[Dave Ogren]

Mike,

I agree with Steve and David, but you have to not let the HSS get too hot, it will draw back the hardness. As soon as you are getting a color past a light tan in HSS you are tempering it. Grind and dip it in water or keep a spray bottle handy, or a wet rag. Best to try and not get any color into the HSS. Good luck and happy turning.

Dave Ogren

[Scott Conners]

Mike,

I agree with Steve and David, but you have to not let the HSS get too hot, it will draw back the hardness. As soon as you are getting a color past a light tan in HSS you are tempering it. Grind and dip it in water or keep a spray bottle handy, or a wet rag. Best to try and not get any color into the HSS. Good luck and happy turning.

Dave Ogren
Actually, this is only proper advice for carbon steel, NOT high speed steel. High speed steel is designed to work at high cutting edge temps, and won't lose it's temper even when ground to a dull red glow (turn your worklight off if you're grinding this hard). Water cooling HSS is NOT a good idea, as HSS is not tolerant of temperature shock, and hitting hot HSS with water can cause crazing and cracking.

Here's a quote form a senior mettalurgist at Carpenter Technology:


Most HSS today is tempered at 1025 deg. F (triple tempered, and held at
tempering temperature the first time for 4 hours -- don't try this with your
propane forge...). As long as you stay below that temperature, you won't
hurt the steel. Don't dip it in water if you grind it hot enough to show any
oxidizing colors. (That occurs at around 275 deg. F, I think, for light
straw.) It can't take the thermal shock. Also, if you raise it to 1400 deg.
F too quickly, it can crack without water-dipping it. But the tool is
wrecked by then, anyway, so it doesn't matter much.

If you get it a little bit red at the edges, a low-pressure dressing pass
will take off enough steel to clean up any marginal material. As long as you can't see anything above dull red, you're OK.

[Mike Peace]

It wasn't as difficult to regrind as I thought it might be. Marking the outline helped. The 6" grinder's coarse wheel seem to shape the blade quickly. It was not necessary to use the Dremel or the belt sander.

I hear conflicting advice on cooling HSS steel when grinding. For me, keeping the tool from getting too hot to handle seems like a good idea and makes the tool easier to handle when doing a lot of grinding.