Facts regarding grinding HSS

[Boucher]

I normally defer to people that obviously have much more experience than I do. I don't remember who posted it but there is a very good and informative thread with detailed instructions on grinding HSS tool bits. The concept presented that I seriously Question re Using belt sanders. It is stated that the pressure of the bit against the belt causes sort of a slack bulge just above the cutting edge rounding it and therefore ruining it. To the best of my limited knowledge I just don't think that is True. I would like to know what others think on this subject.

This kind of reminds me of that old Quip," Who are you going to believe Me or your lying eyes."

[Doozer]

Get some of those diamond lap hand held files.
The ones with different colored handles for grit size.
They are real nice for final edge prep when sharpening toolbits.



--Doozer

[Carld]

I don't know why but a belt sander won't leave as sharp an edge as a grinder wheel does. I use a belt sander to rough the cutters and drill bits to size/shape sometimes but I finish on a grinder wheel and sometimes hand dress it.

Maybe he saw the same thing I have. It works better when sharpening a drill real fast but you still don't get as sharp an edge as a stone gives.

[Lew Hartswick]

I would say "it depends". :-) In particular on the SHAPE of the
backing of the belt. If the the backing is a flat and the belt is "not
quite" dead tight against it you will get rounding of theedge.
But if you use the place where the belt goes over the large round
wheel (just like a wheel on a grinder) it will produce a surface
just as the wheel will but will be a cooler cut.
...lew...

edit. It depends on the grit used to, usually a belt grinder/sander
has a lot coarser grit than yout typ. grinder used for bit sharpening.
..l..

[JCHannum]

Hold the bit upside down if that is a concern. That will put the dull side on the bottom.

I don't use the belt, but I do use the disc on my sander to touch up HSS tools.

[Black_Moons]

iv used verious sanders. and holding the bit 'upside down' is good advice as I find on sanders the bit sometimes 'grabs' and tilts slightly in your hand before snaping back into place, THAT will round the cutting edge for sure.
Finishing with a diamond lap is a good tip even for wheel ground tools. a fine smooth finish on top will likey help reduce material welding to your tip as well
Also all you need is a few licks with a lap to resharpen if you don't let it get too dull. (laping the cutting edge becomes easyest with a hollow grind, this is the 'advantage' of a hollow grind as you only lap the cutting edge, not the whole face)

Diamond coated files are also good for tweaking chip breaker grooves (I usally start the grove by gnashing with a 1~4.5" cutoff disk, and finish with a very small round diamond coated file), and laps/coated files can be used to tweak HSS bits geometry with extream precision (ie getting the last degree or two on your HSS threading bit, using the fishtail gage as a visual refrence, you can adjust the angle by applying more pressure to one side of the file or the other while fileing the sides.

[lazlo]

I use a 1" Zirconia belt one an old Delta/Rockwell belt sander/grinder to touch-up HSS, and it works great.

Seriously, it doesn't have to be perfect -- when I buy lots of HSS on Ebay, some of the hand-ground tools that come out of Pro shops are astonishingly bad, and they're putting dinner on the table with them.

[Machinist-Guide]

Tool Bit's

I use the belt sander from time to time I think the most importand thing is to not get the bit too hot. Your cutting edge will heat up faster on the belt sander. Dip it in water often. Don't wait till it gets hot to dip it. Dip when you first feel it getting warm. If you let it get hot it will anneal the cutting edge.

I am posting a link to a retired machine shop teacher that has made 3 videos on sharping lathe bits. He has done a really good job with his video. He uses large wooden blocks as a tool bit model to show all the rake and clearance angles

Here is the link

Tool Bit Sharpening Video

[recoilless]

Another Reference

This was touched on in one of Harold V.'s posts over on Chaski's site.

http://www.chaski.org/homemachinist/...ic.php?t=75985

[Peter N]

I use the belt sander from time to time I think the most importand thing is to not get the bit too hot. Your cutting edge will heat up faster on the belt sander. Dip it in water often. Don't wait till it gets hot to dip it. Dip when you first feel it getting warm. If you let it get hot it will anneal the cutting edge.

????
High Speed Steel is chosen primarily for its property to retain full hardness even at red heat, so I doubt that a belt sander will anneal the edge - except at maybe a microscopic level.
Dipping is a good idea though, as it saves your fingers getting burnt.

Peter

[Boucher]

Quote: It depends on the grit used to, usually a belt grinder/sander
has a lot coarser grit than yout typ. grinder used for bit sharpening.

No No No..... That is the beauty of a belt sander you can change grit size in 30 seconds.

The belt sander is 5 times faster.... and cooler cutting than the grinding wheel.

As for turning it upside down, I normally set the angle of the table at 7° for the relief angle. I can't quite visualize the grinding with the table tilt in the oposite direction but you can bet I will check it out. If it works that is a great idea.

I really appreciate this site. My brain doesn't work like it should, or like it used to, but the inputs here help me. Thank you!

[SVS]

I have a 30's era Oliver drill grinder. The manual goes on at length concerning intermitent cooling of HSS during grinding-essentially stating "grind dry or under flood....dunking causes stress cracks."

Since reading that I've gone to wearing gloves or doing something else while the bit cools enough to hold. Nothing scientific, but I think my results are improved.

Same school of coolant theory as applies to turning and milling with carbide.

Scott

[vpt]

When I was in school I was told to always grind with the tip or sharp end up. For tig welding they tell you to grind your tungsten with the tip facing up on the wheel so the crap and the (slag) will be pushed back away from the tip.

As for the cutting edge of say a knife, lawn mower blade, HSS lathe tool, I was told you will get the sharpest cleanest edge grinding with the sharp edge/tip facing up on the grinder. Maybe a belt sander is different but a stone wheel will always leave a bit of slag on the bottom edge of a grind that will leave a dull edge when cleaned.

[Boucher]

vpt: You are right the top edge up is the correct orientation to grind the tool. Also when dressing the edge the stone is supposed to move over the it in the same direction that the chip does.

Scott: I know that carbide is sensitive to thermal stress/cracking. I don't think that HSS is. I don't know if this is related to improvements that have been made in recent years. In any case I keep a paint can of water handy for cooling.
Again it is surprising how much cooler the bit stays when grinding with the belt sander.

I started using some Norizon belts recently and they are way better than the old ones that I have been using.

[oldtiffie]

Hollowed out

This is my disc and belt sander - on my pedestal grinder:







I never use the guides on the disc for grinding tool bits - although it works well. I use it occasionally for "other stuff" as I free-hand grind most of my HSS turning tools.

I NEVER have the sander going from the top (cutting edge) to the bottom of the tool-bit on the sanders - I use that "top to bottom" technique on the "emery" wheel on the pedestal grinder. If the tools need a lot off they get "the treatment" with the angle grinder and a bucket of water. THEN its off to either or both the "emery wheel" and/or sanders - and bucket of water.

Reason is that the belt is flexible (emery wheel is not) and belt-sanding from the top down does cause a slight "rise" on the face edge neares the cutting edge where the belt first contacts the face being sanded. Going from "bottom up" leaves a fine sharp feather edge on the "top" of the tool which is soon eliminate as part of the follow-up hand-honing.

(Hand hones are mainly "diamond laps/sticks" - but are sometimes "oil stones" - it depends on the edges being sharpened).

The belt sander has a flat support plate under its "flat" section - which I don't use much either. I do all my work on the front (curved surface) of the emery wheel and the belt sander.

The "wheel" under the front of the belt sander is "vented" and "ribbed" to pass air through which keeps the belt and tool much cooler than working on the face of the emery wheel.

I prefer a "hollow-ground" face to all my tools as I hand-hone them - I need only the top and bottom of the curves - not the whole face as would be the case if the face were flat. So re-sharpening with a hand-hone is quick and easy - on the lathe or off it.

I have range of belts (36" x 2") "grit" sizes and types as spares and for a range of uses and applications.

Here are some of the diamond grit hand hones: