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Bench Grinder Question
- Thread starter YYCHM
- Start date
trlvn
Ultra Member
I hope you didn't think that I was attacking your work. Just trying to help you get a good result.
The Tom's Technique video guy explains that he doesn't believe that back rake is necessary or desirable. OTOH, all the other references I've seen always specify back rake in the tool's geometry. For example, see p. 77 of the classic book "The Amateur's Lathe" by L.H. Sparey. Etc, etc.
My understanding is that back rake reduces the cutting forces required by presenting a more acute cutting angle to the work. Also, it helps clear the chips for softer, gummier metals like aluminum and copper. I think the cutting force reduction is really important for smaller, lighter hobby lathes. A big heavy powerful lathe can just bull through the cut
There is a VERY LONG thread on Hobby Machinist about grinding lathe tools. The main author, Mikey, happened to address the question of back rake (referencing the Tom's Technique video):
"I know that eliminating back rake is a favored thing to do by some well-known guys, and even some guys here on the HM forum. Invariably, they say this makes re-sharpening easier because it does. However, I highly recommend that you grind a tool with back rake to compare performance before you blindly follow their advice. Without getting too technical, back rake reduces shear plane length and this has a significant impact on reducing cutting forces. It also focuses those forces at the tip of the tool and this enhances finishes significantly.
I have some tools in need of re-sharpening. They are all at or beyond a decade of regular use and all have back rake ground into them. They have, and continue to perform as well as they did on the day they were ground because I hone them regularly. For me, honing for a few seconds works better than re-grinding a tool to re-establish a cutting edge. Plus, I have the performance advantages that back rake provides.
Again, sort it out for yourself. Grind a tool with and without back rake and see. I'm guessing that you'll cut deeper without chattering and you'll finish finer."
https://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/#post-439051
Craig
@trlvn No offence taken at all. Apart from re-sharpening a few HSS this is my first attempt at grinding tools from scratch. I've looked at quite a few grinding tutorials and such, and for the most part the primary face angles agree but details as to back rake or not back rake vary. Going to give my grinds a test drive this morning and see how they perform and go from there.
@Dabbler I have a few tools labeled HSS COBALT that I want to regrind. Can I do that on my bench grinder?
BTB - Close inspection of the wheel I replaced revealed that is glazed. Didn't look that way when it was mounted. A good thorough dressing would probably fix it right up.
Craig
@Dabbler I have a few tools labeled HSS COBALT that I want to regrind. Can I do that on my bench grinder?
BTB - Close inspection of the wheel I replaced revealed that is glazed. Didn't look that way when it was mounted. A good thorough dressing would probably fix it right up.
Craig
Craig, I think there is lots of good advice in this thread, but also it is clear there are some nuances here that could be clarified by professionals. I had good luck with AA Abrasives / Norton in the US years ago WRT abrasives. They are one of the big suppliers. They have a toll free number as well as an online chat at https://www.aaabrasives.com/contact-us/
All the charts and numbering can be confusing I know. But I trust once you find the right wheel you will be happy and can share with us.
All the charts and numbering can be confusing I know. But I trust once you find the right wheel you will be happy and can share with us.
Dabbler
ersatz engineer
@YYCHobbyMachinist Using a silicon carbide wheel reduces the heat buildup somewhat. It can cut a little faster on cobalt enhanced HSS tools.
Both AO and SC wheels can make a HSS tool bit, even a cobalt one.
Both AO and SC wheels can make a HSS tool bit, even a cobalt one.
After having a similar experience as yours Craig I followed Leonard Lee's (of Lee Valley fame) advice and bought a soft open wheel for grinding any type of HSS and other non carbide tools.
The white 6 '' wheel is a HK2A8OH12. It does not glaze over, cuts cool and quickly. There is no more discoloration of the HSS from overheating. I was a little reluctant to spend more for a good wheel but now it looks like a bargain.
This is an example of this type of wheel https://www.kbctools.ca/products/search/1-595-38613
The white 6 '' wheel is a HK2A8OH12. It does not glaze over, cuts cool and quickly. There is no more discoloration of the HSS from overheating. I was a little reluctant to spend more for a good wheel but now it looks like a bargain.
This is an example of this type of wheel https://www.kbctools.ca/products/search/1-595-38613
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francist
Super User
I’ve been using this one recently and am very happy with it. I went directly from an ordinary grey wheel to this and skipped the white AO altogether so I can’t compare those two, but from grey to this was night and day. The grey wheel (and I used it exclusively for about seven years) always felt like it was supposed to be doing something but just wasn’t quite pulling it off. I put one tool against this wheel and went Ahhh, there we go, that’s more like it. I think this one is supposed to wear a bit better than the AO white wheels, but as I said I can’t say that for sure. Would be nice though if it did — it’s almost double the cost!
-frank
-frank
Ahhh: the sound you make when you discover the right tool.
Ok, I finally bit the bullet and got this......
CGW-PASCO,6X3/4XH 60K CGW WHITE A/O GRIND WHEEL,1-595-38613,KBC Tools & Machinery
Scratch grinding a 3/8" HSS blank now takes 10-15 min at most. Made a huge difference!!
Thanks for all the help sorting this out.
Craig
CGW-PASCO,6X3/4XH 60K CGW WHITE A/O GRIND WHEEL,1-595-38613,KBC Tools & Machinery
Scratch grinding a 3/8" HSS blank now takes 10-15 min at most. Made a huge difference!!
Thanks for all the help sorting this out.
Craig
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Tom Kitta
Ultra Member
If you want more cheap wheels for your 6" grinder PA has them on sale - 2 pack for just 8 CAD! That is by far the cheapest grinding wheels I ever saw. Note that these may not be that bad for certain uses like soft steel - the wheels are probably very "hard" i.e. they shed cutting particles rarely.
Also I noticed that Canadian Tire grinding discs, especially cutoff are made with mostly bound dust and few carborundum particles - hence why they last so little when cutting compared to say Makita brand.
Same may be true for cheap grinding stones - most of the material can be raisin with some filler and only little is actual cutting compound.
Also I noticed that Canadian Tire grinding discs, especially cutoff are made with mostly bound dust and few carborundum particles - hence why they last so little when cutting compared to say Makita brand.
Same may be true for cheap grinding stones - most of the material can be raisin with some filler and only little is actual cutting compound.