Sharpening HSS w/diamond---'thought that was a no-no

[Arthur.Marks]

I have acquired the impression that all diamond wheels are unsuitable for (primary) use on HSS (or steel in general). So why aren't these?

"GRS Power Hone uses diamond wheels to sharpen hardened steels, high speed steels and carbides. You can now choose the best tool material for each job because you can sharpen them all."

http://www.grstools.com/tool-sharpening/power-hone/power-hone-basic.html

Can someone explain the apparent contradiction?

[kendall]

Think it would primarily depend on the surface speed. Slow speed makes a diamond great at sharpening.

[Arthur.Marks]

The manual lists 240rpm for the spindle with a 5" diameter wheel (diamond) or 6" diameter lap (ceramic).

[Black_Moons]

Yep, surface speed... I wonder if anyone can figure out exactly what SFM before diamonds start to (quickly?) dissolve into steel/hss?

(Its not the heat of the wheel, but the heat of the microscopic point of contact)

Sorta like how over 100SFM with HSS verus steel tends to degrade the HSS quickly, even though the bulk HSS does not heat up much, the atoms at the actual cutting edge become superheated untill they lose strength. (At least, I think thats why higher SFM degrades HSS?)

[lynnl]

I think the whole notion of steel grinding quickly eroding diamond stones/wheels is largely a myth, or at least greatly oversold. Industry does it all the time.

[Evan]

I think the whole notion of steel grinding quickly eroding diamond stones/wheels is largely a myth, or at least greatly oversold. Industry does it all the time.

It's not a myth according to Norton. Industry uses flood coolant.

http://www.nortonindustrial.com/uploadedFiles/SGindnortonabrasives/Documents/Catalog_PDFs/NortonSuperabrasives-NortonToolroomWheels.pdf

[.RC.]

Diamond wheels cost what $20 a pop..... CBN costs probably $100 a pop... (they are bloody expensive compared to diamond)

I go with diamond...

[Arthur.Marks]

So what I am hearing is that there is a generalization of warning being made. Just about every bench grinder, so-called 'carbide grinder', surface grinder or T&C grinder runs at or above 1800rpm---and more often at or above 3600rpm. Given this, the generalization is to never use diamond wheels for sharpening... on such a machine. The more accurate warning is to not use diamond wheels above __ sfm while grinding HSS/steel. Below ___ sfm diamond is quite useful for sharpening HSS/steel. I can follow that. I mean, diamond paste is routinely used for final lapping and honing which is a low-speed operation. For example, brass expanding lap used with diamond paste to finish a hardened steel bore.

[Arthur.Marks]

Diamond wheels cost what $20 a pop..... CBN costs probably $100 a pop... (they are bloody expensive compared to diamond)

I'm not sure what is implied with your statement with regards to CBN (cubic boron nitride). I have seen this designation, but I know next to nothing regarding its use.

[EDIT] Okay, reading further into the Norton link, I see they recommend CBN for use on HSS. Got it.
"Norton B99 cBN Wheels • Sharpening high-speed (M2,D2,T15,etc.) steel cutting tools • Surface and ID grinding hardened steel die components • Precision grinding steel parts Rc50 or harder"

[Tanto]

Diamond is commonly used for sharpening HSS in industry and consumer products. The Drill Doctor is one example everyone here would be familiar with that uses a diamond coated wheel. Many commercial T & C grinders are now also sold with a diamond wheel as standard.

[John Stevenson]

In theory it's probably correct.

In practice the problem doesn't occur. I have had a 4" diamond grinding wheel on my T&C grinder now about 4 years now and can't see any degrading from new. In fact I bought a spare wheel expecting this not to last.

Even if it only lasted a few months, at £10 a pop they are just consumables but this is not happening.

[ammcoman2]

+1 with John's comment.

I use 4" diameter diamond wheels running at about 3400rpm on my home made T&C grinder. Also have a 3 3/4" CBN wheel. They are #150 grit and the results appear to be very similar. I am not, however, running at "industrial rates of removal". I can't tell if there is any difference using the diamond wheels on carbide or HSS.

There may be a difference using a 6" wheel at these speeds but I am not planning a test any time soon.

Geoff

[davidwdyer]

That GRS power hone looks like an extremely over priced little thing. I believe many lapidary shops or catalogs would sell something equal for much less.

[Arthur.Marks]

Am not interested in the machine itself. I was just baffled by the diamond wheel use description.

[Evan]

So what I am hearing is that there is a generalization of warning being made.

No need to get really fussy about it. If a diamond wheel is throwing sparks on steel then it is getting hot enough to damage the diamonds faster than normal.

A lot depends on the wheel itself. Electroplate diamond wheels will withstand cutting steel better than resin bond wheels. The electroplate wheel has the grit in close contact with the metal substrate which helps keep the diamonds cool.

Diamonds are a metastable material which means that the stability is temperature dependent. Diamonds eventually revert to graphite even at room temperature. At room temperature it takes a very long time, many millions of years. At elevated temperatures at around 1000F they last only minutes. Higher than that they break down very rapidly in seconds or milliseconds.

What helps to save them is that diamond conducts heat about 4 to 5 times better than silver. This helps to keep the cutting tip cool by transferring the heat to the bulk material around the diamond.

What affects the lifetime of any particular diamond wheel used on steel is a number of variables. The higher the grit concentration the better the wheel dissipates heat to the substrate. This is especially the case with resin bond wheels and the cheap wheels have low concentrations of maybe 50%. High quality wheels will be 75% to 100%.

At 100% the binder fills only the gaps between the grit which is packed as tightly as possible. This greatly improves conduction and these are the types of wheels used in industry.

Also, industry uses flood coolant when grinding and that keeps the temperature of the grit under control.

Blanket statements about what industry uses are meaningless without qualification as to what industry really uses.