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Hal
01-31-2008, 07:42 AM
Has anyone used the diamond grinding wheels that are available from CDCO for around $60-$70 dollars?

How are they holding up and what grit did you get?

I would be finish grinding carbide tool bits.

Hal

Bill Pace
01-31-2008, 08:09 AM
I recently got one of the side cut 'medium' grit wheels for the carbide grinders, -- have only used it half a dozen times so far, but am well pleased. I was surprised at how much easier the carbide comes off!

DICKEYBIRD
01-31-2008, 08:36 AM
Hal,

Ditto what Bill said. I just got mine (medium, side cut like Bill's) last week and have only sharpened 1 brazed carbide insert boring bar that got chipped but it works great! The diamond layer is thicker than I expected and should last a very long time. Time will tell.

The medium grit is finer than I expected but still seems to cut pretty fast and leaves a great finish.

Evan
01-31-2008, 09:08 AM
Just don't grind ANY steel or you will be surprised how well the diamond comes off.

gld
01-31-2008, 12:39 PM
OK! So why does grinding a material softer than carbide cause the diamond too come off?????:confused:

We use diamond hones to sharpen knives.

I have a diamond from CDCO. have not used it yet, but had planed to use on steel..I thought diamond produced less friction thus less heat.

DICKEYBIRD
01-31-2008, 03:40 PM
It's been posted here and on other machining sites that the carbon in steel dissolves the diamond.

I assume that the wheel's speed/heat must be a major factor because there's probably thousands if not millions of hand laps and sharpeners in use every day that last a very long time; not to mention the diamond burrs and small wheels that are used on steel.

Then there's the fellow in HSM magazine that did the article series on modifying his ShopSmith. He says he uses a diamond wheel for HSS sharpening with no problem. He mentioned (if memory serves) that it causes no problem in the HSM environmnent at a reduced removal rate and that commercial usage is what kills them. Maybe his machine doesn't spin the wheel at 3450 rpm??

Anybody else have any home-shop experience to contribute?

hitnmiss
01-31-2008, 05:48 PM
I'm aware of the "don't grind HSS" on diamond wheels, something about hot steel having an affinity for carbon which it gets from the diamonds...

I do it anyway, don't have room for another grinder in my very cramped 1 stall garage shop.

I do try to rough my HSS bits on a bench grinder though, then touch the edge up on the diamond.

The way my diamond wheel is wearing I might have to buy one every decade or three.

rotate
01-31-2008, 06:09 PM
Drill Doctor uses diamond wheel for HSS and Carbide. I've use it and it works very well.

DICKEYBIRD
01-31-2008, 06:46 PM
I do try to rough my HSS bits on a bench grinder though, then touch the edge up on the diamond.That sounds like an excellent plan!

I have a Drill Doctor too but its wheel is small, doesn't spin very fast and the grit is pretty coarse. The surface speed and the heat generated is probably far less than the 6" CDCO wheel at 3450 rpm.

Endmill
01-31-2008, 07:11 PM
I used diamond grinding wheels and saws for lapidary work and on occasion often cut hardened steel, i.e. drill rode ,lathe tools etc. I use shell pella oil on both the saws and grinder. ( This provided an increase by a factor of 3 in the life of the wheels over water for production cutting of agate.) Go very slow as much heat is produced. If there is too much heat, the nickel sintering used to hold the diamonds breaks down.

Evan
01-31-2008, 07:35 PM
Diamonds are a metastable form of carbon. They eventually revert to graphite even at room temperature. The speed with which this happens is temperature dependent and at temperatures above 800 to 1000 degrees it takes only minutes to seconds. This isn't burning although diamonds will burn too. The point of contact with a grinding wheel can produce instantaneous temperatures of over several thousand degrees. That is more than enough to cause diamond to disintegrate and the presence of iron at that temperature accelerates the process by acting as a solvent for the carbon of which the diamond is made. Diamonds are not forever, contrary to advertising and movie titles to that effect.

You can grind steel with a diamond wheel if constant coolant is used or if the wheel is operated at very low rpm. I have a 10 inch diamond wheel that I run in a horizontal grinder I made and it runs at about 200 rpm. This is slow enough that it won't significantly damage the diamond to grind steel but I still avoid doing so. For grinding HSS and other hard ferrous alloys you should use cubic boron nitride wheels. They are not affected by steel and are nearly as hard as diamond. CBN wheels are not recommended for grinding tungsten carbide so you really need both.

ahidley
02-01-2008, 02:08 PM
To Rocket Scientist EVAN ;) I would think that the bonding agent is what is failing, not the diamonds. Can you explain how the diamonds are held on the wheel?

Evan
02-01-2008, 02:21 PM
That depends on the wheel. The electroplate type of wheels have the diamond encapsulated in an electrodeposited coating of nickel which is worn off to expose the diamonds in use. The diamonds begin to degrade long before the nickel does and for one major reason. Diamonds are incredibly good conductors of heat, many times better than metals so when they are heated by grinding the entire diamond is heated to the point of disintegration rather than just the contact point. The melting temperature of nickel is 2651F which is far higher than the temperature required to destroy a diamond.

Your Old Dog
02-03-2008, 09:45 AM
That sounds like an excellent plan!

I have a Drill Doctor too but its wheel is small, doesn't spin very fast and the grit is pretty coarse. The surface speed and the heat generated is probably far less than the 6" CDCO wheel at 3450 rpm.

BUMP! I just got me an eBay Shimpo DT 107 and my harbor freight tool grinder clocks at 3590 rpm +- 1 rpm :D Someone here on the board suggested the Shimpo so I want to thank them for the idea.

J Tiers
02-03-2008, 11:55 AM
The Drill Quack wheel seems to spin quite fast. it is a universal motor, with no particular limit on speed other than friction.

On the other hand, the wheel is small, electro-bonded, and Drill Quack themselves suggest that the wheel will only last a few hundred drills.

I picked up a used slow speed grinder a while back, 5" wheel, 200 rpm (Glendo). It apparently uses some form of organic binder, and must be used with water. I would imagine it would fail quickly if used dry, but probably from binder failure.

Glendo thinks the wheel will last indefinitely in a home shop if properly used with water.

DICKEYBIRD
02-03-2008, 12:03 PM
BUMP! I just got me an eBay Shimpo DT 107 and my harbor freight tool grinder clocks at 3590 rpm +- 1 rpm :D Wow! If mine does the same, I got more than my money's worth!;)