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PostPosted: Tue Apr 29, 2008 1:34 am 
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Part I: Mini Gloat

Well, I've been casually looking for a carbide grinder for some time. No rush, I use HSS for most everything, inserts for most of the rest, but there is just no (practical) getting away from cheap brazed carbide for certain situations. Not to mention I keep finding or being given brazed carbide bits along the way. So far, I've been borrowing a very generous friend's Baldor and diamond wheels to touch them up (or repair them) as needed, but it's high time I had one myself. I considered a HF "kit", and cheap CDCO wheels, but I have enough frustration in my life already. Not to mention, I LIKE the feel of nice tools. So when I got a chance to pick up a low hours Baldor with both a fine and coarse good quality diamond wheels mounted for less than what 2 good wheels cost, I snapped it up. Only down side is what use it had was with the drip system working. <sigh> What a mess. I don't care anything for restorations and paint, but I can't tolerate built up grime and sludge. But it's ok, all clean now...

Part II: The question.

I really don't know anything much about "proper" grinding of carbide. And I don't recall the angles used on my friend's grinder, and he's out of town now. What clearance is typically used for standard brazed C6, C5, and C2 brazed carbide lathe bits? I know I have to (now that I can) vary based on boring and fly cutters, but what are the general rules of thumb? Seems like I recall 7*? But this is something I've largely ignored up till now, and I would rather not have to guess or experiment. I'm sure it's been covered, but search hasn't produced much.

Also, carbide being carbide, and not suitable for "off hand" grinding, I'll probably also build a protractor for it as well.

Oh, and I also remember advice to "break" the sharp edge with diamond lap to provide a few thou flat in order to prevent premature chipping and edge failure. And clear the steel before using the diamonds on *carbide only*.

Any other advice for a relative carbide sharpening newbie?

Tricks to clean wheels?

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 Post subject: clearance
PostPosted: Tue Apr 29, 2008 11:47 am 
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Location: Castlegar. BC, Canada
I usually shoot for about 5 degrees clearance. Someone else will hopefully tell you how to clean the wheels, never bothered myself. Peter


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PostPosted: Tue Apr 29, 2008 2:42 pm 
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BadDog wrote:
What clearance is typically used for standard brazed C6, C5, and C2 brazed carbide lathe bits? I know I have to (now that I can) vary based on boring and fly cutters, but what are the general rules of thumb? Seems like I recall 7*? But this is something I've largely ignored up till now, and I would rather not have to guess or experiment. I'm sure it's been covered, but search hasn't produced much.

Slightly reduced angles that would be commonly applied when grinding HSS are acceptable. The premise is that carbide lacks the tensile strength of HSS, thus is subject to failure by cleaving the edge when it isn't well supported. Carbide of today is far better in that regard, so you could actually get by with identical relief angles under most circumstances. To insure longevity of your tools, a slightly smaller angle is desired. No hard, fast rules---it's different for leaded brass as opposed to tool steel.

Quote:
Also, carbide being carbide, and not suitable for "off hand" grinding, I'll probably also build a protractor for it as well.

Carbide is best ground from a table, with a constant angle, so a protractor attached to the table is a good idea. Mine isn't so equipped, so angles are a random selection. What is most important is that you get a straight grind on the tools, which isn't easily accomplished with free hand grinding. Rounding of the cutting edge is a common problem, likely due to the nature of using a flat wheel as opposed to one with a radius. You likely don't have that problem when sharpening HSS. I know I don't.

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Oh, and I also remember advice to "break" the sharp edge with diamond lap to provide a few thou flat in order to prevent premature chipping and edge failure. And clear the steel before using the diamonds on *carbide only*.

I'd lose that idea, and fast. I think you'll find that the tools you'll grind are not negative rake, but positive in nature. The principles of machining with one system as opposed to the other are totally different.

While it's true that a tiny flat on the cutting edge of negative rake will prolong tool life, the opposite is true with positive rake. Negative rake cuts behind the edge, while positive rake cuts with the edge. Anything you do to reduce the sharpness of the edge will manifest itself in terrible finishes and the inability to take fine cuts. What is important is that the cutting edge be very finely finished, so it has no minute chipping. That's what's wrong with grinding carbide with green silicon wheels. If your grinder has both rough and fine diamond wheels, as you reported, I think you'll find that the finish that comes from the fine wheel will be more than adequate. I've used only one wheel for all of my carbide grinding as long as I've owned my own shop----a 220 grit wheel. It roughs quickly, and leaves a surface that is very acceptable. I avoid altering the cutting surfaces by any means, which I've found to be degrading, never an improvement. I think you'll find you get the best performance from your tools when used as they come from the grinder.

Do avoid grinding the support steel under the carbide. Relieve it with an aluminum oxide wheel to avoid shortening the useful life of your diamond wheels.

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Tricks to clean wheels?

Check one of your tool supply catalogs for dressing sticks for diamond wheels. They're usually a very fine grained, soft bonded aluminum oxide stick, similar to those used for dressing aluminum oxide wheels. Such a dressing stick should be applied sparingly to your diamond wheels. Run your wheels with flood coolant and avoid grinding steel and they'll actually perform quite well without dressing (cleaning). I highly suggest you replace the drip system with a small pump, to keep the wheels wet at all times when in use. Drip is not adequate.

Harold


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PostPosted: Tue Apr 29, 2008 10:26 pm 
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Thanks, that gives me something to start working with.

However, I'm a bit concerned about the "run it wet" part. How critical is this? I know several folks (including the guy who's grinder I've been borrowing time on) who run these diamond wheels dry. Seems to work fine, but than what do I know? I do know I need to keep the pace/load moderate and generally not over-heat things, certainly not dip them hot, but much like coolant on the lathe, I didn't think coolant was really a necessity. Am I really that far wrong?

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PostPosted: Tue Apr 29, 2008 11:10 pm 
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I'd like to chime in here.
I have never seen a diamond wheel (Baldor style grinder) run wet. (I run mine with drip/spray).

My concern is flinging coolant all over everything, and perhaps coolant goo.

Harold, a mini tutorial about flood coolant for diamond wheels, or a link to a past post would be appreciated. Also, if using flood coolant, is there still the prohibition on grinding HSS. (I'm not talking about hogging, just the final kiss.)

Dave

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PostPosted: Wed Apr 30, 2008 3:14 am 
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mechanicalmagic wrote:
I'd like to chime in here.
I have never seen a diamond wheel (Baldor style grinder) run wet. (I run mine with drip/spray).

My experience with such grinders is limited to wet grinding only, aside from very recent happening. We had a Hammond where I was trained, and it was full flood. When I started my shop, I built one, keeping the design of the Hammond in mind. I provided flood coolant.

The recent happening of which I spoke is one where I have used my diamond wheel dry, for my shop is not in full operation. As a result, I haven't filled the coolant tank because the grinder is not in service. Fact is, the picture, below, is one taken where it sits in storage, obvious by the clutter that surrounds the grinder. I've used it only a couple times to put an edge on a fly cutter needed for a project in support of the house building project that has dominated my time. The difference between wet and dry grinding is like day and night. One of the biggest problems that has become more than apparent to me is the loading of the wheel. Run wet, they rarely load. I use a resinoid bonded wheel, which is the wheel of choice for tool bits.

Quote:
My concern is flinging coolant all over everything, and perhaps coolant goo.

Most diamond wheels are recommended to be run wet, although I can appreciate your concern. My attitude is that if you intend to make an omelet, you must break a few eggs. My shop is intended to serve me and my needs. I can't allow the worries of a little spray to interfere with better performance. It is for that reason that I have run coolant in my lathe. Like in grinding, for me, it isn't a luxury, it's a requirement. YMMV. :-)

I use a small pump, and deliver a constant stream of coolant to the center of the wheel. The discharge is a 3/16" copper tube, with a valve, so I can regulate the amount of coolant dispensed. Even roughing, a full stream isn't required. My wheel has a shroud, so nothing is thrown from the sides, although a small stream can deflect from the top of the tool being ground. A well placed finger deflects the stream back to the table. When grinding wet, rebuilding a chipped edge is nothing-----happens in seconds. Diamond wheels have propensity for moving hard substances quickly, as long as you can keep the wheel cool, and free of loading.

I've posted a picture of my diamond grinder, below, so you can see how I've made provisions for running coolant. A fine mist radiates from the grinder when in use, but there is no puddling on the floor. The coolant reservoir holds less than a gallon of coolant, so losses can't be tolerated. When I was actively machining, coolant losses were from evaporation, not dripping.

Quote:
Harold, a mini tutorial about flood coolant for diamond wheels, or a link to a past post would be appreciated

Sadly, my experience with carbide grinding is limited to that which I have done on my own. I have had no formal training in the art---unlike cutter grinding of HSS. I have simply emulated that which I witnessed in the shop where I was trained. I don't know that I'd feel right in suggesting what others should do, but I can guarantee you one thing----if you follow what I've talked about here-----you won't be disappointed. I know what I do works, and works exceedingly well. So well, that I have never been concerned with making any improvements.

For the record, there's no way in hell I'd consider running a diamond wheel dry on carbide. It just 'ain't gonna happen'. :wink:

Quote:
Also, if using flood coolant, is there still the prohibition on grinding HSS. (I'm not talking about hogging, just the final kiss.)

Dave


It's your wheel, so I'd be out of line telling you you shouldn't be doing any such thing, but if my logic appeals to you, it's like this: diamonds are carbon, which is readily absorbed by iron at high temperature. This isn't speculation. Norton did considerable research on the subject in the 50's, and it has been documented.

In spite of cooling, the temperature at the interface of the wheel and tool is great enough to cause diamond to be dissolved. Dressing a wheel at red heat does not harm a diamond----obvious when an 8" wide (or greater) wheel of a centerless grinder can be dressed with no problems, so there is obviously something going on that is out of the ordinary.

The harm isn't in the tool, but the loss of sharpness of the diamonds in the wheel. When the edge is gone, the diamond ceases to function properly, and performance is restored only by dressing the wheel. That shortens the life of diamond wheels considerably, for the surface of the wheel is eroded, exposing new diamond and liberating the old. It is for that reason that I suggested in my previous post that diamond wheels should be dressed sparingly.

You can conclude that if you slow down the wheel, all of that changes. If the surface speed is too low to create a red heat at the point of contact, diamond will do an admirable job on HSS tools. It is for that reason you see diamond lapping machines for toolbits. The wheel is slow speed, so the diamond isn't harmed.

Harold


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PostPosted: Wed Apr 30, 2008 10:38 am 
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Harold_V wrote:
A whole lot of good information.


Thanks Harold.

Now, if we could only get a "Best Of" forum.

Dave

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PostPosted: Wed Apr 30, 2008 12:02 pm 
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Well, I assume the clogged clotted accumulated mess that I found on my grinder was due to the use of "drip" coolant. At least yours looks clean, and presumably the flood coolant washes away the contaminant rather than letting it accumulate. I do have a small coolant pump/tank with settling compartment that came with my lathe, capacity of about 2 gallons tops. That might work if I can come up with some stainless shielding. But with 2 wheels in play, and needing access to both (abandone one?), that complicates things. Hmmm...

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PostPosted: Wed Apr 30, 2008 2:25 pm 
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BadDog wrote:
Well, I assume the clogged clotted accumulated mess that I found on my grinder was due to the use of "drip" coolant.

I can't help but think that the resinoid bond of the wheel is being overheated by running with a drip system, which likely isn't used routinely because "I just have to touch up the tool". In my mind, especially after my recent experience of grinding dry, where that was exactly the case, the end results are horrible. What has likely occurred is the swarf has been combined with the bonding agent (from heat), to form a new surface on the wheel. It cuts very poorly, by the way.

Keep in mind, the majority of this type of grinder is equipped with silicon carbide wheels------they were not necessarily intended to be equipped with diamond wheels. I firmly believe that's the reason for the drip system, which is, for all practical purposes, totally useless.

I've used diamond wheels for an eternity. When they're loaded, they feel 'greasy', failing to cut well, if at all. A simple touch with a dressing stick and grinding is improved immeasurably.

Something as simple as grinding the base steel under the carbide will change the cutting characteristics of the wheel----so running it dry has to effect the wheel beyond belief.

I've already commented that it isn't my right to tell you how to operate your equipment, but, in this case, please follow my lead and run your wheels wet.

Quote:
I do have a small coolant pump/tank with settling compartment that came with my lathe, capacity of about 2 gallons tops. That might work if I can come up with some stainless shielding. But with 2 wheels in play, and needing access to both (abandone one?), that complicates things. Hmmm...

I used a piece of pipe to make my coolant tank, welding a plate to one end for the bottom, and a piece of angle to the side for use as a mounting bracket. You can do something similar, to keep the tank out of the way. You can see mine in the posted picture, just below the pan. Not suggesting you should duplicate my design, but maybe use it as a guideline for one of your own creation. It has served me perfectly well for years.

As luck would have it, a 1 gallon plastic jug is a snug fit in the pipe, so I use one, cut off just below the top taper, to line the sump. When it gets too dirty, I simply remove it and replace it with a new one. The volume it contains is more than adequate, so you could do something similar. My pan is welded from 16 gauge stainless. Deflectors are made from the same material, but simply held to the pan with screws. You could discharge from both sides to the common coolant tank with a couple ½" hoses. Don't use small diameter tubing on the collecting end-----it's easy to get plugged with refuse.

Quote:
But with 2 wheels in play, and needing access to both (abandone one?), that complicates things. Hmmm...

I use only one, and it serves me perfectly well. You may notice I have an aluminum oxide wheel on the opposite end, for HSS. Just a thought.

Harold


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PostPosted: Wed Apr 30, 2008 2:33 pm 
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Thanks, great ideas I'm going to be looking into very soon.

And the crud is not on the wheel surface, but rather around and under them. It's the typical mud-like grunge seen accumulated on surface grinders and the like (or in the wheel wells of a truck run in heavy mud). The wheel surface itself seems rather clean and not greasy. I tried a few cuts, and the coarse (medium?) side cuts agressively while the other side polishes nicely while still cutting at a decent rate. So I think the wheels are ok.

A friend also gave me a chunk of "white stone" (what he called it) a while back. He gave it to me when I mentioned my diamond laps were getting loaded. Would this be the same dressing stick used on diamond wheels?

I'll be looking for some stainless sheet and other components. :D

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PostPosted: Thu May 01, 2008 3:05 am 
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BadDog wrote:
And the crud is not on the wheel surface, but rather around and under them. It's the typical mud-like grunge seen accumulated on surface grinders and the like (or in the wheel wells of a truck run in heavy mud).

The swarf from carbide is particularly bad. Tends to set up hard, and is difficult to remove. That's one of the reasons I was pleased to find that a gallon jug fit my reservoir. I have a few lengths of 3/4" angle iron in the bottom -(like this--▲) which becomes the base for the pump, keeping it off the bottom. When it gets filled with swarf, I toss the bottle and use another. It's the simplest method I've found for handling the mess from grinding carbide.

Truth be know, the swarf has value, but a home shop isn't likely to generate enough to make it worth the effort to recycle.

Quote:
The wheel surface itself seems rather clean and not greasy. I tried a few cuts, and the coarse (medium?) side cuts agressively while the other side polishes nicely while still cutting at a decent rate. So I think the wheels are ok.

Certainly sounds like they are. If they're resinoid bonded, the surface should resemble dark chocolate-----if they're black, they're coated----and will cut much faster when cleaned.

Quote:
A friend also gave me a chunk of "white stone" (what he called it) a while back. He gave it to me when I mentioned my diamond laps were getting loaded. Would this be the same dressing stick used on diamond wheels?

It certainly sounds like it. Quite soft? 1" square? Fine particles?

Quote:
I'll be looking for some stainless sheet and other components. :D

Luck!

I'd like to hear your views when you get the project completed.

Harold


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