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Whats the benefit of a 2x72 belt grinder

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I have seen a lot of people using the 2x72 belt grinders, and there are a lot of plans for them. I don't get the benefit of using one vs other grinders though. Why are they so popular?

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2x72 inches is an industry standard as such there are *tons* of different belts easily and fairly cheaply available for them; cork belts, micro belts, ceramic belts, Al2O3 belts, scotchbrite belts, single lap, double lap, ....

As an analogy; you ever tried to buy european sized sheets in Lubbock? Better hope your mattress is built to a US standard size!

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Grinding belts have a significant difference from wheels in the cuttings are quickly carried away from the parent stock being ground and no part of the belt is in contact with the stock for more than a couple milliseconds. This means that most of the friction heat generated by grinding is carried away rather than building up in the parent stock. Oh it still gets hot and you can ruin the heat treat by running the temper colors but it's a LOT harder.

Another advantage over wheels is the shape of the grind. Belts are flexible and allow you to change the shape of the point of contact with the stock. For instance if you want a hollow grind like you'd get from a wheel you can pick the diameter of the contact wheel and determine the radius of the grind. Or, if you want a flat grind you grind against the platten which holds the belt flat between it and the stock. And on the far side of the spectrum you can "slack belt" which is the term for grinding on the belt where nothing is backing it so it grinds a convex curve which is a good bevel shape for heavy use blades say axes and machetes.

The last on my advantage list is clearance next to the working area of the belt, from a contact wheel, platten of slack belting there is nothing next to the belt in either direction to get in the way of grinding long stock. I have a 2" x 48" Delta belt grinder that was my main go to grinder but the motor was even with the platten so I couldn't grind anything longer than about 6" without it running into the motor unless I wanted to slack belt it. 

My new club build 2" x 72" is down to the fine bits and it'll be in operation. I'm pretty jazzed. :wub:

Frosty The Lucky.

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Once you've used a good belt grinder you will KNOW!  Wheel grinders are much more dangerous, much slower, far less versatile, inferior in nearly EVERY aspect!  

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Sharpening drill bits, lathe and similar cutters is one place where a belt grinder is NOT a good tool. No matter how tight the belt is it rides up on the leading edge of the grind in a bow wave and makes for a poor edge of the type listed above. A wheel makes for a hollow ground edge of reliable radius and more importantly a hard crisp edge.

Frosty The Lucky.

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On 7/18/2017 at 1:18 PM, Frosty said:

Sharpening drill bits, lathe and similar cutters is one place where a belt grinder is NOT a good tool. No matter how tight the belt is it rides up on the leading edge of the grind in a bow wave and makes for a poor edge of the type listed above. A wheel makes for a hollow ground edge of reliable radius and more importantly a hard crisp edge.

Frosty The Lucky.

I use mine for sharpening drill bits.  I have the belt direction moving away from my cutting edge.  I use VERY light pressure against my 10” contact wheel.  I use a fairly stiff belt with a fine grit.  It works much better for me than my old wheel grinders!  I’m sure that Frosty is more skilled than I at this sort of sharpening but I feel no need to have one of my old grinders set up.  

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I've never worked the contact wheel so my experience may not apply. "Dragging the edge", having the wheel or belt moving from behind the edge rather than towards it,  leaves a rolled edge that needs be dressed out on a stone.  Hey, I just thought of a good visual! Dragging the edge would be just like dragging a shovel on pavement. The way I was taught to sharpen would be "pushing" the edge like pushing a shovel to pick something up. Dad nor my metal shop teachers actually named the right way, they just yelled if you dragged the edge. 

That said I've always dressed the edge on the bench stone, think of it like stropping a razor for final finish on the edge. This is a must if you're cutting copper alloys, a razor edge or needle point tends to tear them so they need to be blunted SLIGHTLY to cut cleanly. There are proper cutter grind angles and I'm sure a little research would turn them up but we always just touched the edge on the bench stone to flatten it SLIGHTLY.

Drag or push does NOT apply to knife blades, a bladesmith who shall remain eternally unnamed by me as a bad guy had perfectly good reasoning for dragging knife edges on the belt. Having no counter argument I've been doing the same since. According to him, the grit plows the cut steel off the parent stock. This I know, I've seen the microscopic pics and it leaves a rolled edge as I mentioned above. This he claimed elongates the grain structure (crystallography) of the edge giving it greater flex strength.

Maybe so, playing to this can't hurt and might help and I like to hedge my bets.

Frosty The Lucky.

 

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Main advantages have been stated, and that is that the 2x72 is a standard size with a zillion belt options.  The better grinders are versatile, in that you can change between a platen, a contact wheel, or a small wheel.  Even better are the ones that are variable speed, so you can decide to screw up your knife slower or faster.

All that said, I'm in Lubbock now after 12 years in Abilene.  Come by the house and I'll show you what I'm talking about with regard to grinders.  I have a 2x42 Craftsman that I made 150 knives with before I built my 2x72.  Drop me an email and we can start the conversation.  fry custom knives at gmail dot com

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2x72 belts are easily found and fairly cheap. Have you personallty tried a 2x72? I suggest that you read the reviews to find out the difference . If you're only planning on making certain types of knive, you can get a cheap belt grinder

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