6x48 belt sander to belt grinder conversion?

I have a couple of belt sanders, 6x48, one is a Craftsman the other an import.

At one point I felt like the 3/4 HP import motor on the craftsman was just not putting out 3/4 of a horsepower....maybe in taiwan they're rating by HP by miniature horses? Either way I pulled the 3/4 HP motor in leiu of a 1.5 HP baldor and have been very happy with that conversion.

Watching a few youtube videos lately (man at arms) it strikes me that for the metal work I do, it would be a good idea for me to replace one of my belt sanders with a belt grinder, to do heavier work faster at a higher SFM. Right now both belt sanders are driven by a belt and pulleys at 1:1 ratio with the motor at 1700 RPM. It would be extremely easy for me to take a 5 HP motor I have lying around and make up a bracket to mount it where the current motor is sitting, and a trip to the local farm store to get a bigger pulley & new belt so I can run at a higher ratio to get the necessary SFM.

I'm curious if anyone here has done it and if so, did your sander hold up under the increased RPM? Is there anything else I'm missing?

Really I'm debating whether I try and repurpose existing equipment or whether I hash out the parts to make a DIY belt grinder on my lathe. Any input is appreciated.

What is the difference between a 6 x 48 belt sander and a 6 x 48 belt grinder?

I use my 6 x 48 for wood and metal. It is the kind with a motor direct driving the lower belt drum and a 12" disc, a Taiwan copy of a Delta Rockwell. The nameplate calls it a Sander-Grinder. The motor is 1 HP 3550 RPM.

Larry

L Vanice said:

What is the difference between a 6 x 48 belt sander and a 6 x 48 belt grinder?

I use my 6 x 48 for wood and metal. It is the kind with a motor direct driving the lower belt drum and a 12" disc, a Japanese copy of a Delta Rockwell.

Larry

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The SFM the belt runs at is my understanding. Regular "wood" belt sanders (which is what I've got) run <2000 SFPM and don't have much in the way of HP. Actual belt "grinders" have about 1 HP per inch width of belt and they operate at 5-7000 SFPM

This has been discussed a few times before, but my search was unable to find the thread. Pity, it had a lot of useful info in it.

The basic difference is that the mental grinder runs much faster. I can't remember the rpm ranges exactly, but I vaguely remember belt sander for wood runs around 3,000 sfm, for metal at 5,000+

And that the basic rule of thumb for grinding metal was approximately 1 hp per inch of belt width.

I have a couple of belt sanders made for wood, they don't move much metal. Can round corners and smooth burs but not much more.

I have a nice frame from an older belt sander, given courtesy of a member here, that awaits restoration. I don't think either of the belt sanders I have would hold up under the increased power.

On edit: green buggy types faster, and remembers the same rule of thumb

greenbuggy said:

The SFM the belt runs at is my understanding. Regular "wood" belt sanders (which is what I've got) run <2000 SFPM and don't have much in the way of HP. Actual belt "grinders" have about 1 HP per inch width of belt and they operate at 5-7000 SFPM

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I have a Delta/Rockwell with a 6" X 48" belt and a 12" disk. It's run by the same 1.5 hp Baldor motor it had when it was in our machine shop at work. With a 40 grit belt it removes metal as fast as you can push the stock into it. It doesn't bog down or shutter. I generally use a 60 grit belt and an 80 grit disk to keep metal removal a little slower. It's easy to remove too much too quickly when making a profile or radius.

2 X 72 Belt Grinder

This is a grinder that I mfg. 1 Hp 3450 FPM, VFD control, 8" contact wheel, flat platen assy., and small roller assy. and work rest. They work great!

I'd be careful. A Craftsman belt sander might not stand having the speed doubled. There are pot metal parts,like the rollers and adjustment parts. How about the bearings?

I "convert" my wood belt and disk grinders to metal, by withdrawing the piece of wood and replacing it with metal.

Oh, and disconnect the wood dust collection hose and replace with vac collection when doing metal.

In other words, the same machines and the same experience as "projectnut." I have two of these units; one with a 40-50 grit and the other with a 60-80 grit on the disc.

Many years ago I ran one of those up to 5500 SFM and quickly found out that it wasn’t such a good idea. Poor balance, not enough crown for tracking during aggressive use, poor tolerances running on 841 bronze, no exposure to the edge of the belt, no slack area for blending, etc. It didn’t get used much. I built a simple 2x48 5400 SFM two-wheel grinder that addressed the shortcomings of the converted one and it is one of the most useful and used pieces of equipment in my shop. I actually converted the old one back to wood and it now lives in the wood shop.
Don’t do it, it’s a trap! The same goes for converting a wood band saw. They both work but you can do better, much better.
I see that some of you are thinking, what’s the big deal, grinder, sander it’s the same difference. You folks owe it to yourself to see what a couple horse, 5000 + SFM grinder equipped with a 40-grit zerconia belt can do. Stock removal rates are much higher than double the sanders rate, amazingly higher.
Mike

mf205i said:

. . . Stock removal rates are much higher than double the sanders rate, amazingly higher.
Mike

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With the same media (e.g. zirconia) and with motors pushed to just below stalling at, say, 3000 and 5000 sfm, I'd expect the metal removal rates to be much more closely proportional to HP than surface speed. In the case noted above we're going from 1.5 hp for the 6" wide combo unit to a 2hp belt grinder.

A dedicated belt grinder usually does have other advantages, such as a variety of wheels and platens. Many (at least mine) are 2" wide and that alone offers faster spot removal rates over the 6" wide unit the OP is asking about. It should both feel and be faster simply because of what amounts to a greater depth of cut when a max of 2" of metal is involved versus 6".

The point is, upping the surface speed a bit is surely of some use -- but it isn't going to more than double the removal rate on metal if the same 1.5 hp motor is left in and fully utilized.

FWIW, I use the disk portions of the various sanders I have for both wood and metal. For these the surface rates is already around 5000 sfm at the periphery (with a 1750 rpm motor). The 6" belt portion is, indeed, too wide and thus too slow for any sort of aggressive metal removal with more than a very few square inches in contact. On the other hand (actually in the other hand) the portable 3/8, 1/2 and 1" belt sanders I have don't go faster (sfm), but feel just fine in various metal removal tasks simply because of the smaller contact area.

Mike's other points at why you don't want to double the belt speed of a typical 6x48" belt sander are well taken. Too many of these already have poorly tracking belts eating through the guards -- no need to do that at twice the rate.

Hi PeteM, it’s interesting that our experiences are so different. My grinder runs at 5462 SFM on high and has a slower speed of half that. On high as I increasingly apply pressure to the cut, I come to a point that the material removal rate rapidly increases. The removal rate is not linear to the amount of pressure, it just takes off. I have always assumed that it had something to do with the amount of heat generated at the intimate junction of the tool to the work. I have never seen this happen while on half speed or when trying to use my wood belt sander on steel. Believe me, I tried.
A belt grinder is one of those tools that have a low perceived value, until you have one and then they become indispensable.
Have fun with it, Mike

mf205i said:

Hi PeteM, it’s interesting that our experiences are so different. . .

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Someone here may know if abrasive belts have some sort of thermal interaction with metal that leads to dramatically higher removal rates once cutting speed goes to some preferred level?

One might envision an abrasive belt as a sort of carbide turning tool, but with thousands of tiny edges. With metal turning, getting metal into a plastic deformation range does slightly increase productivity compared to the same HP cut at lower speeds (but the equivalent of greater depth or feed to keep the HP equal). The bigger issue is often a built up edge at lower speeds, which screws up geometry and can also lead to chipping. It's possible, of course, to load up abrasives - the analog to a built up edge -- which might be an issue when you're running at half speed?

Anyhow, my guess is that doubling belt speeds doesn't double metal removal rates IF the same HP cuts are taken and you don't inadvertently load up the belt. Someone else might chime in if they've seen studies about dramatic increases in metal removal rates if the temperature goes up to very high levels. In my case, I've long since stopped handling the workpiece when it's over a couple hundred degrees.

PeteM said:

Someone here may know if abrasive belts have some sort of thermal interaction with metal that leads to dramatically higher removal rates once cutting speed goes to some preferred level?

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As the speed and power input into the workpiece increases, perhaps the surface heats enough to soften/melt so that it's much easier to cut through.

Noah Katz said:

As the speed and power input into the workpiece increases, perhaps the surface heats enough to soften/melt so that it's much easier to cut through.

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Arrfff...I hope you're just being silly Mr.

Stuart

Nope.

What's silly?

Even at low SFM some white-hot (melted) particles are thrown off.

atomarc said:

Arrfff...I hope you're just being silly Mr.

Stuart

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Noah Katz said:

Nope.

What's silly?

Even at low SFM some white-hot (melted) particles are thrown off.

Click to expand...

Maybe 'cause you dredged up a qty (5) year old thread to add what ?

I came across this thread researching belt grinders.

I thought the question of sudden increases in material removal rate at higher SFM was interesting and as yet unanswered, so I offered what I believe is a plausible explanation.

What's your excuse?

Sounds like friction sawing steel sheetmetal on a bandsaw. Slower speeds don't cut, you have to wind it up to generate the heat.

Right; they make circular saw friction blades as well.