Disk sanders?

I've been looking at power sanders. The combo disk/belt sander seems pretty popular but I'm having a hard time figuring out what you do with the disk part. Or rather, what you can do with the disk part that you couldn't with the belt part. And once you've decided the disk part is rather pointless, why not spend the same money and get a much bigger belt-only machine (like a 6 x 89 belt sander).
Am I off on the wrong track? Is a disk sander something that's actually useful in wood shop?
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"Roy Smith" writes:

If you ever decide to build a boat, you will find no other piece of equipment that can do the job of a good disk sander.
Most of the combo units I seen leave a lot to be desired IMHO, but OTOH, a disk sander can do magic.
As an example, a disk sander will allow you to cut a wheel form flat stock and then sand it to a perfectly round circle.
Sand the end of a piece of molding free hand to some weird shape. It's disk sander time.
I built mine from about 1/2 sheet of 3/4" ply, an old motor and a 12" disk from an old ShopSmith. (Took the plans straight out of Fred Bingham's book).
Like American Express, don't leave home without it.
OTOH, my experience is the belt on those combo sanders walks all over the place, and in general does a poor job.
YMMV.
HTH
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Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
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I'm missing something here. I bought a belt/spindle combo over the disc/belt combo because I thought it somewhat redundant. Especially the smaller ones.
A wide belt moves in one direction. I can hold a piece of wood against it and get a flush, smooth surface. I can move the wood free hand and round corners, bevel edges, etc.
A disc rotates and one side is going up, the other side is going down. It has a 12" cross section and larger overall area than a belt. (my 24" belt is probably 11" exposed at best, 4" high), but does it really do more or different things? Is the circular pattern better for some sanding?
How does the disc sander make a perfectly round wheel? Are you rotating the piece as you push it against the disc? If so, why would a belt not do the same?
The little 1" belt and 5" disc combos looked rather like toys to me and close to useless in a shop, but they make them and people buy them, so perhaps they have some value. Ed snipped-for-privacy@snet.net http://pages.cthome.net/edhome
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"Edwin Pawlowski" writes:

A disk sander is sanding across the grain rather than with it when using a belt.
It provides rapid, accurate stock removal with a minimum of heat build up.
And yes, you mount the wheel blank on an axle pin that is mounted in a miter bar that is clamped in the table.
The blank is then rotated to finish size.

Yep, they sure are cute. Have used the 1" belt to sharpen a pair if scissiors a time or two.
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Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
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OK, that makes a lot of sense. Thanks for the explanation. Ed
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Isn't that just a function of how you put the piece of wood on the belt sander table?

Why any more so than a belt sander? If I put the same grit on both kinds, won't they remove stock at the same rate? Is there any reason the disk should be more accurate?
Is there any reason a disk should heat up less than a belt? In fact, it seems like the belt should heat up less, since a belt (even a short one like a 6x48) has much more total surface area, so the spot that was just touching the wood has more time to cool off before it's touching wood again.
I'm not trying to be argumentitive here, I just don't understand why all these things you can do with a disk sander can't be done as well with a belt sander just as easily?
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http://pages.cthome.net/edhome
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I wrote:

"Roy Smith" asks:

The answer is a definite "maybe"; however, most of the time a disk sander will be operating across the grain.
I wrote:

"Roy Smith" asks:

In addition to sanding across the grain, the disk paper is uaually crossing the wood at a higher rate of speed than with a belt.
The disk also has a more limited contact surface than a belt. Think of it as a line of contact.
This will result in faster and more accurate stock removal.
"Roy Smith" asks:

Yes, since the surface area in contact with the sand paper is smaller when using a disk, less heat will be generated.
"Roy Smith" asks:

It's just the opposite. The material being sanded is the source of the heat, not the sand paper.
"Roy Smith" asks: >

No problem.
IMHO, a belt sander, unless it is the type found in cabinet shops having a cost around $1,500-$2,500, is not a very useful tool.
HTH
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Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
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Gotta do some thinking here.
A given section of belt is in contact with a long edge _much_ longer than a given section on the disk takes to go across the piece.
Then there's the insulating graphite under the belt, rather than the heat sink aluminum under the disk....

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Roy Smith wrote:

Don't ask me for the science. All I have is real-world experience. A disc is *much* faster than a belt at the same grit for dealing with end grain.
A disc is not a good choice for sanding the face of a 12" long board. Either a disc or a belt could be used to sand the end of such a board, so I think comparing end grain to end grain is reasonable.
Why is it so? I'll make an educated guess.
The motor turns both parts of a combo machine at some fixed speed. I don't know what speed it is off hand, but let's call it 2,000 RPM for the sake of argument.
The 6" disc is spinning at 2,000 RPM, and so is the ~4" power roller on the belt. I have no idea off hand how to calculate the difference, but any idiot can see that a point on the outer edge of the disc is travelling much further than a point on the outer edge of the roller in the same span of time. It's spinning the paper right along with it, so I would expect the surface feet per minute of abrasive making contact with the wood is higher with the disc.
People who aren't math retards feel free to step in and explain this with all kinds of mind boggling formulae. Maybe I'm not looking at this right. There's got to be some allowance for the fact that every point along the width of a belt is moving at the same speed, while a disc is slower toward the "eye," so that probably mitigates my point somewhat.
Anyway, I have no real idea why it's so. Just experience that it is.

End grain to end grain, my experience is that the disc will heat up much faster. Probably because it's moving more abrasive in the same amount of time and cutting faster. Probably. :)
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Michael McIntyre ---- Silvan < snipped-for-privacy@users.sourceforge.net>
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You are right.

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I'm lucky enough to have a 16" Apex Patternmakers disc sander in my shop and use it for everything wood or metal. I can trim angles on any materials as accurate as I can set the machine up and it's great for sizing parts to exact length. I've had discs from 8" to 16" now and think 12" is about the minimum size that useful, the bigger the better.
Ed Angell
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OK, I understand that you can do those things on a disk sander, but could you not also do them on a belt sander? Is there something special about the disk that makes it better for these things than a belt?
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Speed. Since the disk sander is usually cutting cross grain it will remove material much quicker than a belt which is cutting with the grain. This feature, plus the others mentioned, is why large disk sanders are the standard in pattern making shops.
A large disk sander fitted with 40grit paper makes an excellent metal removal tool.
WRT to your other question regarding making circles, yes the material is rotated as its held agains the disk. No elaborate jigs are required as long as your layout line is plainly visible. A surprising amount of accuracy can be achieved with a good eye and steady hand.
Ideally, to cover all eventualities you'd want a disk, belt and spindle sander. All serve different functions. If 3 machines isnt an option you need to examine the type of work you do and fit the machine to that.
For the grandmother of disk/spindle sanders see http://www.statemfg.com
No connection, just a very satisfied user here.
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You folks have all missed a very important feature of a disc sander. Since the abrasive is ridgidly attached to the disc it had little or no standing wave just before hitting the workpiece. A belt sander has a standing wave and can and will roll the entry edge of the work. Belts are slightly more economical then discs as there is less waste in the manufacturing but I sure wouldn't have a shop without both. Sanding external contours on a disc is generally much easier then on a belt while internal contours lead you to the drum of the belt sander. Leigh@MarMachine
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Roy - A disc sander is IMHO a very good tool, provided it is of sufficient quality to be safe accurate and fast. I just side lined my combo belt/disc sander for the new JET 708433 12". In just the past week, I have used it a great deal and have not fired up the combo once. If forced to toss one or the other it would be the combo without hesitation.
Dave
Jet disc sander. (Amazon.com product link shortened)

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Roy Smith wrote:

You're not really on the wrong track. It's a good question to ask.
As others have said, the main thing a disc gets you is speed. Real world example, making trucks for BRIO-style train parts. The ones I make are rounded gently to a sort of plateau at the top. I could produce this shape in other ways, but the disc on my combo sander rips through these little pine blocks in a few seconds each. Brrrt, brrrt, done.
Another use is squaring stock. Say you cut a dowel freehand with a backsaw or something, and the end isn't quite square. Slap the miter gauge on the table, hold the dowel against the fence, and sand it square in no time. Also useful for squaring the ends of angle iron and such.
Having said all that, these combination machines aren't as useful as they look. I will probably buy another one when this one dies, but that's because I lack space. If I had space (and money), I would get a dedicated 12" disc sander and a big belt such as the one you're asking about. The 36" belt is really too short for work of any size at all. If you keep the safety fence on the back, you only get to use 3/4 of the length. You have to watch out for rounding long stock in the middle with the crown on the front roller too.
The effective length of work that can be sanded in a tidy, secure fashion is something shy of a foot, I'd say. A bigger belt would be *considerably* more useful if you make anything human-sized. They're great for small projects, but near useless for furniture. Not much good for larger picture frame parts either.
Now that I've discovered the joy of hand planes and scrapers, my belt/disc sander sees more use for regrinding chipped up bevels on plane irons than anything else. I rarely sand wood with it anymore.
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The 6" belt, 12" disk JET or Delta combos are sturdy, have real trunnions on the iron tables, and can be set with precision to use circle-sanding or even miter-sanding (so long shooting board) jigs. While the most useful part of the combo is the disc, there are certain applications like reducing proud dovetails or box joint ends where the belt does a more reliable job.
The safety stop gives full use of the platen, which is the only reliable part anyway, though I mostly keep the iron table on mine for square.

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George wrote:

Hrm... Didn't know that. I know the machines you're talking about. About $250ish on sale? Indeed, one of those critters would be a good step up above my 4" belt 6" disc jobbie.
No more than I use it though, I'd still rather sink the cashola into more hand planes and related whatnots though.
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Roy Smith wrote:

Yes.
Yes.
UA100
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