I've searched the archives on r.w. and the internet about building my own drum sander, but one question remains about the operation these sanders:
Let's say I build a 20" wide unit. Am I able to sand a 40" wide piece by sending it through twice, or will a sanding line develop? If I can't do this satisfactorily, is a 20" useful enough to build?
Thx.
I saw an interesting home brew setup at a local artisan (Keith Allen). He had a long sanding belt (6 to 8 inch wide) strung over a sliding table that slid crossways back and forth under the belt. The belt was driven directly by a 1/2 HP motor with a 4 inch drive. In operation the workpiece would be blocked up so it was slightly below the underside of the belt and he had a pressure block that he moved by hand on the inside of the belt to apply varying degrees of pressure. So he would work the pressure block along the inside of the belt (lengthwise with the workpiece) while sliding the workpiece from one side to the other so the full length and width of the board could be sanded. The sanding rate was a function of grit (which I think he never changed) and the amount of pressure he applied with the pressure block. The length was limited by the length the belt (I think he could sand something up to six feet long) and the width was limited by how far he could reach with the pressure block.
A very interesting and relatively easy thing to build.
TWS
Unless you have a source for metal casting, it's going to be VERY DIFFICULT to build a drum sander on a cantilevered frame that is rigid enough for even, consistent thickness sanding. By far, the most effective way to homebrew something like that would be to support the sanding drum at both ends.
Unless you're going to be doing tabletops or something like that, a 20" capacity should be good enough for most projects. You can always make glue-ups for anything wider.
There are two ways to build a sander - single or double ended. A single-ended machine has a cantilevered beam that's open at one end. You can indeed sand double-width boards by this method. However the obvious problem is that of the beam bending upwards under the working load - this isn't large, because drum sanders only take a light cut, but equally we're talking about fine surface finishing here. It's OK if you machine does deflect a little, but the real killer for home-built machines seems to be if they're poorly damped and they start to "bounce". Bad finishes seems to involve a regular oscillation and regularly-spaced divots.
One day I'll build my own (and a pad sander), but it'll be welded from
1" x 2" steel box, because I know how to make rigid structures out of that. The thickness adjustment will probably be recycled milling machine parts or a lathe cross-slide. In many ways a single-ended machine is easier - fewer, bigger parts will achieve the same result as a double-ended machine that relies on accurate synchronisation.I've seen one home-built machine that was single-ended, but had a (retro-fitted) end clamp to turn it into a double ended machine. This was awkward to fit and was only useful for the last pass, as it needed to be carefully re-adjusted with each thickness change.
For working "double width", you cant the single-ended arm upward slightly, so that the free end is a degree or two higher (this is a critical adjustment and it's timber-dependent for best results). This leaves a surface that's effectively a shallow triangle in section, but it avoids a tramline from the edge of the roller (this is very obvious). Any ridge is invisible in most materials, easily hand-sanded off it it is visible.
I've no idea how to build a drum. Still haven't seen one that's an ugly pig to change abrasives on. If I did build one, I'd probably build several and enable myself to change grits with a quick drum change, not a lengthy belt change.
Weld it. Why would you need to cast ?
That's a pad sander. Much easier to make than a drum sander - there's a sketch in the Taunton "Workshop Book". You can make a successful one from wood, but I've not yet seen a wooden framed drum sander that worked right.
Pad sanders are excellent for finishing and probably better than a drum sander, although a little slower to use. They're also _much_ better on resinous softwoods, the sort that usually foul up a small drum sander and need a belt sander (although CSM's anti-static abrasives would help). What they're not so good at is being a thicknessing sander, for stock preparation in luthiery and the like.
If you have a pad sander, commercial or self-built, then get a graphite platen for that pad. They make a huge improvement - less trouble with the belt clogging from resin and _much_ less belt heating.
I read, in a recent review of a few commercial products, that this happens on a few. IIRC, the reviewer said it wasn't hard to remove.
Andy, the drum on the Performax single end thickness sander has a spiral wrap paper. The benefit of this is that the paper tightens against the drum as it runs and there is a simple clip mechanism to take up the slack. I haven't used one of these so I don't know how well it operates but I liked the concept.
TWS
Trouble with those simple clip mechanisms is that they're easy to make on a production line, a bit harder to copy for a one-off. I wonder if you can get the bits as spares ? 8-)
This critter is a "stroke sander" and is commercially available. I've used one of these (with a graphite mitten) and discovered that they're great for sanding large panels - but they can also spoil a surface almost before you can notice; and they can do a real number on your hand if you're not really careful.
I too been thinking of making a thickness sander, I just can't make up my mind whether to buy a Perform ax 16/32 or make one. This is what I found:
You can buy 5" X12" aluminum (6061 T6) tube 1/2" wall thickness for $32.
I was toying an idea, what if I make at cost an aluminum sanding roller 5"X24" fitted with pillar block bearings, two pulleys ready to install for about $120, you provide the motor and each buyers donate a few bucks to pay for the lathe?
I presume I should also provide a possible dwg of the thickness sander and necessary rollers for the feed belts and the feed geared motor. Ultimately I presume for the sanders should be under $400 including a used 1-1/2hp motor??
I am serious, I am willing to do it for free and you pay for the all the materials....
For a home brew a better bet would probably be the 24" x 6" x 5" ID @ $68.72 by the same eBay vendor.
Having used an Eastern copy of a 20"/40" cantilevered unit, the media holding method is critical. That on this model made for very difficult roll replacement and didn't self tighten, so the results were strips that broke where they passed through the drum.
Most of the better models I have seen have internal webs to stiffen the drum, maybe something like a high density foam would help?
Are the pulleys for the feed system? Most of the contilevered drums are direct drive with a flexible coupling. Also, don't forget a fairly fine thread adjustment method, ideally for a cantilever system this should be a form of acme thread. (Assuming the bed is stationary and the drum / motor is moving).
Lathes are nice, especially metal working ones, but before you part with your cash, take into account that you could easily double the cost of your lathe by the time you add tooling and measurement instruments, and then a little latter on there'll be just this little old mill you just can't live without :-).
Regards.
BWR
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