Drum Sander Alignment the Easy Way
Getting your sander straight without the tears and cursing
Last update: 12/7/09
Drum sanders are a great luxury. Of course, they remove the tedium of sanding. But a very handy use is to remove very small amounts of wood or getting multiple parts exactly the same thickness. While a planer can do the same thing, a drum sander can handle small parts more safely and deliver a finer finish.
Of course, to do the job properly, the sander has to be tuned up properly. The most critical adjustment is making sure the drum is adjusted exactly parallel to the bed. Otherwise, a wide piece will be thicker on one side than the other. Also, narrow pieces will be sanded to different thicknesses depending on where they're inserted.
Unfortunately, this important adjustment is a royal pain in the butt. The typical process, using a small gauge block, is tedious and error-prone because it's very hard to tell if the drum contact amount is the "same" in various spots. Other methods like resting the drum on the bed, simply don't work because the support arm deflects under load once you lift the head.
After trying the various methods I found on the net, I came up with a method that's simple, easy, quick, and lets me get the drum parallel to within a couple thousandths of an inch.
The first thing you'll need is a good straighedge. Not something that's sorta straight, but really really straight. And, even more importantly, with both edges parallel to each other. This method won't work at all if the two sides aren't parallel. I like Veritas Steel Straightedges (available from Lee Valley or Highland Woodworking), very accurate at a reasonable price and very easy to stand on edge. Note that their aluminum straightedges only have one reference edge and won't work for this technique.
The second thing you'll need is a good light source. This can be a desk lamp, a mechanic's florescent trouble light, a window, or an open door. Anything that can give you a good, strong, even light. I use a 4' florescent shop-light I have left over from the old shop lighting.
Step one is to remove the sandpaper from the drum so you have a precise, smooth surface to align. I presume you know how to do this.
Next, you'll need to do is get the pressure rollers out of the way. These are the spring-loaded bars in front of and behind the sanding drum. These put downward pressure on the wood as it passes through. However, since they hang lower than the drum, they block your view. I've found that the easiest way to do this is to cut small lengths of copper wire and bend a flat hook on the end. Notice that you don't need much of a hook at all, more of an "L" shape is easier to get around the roller. Then grab the roller and pull up and bend the wire down over the side.
Now, put the straightedge on the conveyor belt up under the sanding drum. Get it reasonably close to being directly under the lowest part of the drum. Also make sure that the straightedge is completely on the conveyor belt and not setting on anything else.
Next, get your light in place.
The idea is to shine a strong, even light through the back of the planer between the head and the straightedge. In my case, I lay an old shop light on the back of the sander. You could also roll the sander over to a window or an open door. The trick is that the light needs to be even, which is why I prefer the shop light.
OK, you're all set. Now just look though the sander and adjust the head so it's just above the straightedge. Hopefully, you'll see a nice, even line of light across the whole head. In this case, however, you can see that the light gets slightly fatter on the left, showing that the left end of the head is higher than the right. A quick adjustment and you can see in the second shot that the light is now nice and even.
Be careful when you tighten down the locking bolts. Tightening down one all the way before the others can pull your head back out of alignment. If your sander is like mine, there are four bolts you loosen to adjust the head. When I have my head alignment right, I hand tighten all four bolts, then snug each one a little, then repeat each one a little tighter, and then finally crank them down.
Note that it would be possible to use feeler gauges to set the head height and maybe get it perfect. But they'd need to be really long ones or you'd need to use something like machinist's parallels. However, by just eyeballing with the light, I find I can get within one or two thousandths which is really close enough.