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Yeah, we've hijacked this thread, but I do think it's relevant.
[QUOTE=Hesh1956]
Even the line that can result from double pass, open ended sanding does not happen with the machine that I have. It did at first but comes right out with a ROS. The more I used the machine the more the line went away and now I never see it any more.
[/QUOTE]
Interesting, Hesh. Though I am generally happy with the capabilities of the 10-20, this double-pass ridge is an issue I do have some trouble with. I've tried adjusting the drum so that the outboard end is a bit higher, but I've found that I still get the ridge unless I make the outboard end so much higher that the unevenness in thickness across the width of the board is unacceptable. I also find that the ridge is not so easy to sand out with an ROS. The way the ROS rides up on the ridge, it will sand a concave area on the downhill side of the ridge. I have better luck with a sanding block, but it can still be somewhat frustrating. I am able to minimize the ridge by ending my drum sanding with many passes through the 10-20 leaving the depth adjustment where it is (I always end with at least a few passes this way, anyway), but even this doesn't completely eliminate the ridge and is a bit time consuming and frustrating. This is the main reason why I sometimes wish I had a wider drum sander (a wide belt sander isn't even a possibility for me at this point).
It's fascinating that you have seen the ridge problem disappear over time. I wonder what change has happened... I can think of three possibilities: 1) that you've gotten better at wrapping the abrasive very tightly around the drum; I've found that, if there's a little slack in the abrasive wrapping at the ends where it goes into the slot on the drum (an easy situation to inadvertently create), the ridge is worse, 2) that the drum adjustment has slipped slightly into a new position, with the outboard end a bit higher, and 3) that something in your habitual sanding procedure has changed; maybe you tend to take a lot lighter passes, especially for the last several times through. Still, based on my experience, I'm puzzled as to how the ridge problem could have disappeared entirely. Any thoughts on this?
Another issue I have with my 10-20 is uneven thicknessing down the LENGTH of a workpiece. This is really only an issue with thicker boards. I find I end up with a slightly concave board, thicker at the ends, thinner in the middle. I attribute this to flex in the table: according to my theory, as the board enters, it's leading end is pushed down into the table by the drum; the table flexes in the middle, allowing the board to be pushed down, and therefore less material is removed by the drum until end of the board reaches the far side of the table. There, the board is bridging both the front and back edges of the table, where the table is much more rigid, and the board's own rigidity keeps it up against the drum, so the drum is removing more material (this is why, I figure, this issue is minimal when thicknessing thin plates, because the wood itself flexes so easily that it is still pushed down in the middle [along with the flexing table] by the drum). At any rate, I can get upwards of .015" difference between the thickness at the ends and the thickness in the middle. This, too, can be lessened somewhat by taking lighter passes, but not, in my experience so far, fully eliminated. The result can be on the borderline of what I consider to be within tolerances. In my casual examination of the machine, the design/construction of the table is an obvious weak point. I keep thinking about modifying it somehow - welding a couple of beams into its underside or something - but haven't looked closely at options for accomplishing that. Any thoughts on this?
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