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I just picked up this unit with my '88 Mark 510.I attached the belt sander with a good belt installed.It was like this from the other owner.The belt isn't tracking so I adjust the fine tune knob to make it track but no luck.I realize that when I turn thew big knob to snug up the belt it seems to work but when I let go of the knob the knob turns backward in the direction of the belt's movement and subsiquetly releases the belt tension.Shouldn't there be a dog or lock mechanism to prevent the knob from going backward without pushing the release?Any ideas out there?I've tried alittle oil on everything but it doesn't seem to be helping.The idle drum does turn seperately from the knob.

Hope this gives you some of the information that you need. This and much more is available on the shopsmith.com website (Power Tool Wood Working for Everyone).

PS Regretfully, it does not address your problem at all. I'll keep looking. I am sure that this is covered in documents that have been posted here on the forum.

But this might.

Did you set the tension on the belt? Remove the belt and let all of the tension out of the spring by holding the detent down while the spring unwinds. Then without the belt on the machine rotate the tension knob toward you ( CCW as you look at the knob) four full turns and lock it in place with the detent lever. Replace the belt. Press the detent and the knob will spring back in the opposite direction (CW as you look at the knob) and the belt will tension itself. Then just bump the start switch to see which way the belt moves(tracks) and adjust the tension knob slowly. As you adjust the tracking knob with the machine running you should be able to move the belt left and right.
If this helps but you have to chase the tracking while you use the machine then the belt may be the problem. If a belt is used only on one half of the surface then that area will stretch and the tension will not be constant across the face of the belt resulting in constantly chasing the tracking.
If none of this cures the problem then a tear down and complete cleaning will probably be the next step.
Bill V

wa2crk wrote:Did you set the tension on the belt? Remove the belt and let all of the tension out of the spring by holding the detent down while the spring unwinds. Then without the belt on the machine rotate the tension knob toward you ( CCW as you look at the knob) four full turns and lock it in place with the detent lever. Replace the belt. Press the detent and the knob will spring back in the opposite direction (CW as you look at the knob) and the belt will tension itself. Then just bump the start switch to see which way the belt moves(tracks) and adjust the tension knob slowly. As you adjust the tracking knob with the machine running you should be able to move the belt left and right.
If this helps but you have to chase the tracking while you use the machine then the belt may be the problem. If a belt is used only on one half of the surface then that area will stretch and the tension will not be constant across the face of the belt resulting in constantly chasing the tracking.
If none of this cures the problem then a tear down and complete cleaning will probably be the next step.
Bill V

Thanks Bill,i'll do this and see whaether it works.There may actually be a problem with this tensioner thing.Mine does seem to have any unless I rotate the knob CW until tight.With the belt off I can spin it indefinitely and it then releases the detent button going either direction.

Do you have the book? When you rotate the knob toward you, you should feel the spring gain tension. If not, it may be that the spring is broken. With the belt mounted and the tension set releasing the detent will snap the drum up and put the belt under tension.
Bill V

looks like maybe the spring may be broke or the uniot is al gunked uplike the one in the video.I'll probably have to disassemble it and grease it up.It's been sitting around for a few years so not too surprising,i guess.

Thanks Bill,i believe the preloading of the drum spring did the trick.i'll try it out tomorrow and let you know.Seems better now that there is somme spring tension generated on the drum.i couldn't figure out why the drum didn't seem to ahve any pressure on it.I appreciate the help.

This mechanism is counter intuitive. It does not work the way one assumes it should. The arrow on the knob and the spring tension are confusion factors.

Setting tension with the belt 'off'!:eek:

It's all good now.That did the trick.It works perfect today anfter doing the tensioning thing.Thanks again.