SME record clamp causing convex playing surface

I have an SME Model 10 turntable. I recently noticed that by following the manual's recomended procedure for playing records, ie. placing the included washer under the record label, placing the LP on the platter and then screwing down the record clamp, the LP's surface becomes convex. The center of the LP is raised higher than its perimeter forcing the stylus to run uphill as the record plays. I confirmed this conditon with a bubble-level. I also presume this causes there to be a space between the underside of the LP and the platter surface, greatest in the center and decreasing until the vinyl meets the platter near the perimeter, which can't be good. Does this condition, presumably on all SME tables, cause problems with channel balance, pitch, record/stylus wear? It seems to me that the ideal playing surface would be completely flat. Has anyone else made this observation?
You are clamping it to tight
Thanks Pcosta, I thought of that. If I don't tighten the clamp at all, the LP is flat but raised entirely off the platter by the thickness of the washer. If I tighten the clamp just enough so that the outer edge of the LP touches the platter, the LP is indeed pressed into a convex shape. My suspicion is that the supplied washer is simply too thick to allow the LP to both lie flat on the platter and maintain complete and good contact with the micro-grooved platter surface.
Does this happen to all your records?

How thick is the washer. Is it black. What is the diameter.

When I had mine. you tighten it enough so the record does not raise on any part or the record edge. Tap the edge all the way around to see if you got it all, and adjust accordingly.

Is it the factory original washer? Maybe if its a used unit it was replaced and a bit thicker.
This occurs with all of my records, any thickness. It is the original black SME washer that came with the table which I bought new from a dealer. I don't know the exact thickness or diameter of the washer, but I think it is just over an inch in diameter. I will measure it later. I do tap the edge, or check it visually, to make sure there is contact all around the perimeter of the LP and tighten it only enough to achieve this contact and no more.

Having thought more about this phenomenon, I think VTA is constantly changing because the tonearm angle is going up as the stylus is riding up hill slightly with each revolution as it travels toward the center of the LP. Perhaps I should contact SME or Sumiko.
Hi I have a SME 20/2, I bought it new so I know I have the right washer. Mine does the same with the washer. I don't recall that it said to use the washer in most/all cases? I'll get my manual out...

I do notice subtle sound changes depending how tightly you clamp with out the washer. A dealer told me to tighten the clamp until the outer edges lift off the platter slightly then back off a little to get the best "clamp".

I have used the washer, but only for the reverse side of a badly dished record.
It seems to me that the record should be flat in the table in order for the resonances of the plastic to drain away, and not be allowed to affect the
I also have a 20/2 that was purchased new and the same thing happens. Taking the cost of the table new into consideration, I never thought twice about it. Just assumed there was science going on I didn't understand.
The famous SOTA reflex clamp comes with a washer and does the same thing. The idea is to force the outside edge of the record tight to the platter, even if it isn't perfectly flat. If your records are pretty flat anyway, just use a thinner washer; I wouldn't recommend 'no washer' because then you might end up raising the outside edge of the record and you don't want that.

Don't worry about the stylus travelling uphill. It won't even notice it, just reduce the anti-skate a little bit ;-) My Goldmund platter is slightly concave, and the result is about the same when the clamp is set.
This is one of the reasons I gave up on clamps 5 years ago. Sounds better now, too, with a Boston Audio Mat I on the table and nothing on the spindle.

You're right. Page 12 of my manual say put the washer on. Clamp just enough...

So I did it. It does seem to tighten things up slightly. Lil more focus and dynamics than with out the washer.

I'll go to home depot and try a thinner washer for my 180-200 gram records. This washer might be better for thinner vinyl...

Sgs/nsgarch might be right...
Thanks for everone's response. I bought another washer which is half the thickness of the SME washer and did some listening tests. With the new washer, the LP was essentially flat on the platter and tightening the clamp slightly did create good contact between the platter and LP.

For reasons I can't explain, the thicker SME washer produced slightly better sound than the new, thinner washer and also considerably better sound than with no washer or clamp. I heard a little more detail and darker backgrounds during very quiet passages of solo instruments and the overall sound was richer and fuller, especially with full orchestras. In a word, everything became slightly more three-dimensional. But the improvement was very subtle over the thinner washer.

Has anyone else had a similar experience?
Peter, when I used my SOTA clamp, I kept about 3 different thickness washers handy and woud use the thinnest one I could to bring the outer edge of the record down to the platter (which you can never do 100% -- even 50% closure is enough to damp out resonances.

A medium mat (ie harder than felt) can help, just remember the washer still has to sit directly on the hard platter surface for the clamp to be effective. So you'll need to find a washer that's the thickness of the mat (cut a hole in the mat to acommodate it) and leave it as long as you're using the mat. Then stack an appropriate thickness washer on top of that depending on the flatness of the record.