Rega spindle too short

with a vinyl platter you should not use the felt mat. That may help a little with spindle height, and in my experience more than a little in sound quality. As piedpiper says, shouldn't be an issue if you don't intend to use a clamp.

however the Iron Audio acrylic platter does not have a LABEL recess machined into the top surface so if you do not use a mat of any sort, the record will not sit flush with the playing surface. Iron Audio recommends the use of a mat.

bummer. The problem with going to another thinner mat is it may not provide adequate label relief. Other mats like the Sorbogel. Acromat, or Ringmat are thicker (I think) so will compound the problem. I recall seeing somewhere a replacement spindle for Regas that are longer to accommodate a a thick acrylic platter. I'm not sure where to find one or what they cost, but I would imagine they're pricey.

The options I see for you are 1) buy the extended spindle, or 2) scrap the IA acrylic platter in favor of a Funk Acroplat, or 3) try a thinner felt mat, or 4) live with the mat you have.

Personally, I would buy the funk acroplat.

I was wondering what would be the downfall of not having the recess, because I don't think that I will be puting the mat back on soon.

I believe that the idea behind acrylic platters is that the impedance of acrylic is very close to that of vinyl, and with the LP placed directly on the platter surface and clamped, results in an effective LP thickness equal to the LP plus the platter (ie ~ 1 inch). Lacking solid contact you're not receiving this benefit.

That's the theory (and it's better explained in various artical on the web). My own experience is that placing the LP directly on the acrylic sounded profoundly better than with a mat. It also sounded better than my other table that had an alloy platter with felt mat.

I added a Funk Achromat to my table (which already has a 1" think acrylic platter). The Achromat impedance is supposedly perfectly equal to vinyl. While the spindle is too short to use the clamp now, the LP lays so perfectly flat on the Achromat that I think the clamp is superfluous. The sound is even better than with the LP clamped directly onto the acrylic platter. Further, I don't have to hassle with the clamp.

As for having the relief machined, if it were me I'd be tempted to do it - the only reservation I would have is whether the machining is done such that the platter remains balanced. And, not knowing how the IA platter is constructed, whether the machining could affect the structural integrity. And finally, if you ever get to the point you want to sell off your platter for an upgrade, the machining may diminish the resale value.

that's my 2 cents . . .
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the Achromat comes in 3mm and 5mm thickness. the 3mm mat setting on your IA platter may be the ticket. It provides the label relief w/o touching your platter. The 5mm may also work, but that would only leave 1/8" of spindle to center your LP.