Tons of folks (including myself) have used orbital sanders to strip a playfield to bare wood in preparation for a hardtop. No issues a long as you continuously apply even pressure and avoid creating dips.
Quoted from pb456:Early SS playfields - were they using lead based paint? If so, advice on sanding as to not create a hazard?
Definitely true for early SS cabinets, probably true (seems logical) for the same playfields. Use a good rated mask (and protective eyewear) when sanding and attach a shop vac to your orbital sander and you'll be fine. Best to do it outdoors if you can so that any loose, escaped lead laden particles don't perch on your cars, boxes, and whatever other surfaces you have in your garage or workshop.
Don't forget - removing artwork from the playfield is an OPTIONIAL prep prior to putting down the hardtop. I've done it a couple of times just because of my anal retentive nature, but all you have to do is sand off the artwork from your inserts and buff out/shine-up those inserts before you lay down the hardtop (wet sand and/or dry sand + some clear, rattle can ok). One of the reasons I sanded the complete playfield artwork off is that particular playfield surface had some really rough spots (gouges / divots) and I used wood filler to ensure there were no cavities between the playfield surface and the underside of the hardtop.