I've been working off and on to make a horizontal dish type sand mixing machine for mixing up batches of phenolic urethane no bake resin and also sodium silicate binders. This project got under way when I saw two lots of large roller and ball bearings at a local auction house and absentee bid $100 or so for each lot and won them!. In amongst the bearings were a couple of 7318 angular contact bearings which have a 90mm bore hole and would form the basis of the rotating spindle that the mixer dish is attached to and would give a 3 inch plus / 80mm hole for the mixed sand to exit into the waiting container below. At present I'm making both the housing and the rotating spindle tube out of cast aluminium, though I'd originally cast the tube in iron but poured cold and lost the casting and fell back onto the aluminium version cast earlier. To get a nice accurate bearing fit I actually had to refit my lathe's cross slide dovetail to reduce 70 years of wear and tear and also remachine and hand scrape the compound slide base to the cross slide as both had fretting and corrosion damage that allowed the compound base to visibly rock and squirt oil out from underneath. The difference is night and day now with a micron resolution digital indicator showing only a micron of movement during a cut now versus 40 micron before the repairs. At this point the bearings are shrunk fit into the housing and the spindle tube is a snug sliding fit to the inner race bores. I'll have to thread the end of the tube now for a bearing preload nut and also bore the tube to over 3 inches for the sand to go down. I'll have to seal the open race bearings with stacked rubber shaft seals or some metal rotating shaft seals if I can score another bargain for those. After that a sheet metal cover should keep most of the crud directly off the seals.
They're SKF brand so not cheap if you had to pay full retail. A quick trawl of Ebay shows prices from $150 to $1500 depending on the brand and model variant with SKF at the high end of that. I was surprised to score both lots of bearings for cents on the dollar, in the 20 or so bearings is one dual row bearing sells for USD $1700 retail. There's no doubt these are massive overkill for the job but I would have paid about $10 each for them and I'm going to struggle to find uses for the rest of them. I was originally planning to use a farm ploughing disk with a vertical rim welded on but now I'm thinking a stainless steel disc with 5" or so of vertical wall would be better: less abrasion resistance but no rusting issues.
