I'm making good progress on my thickness sander. I've elected to use
3/4 inch plywood for the drum and now have 20 discs that need to be affixed to the 1 inch cold rolled steel shaft. I have no experience with epoxy, so am looking for tips on brand, methods of application, set up time, etc.Thanks!
Larry
I have always used West epoxy. The resin is quite nice. There are multiple hardeners for different cure times. It is a strong epoxy, used for gluing, sealing, fiber-glassing and molding, and I have used it extensively for all of those features.
It's a 5 to 1 ratio. I have pumps for big batches. But for small batches I use cups with the size on it, or larger syringes with ML on it.
It can be used as a finishing resin or gluing as I said.
The longer it takes to cure the stronger the bond. So 5 minute epoxies are not nearly as strong as 20 or 30 minute or 2 hour epoxy.
Full strength is achieved after 24 hours at 72 degrees. But I have found that 48 is really it's full strength when using the finishing resin with a hardener that has a long cure time.
You can get West at auto body, marine and other places.
If you elect to use a simple epoxy (equal parts) consider the 30 minute or 2 hour for it's strength. They are capable of doing what you are trying to do. If you see crystals in the tubes avoid it, it's old stuff.
For application of any epoxy acid brushes work well. You clean up with alcohol, I wear gloves mostly these days since prolonged contact will eventually catch up to you with epoxies and sensitize you.
For sanding epoxy wait a few days for it to fully harden, and clean the sandpaper often. West sands nicely.
Since you are making a drum, you may want to use the epoxy to seal the drum so that the Velcro sticks nicely. First true the drum by running sandpaper through to true it. Then after removing the drum, coat it with epoxy, don't make the batch up in a cup, mix it on a paper plate so you have a better working time. If you mix it in a cup it will probably start smoking and harden quicker .. Only small batches can be mixed in a cup. spread it on with a 1" paint brush and apply it thinly. Wipe off excess with a rag and let sit for a couple of days. And the Velcro will stick nicely to it.
Get a pair of syringes same as the mix ratio - 5:1 like a 10 cc and a
50 cc.Easy to get the mix right in smaller mixes.
IMO, brand doesn't matter all that much. Most all epoxy is made by a very few companies who sell it in bulk to others who brand it.
Application can be by anything. Disposable chip brushes work fine.
Working time is in the range of 20-30 minutes depending upon the amount. Epoxy generates heat so a deep container will have less working time than a shallow one. Figure overnight to set up reasonably hard (to being able to sand it) and several days to fully cure.
To apply, brush on a generous coat and clamp without a lot of pressure. Clean up excess epoxy with vinegar. Once the cylinder is finished, I'd apply a coat over the outside and I'd use a thickener such as Cab-o-Sil so it will fill any small voids. Once thoroughly cured, true the drum.
I would also look for a way to mechanically fasten the drum to the shaft; perhaps Woodruff keys or bushings/plates at the ends of the drum with set screws.
Update: After looking at the myriad choices of epoxy, I decided to try an e= xperiment with gorilla glue and affixed my trial disc to an extra piece of = shaft. After drying, I couldn't budge it and certainly applied more stress= than it will see when sanding. Project -- 80% complete.
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