Perfectly flat steel plate for baking a chassis is pretty tough to come by and if you take a piece of steel plate to a machine shop to have them put it on their surface grinder, then the cost really starts getting up there.
This uses an alinuminum setup tool with a same size piece of aluminum plate attached at the top. The plate was $8.50 at Westbrook Metals and the connecting nuts and screws were $1.50 at Austin Bolt, total $10 if you already have the setup tool. The top will get a chassis laid on it so the “pressure points can be marked then drilled and tapped so that machine screws inserted through the top plate will hold the chassis snug to the bottom plate while it gets baked.
Possibly, but another plate can be fabricated for around $8.50 worth of aluminum, and that might be the way to go. It’s no big deal to drill and tap it. For now, I’m assuming that all of the slot.it chassis are the same or at least few enough in number so as to not cause an issue.
Here it is finished. The small pieces in front of it are small pieces of aluminum cut from some flat stock I had laying around. I used those to cover as much area as possible on the chassis, trying to keep down the number of holes I was going to have to drill and tap.