I'm not quite past the learning curve of tumbling and due to the deadline i'm just going to submit what I've accomplished thus far. To start off a year ago i bought a new Navarro intake, Navarro heads off a fellow HAMBer that are from the 50s, and a 8BA timing cover at a swap meet. They looked nothing alike and i wanted to do something that was really going to make my engine pop. A polisher i know of quoted me $600 plus the 120 mile drive so i explored blasting. $50 later they all looked the same, but not what i was going for. So i came across a old thread on here where a guy was tumbling parts with pretty good results but went AWOL. With a little thought and allot of research i began the design process. The design was based off what i had laying around combined with the shape of my parts. The frame was some 1" x 2" galvanized tubing. The rotating assembly consisted of 4 pillow blocks, (2) 1/2" swivel sockets, a stick of 5/8" rod, and the weight. I made 4 pie shaped eccentrics with set screws which wasn't enough so i added rods until i had it "calibrated". The drive is a 1/2" hp motor with a slight reduction in pulleys. The first part i tumbled was the timing cover that i had already deburr'd. After about 5 hours with these resin pyramids from harbor freight i had a very uniform matte finish. Then with about 16 hours with the walnut shells and metal polish i ended up with this
Since the timing cover was a experiment I didn't document very much thinking I would have this down pat and well prepared with the heads and intake. Here is a video of the timing cover tumbling with the resin pyramids. I bolt the parts down to the box to give it a forced abrasion instead of allowing it to freely move about the media. Here is the final assembly
So here is where i started on the intake. Below are some before and after 22 hrs of tumbling photos I wish i would have spent more time deburring the intake before i put it in the tumbler. I had such great luck with the timing cover i just assumed the intake was going to work out fine. I have since spent more time sanding on it and is back in the tumbler now. Here is a video of the intake tumbling.
I have around $200 in this project and it works very well. I was pretty surprised at how much fine aluminum dust was created. In commercial units you would run water in with the media. This machine does not do all of the polishing for you, but can eliminate half of the work if not more. If i would have not blasted the timing cover it would have gone straight in with no prep work because die cast parts are already have such a smooth surface finish. There were things along the way that i did like other media and blasting that were not productive but a part of the learning curve. PracticalMachinist.com has allot of great info on this topic and about the best thing you can do it just test some parts and inspect along the way. I think some Strombergs would look very nice after a few hours in the walnut / polish.
Rather than sanding, 2" roloc 'surface conditioning discs' (AKA Scotchbrite) work great for prepping aluminum. http://www.xs11.com/forum/showthread.php?t=39869
I used power tools when I could, and could have bought more arbors to make the job easier. I didn't mind doing most of the work by hand, I do wish I was a little more aggressive with the heavier grits starting off.
I worked at a shop that had an alternator/starter bench room, they had a shaker that worked the same way but drizzled solvent in with the media, It was so nice for cleaning up stubborn greasy parts. If someone was to build one of these for polishing I don't see why you couldn't use it for cleaning the rest of the time.
When I teaching Autoshop, we accumulated quite a collection of various used nuts and bolts. I decided that if we cleaned them up, the students could use them on their own cars without having to buy new. So, we borrowed a cement mixer from the Building Trades class and loaded her up. It was so damn noisy that we had to move it outside. Left it run overnight. The next morning we had the most beautiful collection of satin finished fasteners in the state. All the nuts worked perfectly, but couldn't screw a one of the bolts into a nut. The process had peened all the external threads. I told the kids that those were special anti-vibration bolts and not to use them anywhere they would ever have to be removed.
Cool !!! Thinking outside the Box (this time in the box) shows great promise and even greater results. Keep up the Good Work and let us see the other parts when finished.................... Jeff
I would install some bolts into the threaded areas before the process to protect the threads. Especially the spark plug holes. Bolting the part to the bottom of the box is a genius idea. Don't need to worry about the head gasket surface getting messed up.
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