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Thread: Crankshaft polishing
08-18-2007, 01:05 PM #1
I'm looking to polish a crankshaft. I noticed that I need to use around 1000grit wet/dry sandpaper to get a decent finish. But then I noticed they seem to sell emery cloth in grits only up to 600 grit. What's the deal with that? Also, what do machine shops use for final polish?
08-18-2007, 01:35 PM #2
Gregsy, You didn't say what part of the crank you're dealing with, so I'm assuming both mains and throw journals. If you can set up some offsets in a lathe, you can control it better on the throws.
You can get a nice shine on the mains by hanging it between centers on a lathe and using a Dremel tool set up with an extra fine Cratex wheel. Set the lathe to slowest speed and rest your hands on the tool post as the carriage moves at a medium speed. This process works really well for polishing out grooves caused by failed oil seals.
The throws are a little more difficult. A one inch wide strip of crocus about two feet long is the only thing I can think of. WWQ
08-18-2007, 01:50 PM #3
Cut wet/dry silicon carbide sanding paper into strips the width of the journal. Soak in kerosene or similar and wrap around the journal. Then wrap a long shoelace over the top of the paper one and a half times. Then just pull left/right on the shoelace and shine away. This is by hand, no power.
08-18-2007, 02:23 PM #4
I have it in my lather, which makes the mains easy but the rod journals are tougher. The crank is new, so there are no major problems with it.
I've been trying the shoelace method, but I have to think the unevenness of the pressure can't contribute to a good polish. In other words, where the lace is gets more force than where the lace isn't.
I noticed crocus cloth but it doesn't list a grit for it, and it says it is for non-ferrous metals. Is that just BS?
08-18-2007, 03:39 PM #5
You say wet & dry @ 1000 grit and then go on to mention emery paper @ 600 grit.
Wet & dry is available in 1000 grit.
08-18-2007, 03:42 PM #6
I know, I've been using 1000 grit W/D but I would like to buy emery as it comes in long strips(rolls).
08-18-2007, 04:14 PM #7
try 3m they have great products for applications you suggest
08-18-2007, 05:29 PM #8
GregSY said: "I noticed crocus cloth but it doesn't list a grit for it, and it says it is for non-ferrous metals. Is that just BS?"
If crocus cloth is non-ferrous only, I've been mis-using with great results for over forty years now. I did a quick Google search - none of the info sources I checked said anything much other than "for metal polishing", so I think you're O.K using it on your crankshaft journals. It's always worked for me!
08-18-2007, 06:16 PM #9
My old boss had a hand held belt sander type rig that had handle bars like a bike he would use to polish the cranks on his funny cars.
It had super smooth cloth and ran fast and the lathe would be running in low speed.
08-18-2007, 06:58 PM #10
From McMaster Carr website:
Emery and Crocus Cloth Sanding Sheets
All have a flexible cloth backing and measure 9" x 11".
Emery has blocky-shaped grit particles that cut slowly. Good for polishing metals.
Crocus cloth has a soft abrasive. Use for fine hand-polishing of soft nonferrous metals.
08-18-2007, 07:19 PM #11
08-18-2007, 11:12 PM #12
Buy the correct belts there. Make sure you polish in the direction of crank rotation, least that's the correct way to do it . . .
I do my small engine cranks (single throw) on my lathe but my method is not OSHA approved so I won't go into the details.
08-19-2007, 12:02 PM #13
I have a crankshaft polisher built on a goodson design using a Sears/Craftsman router as the drive(with a speed controller) and I use goodson 1200 grit crank polishing belts.Main and rod journals look like a crome finish when done.
08-19-2007, 06:19 PM #14
To finish, turn the sanding belts inside out and use very fine lapping compound or nothing at all on the belt.