Hi all - im slowly putting together plans for a diy crank polisher.. I called goodson and they say common belt sizes are 64 and 72.. i did some ape math and welded a square tube at a right angle to accommodate those belt sizes, except this thing is HUGE. I need at best a 48 inch belt so i found these on amazon https://www.amazon.com/dp/B00TSZ58S2/ Red Label Abrasives 6 X 48 Inch 800 Grit Silicon Carbide Sanding Belts.. and will tear strips to 3/4 and see how that goes.. now im considering using an alu square frame, 2 rollers with dual fidget spinner bearings (608) that i will print on 3d printer or turn on lathe from nylon stock. Has anyone attempted this? I bought a $40 hand polisher with variable speed on ebay which seems to work ok.. im busy putting plans together- but im presuming a lighter and balanced frame would alleviate rod throw jumping - any idea on motor sizing? This will be for small/big block chevys and the likes.. no caterpillar cranks Just light polishing etc- at least i can test each stage before submitting (balance / feel) etc..
Not really, theirs is different.. saw something like what I posted on ebay about 2 years ago and kinda going by imagination.. interesting design theirs ..
Then I don't get it. You have to bill hours to keep the shop open. If you are making a crankshaft polisher, you cannot bill those hours to a customer. I don't know what your shop charges per hour, and that's none of my business, but I can buy a good used Goodson polisher for the equivalent of about one day's billable hours, and it will not only have a spare parts pathway, but will break-even on the 4th crank.
no mention of billing by the hour for anything- i asked a tech question and if anyone had done anything themselves - why on earth would i bill a customer to build my own tool? Just that notion alone is nuts.. Goodson tool was 1100 at some point, I believe i can build something close for maybe 200 at most.. possibly $100... The wifes sewing machine servo motor might be a great option for power. super lightweight and very powerful.. ill shop around and see
Yeh, I get it as a home brewed challenge kind of thing or if you are a backyard onesy/twosy kind of deal but you sure don't want to be doing this every time you want to save a few bucks on equipment for a "going concern".
I considered my similar situation and this what I came up with for a much simpler solution. A polisher for mains and another one for rods, made from s**** 2 x 4s. The journal area is lined with abrasive pads. Be sure to set the crank up in the lathe such that the direction of the polishing action mimics the direction of the rotation the bearing shell sees. Otherwise accelerated bearing wear will occur.
Looking at these two in conjunction for a reversible setup - i dont polish cranks all day long but do a few long/short block rebuilds thru the year.. maybe 10-20. Might step up to larger motor but will see how this 250w unit works..
frenchy now thats a unique solution lol, unfortunately i have various cranks, right now a perkins 4108 for example.. but interesting.. Yes on crank rotation mimicing operation, plus diesels require a much finer finish as well - hence the 800, i might even step it up to 1200 and 1500 if i can find such fine belts in 48"... Off to HD to source some square tubing - took some rough measurements with the wifes measuring tape and tested it on the lathe .. will see how it goes- I might use the 1 inch tubing as a prototype and when im happy ill redo the frame in either 3/4 or aluminum..
I have actually thought of making a pull type single wheel one to mimic the flat strap hand method, which does work quite well actually, depending on your time availability (of which I have just about none!)... and amount of material removal - maybe ill convert the cheapo ebay one i bought to a handheld conversion - remove all the pulleys, glue a nice flat ribbon together as a master and fold in whatever grit you want cut to journal size and have at it..
Fwiw. Make sure lathe runs rotation of engine and polisher runs opposite. I know of a large shop that had alot of bearing failures due to no one noticed polisher was runing same direction as crank rotation. Those microscopic burs were like a file running in the bearings.
We used to dull the belts first on a piece of steel etc first. A new belt of even 600 on a Motorized one can put a few .0001s in taper or bell mouth on a very shiny crank journal in very little time. The micrometers were close at hand and used frequently during the polishing.
Don't laugh too much, but here's an idea from a friend who polished his big GMC 6 cranks for his dirt car. He had a lathe big enough to spin it bolted down to a bench bolted to a wall out of the way from everything else. On the wall behind the lathe was lagged a section of perf angle. Attached to the perf angle was 10 rubber straps cut from inner tubes, all the same length and width. These were long enough to allow him to attach strips of emery cloth, 400-600 grit, that were then wrapped around the journals. He would make sure to spin the crank in a direction that made the wear pattern go with the proper rotation direction so as to not damage the bearings. He'd set up all of the journals, start the lathe and leave it running for some time, usually a half hour. He'd stop the lathe, and mic all the journals, and when one got to the tolerance he wanted, just remove the strap from that or those journals. Usually took a half day or so. Now this was a mechanic that barely made it thru high school, because he was bored. What he figured out was that natural rubber has a force-extension curve that starts out at an angle, levels off to essentially constant force over a significant portion of the curve, then resumes increasing force until failure. The trick was figuring out how much strap was needed to get into that linear range. I studied engineering 6 or 8 years after seeing this setup, and learned about rubber force extension curves and realized just how impressive his setup really was. Pm me if you have any questions or would just like to know more.
You misunderstood. Every hour that you spend building a tool is an hour that you cannot spend billing a customer. If the combined loss of billable hours, and materials costs reaches the value of the manufactured tool, you are better off just buying the tool. If you are using this for fun, at home, that is one thing. If this is being done at work, for work, it is another. No time is free. It either comes out of work, or it comes out of home.
Here is polisher that was purchased many years ago that served me well until I got something better. It’s built off of a Sears&Robuck circular saw motor. I have seen other homemade polishers built the same way.
Hi all thanks for the replies - so i ordered a 250w elec motor from amazon, but this thing weighs 4 lbs- what would be a lighter motor? is 1000rpm enough? thinking about this little guy - 7oz vs 4lbs! I can turn whatever pulley on the lathe plus this is variable so might be a much better option?
The Jalopy Journal
