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I have polished a number of cranks on my old shoptask machine, but this is the first on my new Patriot. Its a lot easier now because of the longer center distances- just grab the nose in the chuck and use a live center on the pilot bushing. The old machine was shorter, so you had to grab the front seal area in the chuck and set up the rear seal area in the steady rest-so it took more time. polishing went fine, then I decided to use the crank to check the machine. The crank was checked for straight and index ground, so I knew it was within 0.0005. My first check was the bed parallism to the spindle- I put a dial indicator on the table and brought it onto the #5 main journal and set it at zero. Then I backed it away and moved to the #4 and brought it back in- doing this all the way down the crank to # 1. I had about 0.0012" total difference. As it got closer to the chuck the better it got, so I may have had a little tailstock sag due to the weight. Before I pulled the crank I decided to check the lathe spindle indexer for accuracy. I set the indexer pin in the zero degree hole and loosened the chuck enough to rotate the crank until the dial indicator on # 1 rod journal was at tdc, then I pulled the pin from the indexer and rotated to 180 degrees and put the pin back in. I re- positioned the indicator to zero at the bdc spot, then pulled the indexer pin and moved the crank a bit- I was about 0.015" off, but not sure how to calculate that into degrees. I am attaching some photos and also a couple of the mill head all the way down and all the way up showing the milling potential. Also a picture of the mill cover prop rod- this is a clever device that works in any position of the mill adjustment. Its a huge improvement over my old machine which had a heavy steel cover that you had to remove in order to adjust the belts.
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To test the crank for runout start in V block's and check the runout of the center's you will be shocked to what you find also check the tir of the seal the timing gear and the flywheel hub the index deg error = {strokeX3.14ect}divide by 360=1deg if memory servs 1deg on a 3.5 stroke is .035" It's not uncommon to find +-.005" stroke and even more on the index on today's low buck inport crank's i'v seen .020 runout on the flang to the rear main that makes for a real leak not to mention clutch or converter proublem's An easy way to QC your lathe is put a lenth of round shaft ground od prefered in the chuck indicate the end for runout while rotating the chuck then mount an indicator on it and check the OD of the tailstock Quill and adjust the tailstock offset from there Good luck Kevin Taylor
Kevin,
For the average street car or rod those imports are fine, but for anything running 6000 + for any time I use a good forged steel crank and always send it in to be checked and index ground. The one in my pictures is a Scat crank that we got right on at 10-10 rods and mains.
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