I may set it in the lathe today, finally got that other job off the schedule. It was EPS in an MGB and required the lathe to be kept open for last minute changes. Anyway that'll let me see what I need for tool bits. There is a special grind I may try for this job. Jim
I got it in the lathe today and ordered a 1/4" wide parting blade (6" long by 7/8" tall) to do the turning work. Jim
Got photos. Note the radiused corners on the tool bit, also the length of stick-out needed to clear the counterweights. Here's the rough turned piece beside the 300 crank. Mains are .030 oversized for cleanup. The oil slinger was not reduced in diameter but did have to be thinned out to fit the 300 block. The seal was turned to .030 over the stock 300 seal journal size. Seal and main journals will be ground to stock finish dimensions. Jim
Nice! How long did it take you? I'm trying to get an idea of how much a machinist should charge for the job.
Oh, well that depends mostly on your equipment. Chatter is a problem you have to deal with one way or another and that can eat up a lot of time, especially with lighter equipment. I spent probably about 4 hours turning it down on a 15" LeBlond, maybe a bit more. But that's because it was quicker and easier for me to use the tooling I had on hand and press on through rather than spend time making up some more specialized cemented carbide tooling that would only be used on one job. It should be possible though to do the job in a couple hours or less with the right setup if you can avoid chatter and take heavier cuts and run higher speeds. But, the nature of the workpiece itself (crank) as a long and somewhat flexible part tends to induce chatter regardless of the stiffness of the tooling, and it may not be easy to find a machinist with experience doing this operation. Machining costs being what they generally are, 4 hours makes it a bit expensive, but maybe you can do better. If I'd had suitable carbide tooling on hand I think a couple hours would have done it easily enough. Jim
In other words it would be cheaper if you have to pay someone to do the job anyway is to have the crank grind shop do it all the way for you. If having to pay for the whole job on the crank anyway, you might want to price out having the block line bored for 2.75" International main bearings if taking only 1/4" off instead of a 1/2" off the diameter of the mains would make the 2 operations less expensive? The plus in doing it this way would to keep the crank strong by maintaining crankshaft overlap and if you can save a few bucks that way.........but possibly would cost slightly more for both? Wouldn't hurt to ask though and if its only a couple bucks more would be a good way to go especially if the line bore on the block you're using needs to be corrected anyway.
Well, with a rigid setup and carbide tooling to do a plunge cut with radiused ends without chatter (That is the tooling challenge but it can and has been be done.) the difference between taking off 1/4" and 1/2" can be as little as 15 minutes. Hardly enough to justify align boring. Jim
Have you ever OD ground anything? Or did you mean as little as 15 minutes longer PER main journal? I know moving the grinding wheel in is really .125" or .250" to remove 1/4" or 1/2" respectively but you only move the wheel around .0005" per revolution trying not to let it get hot so stopping often to let the wheel caught up and the journal to cool. I would guess that it would be around $100 more for the extra 1/4" and probably $200 for the first 1/4" removed(IIRC Chris said he paid $400 to have his crank ground). If that's the case and the line bore on the block being used needs to be corrected anyway, might as well save $100 to put it towards the line bore? Dealers choice.
I was speaking about the time involved in turning the crank, not grinding it. If you can turn it on a lathe as the first step you can remove all but about .020-.030" over the finished size, meaning the grinding operation is then little more than a standard regrind.I thought that was clear from the context, when have you ever heard of anybody using carbide tools to grind something? Most crank grinders will shudder at the very idea of removing half an inch of metal off the mains. In the best case scenario that is about 20 times the work involved in doing a simple regrind. Yes you can shave off the time for load/unload, some of the wheel dressing, and if you are very good you might get away with crush-grinding to hog out the metal faster but you put your grinding wheels at risk doing that and they are very expensive. It is very much NOT a winning situation for the crank grinder. He can't charge you what he should so he is losing money on the job. Most will just tell you No, they won't do it. You rarely find a deal like Chris did, and even then the guy won't like doing it. Jim
