Page 1 of 1
Posted:
Mon Oct 04, 2004 1:50 pmby RRBD
I have been toying with the Idea of building a balancing machine for crankshafts. I would like something similar to the one from Turner Technologies, that can be used on a mill table. The basic construction is very simple, but for me, instrumentation is the difficult thing. A person could use contact points and a strobe on a "degree wheel", but how would you measure the "amount" of imbalance. Another avenue would be using some sort of accelerometer and an encoder and PC base the machine, But my machining skills are much better than my "interface electronics with a PC skills" Any Ideas are appreciated, the simpler the better.
Posted:
Mon Oct 04, 2004 6:40 pmby 84-1074663779
Probably the simplest way to measure very small amounts of movement would be by reflecting a laser pointer off a small mirror (or a journal surface) onto a wall. The length of the resulting trace would be a good indication of the vibration amplitude. As you really don't need to measure it, just see changes. I have never tried this or seen it done, but it might be made to work ???
With the journal, bounce it off the curved surface. As the crank moves, the point of reflection will move to a different point around the curve, and the beam should move quite a large distance on the wall. Different angles and distances should change the sensitivity.
Posted:
Mon Oct 04, 2004 7:55 pmby Terry_Zakis
RRBD, there are portable vibration analyzers and measurement equipment that I've used in the power indsutry to balance pumps, compressors, turbines, etc. There is a company called IRD Mechanalysis that has packaged units that include an accelerometer and frequency adjustable strobe light. Some models have two accelerometers. The accelerometer can be fastened to bearing cradles to obtain measurements in peak to peak displacement (mils), velocity (inches/second), or acceleration (g's). The strobe light is used with a degree wheel to determine the change in the vibration "high-spot" for addition of a trial weight. You can look on eBay to find some surplus to learn with.
Since you'd be removing weight from a crankshaft, I would suggest that you find software that is deisgned for this purpose, and then research the equipment that can work with that software. This is especially true since balancing of crankshafts entails the addition of bob-weights to the throws to simulate the reciprocating mass. Then there's the concepts of overbalance on recip engines, which I don't know that much about.
Either way, this can be getting into expensive territory and is an entire science unto itself. Years back I attended several IRD training classes which were very helpful, but weren't for balancing recip engines. You may also be able to find some of their training materials which can teach you about vibration fundamentals. You may also want to do a google search for "The Vibration Institute" in the US, which I used to below to and they have a great number of technical handbooks and papers.
If this is to save a few bucks on your own balance, I'd advise you shell out the few hundred bucks for a Pro to do it, because you'd be way ahead financially. If you want to get into this as a business, then I'd suggest you find equipment and software that is specifically designed to do this, as again you may be better off in the long run. It probably wouldn't take messing up a few customers crankshafts to hurt the business plan.
Take Care,
Terry
Posted:
Mon Oct 04, 2004 11:38 pmby RRBD
Thanks for the info, guys. It does seem like complicated territory. I dont have any plans to quit having my cranks balanced professionally. This mission is purely educational, I dont know alot about it and would just like to learn how the "old school" did it. You guys are an excellent "think tank"