Can't remove counterweight shaft
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You hit the nail on the head. I just made a washer out of .020" thick cutting board" material that you can buy at Wal Mart or Meijer, etc. for a couple of dollars. It has an extremely smooth teflon like surface on one side and a very slight pebbled [but slippery] surface on the other.
I tightened the shaft as much as I could by hand and it unscrewed smooth as butter every time I tightened it. I too have had issues in the past so I just "touched" the two surfaces when I tightened the shaft down so as not to overtighten and had no further issues. With the "washer" I can crank it down.
----- Original Message -----
Sent: Friday, April 02, 2010 10:18 PM
Subject: [ap-gto] Re: Can't remove counterweight shaft
I have been following this thread on Dec. counter weight shaft seizing problem and I believe there is a misconception as to the main cause of the Dec counter wt shaft jamming on the Dec housing fitting. I believe the primary reason the shaft can seize to the housing adapter has little or nothing to do with the threads or thread design. The pin end of the Dec shaft has a relatively large flat shoulder that mates up with a corresponding large surface area flat on the aluminum housing adapter. When you spin the shaft on and these two relatively large surface area mating surfaces connect, there can be considerable friction generated; especially if one spins the shaft on agressively. The problem may be aggrivated if you couple this with a large temperature differential (warm to cold)between assembly temp and dis-assembly temp ie. warm afternoon set up cold early morning take down. The reason we can get what is in effect a "shrink fit" is not so much the contracting metal housing fitting causing the threads to seize but the cooling of the metal Dec shaft causes the shaft to shrink in length. The threaded pin on the end of the Dec shaft shortens and pulls the two mated metal to metal surfaces tighter together. A change in temp will have a far greater effect on the length of a metal bar than it will on is diameter. Simple physics! If the threads really were the problem, then one would have difficulty un-threading the shaft the entire length of the threaded pin. My experience has been that once the flat mated surface connection is broken, the shaft spins off easily.
As to what is the answer to this, there are of course several and a number have been proposed here. Additional options are:
1. Grease the flat mating surfaces as well as the threads.
2. Don't spin the shaft up tight. It only needs to be made up slightly hand tight. I found this works for me.
Finally, I work in the oil industry and the type of threaded connection used on the Dec counter Wt shaft and Dec housing is used quite extensively in oilfield equipment, especially in sucker rod pumping equipment. We count on the fact that the flat mating surfaces stay tight for this equipment to work.