Got the shaft

[Sam Lust]

I got a (used) stainless steel 1" prop shaft with the Yanmar 3GM engine I bought and installed last winter in my 1983 Hunter 33. I figured that I may as well install it this winter while I'm replacing the bent shaft strut. (That's a different story and post!) The first question is: What would you consider acceptable run-out at the mid point of an approximately 50 inch long 1" stainless shaft. I measure approximately 3 and one half thousandths of an inch. I say "about" because my truing jig is a wooden work bench with cut plywood V blocks. Lots of flex. That and I only have metric dial gages so I have to convert to inch. I have tried correcting the slight out of true using a long lever attached to the bench top, applying about 1 1/2 inches of deflection. I've gotten it to .0015" briefly, and then it seems to spring back to .0035". I've never run into this sort of obstinacy from a hunk of metal before. Am I going to need to apply heat? Or invoke some sort of marine voodoo? Or maybe just ignore it? At about 1380 max shaft RPMs I wonder just how much of a difference it will make.Next subject: You and I discussed your new collet style shaft coupling briefly at the Atlantic City Sailboat show this winter. I would have to cut down the stainless shaft, thereby loosing the keyway, so your coupling and not having to cut a new keyway starts to make sense. Do you have one available for the Yanmar 3GM 30 1" shaft diameter? Is it less difficult to remove and work on than the stock style coupling? What else can you tell me about it? Where do I order one and how much poorer will it make me?

 

[david lewis]

Shaft Runout and Straightening

Do not apply heat to your shaft!!! You could change the properties of the metal. The issue is what is happening at the microscopic level when you straighten. Austenitic stainless steels cold work very readily. As you bend the shaft dislocation entanglement is occuring and atoms are jumping around into new locations. When the load is removed some of this stuff springs back, some of it remains permanently in a new location, and some of the atoms are teetering on the brink not sure which way to go. Over time some of these atoms go back to their original locations which in the aggregate you see as a change in runout. In industry when you straighten you then stress relieve at say 600 degress for 2 hours to remove residual stress and get the material stable. Often straightening is repeated several times to get the end result. Let me make a comment on runout. Runout is a combination of errors. The roundness of the shaft is also contributing to your runout. Make sure you measure the diameter of the shaft with a micrometer or calipers to see if it is round. Straightening will not make the material round. .003 TIR is pretty good for a shaft of this length. You will not see a balance problem from this at this low an RPM but wear of the cutlass bearing is another issue. One technique for straightening is to overstraighten it, in other words bend it in the opposite direction to get all the atomic stuff moved around, then rotate the shaft 180 degrees and straighten it back to what you need. You might find it is more stable, without a furnace I doubt you can heat treat a shaft of this length in your kitchen stove, one option is grind it between centers on an od grinder but a machine shop is req'd.Let me know if you have more questionsdave

 

[Brian Ranniger]

What did you pay?

I'd be interested to know what you paid for the used shaft. I got a new one 46", 1" dia, from "ProperPitch" out of Delaware I believe for about $140. I ordered it and had it in about 3 days out here in SLC. I did have to pay the next day air shipping of $35, but it seems like a good deal to me.

 

[Kevin l. Woody]

Like your title.

Hello Sam,Thanks for the posting. Sorry for delay I was in Oakland for the last ten days doing a boat show.We produce most of our shafts at a 1 to 2 thousandths of run out. 3.5 may be excessive. Prop shaft voodoo does come into play when you attempt to straighten it. We use a press, heat and sometimes water for cooling. I think it depends on how a shop is set up. Some old time shops use water and heat. Voodoo. I would not myself attempt to straighten a shaft practice. If the bend takes place to close to the taper ouch you buy a new shaft. I would think that most local prop shops could place the shaft in a working order with just a few dollars.Our collit coupling will cost you apx. $250.00. If you would like please give me a call and I will talk to you about it. 800-523-7558. Thanks for your letter.SincerelyKevin, L. Woody

 

[Kenneth Pfaff]

Don't have and answer

Sam, I don't have an answer for you, but I see you are from Forked River. I have a lot for fond memories of Forked River, my Grandmother had a summer house down there and we spent every summer down there growing up as kids in the 50's 60's and 70's. Haven't been down in a long time but I expect the area has changed a lot. Well good luck with the shaft.