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My lathe uses babbit bearings and I can approach 500rpm in top speed
Hunting American dentists since 2015.
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07-08-2014, 05:42 AM
(This post was last modified: 07-08-2014, 05:44 AM by stevec.)
Greg, 2½" pipe has an O.D. of 2.875" I assume you'll be turning down the bearing area of the pipe,
just wondering if there are auto/truck engine crank bearing inserts that would accommodate
your turned and maybe ground pipe?
It would save having to cast bearings.
Busy Bee 12-36 lathe, Busy Bee Mill drill, Busy Bee 4x6 bandsaw, Homemade 9x17 bandsaw, Ad infinitum.
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Was thinking of a bearing surface maybe 4 to 6 inches wide Steve. Using existing bearing shells would necessitate precise machining too. The cast shells in the bearings I poured were pretty simple and easy to duplicate.
When the shaft is stationary there must be metal to metal contact, before the oil film is developed. Does this cause a lot of wear on startup?
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Greg
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(07-07-2014, 10:38 PM)f350ca Wrote: Looking at possibilities for bearings on the shaft that supports the paddles on a paddle wheel boat. Im thinking of using something like 2 1/2 inch heavy wall pipe (will fit through the headstock on the lathe). Its a relatively low torque load over a long shaft (about 8 feet between the bearings). Expect something in the order of 200 rpm.
I don't have any thoughts on poured bearings, but here is a comment on shaft design. 8 feet between bearings for a 2.5" hollow shaft is a long way.
At 200 rpm I suspect you will be well below the critical speed unless you have considerable mass mounted on the shaft, but straightness might be an issue. Commercial pipe isn't all that straight. Even with turned ends for the bearings, there is likely to be a lot of "run-out" due to straightness issues with the pipe (unless you are able to turn centers on an 8 foot shaft. Weight mounted on the shaft will also generate deflection - which is amplified by the time it reaches the bearings - flexing of the boat frame also comes into play. Bottom line - you may want to consider some type of "self-aligning" bearing design to avoid shaft binding when in operation. One solution is a spherical mount for the bearing - these are commercially available in both ball bearings and sleeve bearings. Some will accommodate up to 3 degrees of misalignment are even rated for submerged operation. The problem is cost: new mounted bearings of this type in the 2" size run around $400. You might be able to find used / salvaged bearings.
Terry S.
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Good point on the straightness Terry. Can't quite get it between centres, have 80 inches of bed to play with, hoped a couple of back and forths taking a light cut on the surface at the tailstock then rotate that to the headstock and repeat would get the bearing surfaces in alignment.
The weight of the paddles will be right beside the bearings so I don't think the shaft should flex but will run through the numbers.
Hadn't thought of hull flex!!!
Self aligning bearings would be the correct way to go but as you say cost is prohibitive.
Back when these would have been used they wouldn't have had the luxury of self aligning bearings though.
Thanks
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Greg
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The following 1 user Likes Terry S's post:
stevec (07-08-2014)
I agree with the paddle wheel mounting method - if the load on the shaft is close to the bearings, it makes for minimal shaft deflection (either due to dead weight or due to paddling force).
Another option with the bearings is just to leave enough bearing slop to allow for misalignment. You might consider wooden bearings. I once worked on an older Black-Clausin paper machine (built ~1918) that used hard maple block bearings on all the dryer cans. The design used two maple blocks with the bore on the center line. The blocks were clamped down to the frame with a cast iron bolted cap. New blocks quickly "wore in" to alignment. As the blocks wore down, the cap was tighten down to allow for the wear. The blocks ran for months (around the clock operation) before needing replacement. The blocks were lubed with high temperature grease which soaked into the wood. There was 100 psi steam going through the roll journals. On the paper machine, the blocks had to be replaced when the tram of the dryer cans got far enough out to cause defects to the paper. On a paddle boat, you could probably accept a lot more wear than a paper machine - and run a lot longer between block changes.
Terry S.
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Greg, I think Terry's got a point. What would the original alligator used for bearings? I'd bet on maple.
Easy to make and easy to replace on a regular maintenance basis.
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