Babit Bearings

[f350ca]

Was going to throw this in the alligator build thread but thought it might be better here.
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. Roller or ball bearings would work but 3 inch bore bearings get pricy unless of the oriental flavour and Im not going there.
What about welding up a split pillow block with cavities for felt seals and pouring a lead based babit bearing?
I poured some decades ago in the steel mils during a summer job as a millwright helper but thats about it.
Does the shaft have to be particularly hard or should regular pipe work? What about surface finish?
Thoughts and comments welcomed and appreciated, except for thinking Im crazy, that goes without saying or discussion.
Thanks

[PixMan]

Wish I knew more about babbit bearings to give you a good answer. What I do recall is that you do need a VERY fine finish on the shaft to avoid galling and scoring the babbit as it's fairly soft. That speed works out to about 157sfm, that's OK for babbit bearings as long as the load is evenly distributed. As far as I know babbit is used in Ford Model A engines (and many others) and those run at much higher speeds.

[ETC57]

I tend to agree with Pix Man on finish your shaft should be reasonably hard with a fine finish, when I was a much younger lad we used babbit bearings in the the 36" jaw crusher at the gravel pit.
When it was time to re bearing, the crusher went out for service so they could check and resurface the shaft before pouring new bearings.
Simpler times, make small rocks from big ones!

Jerry

[Mayhem]

My lathe uses babbit bearings and I can approach 500rpm in top speed

[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.

[f350ca]

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?

[Terry S]

(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.

[f350ca]

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

[Terry S]

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.

[stevec]

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.