Prop shaft tube, bearings and seal design

[hartley]

Frosty I don't know why you are telling me this either you say and i quote ''a universal joint can take thrust'' I say it cannot ,simple really
.....cheers Hartley

[Frosty]

A UJ in a heavy goods vehicle prop shaft takes many hundreds of ft lbs torque.

The load from the 2 yokes is transfered to the spider and across to the opposing 2 yokes. This load on the needles is no different to load from 90 degrees which would be thrust.

I am sure you confusing this with a constant velocity joint which can NOT take thrust at all and you will no doubt use these on your thrust bearings assembly as do others.

Ask your engineering section, Im sure they will explain to you.

[pdwiley]

Originally Posted by CDK

That's what I meant.
Gerr may state that a taper fit is the best way, but you'll never be able to predict the bearing play until you fasten the flange nut. Is there no slack at all you may have already damaged the bearings and if there is, you have to pull it off again which can be pretty hard. At the next fit it will slide a tiny bit further up the taper.

If you have calculated a straight sliding fit can take the torque, I would do it that way. The only other, stronger option I can think of is splines, but you need special equipment for it. I had my SAE spline adapters made by a friend in a large machine factory and still had to spend several hours with a Dremel grinder in the support of my lathe because the splines weren't deep enough.

I agree completely. Tapers are fine in theory, but there's a downside.

I am leaning towards a keyway plus a Fenner type taper-lock bushing. You can buy the hubs made to have flanges etc welded to them. I have used these successfully on many pulleys over the years and can't see why one of appropriate size for the torque load shouldn't work. What I'm not sure of, as it's never been an issue for me in the past, is if I can get the exact location on the shaft that I need. If not, same problem in essence as a tapered fit, except you don't need to do any machining.

Suitable inboard tapered roller bearings were $AUD 16.50 each and it took me less than 30 minutes to bore a test piece of Schedule 80 pipe to the necessary 62mm inside diameter.

I actually can cut splines if I had to as I have a horizontal mill with dividing head (not that you need one for 6 or 12 splines) and also a vertical slotter for cutting internal keyways and splines. However, it's a pain unless you have a spline cutter of the correct profile and I couldn't be bothered making one for a single job.

A bushing may be better for me than a bearing in the outboard end because, while I can get the bores machined parallel, after I weld the tube assembly into the keel I can't guarantee that the bore will stay precisely parallel. A self-aligning double row ball bearing would be perfect here, but unfortunately I can't find any of the correct size (approx 52 OD, 35 ID).

PDW

[CDK]

SKF only produces 35/72 and 35/80 double row bearings (1207 & 1307), the others normally follow in their footsteps. Your order will not be large enough to make a special.

[Tigawave]

Why not use an oil lubricated plain composite bearing, if there is small mis alignment in the tube, this could be taken up on epoxy bedding. A simple clearance fit plain bearing as used on commercial vessels, some suppliers will supply spiral grooved bearings to actively circulate the oil which also aids cooling. The side loads are small so oil film support will be adequate. These work well for years and there may be no need to reinvent the wheel.

[hartley]

Frosty re uni joints and thrust I dug out an old book by Dave Gerr titled Boat Mechanical Systems Handbook ,under a section "universal joints '' he says and i quote "neither the standard old fashioned uni joints also called Cardan or Hook joints ,nor modern c v joints can take thrust,at least not much '' he goes on to say you may get away with a uni joint and no thrust bearing with a low powered engine ,say 10 hp but don't try it with 300-hp.
cheers Hartley

[Frosty]

I agree I said that a CV can not take thrust.

A universal joint can take massive torque,-- the twisting force from the side is called torque the force from the front or pushing force would be thrust.

As the bearing does not have a thrust side or any side, being roller bearings in a cup then force can be taken anyway including thrust. The limit being the strength of the spider and not the bearings as you suggested.

Now if you are involving mangle then that is a different conversation, and the UJ must be on the output shaft itself as indeed it is on a vehicles prop shaft. One being on the diff yoke and the other on the gearbox drive spline yoke.

Some have centre UJ's but always have a centre shaft bearing holding its position.

[pdwiley]

Originally Posted by Tigawave

Why not use an oil lubricated plain composite bearing, if there is small mis alignment in the tube, this could be taken up on epoxy bedding. A simple clearance fit plain bearing as used on commercial vessels, some suppliers will supply spiral grooved bearings to actively circulate the oil which also aids cooling. The side loads are small so oil film support will be adequate. These work well for years and there may be no need to reinvent the wheel.

Yes, for my lower bearing that's what I plan on doing. I can get ball bearings of the size I need and I can machine the shaft pipe to suit easily enough, but if I get any welding induced distortion there goes the alignment. A bushing is safer.

PDW

[pdwiley]

Originally Posted by CDK

SKF only produces 35/72 and 35/80 double row bearings (1207 & 1307), the others normally follow in their footsteps. Your order will not be large enough to make a special.

Yeah, funny that....

With respect to your outside bearing assembly, I can't see what holds the entire inner assembly inside the 63.5 pipe except possibly the compressed O ring. Is there a plug weld, inner weld or similar that's not shown on the drawing? I can build the same basic assembly except use a longer bushing in place of your ball bearing.

PDW

[CDK]

No, there is just the neoprene O ring.....

Sealing and holding the assembly in place seems a bit much for just a ring, but if the cavity has the proper shape, so the ring doesn't get pinched on the inner side, it exerts enormous pressure on the inside of the tube.
I got the idea when I made a linear motor for outside use. The groove for the O ring wasn't deep enough but I assembled it anyhow, only to find that the shaft seemed to be welded to the cylinder.

The recess in the bearing carrier is somewhat rounded, the one in the cover is flat. I assembled it with the shaft removed, tested it with a heavy object, disassembled it and took a new O ring for the final installation, although the old one didn't show any signs of damage.

[pdwiley]

Originally Posted by CDK

No, there is just the neoprene O ring.....

Sealing and holding the assembly in place seems a bit much for just a ring, but if the cavity has the proper shape, so the ring doesn't get pinched on the inner side, it exerts enormous pressure on the inside of the tube.
I got the idea when I made a linear motor for outside use. The groove for the O ring wasn't deep enough but I assembled it anyhow, only to find that the shaft seemed to be welded to the cylinder.

The recess in the bearing carrier is somewhat rounded, the one in the cover is flat. I assembled it with the shaft removed, tested it with a heavy object, disassembled it and took a new O ring for the final installation, although the old one didn't show any signs of damage.

OK, thanks, I just wanted to check that I was interpreting the drawing properly. I need to think this through a little more but as I'm away from my machine shop etc for Christmas, that's no big deal.

Those drawings of yours are very helpful. I've fabricated most of the bits for the upper thrust assembly now. Mine is completely separate from the prop tube. It gives me one extra gasket to leak, in theory, but makes it easier to manufacture, allows minor alignment tweaks and total replacement/rebuild in the field if necessary. I need to get a taper-lock bushing and see how accurately I can control its position on the shaft before deciding what's best but there are a couple of ways of addressing that including a threaded adjustable bushing between the bearing cup and taperlock bushing or shaft flange. I'd rather not have to, on the KISS principle.

PDW