Shortening Drive Shaft

[a64pilot]

Originally Posted by capt jgw

If you've got a bottom job planned anyway, wouldn't it be easier to just pull the shaft out then and do it with a proper drill press?

That is an option, have to remove the shaft log or the rudder though to pull the shaft, but then you get to inspect it for pitting and straightness, although I paid somone to do that just shy of two years ago.
I keep waffling on that, as is I'll be paying someone to do the bottom job as I work full time still and it all adds up, you know?

[Cheechako]

I would go up on pilot drill size from 1/8" in stainless hand drilling. Maybe more like 3/16". Extra drill bits in one thing, the tip broke off in the hole is another!

[um saudade]

To reiterate a couple of points. If you are off by .010 when the drill bit comes out the far side you are screwed. You will then have to ream it out to accept something else. Think about the fact that it’s not easy to do this in the shop, let alone with a hand drill.


I like to err on the side of caution and I like doing things once.


On drill bits: Assume I don’t know a thing but please take the time to learn. The standard 118 degree bit is worthless in stainless and I don’t care what it is made from. The 135 degree bit is better but still not what stainless wants to make a clean hole with minimum heat. Most austenitic stainless likes a 140 degree included angle and the lip angle needs to be increased from standard drills.


Trying to drill heavy stainless with a standard 118 degree drill is like trying to force a wood bit through a block of aluminum and then bitching about how poor the bit was. Or worse, breaking it off because you were trying to force the wrong tool to cut a hole in your shaft.


With the right drill bits the hole is no big deal. You have some shaft to play with as you will cut it off. Try your method in the part that gets thrown away, just for practice. If it works like a champ I stand corrected.



Good luck.

[boatbod]

Please have a medic and ambulance standing by when you make the cut, for the hacksaw is very likely to be ripped out of your hand and introduced smartly to some other part of your body. Your diesel engine doesn't care about work hardening and tool grabbing.

Since I presume you are talking about a Hurth V drive with a through-the-transmission coupling, it won't actually matter if you make a really accurate cut or not. The more important job it going to be installing the pin, since that is (apparently) what will be transmitting the torque. I do have questions about that though; when I had a similar transmission setup utilizing a Vetus flexible coupling, it was fitted with a keyway to transmit the torque and the taper-pin was just a retainer. Have you disassembled your coupling to inspect it?

[a64pilot]

I've not taken it apart yet, bits I have are cobalt 135 degree.
I am surprised at no key myself, although a key ought not be relied on to absorb torque. I may find a key, if I do then it just became a pro job, and unless shaft is perfect, I assume a new shaft. I have never removed coupling, just separated for alignment is all.
If there is a key, likely it's a half moon key not a square one.
My assumption is its just not that much torque, it's just 44 Hp, not 440 after all.

I had a bush hog that all that transmitted the torque was a bolt through the shaft, it sheared early and nothing but an NAS aircraft bolt seemed to hold. NAS is roughly equal to a grade 8 I think, but that was a bush hog that frequently hit stumps etc. Not a good design, others I have had had slipper clutches

I guess if hole alignment is off a little a way to do that is to drill one hole 90 degrees from existing hole, then slide over the shaft and drill through, that would make the holes match, cause hole alignment does have to be perfect, possibly more so than is achievable with a drill jig.


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[chris95040]

Man, trying to drill a hole like that in situ is stressing me out just thinking about it. (Not a judgment - I'm just a wimp.)

If this through bolt is a sloppy fit, won't it just get progressively sloppier over time? I did something like this on my go-kart when i was a kid. A little slop quickly turned into a lot of slop... Does tightening the through bolt provide clamping force? I guess that would eliminate this concern?

Another thought, if the reason for all this is that you are chasing vibrations, maybe you want a machine shop to fit + face that coupling in it's new spot so you really know it's perpendicular to the shaft...

[pcmm]

just mark the shaft and take it to a machine shop with $20 cash on a saturday to give to the kid there. they'll cut it in a minute flat! way easier than trying to do it by hand.

[a64pilot]

An issue with taking it in is the $350 or so to pull the boat, then I have to pull the shaft log or the rudder. Quickly turns into at least a $500 bill before any work is done on the shaft, and if your going to spend that kind of money maybe just buy a new shaft, and do a bottom job while the boat is out, plus yard fees for storage.
About $2K ought to do it? No sarcasm, it's the way these things go
I'll look at it this weekend, best way I think is to drill one hole in the coupler after drilling the shaft, install the coupler and finish drilling through the coupler with it installed, this would ensure perfect alignment, and honestly I don't think you could get a perfectly straight hole any other way.
An expanding pin would be another way, if anyone has ever pulled blades on a Hughes helicopter, you know what I mean by expanding pin, but I don't know of any that small.


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[Snowpetrel]

Hand hacksaw the thing off, or use something like a multitool, I'd probably just use a angle grinder myself with a skinny inox disk.. There are clamp on split couplings that don't use a keyway, sometimes they have a grub screw as well. Might be another possibility if drilling through the shaft is a problem? http://www.randdmarine.com/downloads/RandD_Damper.pdf

[topmast]

You can pull the coupling off the shaft with a puller if room or put a large socket ( smaller than shaft) in the gap and use longer bolts to force it out.Then if there's no key, just cut shaft with zip blade ,grind bevel the cut and reinsert in coupling, drill away .The whole process sounds tacky to me .If you don't like vibration the shaft should be keyed /fitted and drilled in a machine shop The coupling is faced true to shaft at same time.

[pcmm]

Originally Posted by a64pilot

That is an option, have to remove the shaft log or the rudder though to pull the shaft, but then you get to inspect it for pitting and straightness, although I paid somone to do that just shy of two years ago.
I keep waffling on that, as is I'll be paying someone to do the bottom job as I work full time still and it all adds up, you know?

Just do it as part of your annual haulout and there is no added cost that way!

[Frankly]

I went through a shaft shorting last haul out. My old one was too worn at the cutlass, had a second but it was a little long. Had a machine shop cut the keyway (don't remember why I didn't just have them drill the hole in the shaft while they were at it). Put the aft half coupling in a drill press vice, started with a new bit and aligned the coupling holes, inserted the shaft and drilled away (with a drill press). Worked out just fine. Just cut the shaft with a hacksaw as that end was not critical. Don't think I would try a repeat with a hand drill and in situ.

If your motor mounts are old that might be the reason for the vibration. Just replaced mine for the second time in 11 years (Autoprop is part of the reason). Yanmar recommends replacing those things frequently as they are soft and the rubber is loaded in shear to reduce the natural frequency. Be sitting down when you get a price ($600) for my 3GM.

[Sailmonkey]

Originally Posted by pcmm

Just do it as part of your annual haulout and there is no added cost that way!

In these parts we haul once every 3-5 years......I'd go broke hauling annually


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[UNCIVILIZED]

I'm not sure what IP used for prop shafts, but if it's Aquamet then it'll likely be more difficult to machine than is regular stainless (sic). Since Aquamet is generally harder to begin with, if memory serves. So it'd be worth checking into before setting your plan in motion, so as to avoid any surprises.

[jimbunyard]

If you have enough room to do all this I say go for it, the worst thing that can happen is you have to pull the boat and shaft and do it the 'right' way...

That being said, the idea of cutting the shaft via engine rotation sounds way too scary for me, especially since it can easily be cut with a thin, 1/16" abrasive disc on a 4 1/2" disc grinder. The cut does not have to be perfectly square. The 316, 1 5/8" rudder shaft in the picture below was cut to length with an angle grinder.

Regarding drilling the hole, also in the picture below, the 3/8" bolt hole through the center of the 316 homemade rudderhead fitting and shaft was drilled in one pass (no pilot hole) with a handheld 18 volt Dewalt drill with a single new 3/8" standard long drill bit, with no resharpening. It took one and a half (or so) of batteries, and constant clearing and oiling (motor oil) of the bit and hole. One side of the fitting was predrilled at the shop where we made the fitting, enabling me to use the fitting itself as a drill jig after I had finished the building the rudder. I was leery of drilling it all the way through because of potential alignment issues. Total length of hand-drilled hole was 3 5/8". If you can secure or clamp the flange to the shaft, and if there is sufficient thickness to hold the bit perpendicular, with a steady hand and patience you may be able to do the same.

When I moved onto the land I now live on I too had problems with my bushhog constantly breaking the bolt that held the drive flange to the shaft (it has a pretty loose fit). The fix for me was a used head bolt that was the correct size, haven't replaced it in at least 15 years (it'll probably break tomorrow).