SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

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cyberbadger
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SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by cyberbadger » Fri Jul 29, 2016 4:55 am

Hello,

I didn't realize my 18" diam x 24" pitch prop is tapered.

I just got my order from mcmaster carr that I was going to use and I had planned on a 1" straight keyed SS shaft.

I had ordered a 2ft long shaft, but I have wiggle room in that figure. (There is another intermediate shaft which is unimportant to this question)

Online price listing say about $300 for a SS 1 1/4 SAE J755 propellor shaft, which is what the propellor seems to want.

From 1.030"->1.250" in 3.500" in according to the spec and the propellor as I measured it.

Is there any options for this, or am I basically stuck with buying a new $300 2ft shaft? I have a lathe, but the tailstock is out of commission and I don't really have the personal machining expertise to do a tapered shaft myself.

Are there straight to taper adapters/bushings, any ideas?

$300 just seems a bit much for a 2ft shaft, but maybe I don't have my marine price glasses on my eyes ...

-CB
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by barts » Fri Jul 29, 2016 5:28 am

There are shops which can turn a taper like that on your 1" shaft for a lot less than $300; you want an adapter sleeve (plastic will work fine).

http://www.propshopinc.com/Propeller-Bu ... -p190.html $23.40 in nylon. I have one of these on Otter - no problems at all.

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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by cyberbadger » Fri Jul 29, 2016 8:29 pm

Thanks Bart!

I just found the perfect job shop that's 15 minutes away and has a lower fee schedule for individuals. The one man operation is into hit or miss engines and is very interested in see Nyitra in person - a like minded individual who is willing to work with me.

He's going to make 1 bushing that will go from the 1" straight shaft -> 1 1/4 SAE 755 Propellor shaft for about $60.

I'll post pictures when I get the completed part.

For anyone in the Akron-Cleveland area It's:

Harrison Performance & Machining LLC
1660 S Clevelanhd Massillon Rd
Copley, Ohio 44321
Dan Harrison Owner
themachineshop@live.com
330-576-3220

-CB
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by barts » Fri Jul 29, 2016 10:53 pm

You'll need to machine a small taper or step on the 1" shaft to keep the prop from sliding up.

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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by fredrosse » Sat Jul 30, 2016 12:14 am

Another option for those who do not have a taper turning attachment on their lathe, and do not wish to offset the tailstock center. You can adjust the tool post mount to the proper angle to turn this taper, and take several cuts running the short traverse of this slide. Diameter reduction of 3/4 inches in 1 foot is a cutting angle of 1.79 degrees, make some trial cuts on scrap material to get the required angle close enough.

Although for $60 you are getting a bargain price.

Also note that boat prop shafts often turn up on e-bay
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by Lopez Mike » Sat Jul 30, 2016 4:51 am

I would stick with normal prop tapers on both the shaft and the prop. Fred's solution has worked best for me. And it is important to experiment to get the taper right. Even with a good taper attachment it is not possible to just set the angle and go for it. At least if you want things to work with every other shaft and prop in the world.

I think these taper adapting sleeves are available ready made though it isn't that big of a deal to make your own. I haven't used a plastic one but I have made at least three of them out of bronze.

Here's the drill:

Chuck up some bronze round stock in your three jaw. Face, drill and then bore a tapered hole to match your shaft. You will have to fool around a lot to get the compound set right. You will overshoot back and forth but eventually you will get it right and then can bore the tapered hole to the right diameter at the large end of the hole. As Fred noted, If your compound travel isn't enough to make it with one long pass you will have to do it in two or more stages. This will take some care as you don't want to go too far. If you go a few thou too far then bore out the earlier parts to match.

If the shaft rocks back and forth at all, you don't have the angle right. When it is right, things tend to get stuck.

From here on do NOT disturb the angle of your compound.

Now remove the bored out round stock from the chuck and replace it with your tapered shaft. Try to get it as true as you can. I use a four jaw and a dial indicator at this point. Or a collet. Often I fit some shims where the shaft comes out of the other end of the headstock to keep it from whipping around. Fit the half completed adaptor to the shaft and seat it with a good whack with a dead blow hammer or a hunk of lead. Now turn the outside of the adaptor (using the compound) until you have it down to the right diameter and length to fit your prop.

Now if you had a big enough lathe you could try the prop on the adaptor without removing everything from the lathe. I have a 19" lathe I will GIVE you but you gotta come get it!!! 4000 lbs complete and 12' feet long!

Now you have a bronze adaptor but it needs to be split lengthwise to clear the key and be free to fit the shaft and prop. This can be done on a mill but I do it with a hack saw. Precision not important as long as you make the slot wider than the key. Generously wider. You don't want it to grip the key. As soon as you split it you have a relatively weak thing to don't step on it. Don't ask. When it is in place it is invulnerable.

Now you have to make a custom key. Normal width (1/4"?) but thicker. Thicker by the wall thickness of your new adaptor.

Whang (that's a technical term for moderate violence) it together and tighten the prop nut down.

The one on my sailboat has been in there since 1987 and has stood up to a circuit of the Pacific ocean. So far, so good.
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by cyberbadger » Sat Jul 30, 2016 6:55 am

I sent the machinst an email, this is what I clarified with him and want done. He had to leave for the weekend when I met him and give him the shaft and the propellor...

1) Turn SAE 755 1" Taper in Shaft
2) Cut left hand threads(Your pick) in Shaft [[propellor is right handed]]
3) Create Nylon Bushing SAE 755 1" Taper -> SAE 755 1 1/4"
4) Purchase/Find Brass/SS nut for Shaft

I could specify bronze, but that might be a a higher machining time charge. I have free maching brass round I could give him that has enough material I believe.

-CB
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by Lopez Mike » Sat Jul 30, 2016 1:59 pm

I've never heard of using a left hand thread on a propellor shaft. I'd change that.

My wife owns a 40' power boat/house boat with twin screws and opposite rotations and both prop nuts are right handed.
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by Lopez Mike » Sat Jul 30, 2016 2:11 pm

And NO brass below the water line!!! The zinc will dissolve into the salt water and you will have porous copper left. About as structurally sound as moldy cheese. Make it out of bronze.

A plastic one can work but that has issues as well. Plastic is slippery stuff and that throws the torque on the key. A key is just a weak spine and is only necessary when there is a chance that the prop will come loose on the taper or to index something. With metal to metal contact and a decent job of torquing the nut down, the key does nothing. I used to have a hydroplane with 600 h.p. and had no key on the prop. A keyway would have weakened the prop. It was a 12 x 12 prop turning 9000 rpm and it never came loose.

I use a #4 morse taper with 2" and 3" drill bits on the tail stock of my big lathe and have very little problem with them working loose. No nut. Just whack then in place with a hunk of lead. As you might tell, I have a poisonous opinion of keys.
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Re: SAE J755 1 1/4 Propellor Taper <-> 1" Shaft options

Post by cyberbadger » Sat Aug 13, 2016 5:18 am

Mike,

I followed several bits of your advice.

What I had done was Dan Harrison took a piece of 304 SS 1.25" diameter and made the 4" taper directly in it. The threads are right handed 1"-14TPI. The propellor hugs the taper like a a snug as a bug in a rug. It takes hamering with a rubber/plastic mallet fiercely to free them apart. I am looking at using a thread locker blue for the nut, just so it doesn't loosen by vibration. A 1" washer helps the nut have good purchase on the prop.

I didn't have Dan make it keyed. A few blind holes were drilled so the bearings have purchase on the shaft. Dan explained to me that a keyed shaft has right angles, and you are effectively loosing the full strength of the full diameter of the shaft. He said a hole would be round and distribute the load. That explanation made sense to me.

The different finish is we had a fit issue with the bearings. Can't blame the machinist - I didn't provide the bearings themselves nor a tolerance.
So I tried to polish it down to dimension to save money, ended up slightly damaging a few threads and finally decided I had invested enough already and had to stop and have Dan Harrison do it correctly before I destroyed the piece!!

I don't claim to be more then a hack machinist, and this was a critical component for Nyitra that I knew I don't have the skill right now to do properly.

I also had Dan bore out the timing pulleys to the correct ID. His fees were better then equitable for me. It was a pleasure to work with him and I am sure I will return to him if I run into something I can't handle.

Actually he may have caught the bug. :twisted: When the transmission is complete I'm going to run a dry dock test in my backyard under steam and he is going to pop by when that happens...

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-CB
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