Tapered Thread Question

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NoShopSkills

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Hi all!

I am building an axel assembly to blue prints for a rag and tube airplane. The wheel axel detail on the blueprints shows a 1" pipe thread on the end to retain the wheel bearings on the sleeved portion of the axel. The prints call for a 1" pipe nut drilled for a cotter pin.

Pretty straight forward and I probably have a friend with a pipe threading machine that will be able to thread the end of the .125 thick 4130 steel tube I'll use. I know male pipe threads are tapered, but I can't seem to find a source for a large pipe nut. Are female pipe nuts also threaded?
 
Hmmmm,
I have that "this all sounds very scary, we should all move a safe distance away" feeling.

Could you please elaborate on this "sleeve" thing you are talking about?
What is this sleeve doing? Is it acting as a spacer between the bearings? Is it a crush sleeve? Is it a simple tube that the bearings races ride on.
What king of bearing are we using? Tapered roller like in a car/truck? plain roller/ball like on a wheel barrow? A big sealed unit like used on front wheel drive cars?

I can't think of a worse way to retain a wheel bearing than a pipe thread. Either there is some confusion from the blue print author over pipe threads, or he just had some junk laying around he put to use.

Pipe threads only have good thread contact when they are tight, which will probably not be the correct distance up the shaft for proper preload. The looser the nut, the less thread engagement you have, the nut could pop off the axle even though you think it is threaded far enough on.
This work should be done by a castle nut.

A pipe thread "nut" is a $0.25 pipe cap. Just machine off the top to make it look like a nut and use a crescent wrench to tighten...

The only way this sounds like a good idea to me is if you are using a pair of roller/ball bearing spaced apart the width of the hub, like a wheel barrow wheel. In this case, you want the axle to be overlong so that when the "nut" is fully tightened, there is ~3/16" space between the nut and the inner bearing race. You would then use shims to take up the extra space.

-Josh
 
RJSakowski said:
Are you sure that the thread is tapered. Pipe threads also come as straight thread. These are commonly used for electrical conduit. Anyway check out McMaster Carr. http://www.mcmaster.com/#standard-pipe-nuts/=xgvshy
Click to expand...

Hey; You know you're right. I found some 1" pipe in the scrap bin that is not tapered. looking close at the drawings, they do not specify anything beyond "pipe thread" so I guess if I need to I can turn and thread nuts for the application without worry about how the taper would affect them. Also think I use the 1" pipe I have and sleeve the bearing rest with 1-1/4 .125 4130.
 
joshua43214 said:
Hmmmm,
I have that "this all sounds very scary, we should all move a safe distance away" feeling.

Could you please elaborate on this "sleeve" thing you are talking about?

-Josh
Click to expand...

Well, I'll show you a photo of the print.

axel detail.png axel detail.png
 
pretty standard stuff for light planes. Here's a light sport version of a production equivalent axel and wheel. The aircraft is a Carbon Cub.

IMG_7254.jpg
 
the sleeve is just a surface and yes the bearings are tapered roller types. Tension is typically held by the castled and cottered nut to be just tight enough to stop free rotation after spinning the tire freely in one revolution. Ideally side loads are minimal in the application but no guarantee that poor landing technique won't impart a side load,
 
NoShopSkills said:
Well, I'll show you a photo of the print.
Click to expand...

Excellent, thank you.
The pic makes it all clear :)

I would suggest using a castle nut and special washer from a trailer or truck like this
180px-Castellated_nuts.jpg
Back when I was fixing cars for a living, I saw someone lose a front wheel when the bearing locked up. The last person to pack the bearings used a big plain washer rather than a washer with a tab. When the bearing seized, it just sheared the cotter pin and spun the nut right off. All the debris was still under the dust cap bolted to the wheel.
3/4" is pretty standard on automotive and light trucks. Trailers and 1 ton trucks use bigger nuts.
Just stop by your local NAPA and tell them what you are up to, or hunt around online. You should be able to get a pair of nuts/washers for pretty cheap and it is a simple matter to mill the slot on the spindle. You could even cut the slot with a 4" cut-off wheel if you have a steady hand.
 
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