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Redoing a power wheelbarrow poor wheel design

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modela

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As I have said before, I volunteer on a bunch of projects at Mt Pisgah Arboretum varying from bridge building to equipment maintenance. My last project was to fix a Power Barrow that had a problem with the front wheels falling off. It was another one of those, "What have you been doing? We have a trail building project coming up," kind of things.

The front wheels were held on by a cheap, but shiny drive-on cap. They are almost impossible to get off when you want to get them off in best conditions but in this case they are recessed in the hub. On the other hand they just seem to periodically fall off. I am sure you have had something like that, probably called Tonka or "Big Wheels". Great for toys, but for an implement, I don't think so.


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I liken it to a chrome plated version of the one a friend used to assemble wagons and tricycles when he worked at a department store in High School. He said, "I know exactly the type of axle caps you're talking about." He sent me this picture below.

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I had to destroy the one pictured above to get it off, tearing up the decorative chrome placed cap and then picking at the teeth until they released. It took me about 45 minutes to get the thing off. Thankfully the one on the other side had spontaneously fallen off.

So, my task was to make something more substantial and as usual, do it quickly and so it would last that attack of some of the most machine unfriendly, brutal volunteers. I decided to make a heavier duty, removable set of hub caps. Since the axle is recessed I had to devise something that would hold the wheels on and yet be easily removable to fix flat tires.

I turned the caps on the lathe from 2" diameter aluminum rod to fit the recess in the hub. I tapped 1/2" 13TPI threads in the new caps and ran an all-thread bolt through the center of the tubular axle. I left a little ledge at the center so that it contacted only the inner part of the bearing without touching the seals. I left the inside a bit rough not wanting it to turn.

I made a few passes with the milling machine to make a place to tighten the hub caps. The caps tighten up against the inner part of the bearing. I added the jamb nuts (nylocks) to prevent the caps from loosening.

Tightened, the set form hub caps of a heavier nature that are hopefully up to the task and easily removable when necessary.

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I know I could have really spruced this up, but as usual they needed it yesterday and I turned it out quickly, hand filed the roughness off the edges and prepared it for delivery. I figured the aluminum would stand up pretty well without paint. Besides, I was out of etching primer and it was getting late. I loaded it in my pickup and delivered it the next morning.

Next is the torture test at a Mt. Pisgah trail building project.

Jim

P.S. notice how the front and rear wheels are of different size. The tape was used to see their different rates of turning. They do turn at different rates but it seems to work. There are other shortcomings of the design, like even when you get the hubcap off it is a bear to get the wheels off because their is no adjustment on the intermediate wheel.

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7HC

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Good job! Hard to imagine that those cheap caps were used on a piece of commercial equipment.

I hope they're treating you right. I've known several projects fall apart when the project manager(s) started treating the volunteers like employees. :angry:


M
 

modela

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You are right, it is hard to believe that someone did such a crappy job of design and execution. On the other hand, the units were donated relatively unused because the contractor couldn't put up with the continuing problems. From that standpoint I was glad because the unit otherwise is pretty well designed. I may have to revisit the non-adjustable character of the middle wheel.

One of the things I learned from the volunteer coordinator was that everyone has their unwritten expectations as a volunteer, probably because they are giving something for free. He does a pretty good job of it. Last year they ran me ragged fixing things. This year I have learned to say no. I could be a full-time employee but that is not my desire. Regardless, I know they are really understaffed with tremendous expectations. That is the case for a lot of non-profits.

Having been a boss for over 20 plus years I can understand a lot of those expectations. I just try to be a good employee with a fixed number of hours donated. I try to commit time to things that I know I can do that would be costly if they had them done otherwise, things they couldn't fix in their limited shop.

Some of the projects, like the bridge building projects, are a lot of fun. Even this one was fun, correcting manufacturing deficiencies. By the way, this model has been discontinued.

Jim
 
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