Framebuilding questions

If you equate paying more with better quality.

George Barns gave me the tip to buy from the Chassis Shop it is the exact same stuff at a lower price. All their seamless 4130 tubing is aircraft quality spec MILT 6736 B.

They are mainly selling to people building race cars and their catalog is a harder to figure out, their pricing is by the inch. They have the lowest prices I have found anywhere and I have looked around quite a bit they also have reasonable shipping costs they only charge you what it cost to ship UPS ground.

I’d suggest that you rent a proper welder. A unicycle should be a fairly fast project if you have all the parts cut and ready to go when you pick up the welder.

Sorry; I was thinking this was a local Colorado company. Do you have a link to their website?

Is it this company?

I do know how to Google. I just didn’t look before I posted.

yep, that’s the place, i think i’ll probably check them out after i check my local connections, their prices may be better than i can find from a local shop. any ideas on where to get bearing holders? it doesn’t seem to have come up yet in this thread, just curious what people’s thoughts were.

you could use 4 of the bottom bracket things and weld 2 to the frame, or use a milling machine and drill out a block of metal, but that could be awkward. or if you are really bothered cast your own, but youd need molds and a a forge and something to melt enough metal, and that makes that way kind of hard thinking about it
i think the bracket idea would be the best way to go really

buy the pressed steel bearing holders, as linked before, or buy some 40 or 42mm split machine collars and weld small plates on the same to stop sideways bearing movement

As long as we are talking about sources for things, does anyone know where a good place to find machine collars would be?

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http://www.unicycle.uk.com/shop/shopdisplayproduct.asp?catalogid=1048

Unicycle.com has recently made these available. http://www.unicycle.com/shopping/shopexd.asp?id=1182
I havent had the chance to order some to check ot the quality but they have to be better than these http://www.unicycle.com/shopping/shopexd.asp?id=513
Which is what I have used mostly before and I think they work ok even though lots of people dont like them. What I like about them is they are light weight the problem with shaft collars is they are pretty expensive and they weigh a ton. I bought a pair of 42mm split shaft collars at $20 apiece from Grainger recently thinking I would try them but they are huge and the pair of them weighs one pound!

Now that the Nimbus bearing holders are available I’m sure I won’t be useing anything else.

Just thinking here:
I was measuring some 2 inch pvc pipe I have laying around and noticed that the interior diameter is almost exactly 40mm. Would it be possible to cut a small section of 2 inch metal pipe and work it somehow to be made into bearing holders? I’ll come up with some drawings later, but just curious if there’s any point in trying something like this.

Something like this:

I realize there would still have to be a lip to keep the bearings in place, but would there be any problems with strength etc? What do bearing holders do, other than hold the bearings? Is there a danger of hurting the bearings if the bearing holders aren’t strong enough? The basic ones you buy from UDC don’t seem very strong themselves, so I’m wondering if there’s any danger of catastrophic failure with something like this. Has anyone ever had a bearing holder fail on them?

Pipe Bearing Holders.bmp (485 KB)

The way you have drawn wouldn’t work very well but you are almost on to something.

The way that was recomended to build bearing holders in Jack Wilies “The Unicycle Book” was to take a piece of 2" pipe and cut two slices as wide as the bearings. Then braze on two short pieces of small tubing on oposite sides then cut the slices in half cross ways then use bolts and nuts to clamp them together around the bearing. You could also use bicycle braze-ons like they use on some bicycle seat clamps. I think this is basicly what a Hunter frame has for bearing holders but they have also been machined to have inside and outside lips. http://www.unicycle.com/shopping/shopexd.asp?id=192

All this would work but it would be a lot of extra work to save $20 over buying a set of Nimbus bearing holders.

You’re right that going the Nimbus route would be easier (and probably result in a better product). My problem is that I learn through experimentation, and I don’t want to buy 10 sets of the Nimbus bearing holders as I learn what I’m doing and destroy everything in the process.

For my final rocket frame, I’m going to go with the chromoly from the Chassis Shop and the Nimbus bearing holders. Thanks for all your help. It will definitely come in handy after I’m done learning what I’m doing.

The stuff they sell at Lowes or Home Depot is normally going to be the lowest-strength stuff they can get. On the other hand, this implies low carbon content, low alloy content, which is good for welding, but not good for trying to build the lightest frames.

I remember finding long ago that when you get into somewhat exotic metals, you could oftentimes buy a finished part for what you’d pay to get the raw material to make the part. The problem is lack of demand. Lots and lots of people buy bicycles, very few build bicycle frames, so the tubing for it tends to be less available. And most people doing welding would want heavier-wall, lower alloy stuff anyway.

McMaster-Carr sells a pretty wide range of materials, but they are mainly a wholesale supplier, not a retailer (IE, they sell to businesses, not individuals).

You might investigate buying junk bikes at a police auction or garage sale and cutting pieces out of those frames.

I’m considering doing that. Our local second-hand store is going to be getting all the abandoned bkes from the university at the end of the month (at the end of the school year, they cut all the locks on any bkes left in the racks and give them away to this store). I’m thinking of grabbing a few frames to cannibalize. I was thinking that at least I could get a neck and seatpost that way. I saw one the other day that was only $5.00 because it was missing the chain.

I think you’re right about finding anything close by. Why deal with the occasional hobbyist buying 3 feet of tubing when they can sell 2,500 feet to a local contractor?

Making pieces out of junk bikes is a great idea.

McMaster Carr will sell any quantity to anyone with a credit card.

Would something like this work as bearing holders?

It would still need an outside lip attached, but I think I might have that worked out as well. They are slightly wider than a bearing, and are already split with attaching screws. And I can get them for $2.50 apiece at Lowe’s.

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those look very flexible. The bearing holder is quite a high stress area, flex here will be highly detrimental to the feel of your ride. Maybe they would be ok for your test frames.

NO, That is a ground clamp and I belive it is brass or copper and it would be far to flimsy. If you want a working model I would recomend the Uni pressed cap bearing holders and at $6 a set they are pretty afordable and you can use the bottom half on many difrent frames so…

I have been meaning to ask, What are you planning to build? Is this the interchangeable fork leg unicycle you were planning a while back?