Unique Aluminum trials Frame

Yesterday I finally comnpleted my first ever aluminum trials frame. Actually, it’s the first frame I’ve ever built, and my first ever machining project, ignoring the bc plates, which I started after it anyways. It has about 50-70 hours of shop time put into it. No more than 20 of those hours actually involved the cutter touching the metal, but setup on a manual mill when you’re a beginner takes about 70% of the time. I think that if I made this exact same thing over again, I could do it in 30-40 hours.

I ended up using 2 major tools on this, the lathe and the mill. Bandsaws were also used, but just because they are fast, efficient, and easier to setup.

The material is 6061-T6 aluminum. I cut the parts out of 3 original forms. A 2"x5"x22" piece of bar stock, a piece of 1/2" plate, and a piece of 1.250"x0.180" wall thickness tubing. The bar was what the crown came out of, the legs came out of the plate, and the seattube was cut out of the tubing.

The frame is 4.75" wide at it’s widest point, but in the end it is effectively 4.5" wide at the crown, where it matters. There is an 8" seattube, which is plenty for me. Good thing, too, since it took 3 tries to cut the right size for the seatpost in it, and by the 3rd try 8" of tubing was all that was left. The seattube is made to fit a 27.2mm seatpost, and there’s about 6-7" of space for the post to fit in. Past that the boring bar chattered too much to be usable on the tube, so I gave up. THe bvearing holders are machined into the frame, and are of a main cap style. They are for 40mm bearings, and have a small lip on the outside to help to retain the bearings. The bottoms are just stamped steel UDC bearing holders. I used 10-32" screws to attach the holders to the frame, which isn’t ideal, but it works.

A quick overview is that I haven’t ridden the frame much, for 2 reasons. The first is I haven’t had time to make a seatclamp for the thing, and the second is that my trials wheel needs a new hub, so I can’t really do any good rides on it yet. The frame felt extremely stiff at the the shop, and there shouldn’t be any of the issues with it that were found on Justin’s SH frame.

The basic design for the frame was taken off of a SH frame design, pictures of which can be found here. You can see a resemblence in the fork legs and crown/forkleg interface, but other than that, everything’s changed. Rather than being 1.5" wide, the crown is 2" wide. There are 2 cross-membery thingies instead of 1, and they are of a different shape. That frame is for a muni, this one’s for a trials. Mine has pins in the crown and seattube, while that one doesn’t. The bearing holders are also drastically changed. My seattube is also thicker walled near the bottom and longer. The crtown-forkeleg is so different there’s no reason to bother trying to explain it. There are other differences, but they aren’t as major.

I plan to put pins in the crown for foot on crown tricks, but my initial attempts at 1fww and standup ww have been already gone well with plenty of grip. Sadly it’s raining right now, so I’m not going to try much more for a while.

The crown-forkleg interface uses 2 1/4" spring steel roll pins and 2 stainless 10-32 screws to attach it, with the heads of the screws reccessed. They are placed at opposite corners to eachother.

The seattube-crown interface went amazingly well. It has a 0.002" interference fit with the crown, plus 2 3/16" stainless roll pins on each side. There is also semi-permanent locktite that I slathered on there before inserting the tube. I put the tube in a freezer for 90 minutes, and then when I tested it on the crown, it had a nearly perfect fit. Now it’s as solid or more so than if it were welded.

If anyone wants details or pictures of fabrication of the frame I’ll provide them, but otherwise I won’t bother. I don’t have pics of the cuts in progress (holdign a camera and running a mill at the same time sucks), but I can get pics of the tools used.

I think I will anodize this frame blue to fit my rim (blue try-all), but I’m open to other ideas. Anything but red, since red, silver, and blue is just disgustingly patrotic (no offense, but I refuse to ride the Americycle). I found a site describing how to anodize at home, and I checked with the shop, and we have all the equipment neccessary for the task. I may anodize it Monday or Friday.

I would like to hear any input you can t hink of on ways to lighten or strengthen the frame, or other possible improvements or changes, since this is just a prototype.

Thanks for reading.

BTW, the pics are cropped so as to keep the file sizes down for those of us not gifted with the power of fast internet access.

Here’s the clearance. It was a bit tighter than I’d like, but I still think it can work.

clearance of tire.jpg



Thanks, but at 50 hours by minimum wage standards in SF ignoring material costs, this frame would run around $400+USD (SF is 8.75 an hour, but I rounded to $8). If you paid a machinist to do this, it’d cost you around $1000-$1500. I’m happy to share the plans with anyone who wants them, but the only other people who will be getting these are the 3 people who have been kind enough to test subsequent models. The material costs for this aluminum actually runs about $75-$100 per frame, but I got a deal so I have enough al. for about 5-8 of these frames for $40. Sorry. It’s also worthy of mention that this frame took 3 months to make, and most aren’t patient enough for that.

damn lol

As a good Socialist, I expect you will be making these for all your Unicycling Comrades. We don’t have the skills, nor the funds to afford such a masterpiece. Please Comrade do the right thing. From each according to their talents, to each according to their needs.:wink:

Nice work! One suggestion I have is to smooth the shoulders where your legs will pass to minimize catching.

That is a very beautifull uni, id paint it maroon…


Slick looking.:smiley:

Hmmm… I have access to a machine shop, get plans… learn things… make cool frame!

Ahh, let us know how it works when you’re riding on it.

Well, I will post the weight when I get it, but I still expect it to be around 1.7-2lbs. Somehow my faith in this number is shaken though, by the fact that it feels a bit heavier than my 20" united frame, which is around 1.9-2lbs. Still, though, it looks cool, and in the end that’s all that really matters, right?

Seriously, I’m thinking of cutting weight by thinning the crown 1/8" on each side, drilling a few more holes in strategic places.

I like the idea of maroon. I’ll look into it.

Bob, are you saying you’d like a set of plans, or are you just reflecting on my attitude towards this project? If you want a set of plans, PM me and I’ll try and dig mine up. I have them drawn, which isn’t ideal, but I figure I could scan them when needed.


Excellent Work!! I can appreciate all the hard work that went into the fork along with the planning. It’s a rush when you spend all the time designing something and building it yourself and then getting to test it. It does really look very very cool.

Wait a few years down the road after you have built a few more and you look back on this fork. I hope to talk to you then.

Keep up the innovative thinking.

Can’t wait for the riding impressions.


That is one fine looking frame!!!

Congrats on your hard work :smiley:

you have to tell us how well it rides

It looks rad, but I am concerned about the sideways force. If you do a side hop down a couple of stairs is that flange at the top, where the screws are, going to hold? It would be really suck if you take it out and bend it.

Aluminum can be tricky.


congrats, great job

Hey that looks great. But unless you really want to be able to fully disassemble the sucker I would think about throwing some welds on the joints unless you want to risk the chance of stripping all the threads out of where the flange and forks are held together. It doesn’t take that much force to strip threads out of aluminum.


Looks good! Congrats on sticking with the project through to completion. It is a lot of hard work and you should be proud to have done that at your age. It doesn’t matter if it turns out to be light or heavy, strong or weak, at this point it’s all about the process.


Scott, I agree 100%. It’s really nice to hear that from you, knowing what kind of work you’ve done.

This frame is NOT disassembleable at all, with the exception of the bearing holders. It’s hard to tell without reading my first post (which I now notice to be exceptionally long), but there are only 4 screws in the crown. Two on each side, and then the other two things are spring steel roll pins, which are extremely strong. The seattube also has 2 stainless roll pins in it.

Welding aluminum means it has to be heat treated, which means it can’t be fabricated in a small shop such as mine, which means it’s not something I want to do. Thos roll pins are extremely strong, and I’m not concerned about it coming apart. Lateral forces could be an issue, and the only thing I have to say to that is we’ll find out.

I have decided to take 1/8" off the crown in front and back to cut weight, and also drill it out a bit more. If it’s overbuilt on the first prototype, and nothing flexes, then I learn nothing about the limits of it, and where’s the fun in that?

Awesome job! That is a very nice frame and it must feel great to have finished such a master piece. I’d love to be skilled like you and have a go at making my own frame, but thats not going to happen so I’ll marvel at your skills instead :smiley:
I think the only difference could maybe be a bit more clearance :stuck_out_tongue: because even if your riding trials a stone could get stuck in your tire and that could chuck you off, stones always get stuck in my tire, luckily my frame has lots of clearance. Anyway good job!