7005 Aluminum frame build
 

As a hobby framebuilder, I like to keep learning new skills and testing myself. I've built around 20 steel frames, starting with a lugged frame and moving to fillet brazing and then TIG welding. I was interested in trying to build an aluminum frame, mostly just for the challenge of doing something new, but there isn't very much information or materials available to the hobby builder.

I did some research and found that 7005 aluminum is the best option for a hobby framebuilder, since it doesn't require a solution heat treatment after welding. Most of what I found recommends an artificial aging process for 7005, which can be done in a powder coating oven over the course of about 10 hours. I'm sure my powder coater would do it for me, but I didn't want to tie up his oven for an entire day for a single frame. I read on various forums about room temperature aging of 7005, but had some difficulty in finding actual data, especially data concerning bicycle frames. I got lucky and one of my Instagram followers from the UK(who has loads of experience in the field and I don't know if he wants to be named here) sent me some scientific research on the subject, which confirmed that 7005 can be naturally aged at room temperature(70F) and achieve most of its pre-welded strength after around 30 days. Elongation properties are not as good, but most other values are near the same as the artificial aging results. With this information, I decided that I would try to build myself an aluminum Gravel bike.

I had not done much aluminum welding and none on 7005 bicycle tubing, so I needed to get in some practice. Andrew at BikeFabSupply.com set me up with a practice welding kit of various sized 7005 tubes and some 5356 filler wire. After some practice and testing various settings on my welder for AC frequency and balance, I was able to get some welds that led me to believe that I could successfully build an aluminum frame.
https://cimg5.ibsrv.net/gimg/bikefor...89998e3c98.jpg

I ordered most of the materials for the frame from Andrew at BikeFabSupply.com, but I still needed to find a flat mount/thru axle rear dropout in 7005. Framebuilding parts in 7005 are difficult to find and raw material to make your own is non-existant in the US. Luckily, Mike Ahrens makes the perfect dropout, with a weld-on flat mount, that use a commonly available Paragon derailleur hanger. These are basically Paragon round 12mm thru axle dropouts in 7005 aluminum.
https://cimg2.ibsrv.net/gimg/bikefor...4cc460e0f4.jpg

I decided to make this frame as an aluminum version of my steel gravel frame, since I was happy with the handling of that frame and it would be an opportunity to see if the aluminum version would feel any different from the steel.

The mitering and fit up of the tubes was the same as any other frame, except I didn't have any 42mm tube blocks for the down tube, so I 3d printed some to use for holding the tube on the mill and to keep the miters in phase. (I don't have any pics of the tube blocks to post here, but they are on my Instagram @Starrcycles). You can see a bit of one on the downtube, in the picture below.

https://cimg0.ibsrv.net/gimg/bikefor...9236f358f6.jpg
https://cimg5.ibsrv.net/gimg/bikefor...c238af0a9f.jpg
https://cimg9.ibsrv.net/gimg/bikefor...f396d54331.jpg

I decided to weld in the bottle bosses on this frame and that turned out to be a bad decision. I did a test in a scrap piece of tubing and ended up completely melting the boss, because the arc tends to jump to the sharp edge of the boss and there isn't much mass, so it just melts. I did get the two bosses welded in to the seat tube, but it wasn't pretty and I ended up going to the mill to mill the faces flat. The bosses on the down tube went a bit better. I tried putting a stainless bolt and washer in the boss, while welding, to act as a heat sink and the washer helped with protecting the edge of the boss. I also raised the AC frequency, on the advice of someone who had experienced the same issues, and that also helped. I can say with some degree of certainty that any future frame will have Rivnuts installed for bottle bosses.
https://cimg1.ibsrv.net/gimg/bikefor...f342e78bc9.jpg

The welding of the rest of the frame went as well as could be expected for my level of experience in welding aluminum bike frames.

https://cimg2.ibsrv.net/gimg/bikefor...73f4c0517b.jpg
https://cimg6.ibsrv.net/gimg/bikefor...100bfb8ea3.jpg
https://cimg0.ibsrv.net/gimg/bikefor...4b5b2c3a41.jpg
https://cimg7.ibsrv.net/gimg/bikefor...ea8eb8c57a.jpg

Finished frame pics. As I said earlier, raw material in 7005 is not available in the US, so I had to use a cutoff from one of the seatstays for a bridge. I would have preferred to have a curved tube, but that wasn't an option.
https://cimg9.ibsrv.net/gimg/bikefor...d64870e21d.jpg
https://cimg1.ibsrv.net/gimg/bikefor...888d4c61c3.jpg

This is the completed bike. I put it together as inexpensively as possible, using some parts I already had and a Sensah SRX Pro 1 x 11 group and Tektro mechanical disc brakes. The Sensah rear derailleur needed some modification, but otherwise the parts have worked well for the price($120 I think?). The bike has a little over a year and several thousand miles on it with no signs of cracking.
https://cimg2.ibsrv.net/gimg/bikefor...4399f7763c.jpg

I forgot to mention the cable guides. The downtube has 3d printed guides that bolt on to more bottle bosses welded on the underside of the downtube. After the bottle boss welding, there was no way I was going to try to weld the cable guides on the chainstays. I was going to use rivet-on guides, but Nova wanted a fortune to ship 3 guides and 6 rivets and eBay from China was going to take a month or more to arrive. I already had the weld-on guides, so I searched for an epoxy that would also withstand the heat of powder coating, in case I ever decide to coat the frame. I tested several super glue adhesives and they all failed with very little stress. The winner tuned out to be JB Weld. I attached them with JB Weld and clamped them for 24hrs. before use and none of them has failed.

Nice work and story! Andy

Thanks for posting this thread. I applaud your desire to learn new things. I'm waiting until you decide you have to build a Ti frame.

JB weld is a metal filled epoxy. So it's not too surprising that it worked. IIRC, Devcon is part of the same company, and they make some amazing metal filled epoxies if the JB weld fails

Fantastic build thread! Thanks for sharing!

How about a comparison with your similar steel bike? Please share, including info about the builds in terms of tubing used.

Thanks.

I'm not picky about what tubing I use for my frames, as long as the butting meets my needs for the main tubes, so I don't remember what exact tubes I used on the steel frame. I ride my gravel bikes on some pretty rugged MTB trails, so I usually build them like an MTB frame. I think I used 9/6/9 tubes with a 34.9 downtube and 31.8 top tube, external butted 1.1/.6 seat tube for a 27.2 seat post. Chainstays are 3/4" 035" round 4130 and the seat stays are 1/2" .035" 4130.

The aluminum frame has a 34.9 top tube and seat tube with a 42mm down tube. I don't remember the tube thickness, but they were Dedacciai tubes. Chainstays were Dedacciai MTB bend and seatstays were the gravel/CX bend.

Aside from the differences with the 1x drivetrain on the Aluminum and the 2x on the steel, there is not much difference in the ride. The aluminum bike has a slightly harsher ride, but I attribute that to the lower volume tires (700 x 40mm vs 650b x 47mm) and the larger diameter seatpost (31.6 on the Al and 27.2 on the steel)

This last post should be read by every rider who hangs on popular media madness about weight, stiffness and other trendy measurements that have little real effect on riding joy. Andy (sounding somewhat cynical after 2+ hours on tech support for his email that was for naught)

Thanks for the comparison dsaul.

With a non suspended frame how much difference in ride can there be anyway? My question about that was predicated on your comment early in the thread mentioning the experiment.

Cool thread!

Great looking bike, well done!

Another good source for 7005 tubing is faring/ bicycle frame depot.

Last I checked fairing requires that their customers be an actual business, with all the bureaucratic aspects like insurance, business licence and sales tax registration with your state. Andy