Welding custom rear racks

[commuter ebikes]

I need to make two custom rear racks in the next few months. I was going to make both out of aluminum, but now one will be 4130 chromoly tubing and one will be aluminum.

The first rack that I will make will be a copy of the rack (pictured below) that is integrated into my Design Logic Da Phat frames. If I do that, then my battery boxes and controller heat sinks (and their thermal padding) will be interchangeable between all of my ebikes. I tried to come up with a better design than what is pictured below, but I could not think of any improvements. The frame builder that designed and made this has been doing this full time for 35+ years, so it is no wonder that I failed to come up with a better design.

The rack in the photos is for a longer wheel base bike than the new (standard wheel base) frame that needs a rack. I have standard wheelbase Design Logic frames like this, but I don't have photos available of the bare frame. When I copy the dimensions, I will strip that bike down enough to get all the dimensions needed. I will post photos when I do that.

[commuter ebikes]

I will need a tube bender for the 90 degree bends at the front and the more extreme bend at the rear. I will get this tube bender: http://www.anvilbikes.com/portfolio-...ing-rodriguez/.

This is 3/4" tubing. Online metals offers .035", .049", .058", .065", .083" and .095", .12", .156", .1875" and .25" walls: https://www.onlinemetals.com/merchant.cfm?step=2&id=250.

This page https://www.cmrp.com/blog/bending/tu...d-to-know.html says "The heavier the wall thickness, the tighter the bend radius that can be achieved with less distortion. If tubes are to be architecturally exposed then more consideration is required to produce the clean bend." This page http://www.instructables.com/id/Bend...-and-furnitur/ says "One of the biggest problems about bending tubing in the DIY world is wrinkling in the corners when bending past 45 degs on thin wall tubing." The guy in the second link is a big fan of packing in sand.

It sounds like I should choose the thickest wall that I can stand for weight considerations. The curb weight of the bike is already 90 pounds so I don't want to go crazy high with wall thickness. .095" might be a good balance.

I will have a lot of time to think about it because it will take months for me save up to buy the tube bender.

[commuter ebikes]

I am making some progress on this project. I have obtained two good 5/8" tube benders https://www.youtube.com/watch?v=XZNT0Zcd-Dc and http://www.testequipmentdepot.com/ye...inch-60378.htm

I also bought 10 feet of 5/8" O.D., .065" wall 4130 Chromoly tubing https://www.onlinemetals.com/merchan...=250&top_cat=0 This tubing costs $7.17/foot plus shipping.

The .049" wall 4130 chromoly is really difficult to bend. I will be buying some of the same material with a thinner sidewall.

I am trying to find time to work on it. I will post pictures.

[MoneyPit]

Bending chromoly by hand can't be any fun at all. Super interesting project though.

[commuter ebikes]

Bending chromoly by hand can't be any fun at all. Super interesting project though.

The Yellow Jacket 60378 tube bender worked fine. I had to put the tube bender in a vise.

[CPG]

I built a rack for a weird little 20" fat bike, and I also used CM, from Aircraft Spruce. No curves though..... and .035 max wall thickness. The stuff is crazy strong, and I would have gone even thinner but my welding capabilites needs thicker! Nice bender. And a nice work area from what we can of it!

[commuter ebikes]

I built a rack for a weird little 20" fat bike, and I also used CM, from Aircraft Spruce. No curves though..... and .035 max wall thickness. The stuff is crazy strong, and I would have gone even thinner but my welding capabilites needs thicker! Nice bender. And a nice work area from what we can of it!

Remember that you can use pulse on the thin stuff. For .035"-.045" 4130 Chromoly tubing try using the lay wire technique with the following settings: 160A peak, 1.8 pulses per second, 30% on time (pulse ratio) and 10% background current. I use 1/16" diameter, 2% lanthanated tungsten electrode ground to approximately 30 degrees with the tip not blunted. I use a gas lens and #12 cup. Argon flow is approximately 25 cfh. I like .045" and 1/16" ER70S-2.

I was just welding on thin sheet (no pulse, mild steel) tonight. A lot of burning holes. Not pretty.

I will have a chance to finally build these racks in about a month. I have two tube benders and all of the material. Just need the time.