Framebuilders - front racks

Anyone have an idea on the proper gauge to use for building a chrome moly front rack. I know 3/8 and 5/16 O.D. tubing but what wall thickness?
I plan on building one for my Long Haul Trucker frame and may build a back one also. Going to have them powder coated to match the frame color and will include light mounts etc.

I've been looking into the same thing, the consensus seems to be .035. I'ts very stong, light enough, and is thick enough to sleeve nicely when you connect a loop.

There isn't any right answer. I think I used .049 on my recent rack, but you really have to consider design. Like for the surly, on the touring board someone mentioned the weight of the nice racks. Well you can "engineer" back from that for your own rack. What is in your weight budget; are you using a simple design, or will you use a lot of struts or triangulated elements. You can use more than one weight of tube, just as with a house, posts don't need to be as strong as beams. Don't worry about sleeving it with 5/16" (.028 wall). First, that makes the rack too flimsy for heavy use according to Paternek, so you know right there that would be a light rack if you followed something similar to a Blackburn design. Second, the thicker walls are easily fixed with a cheap chucking reamer if you want to insert some 5/16" for a joint. You also have to consider joinery if you are welding for instnace. I silver brazed mine and it seems fine for strength and obviously wasn't fussy on wall thicknesses. Bends and hardware are the most interesting parts.

Thanks guys.........its kind of what I thought. I plan on a front rack for a small bag and a halogen generator light. The rear may be a duplicate or a larger one for lightly loaded panniers someday. I don't see myself doing tons of heavy, high mileage, loaded touring but more like an overnighter or two while camping in mild weather. For commuting, I want the option of carrying extra clothing and perhaps my musical instrument, although that would force me to build a larger front rack.
I have access to a milling machine and a lathe so I can make any fittings I want and I plan to braze or silver solder since I am familiar with that process due to my daily work. :)

By the way......nice rack!

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Thanks, here is a picture of it in use.

I have a mill and all that jazz, 3 metal lathes. All bought recently, so none of it is set up. I really did find the rat tail file was fast and easy for all the joinery. I started cutting with a fine chainsaw file, until I had a gutter established, and then changed to the Nicolson 10" which is rough cutting for the start but does a good job, the cuts are perfect in 3/8s right from the file. I wish I had had the lathe set up to do a few details that I had to improvise otherwise, like the tabs for attachment purposes could have been barrels.

Sometimes hand tools are faster in skilled hands for certain things. Many old shotguns are hand fitted after machining to create that "bank vault" fit. I'll bet a old school frame builder (if they still exist) could build a frame with hand tools only, that would rival machine cut and jigged stuff.

Thanks, here is a picture of it in use.

I have a mill and all that jazz, 3 metal lathes. All bought recently, so none of it is set up. I really did find the rat tail file was fast and easy for all the joinery. I started cutting with a fine chainsaw file, until I had a gutter established, and then changed to the Nicolson 10" which is rough cutting for the start but does a good job, the cuts are perfect in 3/8s right from the file. I wish I had had the lathe set up to do a few details that I had to improvise otherwise, like the tabs for attachment purposes could have been barrels.

" that would rival machine cut and jigged stuff."

No doubt on quality, speed is often also true if you are making one offs. For instance one of the really slow things is fitting. One doesn't always know what the joint needs to be, so one can't cut it on a machine or by hand to be perfect on the first try. Sometimes one gets relatively quickly to the exact point, more often than not really, but other times something goes wrong and one is back and forth. That kind of thing would be insane where every cut required a the piece to be re-clamped and indexed in on a machineetc... With a file you can almost hold it in one hand and swipe it with the other. Though a vise is more efficient. I find all this kind of work pretty familiar since it is just like cutting joints in wood.

On runs machines can be set up to cut out the parts. Gordon has a little double headed milling machine to cut out rack crosspieces with.

A lot has changed in the last 20 years what with CNC and all that. I remember an article I read when I started out in craft, back in the 80s. It gave three then prominent examples of stuff that could only be done with hand tools, or in one exanple, old tech. I only remember two which were. Hand scraping the ways of surface grinders. If you have ever seen one, you might wonder how such a jumped up grinder might cost three times similar machine tools. Apparently one could only get above milling machine standards of accuracy because they had hand scraped ways. Also, at the time, Canada was helping out in the Shuttle program by producing the Cargo arm. Spar Aerospace had the contract, and the arms used helical gears of great complexity that were cut in Toronto by some very old machinist whose shop had a line drive. The Spar wagon was apparently a fixture in their lane. That is hand work in a certain sense.

CNC has changed my trade. Making miniature "parts" out of wax and plastics for investment casting has been slowly changing the industries need for my specialized skills. It only took me 28 years to get good at something and now it seems, I'm a dinosaur.........not to mention, much of the work I used to do, is being done in Asia.
I don't think hand skills will ever go away but its true that many old techniques are no longer practiced and with technological innovations replacing older methods, some fundamental skills are disappearing. :cry:

One thing I don't understand is whether any of these new technologies make it possible to eliminate scraping. In the old days if you wanted to make a machine that was one step more accurate than those you had, you couldn't get a machine to do that. There seem now to be a lot of extremely accurate machines around holding very tight tolerances, and I don't really know how they got there. This stuff keep me up at night...

I think they use laser measuring devices to machine things straight and flat. Tolerances are less easy to maintain than many think. A .0005" tolerance is extremely hard to maintain in production and probably requires temperature controlled machining rooms etc. Grinding or lapping would seem to be more accurate provided there is some way to measure the accuracy. I spent quite a bit of time doing precision long range target shooting at 1000 yards and we used to go so far as to measure bullet jacket thickness with an electronic device along with measuring things to .001" and weighing case volumes etc. It was kind of like chasing your tail and random variables often spoiled all the anal preparations. I will say some amazing things were done resulting in ten shots into 4 inches at 1000 yards........pretty impressive. That measurement equates to .4" at 100 yards which is slightly less than double the caliber of the bullet. Basically one hole ten times in a row.
As far as bicycle stuff is concerned the only thing that comes close is mitering tube angles for silver brazing and ceramic bearings. I've seen so many off tolerance bicycle parts that it makes me wonder how anything works but it does, thankfully. Makers like Phil Wood, White industries etc. are essentially machine shops making nice American made parts. I'm glad those guys are around and I have and will continue to buy from them and support quality stuff being made in America. :)