Fabricating girder forks - help sourcing tapered tube?

[FlatBlackWillWork]

I'm an ..... noob builder, and the Webb girder forks from the '20s have always fascinated me. Buying a set isn't possible, so I want to build a set. The geometry isn't that hard and there's plenty of reference out there online for it. I am learning to weld - and after enough practice I will be trying to make a set of these.

Trouble is, the tubes used to build the triangular girders on the ones I like best (for looks) are *tapered* from 3/4" to 5/8" over a run of about 13". Those are motorcycle forks though so my tube needs to be a smaller diameter.
Take a look at http://velobanjogent.blogspot.co.nz/2011/06/webb-girder-forks-general-look-at-some.html to see drawings of the forks.

My existing forks are about 11/16" at the top and taper along the curve to just under 1/2" - and that diameter will work well for the girders cosmetically.

I see online that 'real' fabricators can and do cut a skinny wedge out of standard tube and re-weld it to get tapers.
But yeah, nah. As I said, I'm a noob to welding. I am willing to weld the joints between tubes but a whole structural line? Too risky.


I have been wondering about steel tapered table or chair legs - but have no idea if they would be strong enough to do the job without being dangerous. Wall thickness/quality of steel?

Also wondering about using tapered 'seat stays' scavenged from other bikes (tubes from seatpost to rear axle mount). But again, strength is an unknown to me - maybe you folks will know if those are suitable to use.


So does anyone know where to get/scavenge/adapt tapered steel tube that roughly matches the taper above and will be strong enough to use as fork material?

 

[RustyGold]

Look at custom bicycle tubing sources, like nova cycles...
http://www.cycle-frames.com/bicycle-frame-tubing/home.php
...a browse brings up stuff like...
http://www.cycle-frames.com/bicycle...14mm-SINGLE-TAPERED-SEATSTAYS-560mm-LONG.html

Henry James might be another...
http://www.henryjames.com/

Companies that supply materials for home/experimental/hobby airframes builders

Jason

edit...table legs and such are viable as well, if a table can support the weight of a person or two, triangulated/braced should be usable for girder components....just make sure the tubing is thick enough for you to weld.

 

[TroutFishingInAmerica]

Framebiulders Supply has an assortment of tapered fork blades.
framebuildersupply.com/collections/fork-blades

 

[Bicycle808]

Easiest move would be to look at round tapered fork blades. Chain and seat stays might work, but they will tend to be smaller diameter and thinner walled than fork blades. I think stronger is better for bike forks whatever the design is, and for a new welder, thicker walls will be more forgiving.

Here is my pick, based on the criteria you offered in the original post:
https://framebuildersupply.com/coll...omor-fork-blades-24mm-round-9-wall-length-390

 

[FlatBlackWillWork]

Thanks to all posting the frame builders links to the available fork legs. Regretfully all those have a really large diameter at the larger end. 24mm is the norm. That is way too big for what I'm doing - which is a bummer because those are actually made to be forks.

So onward... anyone know of tapered tube material more closely matched to the "5/8 to 1/2 over 13" spec?

I'm heading to a used furniture place later this week to investigate the chair leg idea and will post what I find out after I do.

 

[TroutFishingInAmerica]

This no name Chinese girder has tapered tubes. Quality is just okay, I don't know if you can see the taper in the pics.

This absolute great quality German made girder has no tapered anything. Quality is outstanding.

I know you are set on tapered tubes, but there are some sweet girders without taper. Definitely easier to source material, probably easier to manufacture also. Just thought I'd throw this out there in case you don't find your correctly tapered tubes. Good luck.

 

[Jaxon]

I make a few different bicycle chopper forks. The top fueler forks on the bike in my avitar are 120 walled 3/4"tubing. I also use 065 wall tubing on shorter straight or slight curve forks. Those girder forks are really cool. Good Luck with the build

 

[RustyGold]

So onward... anyone know of tapered tube material more closely matched to the "5/8 to 1/2 over 13" spec?

The seat stays I linked from Nova...
EL ROAD SEATSTAY SINGLE TAPER 14mm
14 x 0.6 x 560
14.0/10.5 diameter
290mm long taper at bottom

what that appears to state to me, is a taper from 14mm (slightly less than 9/16") to 10.5mm (slightly smaller than 27/64") over an 11.5" length with a total length of 22"...so, the first 1.5" of your 13" length would be untapered...you would have to really eyeball it to probably notice it. I don't know what the tubing thickness is, but, even if it is on the thin side...the design you posted is triangulated on the top and bottom halves...with another brace on the bottom triangle. Should be plenty strong.

Jason