I’m working towards building up my first fork as I (re)start my framebuidling journey. I am currently working on building a wooden bender roughly following this design, which has been shared elsewhere.
The piece that I’m a bit uncertain about is how best to size the groove that the tubes will actually sit in. v-shaped? u-shaped? depth/width relative to the size of the blades?
I’m sure there are a number of dfferent valid approaches, but curious if folks could share what has worked for them and what trade offs I might not be aware that I am making.
fwiw, I’m building this jig out of two slabs of maple that I plan to glue up.
The usual (if one can call this about our niche craft) is a “V” groove and often at a consistent depth. My concern about a “U” groove is that many blades have a taper and the U would be hard to taper too. The V will self correct WRT blade diameter all along the curve. No mater which you use expect some blade width flaring out at the curve. Over raking a touch and clamping the curve in a bench vise to squeeze narrow again will unrake the blade a tad back. Andy.
Decide on the largest diameter tube you’ll want to bend and make sure the V groove is contacted within the groove and not just of the corner, That’s you’re max depth.
OK so I just measured the two different bending forms I have. The Hamill (sp?) has a .7” wide at the top/most open part, .5” along either side (angle is 90*)* and about .35 deep. The wooden form (made by someone I now forget) has a shallower groove at .55” across the top, .4” a side and about .27” deep (also a 90 cutter). I prefer the Hamill’s larger groove as far as blade fit goes. The Hamill has about a 12” radius, my wooden forms have about 9” and 6” curves.
A huge aspect of a bender is how well the tip of the blade is held. There will be a huge lifting force the blade is seeing and any lift off of the blade from the groove will result is the curve starting further up the blade and away from the tip/dropout (BTW most will rake before attaching the dropouts), currently having the blade’s curve start right at the dropout is the fashion. making a solid and minimal flexing blade end clamp will be rather important. This is where the wooden forms I have are not as nice as the Al Hamill’s clamping. Andy.
Mine has a 1/2” or so channel over its length.
I think I even added it with a rat tail file ?? decades ago.
Regardless, the shape and depth aren’t critical dimensions.
See link and image.
Ignore the op-ed nature of my text at your own peril.