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Step 6Front-Center adjustment
The next step in setting up the jig for a frame would be to set the pseudo-front-center. It's not the real front-center (the distance from the bottom bracket to the front hub axle, but actually the horizontal distance from the bottom bracket to the steering axis.
I design my bikes in CAD so this is an easy number to find. If you don't use CAD you will have to draw a scale drawing to correctly set this distance.
You could certainly set the location of the head tube by trying to measure the top tube length from beam to beam but that seems a bit finicky and vague on this design. However, there are lots of grooves on the extrusion to give you something to measure off of.
This part is just another 3/8 T-handle and a modified carriage bolt. To give me a more accurate point to measure to, I chucked a 3/8 stud in my lathe, threaded on the T- handle, and drilled a small indicator hole on center. The T-bolt goes through a hole drilled all the way through the adjustable beam.
Like on the seat beam, even if you bore the hole through the beam to an exact fit, there will be some play between the T-bolt and the main frame. You could take up this slop with a small piece of brass rod turned to fit. However, for most garage builders, I don't think the slop will make much of a difference.
I design my bikes in CAD so this is an easy number to find. If you don't use CAD you will have to draw a scale drawing to correctly set this distance.
You could certainly set the location of the head tube by trying to measure the top tube length from beam to beam but that seems a bit finicky and vague on this design. However, there are lots of grooves on the extrusion to give you something to measure off of.
This part is just another 3/8 T-handle and a modified carriage bolt. To give me a more accurate point to measure to, I chucked a 3/8 stud in my lathe, threaded on the T- handle, and drilled a small indicator hole on center. The T-bolt goes through a hole drilled all the way through the adjustable beam.
Like on the seat beam, even if you bore the hole through the beam to an exact fit, there will be some play between the T-bolt and the main frame. You could take up this slop with a small piece of brass rod turned to fit. However, for most garage builders, I don't think the slop will make much of a difference.
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Jul 28, 2010. 3:31 AMmcflorry
says:
this is an awesome frame jig! Thanks for the inspiration :D just one thing,what length did you make these angle beams?
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Jul 28, 2010. 9:57 AM
drwelby (author)
says:
drwelby (author)
says:
I think they're around 55 inches. You might want them taller if you're building frames for longer travel forks.
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