Homemade Jig & first fillet mtb

[christo]

Bonjour everyone,
I've always used my flat table so far to build my frames. But i couldn't resist to build a jig, eventhough a flat table with the right fixtures is a just enough for the hobbyist. That's the only justification : i couldn't resist to build my own stuff.

The inputs were :
- not expensive
- no need to use a mill
- simple to adjust, and easy to get the frame in and out
- rigid and precise enough, mostly used for tacking the frame (front and rear triangle)

After hours of reading, i decided to go with a design based on a strong reference : the seat tube and the center of the bottom bracket. From this point (BB) and this axis (ST), all the other points are determined, ie bottom and top of head tube, coordinates of rear axis. Those coordinates can be easily extracted from BikeCad (with additional little maths). I use only cartesian coordinates, no angle at all.

Jig.png

I turned the BB post at the right height to accommodate a 68mm BB, and the cones with a spigot to fit into the slots of the aluminium squares. I used extruded aluminium that i found in Germany for a very competitive cost : the entire jig is around 400€, the most expensive parts being the fastlocking screws that are optional of course, but very nice to set up the jig, and to get the frame in and out quickly. I assembled the jig on my surface plate to get the best alignment.

DSC_0009.JPG DSC_0032.JPG

DSC_0035.JPG DSC_0037.JPG

Tacking the frame in the jig is way easier than on the surface plate, especially on the sides of the joints. The tacked front triangle came out of the jig absolutely straight, which is a good sign of the alignment of the jig. But i must confess that after building the filets, the frame is a little distorsed, meaning that i need not only to improve my fillet technique, but also the sequence of brazing.

DSC_0055.JPG DSC_0053.JPG
DSC_0057.JPG DSC_0060.JPG
DSC_0064.JPG

It's all about finishing the fillets now (a few pits so far, and a biting frame also). More to come in the next weeks

Thanks for reading, and a Happy New Year for all of you ...

[jclay]

Formidable! Really nice work!

[Andrew R Stewart]

A modern version of the classic British window frame jig. Very useful and easy to work with. Check out Doug Fattic's posts for more info. Like the blood shot, been there bled that. Andy.