Unicrown fork mitring jig
06-26-21, 06:50 AM
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Unicrown fork mitring jig
Having found the last time that these are very tricky to do by hand (at least for me) I thought I'd have a go at making a jig to hold things steady for mitring with a hole saw. Actually worked out better than I was expecting.
Simple construction out of 3/4" 16-gauge square tube, but plenty stiff enough not to move. The blue thing holding the hole-saw was unbolted from my inexpensive Metz tubing notcher (which I actually rarely use normally preferring to hand-mitre). The jig was made deliberately to place the hole-saw a little bit low so it could be put into the exact right place with shims. It's bolted to a 3mm plate welded in there with the holes a little oversized to allow fine adjustment of the angle.
Having bolted the fork ends in securely I TIG-brazed the ends of the fork not only to each other but also to the cross piece (which is bolted in so it can move around a bit), at the end of the cut:
Horrible gap on the ends of those forks but this actually worked to my advantage as that ugly bridge tack stayed in place the whole time:
Great success! Hole-saw spun nice and smoothly (with a cordless drill driving it) and nothing shook around or bent or did anything bad.
After a very little cleanup here is my fit:
Certainly good enough for the girls I go out with. Not 100% perfect as the hole-saw is 28mm, not 28.6mm. I'll clean it up a little bit more but I'm going to be TIG welding this and I can fill much bigger gaps than that (don't ask me how I know this
Simple construction out of 3/4" 16-gauge square tube, but plenty stiff enough not to move. The blue thing holding the hole-saw was unbolted from my inexpensive Metz tubing notcher (which I actually rarely use normally preferring to hand-mitre). The jig was made deliberately to place the hole-saw a little bit low so it could be put into the exact right place with shims. It's bolted to a 3mm plate welded in there with the holes a little oversized to allow fine adjustment of the angle.
Having bolted the fork ends in securely I TIG-brazed the ends of the fork not only to each other but also to the cross piece (which is bolted in so it can move around a bit), at the end of the cut:
Horrible gap on the ends of those forks but this actually worked to my advantage as that ugly bridge tack stayed in place the whole time:
Great success! Hole-saw spun nice and smoothly (with a cordless drill driving it) and nothing shook around or bent or did anything bad.
After a very little cleanup here is my fit:
Certainly good enough for the girls I go out with. Not 100% perfect as the hole-saw is 28mm, not 28.6mm. I'll clean it up a little bit more but I'm going to be TIG welding this and I can fill much bigger gaps than that (don't ask me how I know this
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