Frame Jig needed.
Wladi labraña
Looking frame jig used or second hand, in April I moved to Mexico to live and need a frame jig to continue working on my new city. if anyone knows of any sale please let me know.
regards
Wladimir.
one80...@gmail.com
Andrew R Stewart
Rochester, NY USA
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Alex Wetmore
I built a blantant ripoff of the Arctos and don't share my CAD drawings because I feel like it is okay to build a blatant ripoff, but you should at least figure out how to rip it off yourself.
The jig below isn't a blatant ripoff of the Arctos. They put the main beam lower on the jig so that they can have a real pivot (Arctos has a virtual pivot). The main thing in common is having a center beam and using 80/20 or Bosch extrusions as the basis of it.
http://bicyclemanufacturing.co.uk/?page_id=20
It has my normal complaint about copies of these jigs, which is that I don't think you can pull a nearly completed frame (front and rear triangles tacked) out of it without changing the jig adjustment. I worked hard on my Arctos-inspired jig to make sure that nothing that sets the jig geometry needs to be touched to take the frame in and out.
It looks pretty nice for $2500-3000 US.
alex
Sent: Friday, April 1, 2016 6:24 AM
To: one80...@gmail.com; Framebuilders
Subject: Re: [Frame] Re: Frame Jig needed.
Wladi labraña
Alex Wetmore
Frame jig:
I built a copy of the Arctos using 80/20 extrusions. I used the 15 series stuff. There are photos of my jig here:
http://photos.alexwetmore.org/Bicycles/Fixtures/Arctos-Clone-Frame-Fixture
There are important details to get right when you copy the Arctos:
* The seat tube must pivot around the BB, so that you can adjust the STA without adjusting the BB position. Many if not most clones get this wrong. I copied Arctos's method of using a virtual pivot point by CNC cutting some concentric arcs, but you can also just make a pivot plate that hangs down to the BB as bicyclemanufacturing.co.uk did on their fixture.
* The head tube must pivot around the bottom of the head tube for the same reason.
* You want the dummy axle to drop out to the bottom of it's holder. This allows you to remove the frame from the fixture by sliding up the cone for the seat tube and head tube and rotating the frame backwards to pull it off of the BB support. If the dummy axle comes out of the front of the holder then you need to move the rear dummy axle holder back every time you remove the frame. I wanted better repeat-ability than that.
CNC is helpful for making it, but you could do it on a manual mill with a rotary table (for making the arcs).
A couple of material tricks were using large angle extrusion for my towers (rather than making them from scratch). I used ebay sourced Mic6 plate for my pivot plates. I made all of my sliding surfaces slide on ground pins that very accurately fit the 80/20 extrusion to avoid any slop. These were installed into reamed (not drilled) holes for accuracy.
I only made a few frames on my fixture before taking a break from the framebuilding hobby (my free time got sucked into sailboat racing), but I found it to be a great fixture to build from and as accurate. Comparison fixtures were time spent with a Nortac (ugh!) and earlier home-built designs and playing a bit with a Henry James (but not using it).
Fork jig:
There is enough information in this webpage to make a fork jig similar to the ones that I used to sell. I based them on 80/20 extrusions (and it could be done with any of the clones). The only part that really needed to be custom made was the dummy axle holder, and it is a trivial part to make on a manual mill (all operations are at 90 degree angles to each other):
The design worked well for me and there are a few pro builders still using them.
The V-block was made by getting 1545 80/20 extrusion (that is 1.5" x 4.5") and cutting off the top to get the V. Check the extrusion carefully, there is usually a small rib in one side. You want to cut the end that has no rib so that nothing gets in the way of your V.
alex
Sent: Tuesday, May 10, 2016 10:04:20 AM
To: Framebuilders
Subject: [Frame] Re: Frame Jig needed.
Mark Bulgier
> There are important details to get right when you copy the Arctos:
The head tube can also be made to pivot around the front wheel axle, as with the Bike Machinery Hydra jig. Just a different philosophy of what’s important. But I loved working on a Hydra. In theory at least, it lets you design the frame right on the jig, with no drawings or calculations. I didn’t actually do that, I always had a design in hand before going to the jig, but I liked how the jig design matched my design process.
The Hydra, to pull this off, has a lot more complexity, more sliding surfaces and thus more places for inaccuracy to creep in. An actual Hydra is plenty accurate enough (though some pro builders who use one have shimmed them here and there to improve their results). What I’m getting at with the inaccuracy comment is thinking of an amateur machinist trying to make one. That would be crazy.
Given what a can of worms that would be for a hobbyist, I think Alex’s design is right and proper.
I can also imagine a jig where the headtube holder pivots around the intersection of the TT and HT centerlines. Then, adjusting the head angle wouldn’t change the TT length. Getting into another whole can of worms there though, what with all the range of frame sizes you’d need to support. Forget I said anything!
Mark Bulgier
Seattle
Wladi labraña
El lunes, 21 de marzo de 2016, 21:01:18 (UTC-6), Wladi labraña escribió: