Monday, February 27, 2012

Jigs and Rattlecad

It's Time For a Jig

I've decided to make a jig to hold the frame tubing while I tack things in place.  It's possible to do the job without a more formal jig, but I think that I'm going to be better off with fewer things to think about while I'm putting everything together.  I'll still have to get my skills pretty sharp to keep the frame straight, but at least this way I have a good solid place to start from.

I've decided to make the Jig out of 80/20 aluminum extrusions.  Basically, 80/20 is a system of interlocking parts for building frames, jigs, supports, etc.  They bill it as "the industrial erector set" and that's basically what it is.  Here's an example of one of the extrusions.

This isn't too much of a shot in the dark.  Many builders have made their own 80/20 jigs, and a few pro's have even made production ready jigs out of it.  Mine won't stack up next to an Anvil, but if I'm careful about aligning everything, it should be good enough for me.

I'm basing my design on Suzy's over at Little Fish.  She's been cool enough to put up a plan here.  I'm going to use similar extrusions, but I'm going to move the vertical braces to the front of the jig.  That will make it a bit harder to line up, but it should also allow me to work with a shorter head tube.  As it stands, it looks like you need a really long head tube in that jig to clear the central spine, and then cut it down later.  This will also mean that I'll have to remove the dog leg that centers the axle.  It won't be as precise, but I think it'll serve.


I discovered a discrepancy today in the spec's for the fork I'm going to use with my frame.  It's a Surly Pacer fork and I've found the distance between the dropouts (where it holds the wheel) and the crown (where it fits into the bearings of the headset) listed as 371 in one place and 376 in another.  Yikes!

I've mentioned before that I'm using RattleCAD to make my plans and diagrams, instead of normal CAD software or BikeCAD (which you really need to pay for to get all of the information that Rattlecad gives you).  It seems to be the best option for new builders, but it's also being constantly updated (at least 3 in the last month, maybe more).  So, while adjusting the diagram to find out what the changes would have to be if that second number was the right one, I noticed that I could no longer manually change the virtual length of the top tube.  That's the length that it would be if it didn't slant down a bit.  For non-bike people following: this is a really important number because it has a lot of impact on where your handlebars end up.

I made a post in the RattleCAD forum about it and had an answer from the person making the software in less than a day.  And it worked flawlessly.  That's service, and on free software to boot!  So yeah, if you're looking for a way to design your first bike or two, give it a try.

Full disclosure: I don't work for Rattlecad dude, nor do I sell 80/20 as a side gig... I just think they're neat.

1 comment:

  1. How did the jig turn out? Are you able to post pics?


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