Sunday, 20 October 2013

Day 9: Sunday

Rear triangle and more filing.

I was looking forward to today!  Today marks an important point in our frame building - cutting and filing the final parts to make a complete frame.  Once this is complete, it'll just be the forks to make.

The rear triangle of a bike frame consists of chainstays (along the bottom), seatstays (from the seat tube down) and the rear dropouts into which the rear wheel is clamped.

First off I had to mark out and mitre the chainstays at the bottom bracket end.  Easy enough with the mitre templates provided by Bike CAD Pro, once you've measured a few lengths and done a little maths.  It would have been a little tricky without the computer-generated mitre templates because the chainstays meet the bottom bracket at 90 degrees in one plane but are angled out by a few degrees in another plane to give enough width at the dropouts to accept a 130mm rear axle.  

Another tricky bit was accurately marking the centre line along the top of each chainstay.  If I were to do it again (or rather when I do it again!) I'll use the mitre template to cut the mitre as it's obvious where the top of the chainstay is (it's oval in cross section) and then use the jig to mark the top at the dropout end once it's fitting snugly to the BB.

Anyway, once the mitre is cut, you can then cut a slot at the dropout end using a hacksaw and then a file to tidy it up.

The seatstays are even easier, especially since I'm using some very nice wrap-around tops for mine which negates the need to cut a complicated mitre at the seat tube end.  So it was just a case of cutting the slot for the drop out at the thinnest end and then reducing the length by chopping bits off the top end until it all fits nicely.

It should also be pointed out that before while doing all of the above, there was a fairly lengthy session setting up the jig and rear dropouts.  I've intentionally left the rear dropouts a little flatter than the Raleigh frames that I've seen so that if I want to go fixed at any time in the future it'll be easier to get the chain tension set up.

Here's the complete frame in the jig:

Once that was set up, it was time to decide on the braze-ons that I'll need.  Here's the list and  parts laid out:

They'll go on tomorrow when the rest of the frame gets brazed. 

When I'd done all that, I got on with a bit more filing to tidy up the brazes on the front frame triangle.  They're not perfect but I'm fairly happy with them now they're filed down.  Not too bad for a first effort and I know what to do in the future to improve matters.

It got to about 5pm and I was knackered!  Think it's been a pretty steep learning curve so far and my head is feeling it a little. 

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