Friday, December 03, 2010

Chain Stays and Dropouts

I've been tending to mitre the front triangle and chain stays together, braze that whole thing, then do the seat stays.  Here's some pics of the chain stay/dropout work I did yesterday.

Here's the addition I do to the drawing to account for tire and chainring clearance when building the rear end.  Using the centerline of the bottom bracket from the original drawing I draw the back half of the BB shell--this one is 68mm--and extend a centerline to the rear axle to split the difference of 135mm.  I draw in the chainrings by using an assembled crank and BB.  This one is an old XTR square taper with 26/36/48 chainrings that is close to what Shawna will be running and for mock up I used a 107 mm shell.  Little rings have shown to be the biggest obstacle in chain stay clearance.  The vertical line to the right of the half bb shell represents the minimum chain stay spread at that point (i.e. tire clearance).  For this drawing I wanted 55mm spread at the full diameter of the tire.  I lay the stays down and line them up to see if they'll fit how I want.  This bike is getting True Temper bent oval chain stays.  Recently I've been using the S-bend stays, but the single bend ovals are good riding stays and I think they will fit this bike quite nicely.  They will take some working though.

Into the tire clearance machine.  I came up with this along the way last winter after seeing how some bikes needed more clearance.  Here is the chain stay pre tire clearance.  I mark the block so the stays sit at the same place and check the alignment as all parts of this machine sit pretty loose before clamping.

...and after the squish.  I measure the jaws to ensure they get squished the same.

Finished product.  I drew the lines on the stays thinking that's where I would center the bend, but I wound up not using that...mostly because the machine didn't want to do it that way.

Chain stays and dropouts brazed.  This bike is using Henry James cast stainless plug dropouts.  These things are super easy to use and make for a seamless finish.  The double eyelets are cast into the dropout and are very clean.  That's all for now.  I put in a late late night last night but the front triangle and chain stays are all brazed up and its sitting in the soak tank now.  I'll probably get back at it next week, but maybe I'll get some pics of the brazing up in the meantime....peace.

1 comment:

  1. good stuff man....Im getting some training via the internet. Thanks