Chainstay mitering

I’ve got the rear triangle all coped and cleaned and ready to be tacked very soon. This process too me a long time. For one, I just have not been getting down to the shop very much.  I also learned the more difficult way that BikeCAD needs to be watched closely – or that I needed to know that you must input the dropout measurements into the program or else you get the incorrect CS length).  Once again, a model is only as good as the data you put into it.  Let’s just say I got some ‘extra’ practice at slotting the chainstays and using the new Sputnik chainstay mitering fixture.

This fixture is awesome. It’s HEAVY, and rigid as all hell.  I got an angle plate that this bolts onto so it can be used on a vertical mill easier.  I thought this thing would be cheaper than an Anvil but it turned out to be about the same since I got two sets of blocks for different sized chainstays.  That’s the thing you need to realize about this fixture –  each significantly different size of chainstay needs a different set of blocks and they’re $100 each.  This is because they clamp onto the oval or round CS’s as tight as possible and allow absolutely no slip or movement in any way.  The dropout side of the CS’s also need to be unique depending on what style dropout you use.  The picture above is for slotted drops, but I also got on for Wright/Breezer style dropouts since I plan to do that for most MTB’s and slotted for CX frames.  I’m only starting to learn the intricacies of this fixture obviously but it really is pretty straightforward for the most part.

You simply get the measurements of the actual CS length from BikeCAD or your drawing (the actual CS length and not the effective length of the CS – BB to axle), set the fixture to the right CS length, miter/slot the CS’s at the drops, put the stays in the blocks and tighten down snug, adjust the wheel and tire diameter set-screws to space the CS’s to the right distance from each other, put the stays in the fixture, and place the rectangular block on top of the CS blocks and tighten down. There are spring-loaded screws that fit in the back of the blocks to make sure they are in the right place and parallel to each other – which does take a little bit of fussing with to get right but not much.

You need to pre-miter or slot the dropouts, unlike the Anvil fixture I believe. This supposedly is better and quicker in the long run but I have yet to ‘get it’ yet.  I’ll update when I get it.

The angle plate looks like he didn’t make it but just drilled holes in the right spots so to fit the fixture. It is solid and set up really easy. The spring-screws are seen to the left of the angle plate and screw into the back of the tubing blocks to allow “float” to a certain extent allowing for tire width adjustments.

The picture below shows the empty fixture and the empty blocks for 30mm diameter oval CS’s.  The rectangular block is on the table there and fits above the blocks and keeps it all set steady with that screw.  The wheel and tire set screws are seen to the left of the blocks and are pretty simple, probably the thing that could be made better.  They are a bit loose so I had to use a bit of locktite so they’d stay put.  That, and you have to move them individually and measure to the right width which is more of a PITA than the Anvil design but it works just fine.

Once the  CS’s are in the fixture, it’s really the same as any other miter with the mill.  This setup does NOT MOVE. It’s definitely as rigid as it gets.  The hole saw is the weakest link in this setup but for the most part the cope is perfect the first time! (If you have all the measurements correct of course!)

And for next time, the clunky yet functional seatstay fixture (an Anvil fork fixture that will also help make wishbone SS’s).

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