…and the cradle will rock

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Frame 11 is coming together, slowly.  It may look weird right now, but each tube has a purpose and even though this will be one heavy frame relative to a ‘normal’ two-triangle frame, it will be sweet to ride this fatty.  It’s been a slow process but mostly that was because jigging this thing up was so freaking difficult.  That’s part of the fun though, i have to admit – making what you have (brains and tooling) work for whatever situation arises!

Some things people will probably wonder about when seeing the pictures:  The plate or cradle is 0.062″ thick 4130 plate. Retrotec uses 0.04 or 0.05″ depending on the frame.  I went thicker since, well, that’s what I could get, and this will be a high stress area where the chainstays will be trying to twist.  I’ve not seen a bike with a plate for the chainstays, instead for the top tubes/seatstay junction.  The plate is MUCH wider than any Retrotec plate since it needs to fit a 4.5″ tire.  So, since the increased span, and increased torsion that’ll be applied, I chose thicker.  Also, it is cut in two pieces since I wanted to get a little angle to match the angle where the DT and CS tubes meet.  The twin downtubes are 16mm diameter x 0.9mm wall thickness and span from the head tube to the plate where they ‘turn into’ chainstays.  The chainstays are actually 16mm True Temper round S-bend seat stays.  I used a 170mm Paragon head tube, super beefy to hold all those tubes with no problem. That’s a 31.8mm 8/5/7 top tube, going back to a 34.9mm seat tube with a sleeve cut from the left over from the same tube. The reason I did this is because the seat tube is already 1.2mm up top and 0.8mm down below where the ‘legs’ take off to the BB.  Adding another 0.058″ walled tube sleeve to the top of the seat tube seemed like overkill so the extra 0.8mm was what I chose. It’s not a full sleeve, it is spliced so it will fit.  I needed a sleeve since the top tube comes in lower than the tube’s butt, so the sleeve helps me extend the effective butt length in a way.  So…why a 34.9 seat tube? I need to fit a Joplin drop-post on this frame so with a 32.4 – 31.6 USE seat post shim it’ll span the difference between the 32.5 (I.D of the seat tube) and the 31.6 diameter seat post. (Sorry if this is way too much detail, but it’ll help me when I forget what I used in a month…)  The seat tube legs are 16mm x 0.9 wall 4130 steel that are used to increase lateral twist in the bottom bracket area. The BB is 100mm instead of a normal MTB’s 73mm so this was the way T wanted to combat that twist. There will be gussets of some sort at the BB/DT joint as well but it’ll look much different from the seat tube legs.  The downtube/chainstays meet at the cradle plate with an angle.  To help braze this connection, I whittled down two short pieces of 14mm 4130 and used them as inserts to connect the DT/CS tubes.  This also helped fixture all the tubes together.

For process, I first fixtured the plate to the seat tube at the right height and tig-tacked it to the seat tube. For the twin downtubes, I did a half-fastback seat stay miter on them to braze them on the head tube.  It looks totally sweet IMO. I forgot to take a photo so i will next time.  For these I had to braze on caps before brazing them to the HT.  Once all this was done, which took a hell of a long time to miter/fit/fixture…it was time for brazing.  It took me a long time to braze this all at once.  I started at the head tube and did the front of the twin downtubes, then went to the plate where I brass-tacked everything together and let it all cool down. I added even more flux to the plate and started fillet brazing it all together IN the fixture.  Most builders don’t braze in the fixture, and I usually don’t either, but with the Access65 it’s quite easy to do so and it keeps everything in the right place.  Especially with this weird type of frame, I wanted to keep it all jigged up tight while brazing.  Anyways, so far, the only things I’d change are that I’d make an attempt at bending the downtubes and/or chainstays in the vertical plane so that it has smoother and less angular lines.  But functionally, I’m not sure that’d make a bit of difference.

This is a total prototype.  On my snow ride today (awesome, btw) I thought how funny prototypes are.  The thing about them is that you usually ride them a few times and then put them on the shelf and make another because they totally suck or weren’t what you were expecting.  We’ll see how T likes it.  I just hope I can finish it before winter ends! It must be ridden in the snow!

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