Custom Fat Bike - Front Triangle Pt.2

After last week's brazing work was soaked I got a look at the DT-HT joint and decided the penetration was acceptable.  I also took some measurements of the head tube and it appears that the distortion wasn't enough to be a concern.  So back to work...

I checked the HT-DT assembly and it matched up with the drawing nicely.  The next step was to cut the compound miter at the bottom bracket shell.  I had already cut the miter for the BB, but I had to cut the notch for the seat tube.  This ended up being a tough one... there was a lot of back and forth between filing the miter and checking the fit.  In the end the best approach was to use the jig.  With the BB-ST assembly held solidly in the jig I could quickly install the HT-DT and check for fit and angle.  Finally I reached a point where it was as good as it was going to get, and I prepped it for brazing.

After the brazing was done and the frame got a soak, I checked the frame against the drawing.   It ended up needing a bit of cold setting, and I was surprised at how little pressure it took to make adjustments to the frame's geometry.  It isn't perfect, but every time I do a frame check I'm pleased at how well the frame is turning out.

Like I said before, the DT-BB-ST was a tough miter, but in general I think I'm getting better at mitering tubes; the top tube went much smoother.

With the front triangle together, the frame is about 1mm shorter in length than planned but all the angles are within 0.1 degree of where they should be with the bottom bracket shell and lower end of the head tube lined up with the drawing.  How the overall alignment comes out remains to be seen.  The BB isn't faced yet (I'm waiting until I get the chainstays installed), but at this point it looks like there is a bit of twist around the BB-ST.  I don't expect it to be anything major, especially for a first frame that only I'll ride.

Next up, the chainstays.  This should get interesting...

Custom Fat Bike - Front Triangle Pt.1

I haven't done much riding in the past week, but I have been busy working on the custom fat bike.  First off, I once again modified my frame design.  I figured if I'm going to build something custom, I should try something different... it should be something that a stock frame can't give me.  So I made the front end longer.  The angles are all the same, but the front end is stretched out a bit.  I want a bike that I can run a 100mm stem on... I'm sick of 135mm stems.  So after a new BikeCAD design, I made a new actual size drawing and I began cutting miters, drilling vent holes and cleaning tubes.

The first task was the seat tube/bottom bracket shell joint.  Here it is, before and after brazing:

I'm not going to bother filing/sanding it much since the down tube will be covering up a good portion of this joint.  Next up was the sleeve for the top of the seat tube:

The sleeve is an external reinforcement for the seat tube.  It adds more material where the top tube and seatstays attach.  Both projects went very well, with relatively no warping of the BB shell or the seat tube.

The next joint was the down tube/head tube junction.   Having an extra BB shell made this process a lot easier.  With the down tube mitered on both ends, I mounted it in the jig and brazed it to the head tube:

This joint didn't go as well as the others.  Penetration wasn't as good as I'd like, so I went back to draw some more brass into the joint.  I think it was then that I overheated the head tube and it got slightly warped.  I'm still researching the issue, but I'm hoping it isn't scrap metal now.  I'm skeptically optimistic that I'll be able to find a solution as long as the penetration ended up sufficient.  A couple more hours of soaking to remove the flux and I should be able to get a good look at it.

So some good, and some not so good.  It's a learning process.  I couldn't have expected my first frame to go too smoothly, right?

Another project I worked on this week was a head badge.  I'm still deciding whether to paint the frame myself or have it powdercoated locally; either way it will be a plain, single color frame.  I figured to spruce it up a bit, I'd give the frame a copper head badge.  After a couple hours playing with the font and size I came up with this:

The number 56 is in reference to the Iron atom, the predominant element in steel.  I think the head badge turned out nice, and should look good with whatever dark color I end up painting the frame.

Next week I hope to have pics of a completed front triangle (or if my luck runs out, pics of me building another head tube/down tube assembly).

Murphy Ride

I hadn't been out to Murphy at all this year, so when I had the opportunity for a morning ride this week I could't pass it up.

It was also the first ride using the large Tangle Bag from Revelate Designs, and it worked out great.  I really like the clean look of the bike... no water bottle holders, no pump, no rear rack.  Along with my repair kit, I had a 27 oz water bottle in the bag.  There is room for two 18 oz bottles, or possibly a small bladder, if I ever want to carry a bit more water.  The Revelate Feed Bag carried my camera.

It was a ton of fun to be riding the Murphy singletrack again... it has been too long.  The trail has gotten rougher over the years, which is understandable; mountain bike trails do not live a static existence.  I think it's especially noticeable to me since I used to ride Murphy so much back when it was fresh, and now I only get out there a couple times a year.  I also used to ride it with a full suspension bike, which makes a big difference.  It makes me want to ride Elm Creek or Carver Lake while they are still fresh.  Not that I don't like rough trails, it is just so fun to ride fast, smooth singletrack. 

This is another 2 post weekend... scroll down for an update on the Custom Fat Bike project.

Custom Fat Bike - Full Size Drawing

I spent some time this week working on the custom fat bike project, specifically the full size drawing of the frame...

The drawing gives me the angles at the joints, the lengths between the miters on the main tubes, and a template to check the geometry of the frame during the build process.  I made a measuring mistake early on that changed the design a bit; the front center (and top tube) ended up a little shorter than my original design.  The top tube and front center lengths are 9mm shorter than planned, but I'm just gonna to go with it.  The 640mm top tube and 670mm front center are still respectable numbers for an XL sized bike.  Next time I draw up a frame I'll buy a longer ruler.

I also spent some time working on a "practice frame" I made from cheap, straight-gauge 4130.  It's similar in diameter and wall thickness to the tube set I'll be using for the real bike.

I think I'm getting better at controlling the heat (not getting the joint so hot that it burns the flux) and getting enough brass penetration to make a strong joint.  The practice frame also gave me an opportunity to use the jig before I started work on the real thing.

The next step is cutting and mitering the tubes that will actually become my new fat bike!!

Metro Metric

We recently ended a heat wave here in Minneapolis... 8 days in a row above 90, with a couple of those being over 100.   I'm not a fan of hot and humid, so I haven't been riding much.  When the high temps and dew points finally broke this weekend, it motivated me to get out for a longer ride.  I originally planned a 100 km ride using only the bike paths in Minneapolis and St. Paul, but that route included a rather boring "out-and-back" portion through St. Paul.  When I woke up Sunday, I decided to extended the route choices to the first-ring suburbs.  Doing so allowed me to plan a route that minimized riding the same section of trail more than once.  I planned to post a GPS map of my ride, but I forgot to turn on the "track" function, so I'll just have to use words and photos.

The ride was also a test run for a new way of carrying water on the Fargo...

There is a 2-liter Camelbak bladder in the rear rack trunk, and an extended hose running up to the handlebars.  This was my first ride with this set-up, and it had its advantages and disadvantages.

Advantages:
- the water/ice capacity of a Camelbak, with nothing on my back
- stays cold longer than bottles (in fact, I ran out of water before all the ice melted)

Disadvantages:
- water in the tube gets warm (blowing the water back into the bladder prevents this, but with the long tube takes a lot of effort and makes it harder to get a drink the next time)
- more stuff on an already busy (and heavy) bike

I'm still working out the bugs of this set-up, but it has potential.  If it doesn't work out, I'll look into running a bladder in a frame bag.

The route starts along the Minnehaha Creek, then up around Lake Harriet and Calhoun.  At the north end of Calhoun I took the Cedar Lake Trail out to the Depot in Hopkins, and then headed back toward the city on the North Cedar Lake Trail...

Shortly before getting to downtown, I hopped on the Kenilworth Trail in order to connect with the Midtown Greenway...

The Greenway ends at the Mississippi River trails, at which point I turned north toward the Plymouth Bridge (my northernmost point).  Crossing the bridge brought me to Boom Island Park which connects to Nicollet Island...

I love the fact that in Mpls I can be somewhere like the photo above, and a few minutes later I can be somewhere like the photo below...

After riding through Nicollet Island, which included about 4 blocks of low-traffic neighborhood streets (the most non-path riding I did all day), I followed the river past St. Anthony Main to the Stone Arch Bridge (above).  Crossing the river again, I repeated a short section of trail in order to cross Bridge #9, a ped/bike bridge that connects to the East Bank of the University of MN...

The Weisman Art Museum on the University of MN Campus

Below campus I hit the East River Flats trail.  It was nice to get away from the crowds of the more popular trails...

I kept following the east bank of the Mississippi, through Hidden Falls and Crosby Farm, all the way to the 35E Bridge.  Crossing at 35E brought me to the Big Rivers Trail, which I followed to Mendota.  I then I continued southwest along the river on the dirt/gravel MN Valley Trail...

At the 494 bridge I joined up with the Big Rivers Trail again and headed back to the Mendota Bridge, crossing the river to Fort Snelling State Park.  I had planned to ride a loop around Snelling Lake, but the gravel trail on the east side was closed, so I ended up doing an out-and-back to the south entrance (this was my other repeated section of trail).  I then rode up out of Ft. Snelling, through Minnehaha Falls Park, and followed the creek trails home.

Roughly 100 kilometers (65 miles), through city and forest, on pavement, gravel and dirt, almost entirely on bike path and trails.  Have I mentioned I love this town?  Minneapolis gets a lot of press about being a great bike town; hopefully this post helps explain why that is...