Tuesday, May 24, 2011

Monday, September 17, 2007

These worked great on the main tubes. However, I need to fab up something smaller for the stays.

Time for the braze-ons. As you can tell, I like making tools. These are off the shelf Pony brand spring clamps with the rubber protectors removed. I took a some pieces of 1/8" welding wire and bent them into shapes and silver brazed them into the convenient groove in the clamp.
It's precarious, but it held. Again, joined with 56% silver.

Scribed for bridge placement. I checked with a wheel to make sure I wasn't being a moron.

It worked well though. Much easier than trying to clamp a 2" long piece of tubing in a tube block. The bridge is 1/2" x .028

Pretty straight forward. Nothing more than a stick with a hole and a pinch bolt/slot.

Here is a simple clamp I made for mitering the bridges. I made one for 5/8" and one for 1/2"

The tool stays on during brazing. I'll be attaching everything with 56% silver.

This is the tool that I made to help me miter and position the seatstays while I join them to the back of the seattube. It's very simple and does nothing more than clamp the stays at an angle and allow me to test fit them on the jig and then return them to the vice for some more filing.
It's a block of aluminum about .75" x 1.0" with 3 tapped holes in it. Above it is a clamp with corresponding holes and 1/4" cap screws. Sandwiched between are 2 mini V-blocks. They are attached from the back with 2 more 1/4" bolts so the angle can be adjusted independently of the clamp. Considering how many builders regard hand mitering S-bend fastback stays to be nearly impossible, this tool worked very well.

Thursday, May 10, 2007

Ready for some stays.

This worked well. The pins are tight but can be removed easily with a pair of dike cutters. The bullets are a bit floppy but don't wiggle at all when the stays are installed.

It then used a transfer punch to mark the dropout and drilled it out as well. I initially tried using an undersize drill so that the spoke would have a press fit. My plan was to grind a taper on the pin so I could get it started. This didn't work so well. I discovered that the pins don't need to be tight to work in this application. Instead, I made the holes oversized and bent the pins slightly before tapping them in.

In order to keep the SS plugs on the dropouts while I was fitting/brazing the stays, I decided to pin them. This is a common technique for those building using tradition methods and lugs. The standard "pin" is a soft nail. Some builders even use square nails because of their natural taper.

I've never tried using pins myself so this was new territory for me. I chose to use an old 14ga stainless spoke as the pin since this area will not be painted. I first drilled an .080 dia hole in the bullet. Location really didn't matter.

Friday, April 27, 2007

1 pair of stays with S-bends. I was initially worried about making sure the bends were in plane to each other. I realized that you only have to get close. Checking them on flat surface is easy and minor corrections with a vice are also quick and easy. Also, do the larger bend first.

I did a couple of test bends. I got a piece of 3/4" x .035 to 25 deg before it started to crimp. Plenty good enough for S-bend stays. I can put the bends about 4" apart if I move one of the outside dies towards the center. This limits the bend to about 18 deg.
My old mill vice makes a decent press. It takes a couple of extra hands to get everything lined up but it's better than buying an arbor press.

This is my stupid simple tube bender. It's a blatant rip-off of the one I found at Steve Garro's blog. I modified only to fit the materials I had on hand. The "dies" are all machined from 7075 alum. The base is simply a piece of .120 wall scrap tubing with 2 pieces of mild steel bar stock stick welded on it. I did key the pieces of bar stock to make sure they ended up on there straight. I made all the dies on a vertical CNC mill and surfaced the curves.
Fit up and ready for some seatstays.

Radiusing the tops of the dropouts

Originally I was planning on using 3/4" x .035 for the seatstays as well as the chainstays. After getting the yokes all done, I was amazed at how stiff the chainstays were and realized that 3/4" was overkill for the seatstays, especially on a bike that I'm trying to keep light. I switched to 5/8" x .035 This meant that I needed to make new bullets. These are much lighter. I even added a little cutout on the side just to save those precious 2 grams.
A view from the bottom.

The cups worked. I also used my normal Harris white flux and tried to be a bit more patient with the heat. On the second of the 2 frames, with more BB warpage and therefor more gap in the joint, the silver flowed very easily. If I did this type of joint again, I would rethink a few things like designing an intentionally smaller radius on the yoke to create a larger gap with the shell.

And with the bike....

New cups installed on the frame fixture.

My solution to the heat control issue was to make some new BB fixturing cups. My standard setup is a stainless insert that is a light press fit into the BB shell. This slides on a 1" dia post on the fixture. The insert makes near full contact on the inside of the shell. These new cups only hold the outer .200 of the shell on each side. This will allow the center of the shell to reach brazing temp with less heat. I made these out of 6/4 titanium. Why? Because Ti is a crappy conductor. I wanted a material that would help contain the heat in the frame. ( I couldn't afford ceramic)

Well that didn't go as planned. It seems my fit between the yoke and the BB shell was a little too perfect. There wasn't enough gap to pull the silver into the joint. I also had heat control issues. I tried using black flux since I was anticipating some overheated spots. The BB post of the fixture acts as a massive heat sink and prohibited me from getting the shell hot enough.

Sunday, April 15, 2007

Everything fit up (minus the front end)

Checking fit. I took this whole assembly and installed it on a wheel to make sure I wasn't doing anything stupid.

Checking for square.

Trimming the chainstay to length with a file.
Small .050 vent holes in the yoke were an after thought.

Trimming the chainstays to length. This isn't that critical as my yoke design allows for lots of slop.

Checking to make sure the new block/dummy axle is square.

Here is my scabbed on block to extend my dummy axle.

I ran into a couple of snags on the frame jig. This is really the first complete bike I've built on this jig. First off, it isn't adjustable enough. If you build your own jig, make sure it can go well beyond any norms for geometry and size. This bike has such a low BB, that the headtube adjustment is maxed out and the dropout is well out of range. Another issue was the headtube cups. The originals were stepped. This made setup easier and more accurate, but when the headtube ovalized slightly during brazing, the cup was stuck. Combined with the cooled flux, it was a chore to get it out. Tapered cones are the answer. I will still use the other ones where I can since they are easier. Another lesson I learned is to allow more slop. My old headtube cups had .001 of clearance on the ID. This would have been plenty if it hadn't gotten hot. The new ones have .003. Same with the BB post.

Sunday, March 4, 2007

Tabs removed.

Second side complete but with the tabs still attached.

Part bolted to the fixture. I start out with just 3 bolts and machine around them.

Simple fixture for the second side. It's just a piece of scrap with the bolt pattern drilled in it to match the part.

First side complete. The holes are "tabs" for holding the part for the second side. 2 of the holes are reamed for a .250 dowel pin. This ensures the features on the second side are in perfect relation to the features machined on the first side.

Into the mill. The first side can be done in a vice.

The part starts as a 1" thick piece of 4140. Cut to length, and well deburred.

Friday, March 2, 2007

The chainstay yoke: This will be machined from a solid chuck of 4140 plate. Modeling done in Solidworks. Programming is done in Mastercam.