Assembling and Welding an Aluminum Bicycle Frame
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Assembling and Welding an Aluminum Bicycle Frame

October 13, 2019

In the last video, I made the fixture
that holds all the frame components in the proper location. This time, I’ll cut
the monocoque elements and curved tubes to fit. The seat tube needs to be notched at
a 12 degree angle where it meets the housing for the rear shock. I’m using a strip of metal to mark the
location of the notch. The C tube is held in the milling
machine vise and I’m using a square to make sure it’s properly aligned. I’m
using a digital level to set the card at a 12 degree angle. A hole saw is placed
in the mill and centered on the part. The kind of started off the mark and the
milling machine table is moved to bring the cut to the line. Now, the plunge cut
is made with the hole saw. The fit is nearly perfect. I’m using a
stainless steel brush to clean the joint for welding. The joint is tack welded in several
places with the tacks completed, the joint is
welded fully. The monocoque seat tube cover is fitted
next. It needs to be notched too. This is a very fragile part, and it needs special
fixturing to be cut on the mill. I’ve made a slug that fits tightly inside. It
has a threaded stud that sticks out. The slots cut in the slug allow the
chunks to fall out as the part is cut. I made a very simple fixture that holds
the part at the proper angle. There’s one more piece that allows this to be held
in the milling machine vise. I’m using kerosene as a cutting fluid. You can see how well the parts fit.
Now, I’ll tack weld the part into place. Next, I’ll lay out the cuts on the curved
monocoque section. The monocoque is aligned with the rear edge of the pivot.
I’m marking a line parallel with the shock housing. The wooden slug is slid
forward, allowing me to cut grooves for removing the waste. Now, the slug is tapped
back into place. The part is held in the vise keeping the scribed line vertical,
and now the plunge set is made, stopping to remove the waste so it doesn’t clog
the hole saw. To lay out the bottom cut, I’m
positioning machinists’ blocks so they touch the pivot centerline. Now, the
pivot housing is removed, and the spacer is used to hold the monocoque at the
proper height. I’m using threaded rod to push the monocoque tightly against the
shock housing. Now, I can mark the vertical centerline of the cut parallel
with the blocks, and I’ll use a dial caliper to make sure it’s center right to
left. I’m marking the location of the cut so I’ll know how deep to make the waste
removal slots. Now, the part is placed in the mill,
centered on the spindle, and clamped to the milling machine table. Even though the hole saw has coarse
teeth, it cuts the thin aluminum cleanly because of the tightly fitted slug. The slug is tapped out, the part is deburred, and the fit is checked. Tight fits are essential for good welds
on thin sections like this. I’m using the same strategy for laying out and cutting
the monocoque section for the bottom bracket. The careful layout and cutting ensures
tight fits. The lower curved tube is positioned in
the fixture and aligned with the bottom of the swing arm pivot. I’m doing a rough
layout so I’ll know how deep to make the waste relief cut. The round tube has
enough stiffness that it doesn’t need a slug inside. I’m aligning the outside of
the hole saw with the inside wall of the tube. Again, I’ll make a plunge cut. The test fit shows good alignment, so
it’s time to lay out the front of the tube. I’m using a plate to lay out a
straight line on the tube, spaced one inch away from the center line of the
head tube. A rough cut is made on the bandsaw, and a disc sander is used to
sand right up to the line. The tube is positioned in the mill making
sure the cut end is precisely vertical, and it’s clamped securely. I’m using an
edge finder to center the spindle over the cut end of the tube, and then I move
the table one inch to the center of the cut for the head tube. Now, the cut can be
made. A bandsaw is used to remove the bulk of
the waste, and a disc sander is used to round the ends of the notched area. I made a special dolly to fit inside the
tube. This eases the process of rounding the end of the tube where it fits
against the head tube. Now, I can pack all the components together on the fixture. With the tacks completed, I’ll finish weld
each joint on the bench so I can rotate the parts to allow full access for all
the joints. the filler rod is 5356 alloy, a 3/32 inch
diameter, or 2.4 millimeters. With the monocoque fully welded all the
parts go back on the fixture and I can check the fit of the round tubes. Now
these are ready to be tack welded and then finish welded. Welding round
tubes is challenging, your hands are constantly moving, keeping the torch at
the correct angle, and feeding the rod into the puddle. I’m using a 2% Cerriated
Tungsten, 3/32 inch diameter, or 2.4 millimeters sharpened to a fine point. The last welds will join the top tube in
the down tube to the head tube. And here’s the completed frame with all
the accessories added. It was a great honor for me to help Spencer Owyang
develop the prototypes for this striking design.

Only registered users can comment.

  1. That was great getting to see your approach to making this. I thought this was an old video, but that clear cup with lens I thought was pretty new. Thanks.

  2. Great video as always Ron. It is amazing what you can build when you just break it down into the simple steps.

  3. I just imagine Fabio Lanzoni rocking this bike with a bandana and white Nike Airs. Great work, I just love that jig you made. I think 3D-printing shapes to form aluminium around could be a great life hack

  4. i love your practical and logistical approach to even the smallest of tasks. it makes it seem accessible to even the beginner fabricators. thus pushing everyone forward. great work.

  5. This has been a great little series, and you do beautiful work. Are you going to build the bike and ride it? There are some great trails in your area. Thanks.

  6. Excellent series, as a fabricator of 27 years making all manner of items in that time I'd say your skills are amazing , the real deal 🙂 🙂 🙂 I've made my own downhill frames over the years and now you've made me want to have another go at some of my more updated ideas with this video. Lol you just cost me a thousand dollars hahaha, cheers mate, New sub! 🙂

  7. I didn't see anything about normalising the heat affected zones near the welds and realignment of the frame post welding/heat treatment. Is it not required in this fabrication?

  8. Great video series! The whole reason I ever learned to weld and machine was to make bikes. Ive finally got my aluminum welding skills up to speed and an it's time to move onto a full aluminum bike. The advanced TIG DVD sounds interesting

  9. I liked watching this video.Explaining how you layout the work from square dimensions into cubic is really insightful and inspiring.

    Thank you for sharing your work with us!

  10. hey Ron! I had an idea for a video that I would really like to see your opinion on. Have you heard about people DC welding with helium? could you please break this down for us? your professional opinion is needed.

  11. Was Your choice of Ceriated vs Thoriated a personal one ? I use 2% thoriated for Aluminum and want to know if the latter is a better choice for some reason ? I missed Your visit to Minnesota due to family health issues, I was sad I had to but family comes first. Hope You felt welcome in Minnesota and hope to someday catch one of Your shop classes/demos.

  12. my winter project 2018

  13. Amazing work! Does the bike go on to be heat-treated, since welding aluminum makes it a bit weaker, or is it still strong enough to be rideable right away?

  14. I am planning on building my own recumbent Ebike. I worked as a welder in europe in the 80's. My wife had concerns about my idea until I showed her what proper technique is with this video. Now she's ok with the project because she knows what my standards are. Beautiful flawless work sir. Thank you!

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