On Fri, 10 Aug 2012 05:37:58 -0700 (PDT), stryped
wrote:
On Thursday, August 9, 2012 7:52:51 AM UTC-5, stryped wrote:
I dabble in metalworking for fun. I also run marathons and some triathlons. Been thinking it would be neat to be able to say I built a bike and used it in the triathlon. I have a road bike but not a triathlon bike.
As far as frame, I am limited becasue I dont have a tig welder. I do however have a mig, oxy torch/weld set and arc welder.
I am guessing my choices are aluminum tubing or chrome moly steel.
I can mig weld the tubing with argon and aluminum wire but not sure if this is ideal. I have read you can braze it.
I have read conflicting advice as to whehter it is recommended to mig 4130 or not. (The same for brazing it).
Weight is an issue. I want it to be light but at the same time be strong enough to do a half or full ironman. 56 miles/112 miles.
I appreciate it!
Very interesting. Again, I am not as experienced as you guys as to metalworkig here. I have the equipment but have never brazed. I have miged, however heard mig is not good for 4130. (NHRA does not allow it). I have read on brazing and it sounded simple enough, get the temp to a certain point and melt the brazing material into it. Capilary action would fill the joint.
What you are describing is the technique used to braze lugged frames
usually with silver. There are also frames made by fitting the tubes
and then brazing the bare tubes. To reinforce the joint a fillet of
brazing material is made.
Most bicycle frame tubes are not SAE 4130 but are slightly modified
alloys. for example Columbus says:
NIOBIUM is a special steel with manganese, chrome, nickel, molybdenum
and niobium. Columbus's special chemical composition, the combined
effect of strengthening for precipitation and reducing the alloy
grain size are incredibly enhanced compared to standard steels.
Niobium proves more effective than Vanadium as an alloy-strengthening
agent. After specific processes of progressive drawing and forming,
NIOBIUM undergoes a special heat treatment that gives the steel its
final characteristics. It is a steel designed to provide superior
mechanical characteristics and higher resistance to environmental
effects than conventional carbon steels. The only serious choice
for a competition or top-of-the-line frame, where lightweight and
reliability are essential.
Mechanical characteristics: Rm = 1050÷1250 MPa, Rp0.2 \u2265 750 MPa,
Ap5 14%.
Material suggested for TIG welding: OK TIGROD 13.12 (AWS 5.28 ER
80S-G). MIG: OK AUTROD 13.12 (AWS 5.28 ER 80S-G).
I have toyed with the idea of buying a cheap harbor freight tig. However, I know some of you would frown on harbor freight stuff.
You only need the TIG machine if you are welding the frame. You will
need some practice to make consistently good welds. The top of the
line Columbus tubes are butted 0.5 - 0.38 - 0.5mm wall thickness, or
0.018 - 0.014 - 0.018 inch.
You are right, the weight concerns me and most of the bikes are carbon fiber. I have toyed with the idea of carbon, but have no experince with it and not sure how to ensure it would be safe enough when complete to average 20-30 mph.
It might be that learning to built a carbon frame would be easier then
learning to weld thin steel tubes.
As for 30 MPG crashes :-( If you are building a carbon frame you
usually use a purchased carbon fiber fork rather then trying to build
one. If the fork breaks you are in serious trouble but if, for
example, the rear part of the frame breaks you probably won't get hurt
badly.
The only advantage to steel, as I have read, is I have heard it is more "comfortable" for lack of a better term longer distances, something about absorbing road bumps. This would be benificial in a long triathlon in terms of saving your legs for the run.
This is a highly over rated subject. If you are talking about riding
on extremely rough pavement then yes, steel might be a bit more
comfortable, but how many events are run over cobblestones? I have
ridden steel, aluminum and carbon frames and to my mind the tire size
is a far more important factor then type of material. A 19mm tire
pumped up to 150 psi rides a whole lot harder then a, say 25 mm tire
at 90 psi.
But I agree, lighter is better.
Again, I am new to all this so forgive my ignorance but the lugged frame set up looks like you would just stick the tubes into the lugs, that the tubes would not have to be mitered. Is this true? (Kind of like thise strong tier kits you can buy to build a table ot whatever without having to cut miters).
No the length and thickness of the lugs themselves is insufficient to
make strong joints. Remember that the silver braze is not as strong as
a TIG or bronze welding, so lugged joints are first mitered to fit
then inserted into the lugs and brazed.
You can do this by hand (or actually a combination of grinding and
hand filing) but the alternate is having a milling machine and tooling
to accurately cut the bevels. Doing it by hand takes longer but is as
accurate and notably cheaper :-)
I have no jig and would have to rely on a table or system of 2x4's. Some kind person on here mentioned somethign that I had read but forgot about, pinning. Seems the old timers if I understand it correctly would drill the lugs and tube and insert "nails" to hold the assemply togther before brazing. WOuld this negate the need for a jig?
A couple of points. First, you are talking about some fairly small
variations here. Example, a normal road bike seat tube is at an angle
of about 73 degrees and the head tube is, perhaps 72 degrees. These
angles can vary but if you design for, say a 72 degree head tube and
then you can't hold the tolerance it will change the geometry of the
front end and the bike may not handle as well. Additionally it will
effect the angle of the other tubes that you have so carefully mitered
to fit your original design and they may no longer fit.
As for pinning joints. It isn't fool proof. You usually use two pins
(nails) at 90 degrees to each other but after you nail the joint you
can still flex it so it isn't a bullet proof way of making joints.
Pinning or nailing is done mostly with lugged frames.
Yes, you can build a bicycle frame on a wooden frame but it probably
won't be as accurate as a proper jig - which costs a fortune. On the
other hand there are a number of jigs that people have built from some
sort of pre-fabricated aluminum material - look at
http://www.littlefishbicycles.com/ for additional information but I'd
advise taking most of her comments with a grain of salt as a lot of
what she says is a bit.... well. Her first frame broke at the bottom
bracket. Later she cut the broken joint apart and discovered that it
broke because she hadn't brazed it completely. But she never seems to
have drawn the conclusion that if you've never done it before maybe a
little practice is a good idea :-)
I am just mentally trying to grasp all these concepts.
Really, truly; download a copy of the Paterek manual that I mentioned.
Reading it will answer most of your questions.
Thanks,
Don.
Although you haven't mentioned it you will need access to some
specialized tooling.
You need a tool to recut the threads in the bottom bracket and face
the sides. While most bottom brackets are tapped when you receive them
you usually need to re-tap and face the sides after you weld/braze
them together.
You need to face and ream the head tube to fit the head bearings as
welding/brazing usually distorts the tube.
You need to ream the seat tube to fit the seat post after you
weld/braze it.
There are fairly expensive tools so you don't want to have to purchase
them. You can usually find a bike shop that has a set and pay them to
do the work.
If you use steel fork you probably will want a fork blade bending jig.
Somebody mentioned pressed lugs. don't bother with them as the cast
lugs and bottom bracket are much more accurate. It takes me a good
part of one day to fit the three lugs, the bottom bracket, the fork
crown and the front and rear dropouts. Using pressed lugs and bottom
bracket might double that time.
Cheers,
John B.