Newbie Builder Questions

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I want to try building a swb recumbent similar to HPVelotechnik

Street

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Machine (http://www.hpvelotechnik.com/produkte/sm/index_e.html), but

without

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suspension. Would exhaust tubing be strong enough for the main frame

tube?

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Otherwise, does anyone have any good recourses for acquiring the

proper

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steel tubing (small amounts, of course)? Once built is chroming okay?

Any

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drawbacks? Powdercoating? Again, does anyone have some resources to

get the

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chroming or powdercoating done?

Lemmee tell you, sonny boy, about how I built a recumbent out of a
piece of driftwood and some chewing gum...

On the other hand, I'll just answer your question. I built a lowracer
recumbent similar to a HP Velo Speedmachine back in 1992. (I'm aware
you're copying a Streetmachine, which is different, but bear with me.)
I used 2" diameter exhaust pipe for the main frame, with one welded
gusset at the main bend under the seat mount.

Even though the frame came out kind of catywumpus (freehand cutting and
brazing will do that to you), it was rideable- kind of funky in the
turns, but it started, stopped, and steered OK. I was close to 200
pounds then (and well over now), so 2" exhaust pipe is just fine (if
not overkill) for your frame.

A good friend of mine built a recumbent around a straight piece of
exhaust pipe and rode the heck out of it. I never saw him have
problems. He's since graduated to homebuilding with carbon fiber- his
latest projects are on his blog:
http://homepage.mac.com/john4bho/iblog/

Exhaust pipe is mild steel. It's just as strong as any other steel
made. Better grades of steel (4130 "aircraft" chrome-moly, for
instance) are more fatigue resistant and can thus use thinner and
lighter walls, but they're not any stronger. If you like, short lengths
of chrome-moly are available from the homebuilt aircraft suppliers,
such as Dillsburg or Aircraft Spruce.

I would not chrome the frame afterwards. You run the risk of hydrogen
embrittlement, and the cost will likely be more than the rest of the
frame. Powder coaters are in any large city- look under "Coatings" in
the Yellow Pages. Alternatively, ask at the local motorcycle shop-
powder coating a bicycle frame is not that different from a motorcycle
frame.

Jeff

Jeff Wills said:

...
Exhaust pipe is mild steel. It's just as strong as any other steel
made. Better grades of steel (4130 "aircraft" chrome-moly, for
instance) are more fatigue resistant and can thus use thinner and
lighter walls, but they're not any stronger. If you like, short lengths
of chrome-moly are available from the homebuilt aircraft suppliers,
such as Dillsburg or Aircraft Spruce....

??????????????????????????

Spend some time browsing here under the "Ferrous Metals" category:
<http://www.matweb.com/search/SearchSubcat.asp>. Note the wide ranges in
yield and ultimate strengths, hardness and ductility. (Also note the
modulus of elasticity does not change significantly with alloying and/or
heat treatment.)

--
Tom Sherman - Earth

Thanks for the excellent advice. Sounds like you have already done what Iwant to accomplish. My main concern was bending/flexing the main tube undermy weight. I'm also over 200lbs. I'll steer away from the chroming also asper your advice. This makes it easy for me as I can acquire the exhausttubing locally and there's a powdercoater nearby.

I've built 3: last a Vrex clone. Here's what I learned
1. Ya gotta be a "builder" kind guy. One who gets as many grins out of
the building process as from riding. If you're doin it for low cost,
take my advice and find a used bike. You'll be happier in the long
run. Nothing is cheaper.
2. Quality in building is everything. Ten dollars or 2 weeks spent
attempting perfection is money/time well spent. NOTHING is more
satisfying than when someone looks at your work closely and sez "
man....nice bike".
3. Use .035 4130 from Dillsburg rather than exhaust tubing. The
marginal cost of doing so is more than offset by the weight
differencial. I'm 200# too; no strength problems. Braze the frame
using high silver content rods. Buy some scrap and practice before you
start. Have a professional builder ream and true your head tube before
you put the headset in; it's cheap and makes a world of difference.
4. Use a joint jigger for your fishmouths, and lots of oil and NEW
bimetallic hole cutters. Use good quality files, new if you can. Buy
these from a machine tool supply place, not Home Depot. Refer to step
2.
5. Have fun. I LOVED building mine, and they came out great. Steepen
your learning curve using the framebuilders web discussion group; but
don't let the technicallity of the discussions intimidate you. Go for
it !

Duncan Cooper

Duncan Cooper said:

...
3. Use .035 4130 from Dillsburg rather than exhaust tubing. The
marginal cost of doing so is more than offset by the weight
differencial. I'm 200# too; no strength problems. Braze the frame
using high silver content rods. Buy some scrap and practice before you
start....

There are a lot of TIG and MIG [1] welded 4130 Cro-Moly frames around.
Any reason why a homebuilder should avoid welding?

I have also known cases where the builder did a trial run with “muffler
moly” while all the “issues” such as idler placement and seat mounting
were being sorted out, then did a final frame with better quality tubing.

[1] Many older US made RANS and some Greenspeeds were/are reportedly MIG
welded.

--
Tom Sherman - Earth (Illinois)

Tom sez: There are a lot of TIG and MIG [1] welded 4130 Cro-Moly frames
around. Any reason why a homebuilder should avoid welding?

Good question.

In my experience large diameter thin walled 4130 is difficult to gas
weld. You can't simply pull the heat off it when you're done, but must
slowly and uniformly cool the joint to avoid stress cracks. TIG
welding is a great process, but as much for production purposes (leaves
no [censored] and is immediately 'pretty'😉 as for strength. Brazing is a
much lower temperature process which is a little more tolerant of
homebuilder skills (or lack thereof). Properly done it's just as
strong as TIG'ing, and for me is easier in my shop. Downside is ya
gotta deal with the glass from the flux. Takes time and effort, and if
ya soak it off can leave corrosion issues inside the fused area. Most
all of the professional high $ handmade steel frames are brazed rather
than welded. Colnago, Serotta, et all. Plus, I don't have a TIG
welder.... (guess I coulda saved a lot of verbiage by just saying
that) It's on my short-list of future toys, however....

MIG process is great for automotive stuff, but lightweight thin walled
tubing takes real skill. Not that it's impossible, but I've never been
able to get consistant results on .035. As said before, quality is
everything.

This is just MY experience. The pro's have eye-watering skills and
tools which I don't need to invest in. I'm just bangin around on a
homebuilt bike, not racing the Giro. Still, the frame's gotta be safe.
Engineering is all about tradeoffs......

Unrelated aside: Seems this usegroup is returning to a more normal
state than the rancor of-late. It's a pleasure to be back.

Coop

Quoted message said:

Tom sez: There are a lot of TIG and MIG [1] welded 4130 Cro-Moly frames
around. Any reason why a homebuilder should avoid welding?

8<

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In my experience large diameter thin walled 4130 is difficult to gas
weld. You can't simply pull the heat off it when you're done, but must
slowly and uniformly cool the joint to avoid stress cracks. TIG
welding is a great process, but as much for production purposes (leaves
no [censored] and is immediately 'pretty'😉 as for strength. Brazing is a
much lower temperature process which is a little more tolerant of
homebuilder skills (or lack thereof).

what equipment is required for the homebuilder?

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Properly done it's just as strong as TIG'ing, and for me is easier in

my shop.

what about using, say stainless steel exhaust pipe?

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Downside is ya gotta deal with the glass from the flux.

how does one deal with that?

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Takes time and effort, and if ya soak it off can leave corrosion issues
inside the fused area.

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Most all of the professional high $ handmade steel frames are brazed

rather

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than welded.

is there any benifit going to a larger diameter?
say 2.5" or 3" for the main boom?
is the weight worth the increased torsional rigidity and larger area to
hang mounts off?

i'm also exploring the options of a trailer built with small diameter
exhaust tube.

cheers,

kim

Duncan Cooper said:

...
Stainless Steel exhaust pipe:
- Do you see many SS bikes out there ? No. Tough to weld, poor for
stiffness. As I said before exhaust tubing is REALLY heavy. All the
large diameter tubing frames are made from Al, like the Trek was. (and
I believe it was heat treated...a process beyond our abilities) As
opposed to cheap muffler tubing, a couple bucks more buys you a much
lighter frame in annealed 4130. Torsional rigidity of 2.00 od x 0.035
is plenty for a 200 pounder like me. (also works on the RANS Screamer)...

Austenitic (stainless) steels do not differ significantly in elastic
moduli from alloyed carbon steels (e.g. 4130). So frame stiffness will
depend solely on moment of inertia of the tube (i.e., diameter and wall
thickness).

The Thebis [1] used a large diameter magnesium alloy frame tube, but is
certainly an oddity in many ways.

[1] <http://home.mindspring.com/~kb7mxu/images/thebis.jpg>.

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

First time builders should avoid cromoly. It is more expensive, more
difficult to machine, nearly impossible bend and much easier to creat a
embrittled joint due to excessive heat. TIG and oxy-acetylene (for both
welding and brazing,)is the preferred jointing methods on cromoly. MIG
(GMAW) was never designed for thin walled applications, and not the
best choice for cromoly. It is however, fast and efficient and the
prefered choice for thicker mild steels.

If the beginner only wishes one frame, then consider a welding class at
your local Community college. You'll have access to everything needed
to build a sweet frame, and the professional advice to answer the tough
problems. If more than a few bikes are in your future, then your FIRST
major purchase should be a oxy-acetylene set. You can braze, solder,
weld, cut-up a bike frame in 60 seconds, thaw frozen water pipes or
even toast a hot dog. It's also portable and doesn't need electricity.