Newbie Builder Questions

[[email protected]]

I want to try building a swb recumbent similar to HPVelotechnik Street
Machine (http://www.hpvelotechnik.com/produkte/sm/index_e.html), but without
suspension. Would exhaust tubing be strong enough for the main frame tube?
Otherwise, does anyone have any good recourses for acquiring the proper
steel tubing (small amounts, of course)? Once built is chroming okay? Any
drawbacks? Powdercoating? Again, does anyone have some resources to get the
chroming or powdercoating done?

[[email protected]]

wrote:
> I want to try building a swb recumbent similar to HPVelotechnik
Street
> Machine (http://www.hpvelotechnik.com/produkte/sm/index_e.html), but
without
> suspension. Would exhaust tubing be strong enough for the main frame
tube?
> Otherwise, does anyone have any good recourses for acquiring the
proper
> steel tubing (small amounts, of course)? Once built is chroming okay?
Any
> drawbacks? Powdercoating? Again, does anyone have some resources to
get the
> 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

[Tom Sherman]

Jeff Wills wrote:

> ...
> 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

[cyphus]

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

[[email protected]]

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

[Tom Sherman]

Duncan Cooper wrote:

> ...
> 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)

[[email protected]]

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 slag 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

[Kim Hawtin]

wrote:
> 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<
> 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 slag 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?

> 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?

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

how does one deal with that?

> 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.

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

[[email protected]]

Kim, newbie builders:

Concerning equipment, here's what I have
- Flat work surface on which you can weld/braze without burning down
your house. I have a 60x24 piece of 1/4 in mild steel which is very
true for the alignment of the frame . Big powerful light for the work
area.
- Drill press with joint jigger, grinder, dremel tool with multiple
grinding tips
- angle measuring level
- flat, found, and half ******* files in rough and finishing
coarsness
- gas welding torch. I use a Dillon Henrob with very small tip
- a package of new hacksaw blades. Old ones stink
- a pair of good safety goggles with new "glass". All the
abrasives eat the replaceable plastic visors up. Good vision is
paramount. I use 1.25 diopter reading glasses beneath the gogles.
Guarenteed you'll get a metal chip in your eye sometime in the process.
Guess how I found out........

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)

Flux removal:
- Soak the joint in a tub of water for about 12 hours. Stuff comes
right off, but ya gotta be careful about corrosion inside the joint. I
dry the insides of the tubing with a rag on a long welding rod, then
actually paint the insides of the tubes before finishing the bike.
(some think that's a little anal)

Just build a bike and the lessons become self evident. I really
enjoyed the challange. Given the number of hours I put into the
projects I can't see HOW the manufacturers can make any money doing it.
Betcha can't build just one ! Enjoy :)

[Tom Sherman]

Duncan Cooper wrote:

> ...
> 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)

[MagicFingers]

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.

[Tom Blum]

I built a Speed Machine Clone out of muffler pipe (2")

The only problem I had was at the head tube frame juncture, where a fatigue
crack developed after several months use.

I added a gusset and had no further problems.

Tom