bent thinking for warped ideas

[Bob Flemming]

been fantasizing at the dark side now for some time now...

ok, i have ambitions to build a bent from old bike frames....not exactly revolutionary in itself,
but a big undertaking for me...

to begin with, two things:

1. wheelbase. from what I can ascertain there are two basic types of bent - the long wheel base
<LWB> holding steady to the road, but turning on a very large sixpence, and a short base <SWB>,
more commonly referred to as a bent 'racer', or a machine more designed for speed, but arguably
more difficult to control at speed?

My question here is: how 'steady' are the shorter wheel base machines? My inclination is towards a
'tourer type' machine, as this is my 'type' of cycling, but I would also like the option to 'give it
what I could' in terms of speed. When I look at designs, I feel more drawn to the type that has the
front wheel 'underneath' the legs as opposed to the front wheel 'leading' the bike, which is more
the 'racer' type design, eh?

2. Drive. What's the difference between front-wheel-drive and rear- wheel-drive. Just looking at the
basic design of a bent, all models of which have a common similarity in that rider is
'essentially' in a lying position as opposed to a 'butt-supported' position - this meaning that
the chainset is invariably in a frontal position on the bike, so why is not more common to make
bents 'front wheel drive' as opposed to rear wheel drive? What's the advantage of having rear
wheel drive with a chain stretching 6 feet to the drive wheel at he rear, when it could just
stretch 2 feet to the front?

3. Welding. I would envisage building this from older bike frames. It would appear that a mig welder
is the cheapest welder to buy, but I'm, getting mixed reports<reading Goog;e> about the
suitability of using mig welders for bike frames. As far as I can see, gas assisted migs are
better than 'wire flux' welders, giving a much cleaner and easier weld at the end of the day. Is
this true for bike frames? I cannot see using a welder for anything other than bike frame tubing
at the moment, so would a cheapo gasless mig be ok - providing I master the technique of welding
of course??? I'm only concerned about the strength of the weld, the beauty of the thing I can
forsake just now...for the times being anyway

The cheapo gasless welders claim a maximum mild steel weld to be 3-4mm....bascially ok for
bikes, yeah?

I'm really into this idea at the moment. Crazy it may be, and therapy I may need, but I'd still
appreciate any experience on these three points.

many thanks

bob <pipe-dreaming

 

[Bob Flemming]

and this is the most appealing frame I've seen yet.....something in this style of this is what I'm
aiming for..

http://www.ajobikes.com/turner_review.htm

bob

 

[Ian Smith]

On Sat, 07 Jun 2003, Bob Flemming <[email protected]> wrote:
>
> been fantasizing at the dark side now for some time now...
>
> ok, i have ambitions to build a bent from old bike frames....not exactly revolutionary in itself,
> but a big undertaking for me...

Have you seen the recent threadlet on teh 'dutchbike' (I think it was something like that). A kit of
parts that you combine with a donor bike and a hacksaw to produce a recumbent.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

 

[Arno Seitzinger]

Bob Flemming wants to build bent from old bikes...:

>
> My question here is: how 'steady' are the shorter wheel base machines?
I have tho bents: a LWB Peer Gynt and a SWB Baron Lowracer. Though the Baron was a bit harder to
control for all persons who test-rode it, no one needed more than 15 mins. The SWB feels very stable
at all speeds, too. The main problem with SWB bents which are not lowracers is the high point of
gravity which may lead to rear wheel lift off when braking hard. No problems with the Baron because
it has a quite long wheelbase and a low center of gravity

> What's the difference between front-wheel-drive and rear- wheel-drive.
Like cars with FWD and others with RWD, no one design is clearly superior to the other. I don't ride
a FWD because
a) my favorite bike (Baron) happens to be RWD
b) FWD looks somehow odd (IMHO)
c) It is hard/impossible to start a FWD uphill when the road is wet because of the wheel slipping
But if I wanted a folding bent I'd probably go for a FWD and have the whole drive at front.

> Which type of welder?
I've never tried one of those gasless MIG sets. In general, I'd recommend MIG welding *only* for
cheapo thick-wall steel frames because high quality CroMo&other steels will be destroyed by the heat
of the weld. Those can only be MIG welded with an insert tube which reinforces the weld. Good steel
should be WIG welded or brazed (recommended) with an acetylene-oxygen torch (a simple propane burner
will *not* do). And you need enough practice - imagine the bike disintegration while speeding over a
bump @ 80kph and with a 30 ton truck behind you.

Anyway, consider that you'll build three frames before you find a useful setup because you'll forget
so many things that the first designs will be quite undriveable.

Arno

 

[John J]

1 Do lots more research before deciding on a design. There are much nicer bikes out there and lots
of homebuilt sites with ideas you can copy. http://webpages.charter.net/rcgilmore/Illustrations.htm
is probably the biggest resource of human powered links.

2 If you are using it for touring the seat must be comfortable and stay comfortable when bounced
around in for several hours - not easy to acheive as not everybody is the same (a bit like wedgie
saddles really)

3 Welding involves melting bits of material together and usually adding molten bits of the same type
of metal. Cycle tubing is thin. The biggest problem you will have is melting too much metal and
'blowing holes' in the tubing. I have welded thin tube with MMA (stick), mig, tig, and oxyacetylene.
I haven't tried gasless mig but anything is possible with practice.

4 Use heavy 'gaspipe' bikes from a scrapheap for experimentation - you will probably not get things
right first time.

5 (And most importantly) Don't be put off. Advice is just someone elses viewpoint, find out how
experienced the advisor is before you trust their judgement. It can be done - if anybody tells
you that you can't or shouldn't - take it as a challenge, prove them wrong, it's THE way to
make progess.

John J http://xntrick.co.uk

 

[Jim Price]

Bob Flemming wrote:

> My question here is: how 'steady' are the shorter wheel base machines?

Mine is as steady as the bike (frame) it started out as - a bottom of the line CroMo GT. I've put a
few pictures up here:

http://www.jimprice.dsl.pipex.com/

By way of a little explanation, the second pic is showing how the seat folds to make it easier to
get on the thing. This was my preferred solution to having the steerer tube fold or underseat
steering. The third pic is a closeup of the welding. As I knew this was not going to be a
professional job, I tried to design in as much strength as possible using the materials available.
It ain't pretty, but it works, and its so far only cost £89.

> My inclination is towards a 'tourer type' machine, as this is my 'type' of cycling, but I would
> also like the option to 'give it what I could' in terms of speed. When I look at designs, I feel
> more drawn to the type that has the front wheel 'underneath' the legs as opposed to the front
> wheel 'leading' the bike, which is more the 'racer' type design, eh?

Legs Larry would be your man for expertise on that, but low and leant back a lot seem to be the
racer type characteristics, along with fairings for aerodynamics.

> 2. Drive. What's the difference between front-wheel-drive and rear- wheel-drive. Just looking at
> the basic design of a bent, all models of which have a common similarity in that rider is
> 'essentially' in a lying position as opposed to a 'butt-supported' position - this meaning that
> the chainset is invariably in a frontal position on the bike, so why is not more common to make
> bents 'front wheel drive' as opposed to rear wheel drive? What's the advantage of having rear
> wheel drive with a chain stretching 6 feet to the drive wheel at he rear, when it could just
> stretch 2 feet to the front?

For me, the choice was made for the reason that I didn't like the idea of the FWD drive choice
between either having the pedals move with the steering, or twisting the chain with the steering.
Both of those seemed problematic just thinking about them, and more likely to be a failure when it
came to building them. I have seen one front wheel drive design which was very simle to build, but I
also remember the builders comments about it being like a bull to ride. I chose short wheelbase and
over seat steering again for ease of construction, given what I started out with.

> 3. Welding. I would envisage building this from older bike frames. It would appear that a mig
> welder is the cheapest welder to buy, but I'm, getting mixed reports<reading Goog;e> about the
> suitability of using mig welders for bike frames.

I'm only just learning welding myself, so take the rest of this with a pinch of salt:

I used gas MIG on mine. The problem, I believe, is that MIG welding has a tendency to get things too
hot for thin bike tubes. I used a "gas pipe" old bike for the boom tubes and welded to the head tube
on the original bike chassis, so both tubes were thick in comparison to a quality bike. Also, my
mates mate who _actually_ did the welding did it in short bursts rather than one long go, to try and
prevent too much heat buildup. This was after the "do you want it to look good or be as strong as
possible for a bodge job" conversation.

> As far as I can see, gas assisted migs are better than 'wire flux' welders, giving a much cleaner
> and easier weld at the end of the day.

By 'wire flux' do you mean the traditional arc welder with a rod, or a non-gas MIG? I've only got a
borrowed arc welder, and it seems a lot more difficult than any kind of modern auto-feed welder.

> Is this true for bike frames? I cannot see using a welder for anything other than bike frame
> tubing at the moment, so would a cheapo gasless mig be ok - providing I master the technique of
> welding of course???

I really have to leave worthwhile comment on that to the experts, and say that I am going to have a
go with my arc welder on some junk frames, just to see what happens.

> I'm only concerned about the strength of the weld, the beauty of the thing I can forsake just
> now...for the times being anyway

Me too on that one.

> The cheapo gasless welders claim a maximum mild steel weld to be 3-4mm....bascially ok for
> bikes, yeah?

Its not the maximum I would worry about, its the minimum they'll do which is more in the range of
the sort of size tubing bike come in. A bottom bracket or a head tube would be about the thickest
tube on a bike, and I don't think I have seen any steel 4mm ones.

> I'm really into this idea at the moment. Crazy it may be, and therapy I may need, but I'd still
> appreciate any experience on these three points.

I found it very theraputic, as there were lots of problems to solve. Mine is still a work in
progress. I'm sure I could come up with a tidier job on the handlebars, and the seat was only really
a bodge job to test out the riding position. I would like to change to under seat steering, to get
the size of the thing down a bit, but that is waiting for inspiration and cheap bits to turn up. On
the crazy side of things, its a lot less crazy than the toeclips on a unicycle experiment.

Jim Price

 

[Mads Hilberg]

> Have you seen the recent threadlet on teh 'dutchbike' (I think it was something like that). A kit
> of parts that you combine with a donor bike and a hacksaw to produce a recumbent.

It's a bit overpriced mind. You can buy a complete Azub recumbent for the price IIRC.

www.ihpva.org is a good place to start.

Mads

 

[Mark Van Gorkom]

There's rather more to 'bent design than just SWB-LWB; even two very similar looking bikes like a
Challenge Hurricane and an Optima Stinger have very different riding qualities. A well-designed SWB
can be steered with two fingers at any speed; some LWBs can be rather a handful, esp. going uphill
slowly (not much weight on the front wheel). And than there's C(ompact)LWBs and lowracers
(mediumWB). Nor have all SWBs the same wheelbase, or the seat in the same place relative to front
and back wheel. Seat angle is at least as important as wheelbase and weight distribution, but
happily an adlustable seat is easier to build than a variable wheelbase! Seems to me a
longish-wheelbase medium height SWB would be the best place to start; if you find out you like frame
building you'll probably rebuild it a few times till you find what you like. And wouldn't a SWB be
easier to build too?

Somebody already mentioned Dutch Speedbikes: http://www.dutchbikes.nl/ For recumbent-specific parts:
http://www.zephyr.nl Bulding info: http://www.ihpva.org/people/tstrike/building/

Mark van Gorkom.

P.S.: I like to think I've been on the dark side long enough that I know exactly what I'd want, but
I've a got a few thumbs too many to build my own; hope yours works out!

 

[Bob Flemming]

>I'm only just learning welding myself, so take the rest of this with a pinch of salt:
>
>I used gas MIG on mine. The problem, I believe, is that MIG welding has a tendency to get things
>too hot for thin bike tubes. I used a "gas pipe" old bike for the boom tubes and welded to the head
>tube on the original bike chassis, so both tubes were thick in comparison to a quality bike. Also,
>my mates mate who _actually_ did the welding did it in short bursts rather than one long go, to try
>and prevent too much heat buildup. This was after the "do you want it to look good or be as strong
>as possible for a bodge job" conversation.
>
>> As far as I can see, gas assisted migs are better than 'wire flux' welders, giving a much cleaner
>> and easier weld at the end of the day.
>
>By 'wire flux' do you mean the traditional arc welder with a rod, or a non-gas MIG?

yes, that's it, gasless Mig....these seem to be available for about 100 quid or so, but the gasless
welding wire is a lot more expensive. I wonder how quickly it gets used up? It would appear that the
finished weld is a tad more ugly with these gasless Migs, and leave a significant flux residue after
the job is done, but it sounds as though they may do a job, providing the metal is not too thin.

>I've only got a borrowed arc welder, and it seems a lot more difficult than any kind of modern
>auto-feed welder.

Talking to a guy from the LBS today, who's had some experience of welding was steering me very
firmly away from an Arc welder, mainly due to the ease with which they can punch a nice hole through
a frame! He had used gas/mig, but no experience with a gasless mig system.

Reading more around the subject though, leads me to believe that a oxyacetylene setup is probably
the best thing to have (apart from a mega-bucks Tig welder), as this option gives you brazing and
cutting capabilities as well. I'd overlooked brazing. But again, there is a practical problem of
keeping two gas bottles in a one-bedroom flat!!...<guess, who'd love a workshop?>

Many thanks for the link to the pictures Jim, I've encountered quite a few of these homebuilt
machines on the web of late It all makes interesting reading.

Many thanks for your reply.....and all other replies too. Plenty to think about.

bob

>> Is this true for bike frames? I cannot see using a welder for anything other than bike frame
>> tubing at the moment, so would a cheapo gasless mig be ok - providing I master the technique of
>> welding of course???
>
>I really have to leave worthwhile comment on that to the experts, and say that I am going to have a
>go with my arc welder on some junk frames, just to see what happens.
>
>> I'm only concerned about the strength of the weld, the beauty of the thing I can forsake just
>> now...for the times being anyway
>
>Me too on that one.
>
>> The cheapo gasless welders claim a maximum mild steel weld to be 3-4mm....bascially ok for
>> bikes, yeah?
>
>Its not the maximum I would worry about, its the minimum they'll do which is more in the range of
>the sort of size tubing bike come in. A bottom bracket or a head tube would be about the thickest
>tube on a bike, and I don't think I have seen any steel 4mm ones.
>
>> I'm really into this idea at the moment. Crazy it may be, and therapy I may need, but I'd still
>> appreciate any experience on these three points.
>
>I found it very theraputic, as there were lots of problems to solve. Mine is still a work in
>progress. I'm sure I could come up with a tidier job on the handlebars, and the seat was only
>really a bodge job to test out the riding position. I would like to change to under seat steering,
>to get the size of the thing down a bit, but that is waiting for inspiration and cheap bits to turn
>up. On the crazy side of things, its a lot less crazy than the toeclips on a unicycle experiment.
>
>Jim Price

 

[Jim Price]

Mark van Gorkom posted below my post according to my newsreader, but probably meant to post under
the top post:

> There's rather more to 'bent design than just SWB-LWB;

Indeed, but I'm not quite sure which part of my post you are replying to.

> A well-designed SWB can be steered with two fingers at any speed;

Excellent news - mine must be well designed . I prefer a finger and a thumb, although TwoJags
might not.

> P.S.: I like to think I've been on the dark side long enough that I know exactly what I'd want,
> but I've a got a few thumbs too many to build my own; hope yours works out!

Thanks, it has so far. Um, now it really sounds like you meant to post under the top post...

I'll get me 'bent.

Jim Price

 

[Jim Price]

Bob Flemming wrote:
> yes, that's it, gasless Mig....these seem to be available for about 100 quid or so, but the
> gasless welding wire is a lot more expensive.

Six times the price of the regular stuff for gas!

> I wonder how quickly it gets used up?

Pretty quickly, as I remember.

> It would appear that the finished weld is a tad more ugly with these gasless Migs, and leave a
> significant flux residue after the job is done, but it sounds as though they may do a job,
> providing the metal is not too thin.

You still have to clean the weld a bit after gas TIG, ISTR.

> Talking to a guy from the LBS today, who's had some experience of welding was steering me very
> firmly away from an Arc welder, mainly due to the ease with which they can punch a nice hole
> through a frame!

Yes, been there, done that. Fortunately not on anything important or expensive (the remains of the
frame which got sacrificed for the boom, in fact). I did a welding course 20 years ago, only using
an arc welder, and I've got one on loan for free, so thats what I'm stuck with for now.

> He had used gas/mig, but no experience with a gasless mig system.

They seem quite cheap, and relatively low current (which would help to avoid burning through tubes
too easily), but I've only seen wire for them suitable for welding mild steel.

> Reading more around the subject though, leads me to believe that a oxyacetylene setup is probably
> the best thing to have (apart from a mega-bucks Tig welder), as this option gives you brazing and
> cutting capabilities as well.

In the kingdom of the highly skilled, I'm told that there are men who can braze with just an arc
welder! In the kingdom of the inexperienced (that's right here, right now), if I could control the
holes I'm cutting, I could cut too

> I'd overlooked brazing. But again, there is a practical problem of keeping two gas bottles in a
> one-bedroom flat!!...<guess, who'd love a workshop?>

Me too. The living room is getting a bit crowded, and the welding bay (back yard) seems to
let in rain.

Jim Price

 

[Mark Van Gorkom]

>Mark van Gorkom posted below my post according to my newsreader, but probably meant to post under
>the top post:
>
>
>Um, now it really sounds like you meant to post under the top post...
>
You're right, I should have, sorry about that.

 

[Peter Clinch]

Bob Flemming wrote:

> 1. wheelbase. from what I can ascertain there are two basic types of bent - the long wheel base
> <LWB> holding steady to the road, but turning on a very large sixpence, and a short base <SWB>,
> more commonly referred to as a bent 'racer', or a machine more designed for speed, but arguably
> more difficult to control at speed?

> My question here is: how 'steady' are the shorter wheel base machines?

"it depends". First up, SWB machines are by no means all racers. In fact the majority of Dutch
machines (those people who like nice steady roadsters) are SWB designs. My 'bent (an HPVelotchnik
Streetmachine GT) is an out and out touring design and is SWB. It's very steady, and handles well at
speed but can also be ridden down to walking pace in a straight line okay while carrying a fair bit
of luggage. Full on racers with "tiller" steering can be steady IM(limited)E but are very twitchy
until you've got the hang of the steering. You only need one finger on the bars, but pull on them at
all and I think you may be in a spot of bother.

> My inclination is towards a 'tourer type' machine, as this is my 'type' of cycling, but I would
> also like the option to 'give it what I could' in terms of speed. When I look at designs, I feel
> more drawn to the type that has the front wheel 'underneath' the legs as opposed to the front
> wheel 'leading' the bike, which is more the 'racer' type design, eh?

Lowracers are SWB for the most part, but as above, you can get touring designs built this way
too. The Streetmachine is not a fast bike because it's quite heavy and relatively high (about car
seat height), but it's noticeably easier into a big headwind than an upright and is a screamer
downhill (with very good cornering, helped on backroads by the full suspension that helps it
track very well).

> 2. Drive. What's the difference between front-wheel-drive and rear- wheel-drive. Just looking at
> the basic design of a bent, all models of which have a common similarity in that rider is
> 'essentially' in a lying position as opposed to a 'butt-supported' position

Not really. A Compact Long Wheel Base (CLWB) has a seat but is only half a step away from
semi-recumbents with a saddle, and they're not so good for long tours because your back isn't taking
weight to such a degree, leading to "recumbent butt" over long journeys.

> meaning that the chainset is invariably in a frontal position on the bike, so why is not more
> common to make bents 'front wheel drive' as opposed to rear wheel drive? What's the advantage of
> having rear wheel drive with a chain stretching 6 feet to the drive wheel at he rear, when it
> could just stretch 2 feet to the front?

Generally it's down to steering. Rear wheel steering is generally held to be trickier to do both in
terms of implementing and actually doing to go around corners. Which leaves you with having to drive
a wheel where the rider is ideally in line with the cranks and the cranks are ideally in line with
the wheel: okay for straight lines, but not where you need a lot of steering lock. There are also
aesthetic considerations when it comes to actually selling things.

Can't help you at all with the welding, but for now I'd get out and ride a few at the shops that do
demos (London Recumbents, Bikefix, Futurecycles, Kinetics and D-Tek) and get a better idea of the
differences in SWB machines.

HTH, Pete.
--
Peter Clinch University of Dundee Tel 44 1382 660111 ext. 33637 Medical Physics, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net [email protected]
http://www.dundee.ac.uk/~pjclinch/

 

[Dave Larrington]

What Pete said. The LWB is just about extinct in Europe these days, though the 'melicans are still
persevering with them. SWB's are available in zillions of different types from the flat out racer to
long distance tourer. I should prescribe a prolonged session of web-golfing to see what's available
Out There. Links to shedloads of manufacturer's sites available from
http://www.legslarry.beerdrinkers.co.uk/makers/Manufacturers.htm

FWIW, I believe the term "CLWB" to be a Work of Stan, and the machines to which it is applied are
probably a Work of one of Stan's underlings.

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

[Peter Clinch]

Dave Larrington wrote:
>
> FWIW, I believe the term "CLWB" to be a Work of Stan, and the machines to which it is applied are
> probably a Work of one of Stan's underlings.

Depends what you want them for. If I was rich and wanted an urban bike in addition to everything
else it would very possibly be an HPVel Spirit with a Streamer fairing. Easily the most immediately
comfortable bike I've ever been on and very easy handling, though on longer rides the relatively
upright position relative to the Streetmachine would probably be a bit of a liability, and I can't
see having all the weight so far back will help loaded handling on 30+ mph descents. So not for
touring (and thus not for the OP I'd think) but more Phil[1] than Stan.

Pete.

[1] if unaware of Phil in the Dilbert strips, see
http://www.unitedmedia.com/comics/dilbert/the_characters/html/character4.html
--
Peter Clinch University of Dundee Tel 44 1382 660111 ext. 33637 Medical Physics, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net [email protected]
http://www.dundee.ac.uk/~pjclinch/

 

[Alan Braggins]

In article <[email protected]>, Bob Flemming wrote:
>
>3. Welding. I would envisage building this from older bike frames. It would appear that a mig
> welder is the cheapest welder to buy, but I'm, getting mixed reports<reading Goog;e> about the
> suitability of using mig welders for bike frames.

If it's fairly chunky welded older bike frames, should be fine. If it's more delicate older frames
with nicely brazed lugs, consider brazing instead of welding.

You won't manage something as nice as a Trice's lugs with a MIG welder
http://www.ice.hpv.co.uk/greenlug.jpg

(And more seriously, if the original frames were brazed, there is a chance the tubes were heat
treated in a way which will be weakened by the heat of welding. Frames like that are probably too
good to be being cut up though.)