Hi all,

I'm new to the frame builder forum, and in fact I'm new to building bikes in general, so go easy on me please.

A little background before I get into the questions.

I'm a late 30-something former IT guy who is in the middle of a career change to welding. I'm currently 7 months into the welding program at a local CC. I'm not the biggest bicycle fan out there, but I've always had an appreciation for their design. I'm particularly interested in recumbent bikes, custom (unique) builds and utility bikes, and older bike frame designs from the early 1900's. My understanding of the inner workings of bikes, design, and components are rudimentary at best, but I'm learning more each day.

In September I had started work on a steel square tube recumbent bike using the TIG (GTAW) process and some plans I got from Atomic Zombie. The bike should be complete next week. I deviated from the plans mid stream and changed the designs and bike's geometry. It's not scientific, but it was fun building something I would eventually ride even if only for a short time until I finish my next bike. I'll post some photos next weekend when it's complete.

I have since sold my TIG welder though, because I needed a MIG welder for other jobs I was working on. I'm aware TIG is the better process for this kind of work, however it simply wasn't an option, so I have to work with what I have.

I currently own a Millermatic 211 which will do between 24 ga. and 3/8" steel, using wire sizes of .024 - .045. I also have the Spoolmate 100 spoogun for aluminum work (.030 wire), which will do between 18 ga. to 1/4". I've got two tanks of gas, pure Argon and C25.

I'm looking to start my second recumbent using round 4130 tubing from Aircraft Spruce (which I learned about from this forum).

So my questions are:

1) What wall thickness would you recommend for building 4130 recumbent bikes? Keep in mind the lengths of the tubing for different parts of the bike's geometry will be quite long compared to a diamond frame upright bike.

2) Having never welded 4130 specifically, I'm assuming mild filler wire and C25 will work but I'd feel silly if I didn't ask. Is this a good combination for welding 4130, or would I require wire with a higher tensile strength and possibly a different gas mixture?

3) Can I weld the 4130 tubing to a standard carbon steel bottom bracket, such as this one: https://www.paragonmachineworks.com/s...-10464059.aspx

The last few questions are about Head Tubes, and perhaps this should go in a different thread, but if I wanted to order tubing to use for a custom head tube for threadless forks, what size (ID) would I order? If this isn't a simple answer, I'd be open to reading anything you guys would care to link me to on the subject. I've read a bunch of general info about head tubes, and sized of the forks, but the tube itself seems to be eluding me.

Thanks a ton for any replies on these questions!

Dillsburg is cheaper, but they prefer that you buy in full lengths, which are 17 to 24 feet.

I've heard there are mig'd recumbents out there, MIG is never used on high-end DF bikes. There are recumbent frame forums out there, I recently saw references to them and forget where. I have no idea about wall thickness, but for a very long tube you want to go to larger diameters. .049 seems like it would be pretty safe, but for a big tube you may want to go to .035, I just don't know.

As far as head tubes go, I'm not sure that the general 4130 suppliers will sell you the right stuff because on a welded frame, you want thicker walls. But the ID is the most important dimension. Might be better off going to Nova or Henry James for that. You also need access to a head tube reamer and facing tool. You can use either 1 3/8 or 1 1/4 with threadless, although 1 3/8 is more common.

You can certainly TIG the BB to 4130, I have no idea about mig or fillers. I would think that your biggest problem may be shell distortion. The TIG guys use a heat sink to keep distortion under control.

Having welded and doing most types of metal work for the last 16+ years professionally, I would strongly suggest you NOT use a mig welder for building bikes. It is possible after doing many tests and you might be able to use a dual shield welding wire and get lucky but as unter mentioned you have the distortion problem and then some. Either way if you do plan on mig welding it, plan on repairing it over and over with the hopes of not having a bad accident.
I would sell the mig and get a tig welder. You can tig weld just about anything but you can't mig weld just about anything. Tig welding is more structurally sound and controllable. Also you can get the right type of filler rod for your application (more options). Tig welding is tried and true. Hope that's some good advice! Good luck and be safe.

A few links for you:
https://www.bentrideronline.com/messa...splay.php?f=12
https://recycledrecumbent.com/
https://www.recumbents.com/wisil/whatsup.htm

Nova has a pretty easy to figure out website and was very easy to deal with the one time I needed them. They list steel headtubes in various lengths for 1 in and 1 1/8, some thin walled for lugs, some a bit thicker for fillet or welding. The ID is just a little under finished size, so no boring is needed- just ream when you`re done. If you wanted even thicker wall for MIG welding, I dunno. Probably have to order oversized with monster wall thickness and turn/bore a lot of material out of the way to make your tube.

For somebody who knows, is it really necessarry to use specific headset reamers? Is there any problem with reaming the full length with an adjustable and having a bike shop face the ends?

You can't dual shield MIG (GMAW) wire to my knowledge. Could you be talking about Flux Cored (FCAW) perhaps? Flux Cored can be dual shielded, but I agree it's definitely not the right process for the bike frame. FCAW is designed for thicker metals, burns hotter and has more penetration, not to mention you have to deal with the slag.

I'm using solid wire MIG (GMAW) with C25, designed for thinner metals. I've welded 16ga with no issues, and the welder will do down to 24ga. From my research on MIG vs TIG when welding 4130 tubing (mostly on the auto racing forums), TIG is indeed better if you are a very skilled TIG welder, but MIG is more than capable. I've seen s few builders out there using MIG for their frames, there are even some MIGged frames at Target, though most are TIGged. In my case, the MIG welder I have is infinitely better than the TIG welder I don't.

Here's a guide on the miller web site about MIG welding 4130. Scroll down a bit.

https://www.millerwelds.com/powerclic...lick_0307.html

Thanks everyone for your feedback. Still reading the links you provided Rodar, and thanks for the tip on Dillsburg unter. The HT info was useful as well.

the MIG welded bikes at Target use very thick material. Once you give up on light weight, you can use hand forging or any other process you can think of. I understand the issue with money and no TIG, I have the same problem.

This depends on frame design (mono or multi-tube triangulation), wheelbase and CoM location. Beyond a given WB, mono tubes don't make much sense, not to mention that you'll be forced to go with .049" wall above 1.5" diameters (.035" is rare above 1.5" diameter in 4130). I need more frame layout specifics please.

C25 is fine. Use ER70s-2 or s-6 filler. Do NOT use 4130 filler unless you plan to post heat treat the frame. Be advised, MIG on thin wall (much below .045") is not for the faint of heart. Yes, it can be done, but it's not easy or even recommended. The problem is lack of heat control while under the hood - unlike TIG or O/A where the user has full control when the situation approaches burn-through. It is further complicated when doing compound tube joints where consistent travel speed becomes difficult and tricky to maintain. I can MIG .035" in long horizontal passes, but add thin wall tubing joints and I'm reaching for TIG or gas.

Yes. The same ER70-s2 or s6 filler is used. To help reduce BB distortion, a gapless joint fit is highly recommended, then just lightly screw-in a pair of cheap, steel bearing cups prior to welding.

Go here: https://www.sheldonbrown.com/headsets.html

IIRC, the head tube ID for 1-1/8" steerer should be close to 34mm (or about 1.336-1.338").

A bike shop will have a combo head tube reamer/facing tool anyway -- every tool I've ever seen has both cutters. I've considered getting close to finished dimensions on the lathe, but it seems that the head tube will distort during joining. With lugs, it's nice to have extra head tube outside the lugs so you can flow any extra brazing material to somewhere that you aren't going to need to clean it up.

Hey unterhausen, I just noticed... when did you get promoted? Congrats!..

this week. The only one of my new superpowers that I've used is the highly desired double post feature

on edit: and of course this is the first post today that didn't double post on me

I hear it takes a while to grow into your super powers. Just don't try jumping from skyscraper to skyscraper yet.

Thanks everyone for the feedback. Papa, good info there, thank you.

You guys lost me with the promotion and superpower bit, but... congratulations, I guess.

As it happens, my regular LBS has facers with no reamers. There are plenty of others to ask since that doesn`t seem to be the norm. My employer does have a nice set of adjustable reamers, so I figured to go that route if possible. So far I have the headtube fillet brazed in with about a half inch extra on each end, so plenty of room for facing (looks like a hacksaw job to begin with). I still need to braze on the extended stays that take the place of a downtube (it`s a triangulated SWB `bent) and don`t plan to ream anything until all the brazing is done. Maybe I`ll post a "work in progress" thread next week. Thanks for the answers again.

that's interesting about their facing tool, never seen one. I assume they have some kind of plug to maintain concentricity with the ID of the head tube. I think you should be ok reaming the head tube. I find adjustable reamers to be somewhat unsatisfying though. And reaming the head tube always seems to take a lot of effort so reaming the whole length is going to be a chore.

The purple star to the right of his moniker signifies a moderator or 'MOD" (short for Mischievous, Ornery & Dangerous)

yup, parks head tube facer/reamer has plugs you can swap out for the reamer if you only want to face.

To the extent that you want to use something cheap to weld up your bike, gas weld it. It is really easy if you have a little background in TIG. I think it may be easier than TIG since you only have to co-ordinate your hands, not your hands and a pedal. Many of the problems of TIG don't exist, like getting an arc. There is no flux on regular steel as with brazing. Arguably stronger than TIG, in those theoretical discussions where stronger than strong enough is so important. Point being it probably isn't weaker, and certainly not in any significant way. You can get set up for less money than TIG or MIG, and you really benefit from having gas for all the other stuff it is useful for in bike making.

I think PBB jumped ship and went elsewhere:

https://forum.atomiczombie.com/showthread.php?t=3823

Well, I don`t see anything wrong with boarding more than one ship (hope not, since I do that regularly). I also don`t think his reception here was all that hostile, but I hope he`s comfortable there.

PP, gas welding doesn`t get cheaper than fillet brazing , does it? Just wondering.

I think people here were as helpful as possible considering that nobody here uses MIG. I can't imagine he's going to get much informed help on the framebuilders list or frame forum either.

I would think gas welding consumables would be a little cheaper than fillet brazing, but probably not enough that I would switch. The distortion has got to be pretty big. I'm guessing the OP doesn't have an O/A rig anyway or he would have mentioned it.

As unterhausen stated, not a huge difference in consumables, unless of course, you're torching silver. I just bought 4 TOz of 45T and the bill was just short of $60. I use O/P so I can afford to splurge a little on fillers

MIG isn't particularly cheap either. I have small Hobart I use for jigs and occasional tacking. A 12.5 lb. spool of ER80-D2 was $35, and the C25 was $40 for a tiny bottle (I opted for straight CO2 instead).

Frame forum will be like that scene in Bedazzled where the moment Dudley Moore gets in among the leaping nuns he will be blowing the raspberry to get back out.

"PP, gas welding doesn`t get cheaper than fillet brazing , does it? Just wondering."

Well yes and yes. I mean I assume he didn't have a gas rig, and if he had he probably would be fillet brazing it in which case all would be well for him, and I take your point.

On the other hand, let's just say he actually wants to weld the joint, possibly because that is his skill set, then gas is probably his cheapest realistic option.

And, gas welding is cheaper for several reasons: Start up wise the Mecco torch is cheaper (can be any torch one wants), and one either doesn't need but one tip, and it is also cheaper if one wants more than one tip. One doesn't have to source flux, or use flux which saves money on the flux, a bin to soak frames in, wear and tear on the shop floor and lungs. One uses a lot less filler and it is a lot cheaper. One uses a lot less gas.

To me the biggest cost savings, both as a small shop guy and an out of the US guy is that there is no access to quality bike brazing stuff up here. Sourcing from the US would be no problem for anyone with a serious interest in the biz etc... I get all my stuff from the US for my various hobbies. But stuff like this is kinda expensive to source on small orders, and there is usually an expense to breaking in new suppliers. Every one has a different shipping policy and shipping is increasingly expensive figure the same as the stuff one is ordering. And it won't be overnight, more like over-week to over-month. Compared to just buying a few steel rods from the local welding supply... Of course if you live in the US ... never mind...

I didn't jump ship, I've just been offline a while. Wife had me doing honey-do's most of the spring break. The bike's not finished, but the kitchen looks a lot better now.

I'm not sure the types of bikes I'm building (or the materials I'm working with) are quite in line with the stuff you guys are doing here. I'm more likely to use square tubing and recycled bottom bracket shells. I don't own gas. I'm pretty decent with MIG and until I can add another TIG welder to the garage, MIG will be how I work for a while. While I wasn't complaining about you guys (really, it was the welding forums that were a bit more hostile), I do feel that the kind of builders over on Zombie are more in line with the type of working parameters that I'm using. I'll probably never buy a tubing kit or use gas on anything I build, and it certainly wouldn't be something anyone would want to buy when I'm done.

Anyhow, I hope no one took offense. I do appreciate the feedback.

My last purchase of generic, off-the-shelf, 64kpsi LFB was $7 per pound. At roughly fourteen 36"x3/32" sticks per pound, that's $0.50 per stick. Figure a novice might use/waste three sticks on one build. And for the sake of argument, he gets wasteful and uses $0.10 worth of flux. Total is $1.60. One pound of RG45 is $1.70 per pound, or about $0.12 per stick. Figure 2 sticks. Total is $0.24. Cheaper?... perhaps, but the cost difference PER BUILD is a whopping $1.36 - IMO, an insignificant amount if hobbyist is building only 2, maybe 3 bikes per year. Further, you don't need a soaking tank... wet rags wrapped around the joints, followed by a soapy rinse does fine.

How you figure brazing takes more fuel than welding is beyond me. The melting temperature of mild steel is aprox. 2700f, while LFB is closer to 1600f. My theory says the lower melting temperature filler requires LESS heat, so less heat requires less fuel. It's also important to remember that welding steel needs a LONGER pre-heat time, More heat = more fuel. And, as unterhausen pointed out, the higher temps of gas welding steel (in addition to the expanded HAZ), make warpage much more of an issue.

PhotoByBike, Glad you didn't completely ignore us. I apologize if I offended you, 'twas certainly not my intention.