View Full Version : Welding thinwall cro-mo (structual tip?)

A.K. Boomer
08-22-2007, 08:46 AM
Iv brought up welding this tubing before --- im going to be using my friends tig this winter to build my bike frame, here's what im wondering, has anybody ever tried tigging in structual "gussets" but not like your thinking, im just talking a mild raised straight line that you just hand build with adding from the weld rod, im going to have very good control as my friends got a good machine, so whats stopping from building a little raised area that tapers off, or a bunch of them, you could kinda have a little "spider web" around every joint, just curious as I dont know much about it...

08-22-2007, 10:17 AM
AK...just remember...when you build anything up with weld, it creates tension. The more you build up the more the tension increases. I've used your idea on mild steel but you have to pretty careful when doing stuff like that with moly. Good luck!

08-22-2007, 10:26 AM
C.M. properly sized,fitted and welded shouldn't need any reinforcement.

08-22-2007, 10:30 AM

Is this going to be an artistic statement? If I understand the thread correctly, I don't believe the joint is going to be any stronger than without the spider web. The CrMo tube that is tig welded, is the basis for most pro drag racing frames and road racing motorcycle frames, they use gussets where needed, but the other welds are just a simple butt joints. the last road frame I bought that was CrMo and the only gussets were at the swing arm pivot and at the fork headstock.


08-22-2007, 10:37 AM
4130 Chrome moly tubing is designed to be gas welded. It was developed originally for aircraft use and has the maximum carbon content that is considered to be safely weldable via gas techniques. Gas welding normalizes the surrounding metal and produces a more gradual heat affected zone (HAZ) than electric welding methods. This reduces the chance of post weld brittleness and cracking.

Adding such "risers" with electric welding will only weaken the structure by providing more potential cracking zones.

08-22-2007, 11:03 AM
Several others have already alluded to the reasons why we haven't seen this done yet.
1) The heat affected zone around a weld bead.
2) Stress raisers caused by the discontinuity of a weld bead.

Yes, maybe it would look cool, but I can't really see any purpose in it. Then again I'm not an artist...I couldn't see wasting my time doing it.

Who knows, you probably would sell hundreds of them. Even cycling is full of people with too much time & money & too little sense. Look at the market for sunglasses.....How many designs are possible ? Convince everyone that your bike frame is a lifestyle statement and get rich....It's not at all about making a well designed, useful product, it's marketing.


Forrest Addy
08-22-2007, 11:38 AM
Yup. CrMO air hardens. It need to cool slowly if full joint strength is to be obtained. Older aircraft repair texts refer to a "tempering pass" for electric welded CrMo fabrication. An old welder I knew with extensive WW II aviation metalsmith experience told me he favored heating the general area of the weld to a red barely visible in poor light for a full minute then allow to cool slowly in a place free of drafts. I determined this was 1200 degrees. His advise hass been echoed in many texts I've read over the years.

I ran some tests with TIG weld in CrMo samples for my own information. A strip with a butt weld is likely to brittle fracture when folded back on itself. A strip heathed to 1200 degrees for a minute and allowed to cool in still air was ductile but would still fracture if overbent. A welded strip allowed to cool from red heat in a fluffly theremal fiber blanket (dare I say asbestos? It was that long ago.) was as ductile as an unwelded sample.

Welding aircraft tubing is well documented. You who desire to fabricate high-strength components having many welded joints should research the available material carefully to avoid the many possible pitfalls. There's no reason in today's glut of technical information for a home worker to wander off into unsafe technique. Adding extra filler metal or extending the bead might serve as an artistic statment but it's not likely to produce a stronger more reliable welded joint.

Sitting down with a "Today I think I will weld a bike frame. How hard can it be?" atitude is a resipe for joint failure at the worst possible moment. Prepare yourself and develop your skills before you start welding for real.

What's safe and strong and light all at the same time is never a product of "cool". It's a product of all the traits of nerdiness: study, dedication, hard work, diligence, and especially an other-worldly lack of concern for "cool." What's safe and strong and light is an incremental process where small steps are proven before going on to the next increment. Look at aircraft development in the last century. The pioneers of aviation are survivors of a savagely Darwinian process. Only those who survived those early days went on to make advancements. Many perished in the process.

CrMo frame construction is but one tachnology that is exhustively presented in welding texts, aircraft maintenence texts of the era, and a large body of welding progedures and engineering papers. This is available to you if you'd look in libraries, Google, weld supply shops, etc. The EAA (Experimenta Aircraft Association) has in its archives a huge connection of aircraft DIY technology. They are well worth an inquiry.

The procedures governng welded joints are subject to the dryest form of technical writing. Prepare to be bored out of your skull but you have to stay awake. Hidden in a half sentance might lay a jewel beyond price or the means to avoid disaster.

It's vitally important for a home welder to qualify himself before making high reliability welds. Weld several sample joints, saw them into samples and subject them to hammer and bench vise torture tests layed out in welding texts. The joint fit-up and the first pass are all-important. If the back side of the weld is inaccessible, only good fit-up and first pass procedure will ensure full penetration.

If you wish to develop alternative joints and welded embellishments, do so on sample pieces and subject them to some form of destructive testing. Only after you can duplicate the strength and ductility of the plain vanilla joints should you attempt these joints on a bike frame.

A.K. Boomer
08-23-2007, 10:52 AM
Good info guys , thanks for taking the time ----------- I wonder if a fiberglass blanket is good to use to hold heat for normalizing? It maybe has to much thermal mass to begin with and would suck it off the part, esp. thinwall cro-mo, or worst yet melt, Forest, I remember those old asbestos blankets and they were light and fluffy but i have to admit I wouldnt want one laying around the house,

For the record this wasnt to do with anything esthetic -- I was actually thinking structual and was aware of the fact that it would all have to be re-heated as a unit and then re-cooled but where do you draw the line? wouldnt the entire frame have to go throught this process? otherwise arent you leaving some area's in "limbo" ?

Evan you have always brought up the gas weld and I believe in what your saying if the material does not go through any further process, from what iv been told though is bike frames go through a process as a unit after the welding takes place, thing is Is iv been around bikes my entire life, Iv seen every material ever used on frames including titainium, kevlar reinforced carbon fiber, ceramic impregnated aluminum alloy and cast magnesium just to name a few,,,
If there is an advantage to any material or process in the form of strength/weight/durability therein believe me it will be exploited, you can drop over 5 grand on just a frame easy, it is one of the most competitive markets out there and there are some very very high end Cro-mo racing framesets using the best of easton and columbus tubing, these tubes are not only tapered wall thickness and shape (dont asked me how they build them) they have the Meat only where you need it, im talking cro-mo so thin that you can apply pressure with your thumb and cause the reflextion of the light on the show room floor to distort on the painted frame surface, They dont go through these kind of efforts and then just throw in the towel when it comes time to peicing them together,
And no disrespect to the aviation industry but in many cases these are just over 2 pound items selling for over 3 grand, there is allot of focus, just about everything has been tried, that is why I have to add that if Gas welding was indeed superior I would have seen it bust out big time in the high end cro-mo bike frames, I havent --- Not a one, Not to say they dont exist, its just that the majority are either lugged and brazed with gas or direct tigged, but iv yet to see direct gas connections... or if their doing it their certainly not bragging about it, believe me --- if it was all that and a bag of chips there would be tons of top end companies with pictures of thier machines and in big bold advertizing letters they would be touting "GAS WELDED CRO-MO" Again, not a one...

Aviation only gets it so far with me --- I think it scares allot of people into thinking "well yeah --- its gotta be good cuz its your ass on the line"
Try "flying" down a Mt. pass at 70 mph+ on 3/4" wide tires and a bike frame that weighs just over a couple pounds --- believe me -- your ass is on the line also...
Next time you go and pick up a quart of oil think about something that weighs aprox. the same supporting all your weight for thousands of miles "at speed" and over all types of brutal terrain, hell --- iv pee'd bigger weight than some bike frames, In many ways production Aviation can only dream...:cool:

08-23-2007, 11:55 AM
You won't find gas welding simply because there aren't enough good oxy/fuel welders around. It's out of fashion these days and for good reason. TIG is nearly as good and a lot easier to learn.

BTW, the institutionalized paranoia that goes along with aircraft safety isn't so much because the pilots ass is on the line, it's the passengers and/or the people on the ground that are the concern. This isn't usually a concern with bicycles. If your downtube snaps off it isn't going to wipe out a school full of children.

A.K. Boomer
08-23-2007, 05:08 PM
If your downtube snaps off it isn't going to wipe out a school full of children.

Oh you' be surprised!!! (smaller bus and special kids) :p

Honestly, I cannot believe how well they hold up, Iv seen very few real structual failures and tons and tons of repetitive abuse, and they are extremely lightweight... but point taken, but along with it Id add that if there is just a few good oxy/fuel welders and it was the ticket they would imediatly have a well paid job because there is almost no limit to what the performance cycling industry will support in the means of a better end product, the word "production" does not even enter into the equation.

08-23-2007, 06:22 PM
not tryin to divert this thread but the thing that really amazes me about a bicycle rolling down a hill at 70mph is the brakes on these things, "what brakes?", what is state of the art in bicycle brakes?

08-23-2007, 07:30 PM
not tryin to divert this thread but the thing that really amazes me about a bicycle rolling down a hill at 70mph is the brakes on these things, "what brakes?", what is state of the art in bicycle brakes?

The nice ones have disk brakes.

08-23-2007, 08:30 PM
Isn't the Bicycle Wheel/Rim a Disc Brake itself? As in the Calipers with Rubber Pads, grab the Rim/Disc.


Michael Moore
08-23-2007, 08:33 PM
TIG is faster and often "prettier" than oxy/fuel fusion welding. You also have a cleaner bead and area around it after the weld as the shield gas keeps more of the O2 away.

TIG is basically the same manual dexterity process as gas welding - heat source in one hand, feed the filler with the other. A person who is good with one technique is likely to be able to pick up the other without much difficulty.

If you need to add metal via welding it would make more sense to just add that metal into the tube at the start and increase the diameter. You'd probably find the second moment of area increase from going up to the next size tube is a much more productive use of the metal than trying to add "web" reinforcements of weld bead.

1018 is just fine if you will design the frame so it lets the triangulation in the structure give the stiffness instead of hoping some tube isn't going to be bending. 4130 is something I'd rarely think of using on a motorcycle unless it was going on a dirt bike that could use the higher yield point of 4130 to help avoid picking up dents after you drop it in the rocks.


08-23-2007, 09:25 PM
I've built about 25 bicycle frames over the years, all out of various steel alloys offered by tubing suppliers like Reynolds and True Temper. If you're looking to build a nice light stiff frame I'd suggest you look at the various grades of tubes these companies offer. The tubes are butted internally so the ends are thicker and stronger so the HAZ won't be as much of an issue. There is no need to add gussets unless you deviate far from standard construction or want to build a tank of a bike.

I've built a 3.0lb 58cm road frame that is very stiff out of True Temper S3 air hardening alloy. Check out their website...


Also, Henry James will sell small volumes of True Temper tubing as well as other fittings for bicycle frames.


Do you have a jig or a plan for holding all the tubes in place for tacking? How do you plan of cutting the tubing for each joint? I'd suggest a LOT of TIG welding practice joining thin tubes to thicker tubes before you start welding the real thing.

Nice tight tube joints is going to make your like a lot easier too...


08-23-2007, 09:40 PM
Glenj, how are you cutting those saddles?

08-23-2007, 10:11 PM
I used to use bi-metal hole saws but found the course teeth would catch on the hardened thin wall tubing. I made a mill spindle mounted belt sander instead. I have a selection of drive spindle diameters to give me whatever size joint cut I need. The only pain using it is draping the mill in plastic before I use it to keep the grit from damaging the machine. I now have an old small horizontal mill I'm going to dedicate to a tube cutting sander.


Michael Moore
08-23-2007, 10:35 PM
Glen, a friend made a similar "different ODs of roller" stand-alone belt sander for making motorcycle frames.

If it is a 90* or other easy angle I'll use an appropriate EM in the mill (this presumes a standard 3/4, 7/8, 1" tube butting on another standard tube, not a small tube going into a 2.5" OD headstock). I made some rectangular blocks to hold the tube in the vise so it doesn't crush it but does hold it securely. That's just a simple bore to size and slot on one side. Put the slot "up" and the vise will pinch it shut nicely. With a good fit in the block there is no problem taking it out of the vise and swapping it end for end as there is plenty of friction to hold the block in place. I suppose you could drill and tap for a pinch bolt but it has never seemed needed.

You do need to watch that the EM doesn't grab the side of the tube at the very end and fold it over. What I found helped avoid that is to only feed the EM in to the point where it is just cleaning out the ID of the tube at the pointy-ends of the fishmouth and then stop. If you feed a 1" EM in .500" you are going to have to trim off those "tapering down to nothing" bits on the tube anyway. So just stop in time so the EM can't grab the tube and fold it over.

The "commercial" tube profilers I see are usually pictured with a roughing EM in them. I've only used regular 4FL EMs so I don't know if the roughing EM is because they are using thick-wall tubing or if it is less prone to grab. If nothing else using a roughing EM would reduce the number of steel needles around the work that are waiting to imbed themselves into your flesh.

I haven't yet tried using a small OD EM and letting the mill interpolate the circle to see if that makes it less prone to grab and fold.

With some practice snips and a 1/4 or 1/2 round bastard file will get you plenty good enough. If the tube is too thick to file/snip, it is generally too thick for my frames. :)


08-23-2007, 10:56 PM
The tubing I've been using recently is only 0.020" thick at the ends where the welds are and 0.015" thick in the center. It's also 195,000 psi ultimate tensile strength. Endmills and hole saws just love to catch and mangle this stuff. The advantage to sanding the joints is you don't need to hold the tubing as rigidly as you do for cutting. The forces on the tube are quite low. Also, some of the tubing is ovalized or tear drop shaped so making fully surrounding blocks like you suggested to hold it is much more difficult.

A roughing endmill I have not tried yet and might work but I can get 3-4 frames worth of cuts out of one $8 belt. On thicker round tubing, un-heat treated 4130 etc you have a lot more choices available.


A.K. Boomer
08-24-2007, 10:18 AM
Glen, to build a bike frame on your own and come up with 3 Lbs is amazing, my hat is off to ya,,, nice looking joints, is there any concern at all about using sanding belts and contamination of the joint?

Very cool, iv got a bunch of true temper cro-mo frames that iv gotten from bike shops and will be cutting them up for practice this winter, I know it sounds crude but i will be building my frame and mapping all the angles out on a sheet of plywood, a typical frame jig does not have the needed travel to acomodate what im going to be trying out anyways, thanks for the post...

A.K. Boomer
08-24-2007, 10:38 AM
Isn't the Bicycle Wheel/Rim a Disc Brake itself? As in the Calipers with Rubber Pads, grab the Rim/Disc.


Tattomike mentioned that "nice ones have disc brakes" and you made the above statement,

Im in agreement with you -------- when you stop and think about it the typical V braking system IS a Disc/caliper system, and in my books its superior to an inboard disc, for one you can get ceramic coated rims now and run very hard pads so the worry about to much elasticity in the system is eliminated, two --- you have a "rotor" with aprox an 11 to 12" radius, Thats far bigger than any race car I know of and far larger than the internal 2 or 3" radius disc's for bikes, This large radius not only gives you unbelievable stopping power, it equates to massive amounts of control, some of your best trials Mt. bikes still run the V brake for this reason... Last but not least, the inboard disc superloads bicycle spokes, It torsionally twists the hub from the rim, thats a fuqe --- so bad that the early ones were snapping and disintegrating the entire wheel upon heavy braking until the engineer's finally figured out they better increase thier hub diameters (DUH +=more weight) I dont need any more stress on my wheels and spokes, last but not least the inboard disc sytems are extremely heavy, im already carrying my rotor,why not put it to use? and as far as the V brake component its still way lighter than the inboard caliper,

The advantage to the inboard --- they work better in the rain, I could care, I live in colorado:D plus they make "wiper pads" that clear water and mud away, if i get caught in the rain it does effect my stopping power --- the solution is I just clamp down a little harder on my levers....

One last note, i stop my bike with how a wheel is designed to work, its basically the same type of tension that a wheel see's while rolling, inboard discs utilize half of the spokes in the wheel (the other half go limp) to not only create more elasticity in the system but also increase the internal loading of the rim and aid it in collapsing --- the result is you will see far more "tacoe'd" front wheels if someone hits a massive bump under heavy braking loads, Inboard discs are junk on a bike --- but thats just my humble opinion...

Forrest Addy
08-24-2007, 02:53 PM
I'm a little baffled about the extremes of frame construction. It makes sense to reduce weight for any racing apparatus be it bicycles, rowing shells, or jockeys but isn't there some point of diminishing returns?

There are many variables affecting the outcome of any race. In bicycle racing there are rider variables like physical conditioning, state of health at the moment, rider response to weather, course, competition, psychological factors (placebo effect over a new frame is but one) etc. Then there are bicyle variables like tuning for the course, tires, weight, ergonomics, etc. Also there are bike rider interactions, strategy, teamwork, execution, ect. All this makes a long list of variables that have to be considered and provided for - many of which can trump the effect of a gram more or less in the weight of the bike frame.

Seems to me chasing individual grams at such trouble and expense passes the point of diminishing returns. It's not the lighest bike that wins races consistantly, it's the most effective bike/rider combination; one that's well nourished, well tuned, well trained, well prepared; who is guided by the most effective strategy and is quickest to exploit opportunities that wins.

Has anyone studied this aspect of the equation? Are the bulk of bicycle ethusiasts focusing on ever lighter stronger frames to the neglect of other variables that each or severally might have a greater (but less quantifiable) influence on race outcome?

I recall a local fellow who had me build him some fittings for his bike rack. While we was waiting he spoke of his favirite topic bicycles. In the meantime he swilled about a gallon of coffee from a thermos he fetched and glanced feverishly at his watch until the time finally came when he could have a smoke. I said nothing but the image lingered. Here was a guy driven by the need to excell by racing bicycles yet he was hag ridden by caffine and nicotine addictions both known to reduce physical performance.

A reduction of bicycle frame weight is readily objectified and quantified. The assessment and quanfification of the many other variables are not. Is it possible that pursuit of frame weight reduction has been substituted for a far more productive but exruciating task of coping with ever-shifting variables?

08-24-2007, 03:49 PM

I suspect you're completely right, but what we're seeing is some of the interesting human dymamics that keep life from ever being boring or predictable.

One factor, the guys on the bikes in the race aren't typically the bicycle builders. If I'm interested in bike racing, but really don't have the physique or whatever to race myself, the next best thing might be to build bicycles for the ones who do. And since fitness, aerobic training, (drugs) etc, aren't relevant to my particular discipline, I turn to what I can have control of - obsession about the physical machine.

The next factor is the racers or team managers themselves. Since there are so many things that go into winning, including just luck, good or bad, they might as well try to cover as many bases as possible to reduce the number or things they can't control. Which in this case gets to be like snapping your fingers to keep the elephants away. You mean there aren't any elephants in 300 miles? Must be working pretty well. So the combination of obsessions and superstition translates into $1000 for those next few grams.

In other words, if you just came in second in the race, and all the other factors seemed to balance, more or less, but you were a cheapskate and spent the $1000 in the team budget on say a trailer instead of the more expensive but only marginally lighter bike, wouldn't everybody just kick you? Kind of like the aphorism in the IT departments that no one ever got fired for buying IBM. So, they just spend the money if they can because no one can ever prove that it doesn't help.

08-24-2007, 05:32 PM
In other words, if you just came in second in the race, and all the other factors seemed to balance, more or less, but you were a cheapskate and spent the $1000 in the team budget on say a trailer instead of the more expensive but only marginally lighter bike, wouldn't everybody just kick you? Kind of like the aphorism in the IT departments that no one ever got fired for buying IBM. So, they just spend the money if they can because no one can ever prove that it doesn't help.

Let's examine that last line... Let's say you are in a 100mi MTB race, loop race so elevation loss=elevation gain... say you average 10% grade on the loop you do 5mi of climbing or (5280*5)=26400ft. Let's say you carry an extra 1lb of non-rotating weight... you have expended an extra 26400 ft-lb of energy, just looking at the change of potential energy without taking any recovery on downhills. Converting to nutritional calories you burned an extra 8.55 calories to lug the weight up the hill. Let's say rolling resistance, and hammering out of the saddle with the weight shifting around doubles the figure, I have no idea if this is close. We are at around 17 nutritional calories.
Suppose the race was 6 hours long.. 52800 ft-lb=9.94 watt-hr, so your rate would be about 19.9/6=3.32 watt. I don't know a lot about putting this in perspective, maybe someone here would? Is this significant? Am I way off?

Oh, and on topic, I know reynolds has some really good information on their website for various tubesets and recommended welding procedures.

A.K. Boomer
08-24-2007, 08:24 PM
Weight is a "perspective" thing, their are many many variables, Iv seen many many "racers" that were counting the grams on their bikes when they should have been counting the pounds on their bodies, We call those guys Techno weenies, they either have to much dollars and not enough sense or just plain dont get it, The best one liner that shuts them up is "you still gotta peddel em" Iv also seen kids with the heart of a lion on bikes as heavy as a huffy win novice races (not a small feat) Yet Bike weight can be extremely important or in some races not even relevent, Rdesign just pointed out some interesting specs, and it is with the altitude gain that its the most critical, riding on the flats at a constant speed with the best tires and ceramic bearings a few extra pounds is tough to calculate and pin down, Mt bike circuit races that start from a set place climb and then descent and repeat over and over do not always give back the energy return on the downhill from the extra weight because on many of the tight courses your maxed out on speed anyways and the extra energy just goes into the binders, then theres the Table reverse from road to MT. In hardcore Mt biking its the weight that is enemy #1, in hardcore road its the air, there are so many tricks of the trade and strategy in road riding and how to use up your opponent ------ it gets into psychology with major head games ------- if its road climbing enter in both factors to the extreme, same with Mt. bike races that would allow vast sections for stretching out your legs, then theres the difference between wheel weight and frame weight --- wheel weight is twice as difficult to get moving -- and twice as hard to stop -- so when Mt. bikes hit the circuit everyone thought it was like the Mt. road riding and the lighter the better for responce, yet now its found that their is a limit to lightness, After all --- this is also your gyro effect, extremly light stuff can not only disintigrate from underneath you, it can also make your bike to tweeky so you have a DNF because you never crossed the finish line either because your bike broke or you crashed... One thing about running over heavy boulders at great speed is that if your bikes wheels have some beef to them they will not only take the shot ------ they will keep you upright after hitting it --------- cycling is a juggling act, and there are many factors involved, its why I used to show up at a course a day or two ahead of time and ride it, ----------------------- its also why i used to bring about three different sets (style's) of tires to run, depending on the course it was always about how efficient I could go with still being able to keep good purchase on the terrain...

As far as what Forest mentioned and frames having to stick to certain guidlines I basically agree with him -- till you re-design the wheel, My bike cranks operate totally different from any other on the planet, so much so that it will allow me to take advantage of some very radical cycling positions, the next couple three years will be interesting to say the least ---- I dont work on them in the summer but make some strides in the basement in the winter, I wonder how many others here have trouble being in their basement when its nice out, Im glad its not my living or i think id starve to death.

08-25-2007, 12:26 AM
The main reason so many people seek the lightest possible bicycle is because it's the one part of the performance equation that can be purchased. You can't buy better fitness or pay someone to train for you. It's hard work trying to generate a few hundred watts of power and takes a long long time in order to be able to do so consistently over hours.

As others have said, it's not the best bike that wins the race. It's also not always the strongest rider either. Most of the time it's the person who used what little energy there is available in the most efficient manner, when it was required while using equipment that did not put them at a great disadvantage.

Fitness, brains, experience and equipment...that's what it takes to win a race. Oh, and luck, a lot of luck.

08-25-2007, 12:33 AM
A.K. Boomer...

I clean the tubes quite well after sanding to avoid any weld contamination etc. The 3.0lb frame is made from True Temper S3 tubing...no real magic involved other than trying to weld it together.

I made my own frame jig since the available ones are so expensive. If you have a radical frame design I'm sure you could build your own jig to accommodate it. Look at what's available and start your own...I find it's actually more fun figuring out and building the jigs and fixtures than actually building the frames.

A.K. Boomer
08-25-2007, 01:45 AM
Most of the time it's the person who used what little energy there is available in the most efficient manner,.

In Mt. bike talk back in the day (and actually quite recently) that person would be Ned Overend, in my books the king of efficiency, Ned was a saab mechanic and got a late start but the late start did not matter as he kicked ass pushing into his fifties, imagine being some new 20 something pro thinking your hot stuff and getting totally "wheeled" by a fifty year old, I remember talking with him at an annual race in durango at a few different occations, he was specialized best PR man as he was very technical and made time to talk... nicknamed "deadly Nedly" and "the Lung" --------- He will always be one of the best minds in Mt. bike racing.