Felt welds

<–Tribriguy didn’t write this. I’m wondering who did, and also how it got credited to me.

While on the “throne” this morning I was thumbing through some recent tri mags when something caught my eye. Does anyone know why Felt still uses “unfinished” welds when most of his(their) competitors have gone to some form of “finished” weld? I remember reading that “unfinished” welds leave stress lines for cracks to develop, meaning to me that the writer was suggesting that they were inferior to “finished” welds in terms of resistance to that type of fatigue. Are there other reasons for staying with this type of weld? It would certainly be cheaper since it removes a step in frame finishing but somehow I don’t think that would be a motivating factor for Jim to make his bikes that way. There are too many other areas where he goes above and beyond with his work.

When a weld is filed or smoothed, unless body filler is used, a small amount of the parent material is removed right next to the weld.

Felt prefers a single pass, unfinished weld because it has been their experience that is is the best way to ensure consistent strong joint connection.

If you look at Klein and some others, the welds now are not completely smoothed, they are cometically filed down, but not a true “fillet joint”

No industry uses filed welds in their fabrication other than for cosmetic purposes.

-SD

Superdave is right. An unfinished weld leaves more material at the weld joint for a theoretically stronger weld. Finished welds are also a god way to hide an ugly weld.

Personally, I prefer unfinished.

“Superdave is right. An unfinished weld leaves more material at the weld joint for a theoretically stronger weld. Finished welds are also a good way to hide an ugly weld.”

when i was building bikes we didn’t fatigue test this, but one of our contract builders, kinesis, did. they said their smooth welded bikes lasted twice as many cycles as did their beaded welds, which backed up the conventional thinking.

mind you, this was kinesys USA, the portland factory. it did this study because marcus storck’s bikes were smooth welded, and marcus wanted to know.

but there’s a flip side, as you point out. it depends on how thick the wall is, and who’s doing the grinding. i’m riding scandium bikes right now, and i’d never grind a scandium weld, because the wall’s so thin. with steel it was different, you could lay down a fillet braze and you’d hardly need to grind anything, plus it was easy to see what was fillet material (gold color) versus the silver color of the tube. nowadays, grinding thinwall aluminum to get a smooth weld, it’s hard to tell how much tube you’re hogging out, esp if you’re on an asian assembly line.

so i don’t think you can make a blanket statement about smooth v beaded. depends on the builder, the material, the wall thickness, and of course the price. smooth joints cost money. if it’s a cheap smooth weld, it’s possibly also a shoddy smooth weld. it also depends on what joint you’re talking about. for example, grinding around seatstay-to-seattube joint is really, really hard. likewise dropouts, really anything in the rear triangle.

all things equal, i would guess it’s not to felt’s interest to grind the welds, and if i was them i certainly wouldn’t. but if i was cervelo, with the way its tubes are extruded, the ability to control wall thickness, and the higher price of bikes like the P2K and P3, you bet i’d grind those.

Well, THAT is REALLY wierd! I didn’t write the original post here. How in the world is it credited to me, including my signature? Maybe its just another strange anomaly in Dan’s server changeover.

If the tubing walls are thin enough, I would not do a “smooth” weld. I would definitely use a single-pass weld.

Mr. Felt definitely has good reasons why he does not spec a “smooth” weld, as his experience with the Easton tubing (as he helped engineer a bunch of it) has probably led him to the conclusion that they are, infact, no good for the application.

What way is superior? I would leave that to the particular builder.

When a weld is filed or smoothed, unless body filler is used, a small amount of the parent material is removed right next to the weld.

Felt prefers a single pass, unfinished weld because it has been their experience that is is the best way to ensure consistent strong joint connection.

If you look at Klein and some others, the welds now are not completely smoothed, they are cometically filed down, but not a true “fillet joint”

No industry uses filed welds in their fabrication other than for cosmetic purposes.

-SD

Unfortunately your answer is not completely correct. There are different kinds of finished welds, and not all are filed down. Although there are many variations, the three main styles of welds for bike frames are single pass, double pass and filed welds.

The single pass (usually a “stack of dimes” weld) is the most common weld, and the least expensive since it is the fastest. If the frame and welds are designed with this technique in mind, there needn’t be any issue with the longevity of the frame.

The filedweld actually starts out as a different weld than a single pass, as a different filler material is used to create the right “body” for the weld that can then be filed into the right shape. If done well this results in a stronger weld than the single pass weld, but if done poorly (for example if the filing is done too hastily or without proper care and nicks are created) it can actually shorten the life expectancy of the frame. It is more expensive than the single pass since there is more labor involved, the end result depends very strongly on the skills of the person doing the filing.

The double pass weld is also more expensive, as the initial weld bead is covered a second time, thereby remelting the weld and smoothening it out. This results in a smooth weld without the need for any filing. It is expensive, both because it requires twice the welding time and because it requires very skilled welders, but it is the only weld that allows you to get rid of the stress raisers that a stack of dimes weld inherently has, without the risk of creating stress raisers with incorrect filing. The weld is sometimes not quite as smooth as a filed weld, after all you are working with fluid metal, but it is the strongest without the risk of detrimental results.

My experience with all welds currently used throughout the idustry is that they are adequate. We almost never see failed welds form any brand.

Easton won’t offer a warranty on double pass welded Scandium or fillet finished.

Jim Felt’s experience with Easton (as an engineer) led to the decision.

I’d look to every other industry as well that uses welded construction.

No fillet welds on bridges, race car chassis, airplanes, etc.

Obviously the surface of a fillet joint has fewer stress risers than that of an unfinished joint. I’ve seen a couple hundred frame failures, these are typcially found right next to the weld, through the parent material, not the weld itself.

-SD

One problem with looking at other industries is that they don’t necessarily have the same requirements as a bike.

Their are two good reasons to use a finished weld.

A) Testing has proven that a finished weld is strongest - as long as its done properly.

B) It looks better (somewhat subjective).

For bikes versus most industries looks are important to a lot of customers. The flip side is that the industry as a whole uses somewhat amateur welders, designers and welding techniques. Very few welders are certified to the highest standards (yes , some are), very little true design is done (when compared to an aircraft or bridge) and welds on a bike are certainly not x rayed or microscopically examined.

Even though strong welds are important on a plane or bridge, both industries use the approach that an unfinished weld is easier, more consistant and can be QC checked. They strive for the most consistent weld that is strong enough for the application, not the strongest weld possible.

Back to bikes, virtually all bikes have strong enough welds. Its certainly not something I would pick a frame over.

“single pass … filed weld … double pass weld”

Your explanation is very thorough. Out of curiousity, which welds do your suppliers do on Cervelo’s P3 or P2K frames (what I ride). Thanks.

“single pass … filed weld … double pass weld”

Your explanation is very thorough. Out of curiousity, which welds do your suppliers do on Cervelo’s P3 or P2K frames (what I ride). Thanks.

We use double pass on everything except the ONE, which has double pass in the critical area (bb) and single pass elsewhere.