MFT welds failing

[cfullen]

I am sure this is caused by prolonged stress folding table, and transporting table.  But I really don't use this thing a whole hell of a lot.  It lives folded up 65% of the time in my shop.

And no, my shop was not underwater.  I still have the original top on this thing.  I thought for sure I would have been replacing the top before the legs.  Changing the legs out was never in my mind. 

[attachimg=1]

 

[Peter_C]

Those are NOT weld failures. It is metal fatigue. Your first photo shows the weld still intact with the metal of the leg ripped out. The photos just above show the weld intact, and the metal around them failing. Think beer can effect. We can not say how you used your MFT, but chances are there was a lot of motion involved. I do not personally see it as anything more than heavy use. Uneven terrain may have helped it along too.

No big deal, just clean off the paint and reweld all four legs, then spray something on them to keep them from rusting. A corner brace welded onto each leg would stop it from ever happening again. Also make sure you are tightening the leg bolts enough.

 

[Rip Van Winkle]

Those are NOT weld failures. It is metal fatigue. Your first photo shows the weld still intact with the metal of the leg ripped out. The photos just above show the weld intact, and the metal around them failing. Think beer can effect. We can not say how you used your MFT, but chances are there was a lot of motion involved. I do not personally see it as anything more than heavy use. Uneven terrain may have helped it along too.

No big deal, just clean off the paint and reweld all four legs, then spray something on them to keep them from rusting. A corner brace welded onto each leg would stop it from ever happening again. Also make sure you are tightening the leg bolts enough.

The cracks are right around the weld bead. The weld bead even appears to be slightly uneven, and the cracks follow that unevenness.

That’s a weld failure. If it isn’t a weld failure, than it’s a production, engineering or design failure.

The only way that wouldn’t be considered a weld failure is if the leg was heavily flexed when it wasn’t attached to the MFT, and if that case there would be more distortion of the metal around the weld joint.

Welds are supposed to be as strong or stronger than the material being welded.

The joint fractured right were the welds are. That means the material next to the weld was compromised somehow, such as improper shielding of the weld area by welding gas, or improper temperature of the parent material when the weld was done, or corrosion to the weld joint before the gray “Powder Coat”? finish was applied. Maybe the wrong welding wire/stick type was used.

I’ve seen brazed and soldiered joints that have lasted better than that.

 

[Peter_C]

The only way that wouldn’t be considered a weld failure is if the leg was heavily flexed when it wasn’t attached to the MFT, and if that case there would be more distortion of the metal around the weld joint.

Look again at the photos and look how banged up the legs are. My "guess" is the MFT was used and produced a lot of good work at it's own expense. The MFT is made to be reasonably light weight, therefore the materials are not 1/4" and more prone to tearing. Working on an uneven surface will put a lot of twist into the legs. Put 400lbs of sheet goods on top for cutting, and racking is going to happen. We don't know how this MFT was truly used. I know I use my tools very hard, even if it means sacrificing them to get the job done and get paid! *shrugs*

Welds are supposed to be as strong or stronger than the material being welded.

We agree on that! As shown the welds held and the metal broke out around them on every joint.

The welds are ugly and might have been run hot, but it is the thin material that failed. Engineering issue...sure as it is made to be light weight. How many others are having the same issue with all 4 leg joints failing? Some cracking is okay from a production stand point, as weight vs longevity is a trade off. This is the first report I have ever seen of this issue.

None of it really matters as it is NOT a warranty issue, since it is out of warranty, and the owner of the MFT just needs to have his legs welded and move on. Want to make it stronger; triangulate it with a piece of metal welded at an angle onto the bottom or side of the cross bar to the leg, so a shelf can still sit on top if desired. Maybe he can find someone on here local to help him out. It should take about 20 minutes to fix.

 

[Corwin]

...
The joint fractured right were the welds are. That means the material next to the weld was compromised somehow, such as improper shielding of the weld area by welding gas, or improper temperature of the parent material when the weld was done, or corrosion to the weld joint before the gray “Powder Coat”? finish was applied. Maybe the wrong welding wire/stick type was used.
...

A failure directly around the weld is just what I would expect in a welding related failure. My guess is that with these failures the metal immediately adjacent to the weld is adversely affected from the sudden heating and cooling cycles from the welding process. A simple google search of images of weld failure will demonstrate what I'm mean.

 

[Peter_C]

^Thanks per your link I learned the proper term. "Base Metal Failure".

The capacity of a welded connection is limited by the lesser of the strength of the weld or the strength of the material that the weld is attached to (i.e. the base metal).  The strength of the base metal is the force necessary to cause shear rupture or tensile yielding of the base metal where the weld is attached

http://www.bgstructuralengineering.com/BGSCM13/BGSCM005/BGSCM00504.htm

 

[cfullen]

I should have noted this before to stop all the bickering.

I have 2 MFT's , both are used equally.  Only one is showing weld failures.

 

[WorkingDesign]

Just noticed today the same exact failure on my MFT. MFT is 5 years old. Never leaves my shop and is never subjected to moisture. Same exact break conforming to the shape of the weld bead.  [attachimg=1]

 

[sancho57]

looks like lack of penetration. which is a weld defect. prolly happened when they reprogramed the NC welder at the factory. I havent had a problem with mines. So it was more that likely in a short run of MFTs.

Did the op get a hold of the factory rep have him take a look at it. Festool prolly would have worked with him to correct the issue.