Author Topic: MFT welds failing  (Read 6212 times)

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Offline cfullen

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MFT welds failing
« on: March 10, 2018, 04:15 PM »
Has anyone had these welds just break?  I seem to have noticed it just a week ago or so and then yesterday the first weld just came apart.

To be clear, I’m referring to the cross member that connects each set of legs. 

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Offline ear3

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Re: MFT welds failing
« Reply #1 on: March 10, 2018, 04:17 PM »
That's not good.  I've never seen a complaint about this since my time on the FOG.

How long have you had your MFT, and what's your usage like (lots of setting up/striking/moving, or do you tend to keep it set up for long durations)?
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Offline cfullen

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Re: MFT welds failing
« Reply #2 on: March 10, 2018, 04:21 PM »
I have it in my shop most of the time.  Either set up, or put away in a corner.  20% of the time it comes with me to the job site. 

I’ve had it for about 3 years now.

Offline Peter_C

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Re: MFT welds failing
« Reply #3 on: March 10, 2018, 04:26 PM »
Good excuse to buy a welder? :)

Offline McNally Family

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Re: MFT welds failing
« Reply #4 on: March 10, 2018, 05:49 PM »
Is that steel or aluminum?
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Offline tjbnwi

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Re: MFT welds failing
« Reply #5 on: March 10, 2018, 06:14 PM »
Looks like the metal failed not the weld. Rust issue?

Tom

Offline grobkuschelig

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Re: MFT welds failing
« Reply #6 on: March 10, 2018, 06:22 PM »
That should be steel, I think.

Offline Peter Halle

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Re: MFT welds failing
« Reply #7 on: March 10, 2018, 06:44 PM »
I agree with Tom that it does not appear to be a weld issue.  If you look at the the outside of rim of the break there are rust stains.

That being said I have one of the ugliesr MFT's out there.  Mine has sat in the driveway with the top covered by rubber roofing membrane and the legs have been used as fire hydrant substitutes by the neighborhood dogs.  But my joints haven't failed.

Your local situation and weather are different than mine.  As a moderator I can get a general idea of where you live.  Was your shop flooded?  Any other environmental issues that you might think be part of the problem?

Peter

Offline Retired Chippy

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Re: MFT welds failing
« Reply #8 on: March 10, 2018, 06:48 PM »
That little bit of rust showing in the picture doesn't look like it had anything to do with the failure and probably happened as the weld was breaking.  It looks like it was improperly welded and almost blew through the thin metal leg during the process, but was hidden until stress took it's toll.  I'd push them to send you a new leg or legs no matter what the warranty state is.  If you were rough on that, the weld should have been strong enough that the tubing would have bent first as an indicator.  Just my 5 cents worth.

Offline Bohdan

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Re: MFT welds failing
« Reply #9 on: March 10, 2018, 06:54 PM »
Looks like a fatigue failure possibly caused by flexing the joint each time that you folded up the MFT legs.

Still shouldn't have happened as the legs are designed to be folded up.

Offline TinyShop

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Re: MFT welds failing
« Reply #10 on: March 10, 2018, 07:28 PM »
@cfullen - not sure if you know., but if you're in the U.S. or Canada the MFT/3 is covered by the standard 3-year warranty (it's an exception to the "must have a cord" requirement).

Offline Peter Halle

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Re: MFT welds failing
« Reply #11 on: March 10, 2018, 07:32 PM »
@TinyShop beat me to a follow up post.  I would contact Festool on Monday and take to them.  That is an issue that I don't remember being mentioned here (if might have been and I am not perfect obviously).  Whether or not it would be under warranty they might be interested to get your legs back for examination.  More MFT's are sold here than in any other country.

Peter

Offline cfullen

  • Posts: 58
Re: MFT welds failing
« Reply #12 on: March 10, 2018, 10:47 PM »
I do live in the gulf south region. But no, my shop has never flooded.  I don’t think this is a rust issue.  Guess I could be wrong.  The other welds are showing the same signs of failure.  I will take some pics of them tomorrow.

I’m going to try to contact festool and see what they have to say. 

Offline kcufstoidi

  • Posts: 768
Re: MFT welds failing
« Reply #13 on: March 11, 2018, 07:10 AM »
Could be just the lighting but looks like it had a pretty good impact just above the weld. If the tube is deformed at all, that's your answer. The weld didn't fail the 2 were ripped apart.

Offline Rip Van Winkle

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Re: MFT welds failing
« Reply #14 on: March 11, 2018, 12:31 PM »
Judging by the photo, I would say that is a weld issue. While weld metal is supposed to be as strong or stronger than the metal being welded, the heat of welding can effect the molecular structure of the material being welded, causing weak areas around the weld. There are ways to reduce this problem, but even carefull welds done under strict protocols can have issues, and I doubt Festool is ussing the same procedures as would be used on a commercial jet plane or nuclear facility. If you look at were the joint broke, it’s right by the welded material. Since it’s steel I presume any decent bike shop could weld it back, or possibly a garage, machine shop, school shop, etc. It might be cheaper just to buy a new leg though, if the part is no longer under warranty.

Offline Tom Gensmer

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Re: MFT welds failing
« Reply #15 on: March 11, 2018, 01:30 PM »
The welds failed on one of my MFT/3 tables, but only after many years of use outdoors in the snow and rain. There must have been some pin holes in the paint and the joint eventually rusted and failed when I removed the legs to permanently mount the table on a rolling cart.

In my mind, the legs are a consumable, something to be replaced after many years of service.
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Offline Gregor

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Re: MFT welds failing
« Reply #16 on: March 11, 2018, 05:08 PM »
I’ve had it for about 3 years now.
Call Service, describe problem and ask (if >3 years: nicely) for replacement.
This shouldn't happen that early in the life of an MFT/3.

Offline BJM9818

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Re: MFT welds failing
« Reply #17 on: March 12, 2018, 01:31 AM »
Could be just the lighting but looks like it had a pretty good impact just above the weld. If the tube is deformed at all, that's your answer. The weld didn't fail the 2 were ripped apart.

X2 unless it’s just the pic it looks like a decent Impact above the cross member probably followed by the object hitting the cross member.

Offline cfullen

  • Posts: 58
Re: MFT welds failing
« Reply #18 on: March 14, 2018, 07:55 AM »
Here are pictures of the other welds.

Offline cfullen

  • Posts: 58
Re: MFT welds failing
« Reply #19 on: March 14, 2018, 07:57 AM »
All 4 welds are showing some signs of failure.

Offline cfullen

  • Posts: 58
Re: MFT welds failing
« Reply #20 on: March 14, 2018, 08:02 AM »
I am sure this is caused by prolonged stress folding table, and transporting table.  But I really don't use this thing a whole heck 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. 


Offline Peter_C

  • Posts: 661
Re: MFT welds failing
« Reply #21 on: March 14, 2018, 12:55 PM »
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.

Offline Rip Van Winkle

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Re: MFT welds failing
« Reply #22 on: March 14, 2018, 03:53 PM »
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.

Offline Peter_C

  • Posts: 661
Re: MFT welds failing
« Reply #23 on: March 14, 2018, 05:15 PM »
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.

Offline Corwin

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Re: MFT welds failing
« Reply #24 on: March 14, 2018, 06:28 PM »
...
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.
Looks like your rabbit joint is a hare off! ;)

Offline Peter_C

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Re: MFT welds failing
« Reply #25 on: March 14, 2018, 08:51 PM »
^Thanks per your link I learned the proper term. "Base Metal Failure".
Quote
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

Offline cfullen

  • Posts: 58
Re: MFT welds failing
« Reply #26 on: March 21, 2018, 02:59 PM »
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.

Offline WorkingDesign

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Re: MFT welds failing
« Reply #27 on: July 18, 2018, 10:15 PM »
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. 

Offline DeformedTree

  • Posts: 151
Re: MFT welds failing
« Reply #28 on: July 19, 2018, 12:19 AM »
To be clear these are weld failures, a weld failure doesn't mean the weld itself snaps/breaks/etc, it also involves the metal around it which was compromised by the welding process. Failure of the weld itself isn't a very common failure (you know you made a bad/ugly weld that will fail soon as you make it), it's the material around the weld that fails due to the process of welding. General too much heat, it made the metal in the HAZ brittle, so it now snaps around it.  A proper designed weld/weld process is set up to ensure this does not happen.

I would tend to think these legs might go thru some form of post weld heat treat process, but that's not something to always expect. 

I would ask to those who have failures, what tools do you use with these tables. Do you use things like the orbital sanders or any other tools with lots of vibration and general a lot of back and for motions.  Failures like this tend to be vibration induced.   The constant flexing from the vibration in combination with possibly brittle metal from too hot of a weld could be at issue here. Or the weld was set up proper but the material batch was not to spec so the weld didn't work as engineered.  I would assume festool has a robotic weld station doing these, so the setting should stay consistent, but if someone got the wrong grade of steel, or mislabeled or something went wrong, that could have messed up the process, or if the filler rod was wrong (loaded wrong spool in the MIG).

Also if you say hand sand or doing something putting a lot of body weight back and forth on the table, that might do it, high amplitude but low cycle.

In the end, this looks like a bad batch may have happened somehow.  If Festool got a few of these legs back they could send them to materials/metrology and get them sectioned and be able to see if a) metal was wrong spec,  b) metal was over heated, c) fatigue failure d) environmental caused failure.


Offline jobsworth

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Re: MFT welds failing
« Reply #29 on: July 19, 2018, 12:08 PM »
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.