Frame cracks on Hustler 20/52 Fastrak

bertsmobile1 said:

part was cut out of the sheet in the wrong orientation to the grain direction.

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So you are saying the metal has a grain direction? They are working with steel not wood.

reynoldston said:

So you are saying the metal has a grain direction? They are working with steel not wood.

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Yes all metal are crystaline and have grain structures and getting the grain to go the way you want it to to maximise the strangth so you can reduce section thickness is part of the art & science of good engineering design.

The sheet that part was cut out of was rolled across the photo so it has long grains across the screen.
The frame has weight pulling strait down so it is stressed in the up down direction.
During use the frame gets vibrated in and out, left & right, both at right angles to the grain and the triaxial stresses cause the cracking.
If it was cut with the grains going top to bottom it would not have cracked as readily and required a nothing more than some small flanges to guard against the left right stresses.

This is with respect to the photo

And yes steel grain work similar to wood grain, which is why metallurgists used the term grain in the first place as we had been working with wood for centuries so understood wood grain.
Thus when we saw similaraties in the behavious of metals we grabbed a term that we were all familiar with to descride it.

Yes wood has a grain because a tree grow up and in nature the tree can stand up to the wind. When they pour steel its in a liquid form. Didn't know that a liquid had a grain like wood? So you are saying when they roll out the steel it gets a grain in it? I guess its something I never heard of and you looking at the picture can see this? Is there anybody else out there that can see the grain in the steel because I sure can't. So you are also saying Hustler's engineers don't know what they are doing so the whole machine is made like this? Sorry I just don't buy into it.

Yes all metal are crystaline and have grain structures and getting the grain to go the way you want it to to maximise the strangth so you can reduce section thickness is part of the art & science of good engineering design. ( you are very good with words)

reynoldston said:

Yes wood has a grain because a tree grow up and in nature the tree can stand up to the wind. When they pour steel its in a liquid form. Didn't know that a liquid had a grain like wood? So you are saying when they roll out the steel it gets a grain in it? I guess its something I never heard of and you looking at the picture can see this? Is there anybody else out there that can see the grain in the steel because I sure can't. So you are also saying Hustler's engineers don't know what they are doing so the whole machine is made like this? Sorry I just don't buy into it.

Yes all metal are crystaline and have grain structures and getting the grain to go the way you want it to to maximise the strangth so you can reduce section thickness is part of the art & science of good engineering design. ( you are very good with words)

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And very correct. I watched a "How its Made" or show like it once and learned why they role some metals and cast others. It was very releveling.

In most cases you can not see the grains with the naked eye they are way too fine.
What you can see is the direction of travel and the shape of the crack.
Knowing how steel cracks allows you to make deductions from the appearence onf the crack which will flow along between the grains.
The shape also tells me it was a ductile fracture due to vibrations.
The shape of the frame it self and the position of the engine & mounting bolts + a little knoweledge gaind since taking over the repair run fills in the rest of the story.
There is also a better than average chance that is was made using cheap imported steel with too many impurities laying between the grains which form facture paths.

In a different life as a brand new freshly minted metallurgist I spent nearly a full year cutting lumps of ingots mounting them in Lucite, polishing them till they were brighter than mirror finish, etching them so as to reveral the grains structure then counting the size & number of grains on all 3 axies. Then I graduated to extrusion billets . The the company bought a machine that would do about 50% of the process and 40 technicians ( including me ) got the shove .
With plain black bar rod & plate which is most of what is used there is a specified grain size range and it is pretty broad.
Cold rolling is very expensive but hot rolling is relatively cheap so a lot of imported steel has not benn cold rolled sufficiiantly enough to give it the required strength.
You will notice that come times a lump of plain steel will seem really soft and that is because it has a coarse grain size ( amongst other things )
As you get into engineering grade metals the grain size becomes really important and will usuallay be specified by the customer.

I don't think they cut it wrong as both sides are symmetrically cut. IMHO they removed too much material to make assembly easy and of course to fit the Hydro Motor design. The rest of the machine is built like a tank-it just seems to be this one area is weak. When I get the repair gussets from Excel/Hustler I will take a pix of them for comments. I'm hopeful the gussets will reinforce the area sufficient to eliminate this ever happening again. My plan is to remove both fuel tanks, the engine, the drive motors and the mower deck so the frame can be tilted up on its side. Nearly all welders, certified or not, do a heck of a lot better job welding flat areas versus vertical areas.

If they removed too much metal then there would be necking at the fracture face where the crosssections area was insufficant to carry the load which there is not.
If the corners were cut square then you would have stress raisers but they have been cut nice & round.
It is fairly heavy plate so it can take a bit of a load.
And just because one was cut wrong does not mean all of them were cut wrong.
Come cheaper nesting programmes will happily orient parts the wrong way in order to cut the greatest amount of product from each sheet.
Scrap = lost profits.