Grade 8 shear bolt confirmed!

[Junkman]

</font><font color="blue" class="small">( <font color="blue"> The grade is the number of hash marks + 2.

grade 2 = no hash marks.
grade 4 = two marks.
grade 5 = three marks.
grade 8 = five marks.
</font>

Junkman were you asking me personally or was this posters information correct? /forums/images/graemlins/grin.gif )</font>

No, but you did point out one fly in the ointment that I had originally missed ..... if the grade is the number of hash marks + 2 then a grade 8 having 5 hash marks + 2 would equal a "grade 7".... darn.... this new modern math is hard to understand... /forums/images/graemlins/blush.gif ......

 

[Villengineer]

DO NOT TRY THIS UNLESS YOU WANT TO FIND THE WEAKEST POINT THAT ISN'T THE SHEAR PIN. If you do not get the notch in the shear area of the mechanism you are still trying to shear the full diameter of the Gr8 bolt. If you want to use trial and error method then start with a Gr2 and if it fails under normal use then step up a grade, don't work the other way. Plus why spend more money initially on Gr8 bolts and then weaken them, which requires your time and my time certainly isn't free. It would be vary rare for a manufacturer to use a Gr8 as a shear bolt if for no other reason than they cost the manufacturer more $ than the lower grades. The only reason that I can think of for using a Gr8 as a shear pin would be if there simply wasn't room to use the appropriate diameter Gr2.

 

[keeney]

One thing I learned from doing a lot of technical writing - always leave in a minor error in your documents just to check and see if anybody is actually reading them /forums/images/graemlins/wink.gif

Grade 8 = 6 marks, not 5 as has been pointed out.

I will add from my experience working in the Toro test department that the big companies spend a lot of money DESTRUCTIVELY testing the various designs to gather information about what happens when a cutter hits something hard like a rock.

Yes, it is really fun to run a 1-inch diameter steel "stake" up into a mower deck from a reinforced spring-loaded hole in a concrete floor and see what shear pins break or not (and what else flys off and how high and far it flys) when the company is paying for it, has a concrete bunker to perform the test in, and the information is required by federal safety regulations.

Doing these experiments on your own just for the fun of it can be a very expensive hobby.

A lot of times, the overriding criteria on a design might be safety, not just cost or convenience. In the above example, the safety requirement of nothing flying off to injure the operator might mean that the machine is intentionally designed to fail in some other way to absorb the energy. On the smaller walk-behind mowers, for example, it is common for the crank shaft to bend as well as the shear key to break. Due to the assymetric geometry involved, there is no way for a shear key alone to absorb all the energy of a full speed, dead-on blade strike against an immovable object.

If the crank shaft was made stronger, then the blade mount might fail instead. Or the blade itself would shatter or something else bad.

(The 1" steel bar ends up getting bent at about 10 degrees and has a 1/4" to 3/8" deep divot in it).

- Rick

 

[nomad]

</font><font color="blue" class="small">(
I will add from my experience working in the Toro test department that the big companies spend a lot of money DESTRUCTIVELY testing the various designs to gather information about what happens when a cutter hits something hard like a rock.
)</font>

Did I understand correct? Big companies like Toro destructing the cutters a lot in their labs? I don't find such tests logical tests (unless it's testing/cracking a component or two like the shear pin only) because the crack probability in a cutter with hundreds of components is very big if the whole cutter is under crack/destruction tests. I think they are probably destructing only one of its components or two which are difficult to control their parameters. And, this (testing a component or two) shouldn't cost much money. How many units of cutters did you see they were destroying to fix a design?

 

[Egon]

Back when I was younger and still on the farm we had a shear pin problem on the double tree but Dad just fixed it with a bigger bolt.

Egon

 

[keeney]

They did lots of individual component or sub-assembly tests, but every new model also had to go through some mandatory safety tests that have the whole machine running.

Some examples that I recall:

- The stake test I described where the blade is run at full speed into a pop-up steel bar. Nothing is allowed to fly off beyond some distance/angle.

- Tests involving some number of steel ball bearings (3/8" dia?) introduced into the mower deck. A ring of cardboard is placed around the mower to record where the ball bearings strike. Only some small percentage are allowed to strike the cardboard hard enough to leave a dent more than 1' up at 10' or so radius (I don't recall the exact dimensions).

- For rear-bagging units, one difficult test to pass was the nail test. Some number of pounds of roofing-type nails (of some ansi-specified dimension & material) are introduced into the mower. None can penetrate the rear bag. Sometimes some of the nails would get their heads clipped off and would make their way through some of the bag designs that failed.

- On ride-on machines, they would intentionally tip a machine on a tilt table with a 200lb sandbag belted in the operator's seatuntil it rolled over to verify its actual tip angle. They would do this in all four directions.

- I am unclear on the details, but I also recall some tests where the deck would have to be driven into some kind of fixed obect at the full operating speed of the machine.

Some of the non-safety testing was destructive in that it involves running the machine until it was worn out. A typical non-commercial walk-behind mower, for example is expected to last 1000 hours. Commercial units get 2500 hours or something like that. They had bays and bays of test cells where the machines would run 24 hours a day with some kind of rigged-up varying load simulating actual use conditions.


[ Many of these test cells all had fuel on-tap plumbed from a tank on the roof. Some interesting safety issues with that. ]

A lot of the durability testing involved cutting actual grass. They would hire crews of labor to cut grass. Often they would mow a large field at one setting, then lower the deck and cut it again. It was tough to find enough grass to cut because they didn't want to take business away from the local commercial mowing services who were their customers.

- Rick

 

[Villengineer]

For brand new product lines it's not uncommon for the company I work for to make 10 or more prototypes. We usually do a structural destructive test on at least 2, at least one will be cycled first to the design parameters and then to failure if possible, another one is usually sent to our various design facilities to be reviewed, and the rest usually are given to select customers to operate for anywhere from 6 months to a year. The units that are put in the field are checked regularly and when returned completely disassembled and examined. I know that many companies, over many segments of industry, do similar testing.

 

[nomad]

Such tests being done to the prototypes before fixing final design are being done because of traditions in engineering/manufacturing business. These tests actually aren't very necessary. Why? Because, today, all forces (hit by nails, rocks, etc) can be calculated (approximately) on "table" before making a product (by using a force analyse software coupled with a soild work modelling.) For example, a rock hitting a rotary cutter deck can easily be modelled and the stress flows at every point of all cutter components can be simulated on the computer screen. With this computerized technology available (unlike old days), digitization of whole cutter and design of prototypes are easily possible today and that "prototype on the screen" will be almost exactly same of "real prototype out of the screen". So, why still testing the product by using nails, rocks, etc if these aren't necessary anymore? In my opinion, this is because of old engineers in the field who are used to old traditions. If there are defects in castings, human errors in installing the products, etc., then each product coming out of the factory has to be tested (by using rocks, nails, etc etc) and these tests are actually quality control tests (not designing tests before fixing the cutter.) But doing such quality control tests to can't be done because it will be very expensive if you test each of tousands of products by nails, rocks, etc etc. If they are searching the value of an emphirical parameter in a cutter component by hitting a nail onto, say, its deck, then this can be done by a theoretical experiment using only one deck and one nail in a laboratory with a complex facility. If their use of hundreds of nails is a statistical test work, then the test results may correlate well only with clean fields like the golf turf fields where the nails are a few in. Anyways.. It's still good to see a new designed/made product in the real field to feel sure the product is working as designed on the computer screen. But, I still don't think they are very necessary. Ok, this is a debatable topic. Villengineer, so, you are in manufacturing field? What product(s)? if I may ask.

 

[RoyJackson]

"Such tests being done to the prototypes before fixing final design are being done because of traditions in engineering/manufacturing business. These tests actually aren't very necessary."

In theory, you're correct. In practice, manufacturers do "real world" testing to ensure things fit, or there's no tolerance stack ups or hypotheses (assumptions) made during the design stages were correct.

CAD/CAM can save money and some testing, but don't think it's the do-all/end all it's being advertised as...

The real world has more variables then can be modeled on a computer. Real world testing is to reduce risk and determine robustness of a design.

 

[nomad]

</font><font color="blue" class="small">(
CAD/CAM can save money and some testing, but don't think it's the do-all/end all it's being advertised as...
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CAD (Comp. Aided Design) is only a transformation of formulations into the computer language. So, CAD/CAM is nothing in a development process of a new product. I'm talking somethings different.

</font><font color="blue" class="small">(
The real world has more variables then can be modeled on a computer. Real world testing is to reduce risk and determine robustness of a design. )</font>
We are saying same things that real world has many more variables. Much bigger computers are needed to include ignored variables of real world. These ignored variables in mathematical formulations are so many that you can't make so many real world testings for each of many parameters/variables. You will have to make one test of a mower against rock, another test against a nail, another test against the wetness, etc etc. Tousands of real world tests... and this can not be done unless you spend A LOT. On the other hand, using computers, you can make many many tests which will not cost you much.. Anyways.. I consider such so-called real field tests only as a "show", to show their lab facilities, to show their designs (at tables) are really working, etc.

Ps: By the way, a mower which will mow a golf field can be better approximated by a computer mathematical modelling better than a mower which will be used in the grass field of a farmer. Golf fields are closer to a mathematical grass field formulation as they are cleaner than farmers' grass fields. So, golf field mowers will require much less test than other mowers.