Mower deck construction

Discussion in 'Lawn Mowing' started by marvinlee, Jul 9, 2005.

  1. marvinlee

    marvinlee LawnSite Member
    from Oregon
    Posts: 108

    A healthy debate has raged concerning fabricated versus stamped decks. My view is that either design is capable of being made with quality ranging from poor to superb. The thickness of the deck is obviously a major factor, but not the only factor. Steel quality can vary a great deal, with some steels being more fatigue resistant and others less so. We consumers simply don't know much about the differences in steels used in our machines. Sometimes quite small differences in alloying creates major differences is steel strength and corrosion resistance. I am speaking here of the commercially available steels, not the exotic grades found in aircraft and other very demanding machinery.

    Both deck designs normally feature added reinforcement at key locations. The maker has great latitude on where and how much to reinforce. The choice made surely has an effect on durability and strength.

    From an air flow view, I see no reason to think that a fabricated deck would enjoy any shape-related superiority. After all, the deck shape is a function of manufacturing considerations, not aerodynamics. Neither is it clear to me that stamped decks have an optimum shape. There, too, the stamping shape must conform to the range of shapes into which steel can be drawn.

    I have two stamped decks. The oldest is 35 years old. It has performed well, but has required welding on two occasions. It was quite thin when new, and is thinner now due to corrosion. It came with our ancient Gilson S-14 garden tractor that has been in the family since new. Considering its rugged use and extensive neglect prior to my acquiring it, I am more than satisfied with its longevity. The other stamped deck came with our first-series Kubota ZD-21. It has performed very well since purchase. The cutting performance is acceptable, but not as good as the old Gilson. Kubota has since changed to a fabricated deck whose cut some like and some do not.

    It is difficult to prove that either deck construction is inherently superior. Blade designs vary, blade speed varies, deck suspension designs vary, and so on. In addition, the designer of any deck has many choices as to shape, depth, thickness, baffling, spindle housing shape, etc. With all these variables, who can sort out the effect that only the deck construction--fabricated or stamped--has? I've always wondered how much of an affect differences in spindle setback has. I refer to the distance that the two outer spindles are to the rear of the deck compared to the middle, forward, spindle.

    The entire realm of mowing deck design is ripe for intensive engineering analysis by university engineering research departments. I have yet to read a scholarly examination of all the variables that make decks perform well, or not. If any contributor knows of academic papers or dissertations on deck design, I would like to know the reference to improve my knowledge.

    For the record, my ideal deck design would be machined out of titanium, by a major aeronautical company with absolutely no concern for cost. The overlapping blades would be timing belt, chain, or gear driven and in a straight line. Thus, no more uncut areas during turns. Such designs may be impractical, but we can all hope for further improvements in commercial decks.
  2. HK45Mark23

    HK45Mark23 LawnSite Member
    Posts: 200

    Maybe there needs to be a test deck made where every thing is adjustable and then some one can test every variable and find the superior deck blade design and configuration.
  3. rough cut

    rough cut LawnSite Member
    Posts: 39

    Another question or thought is deck design vs type of grass and height of cut. We in Florida have a problem. We need a deck with great lift and ability to discharge wet St. Augustine well and then the next site might be sparse Bahia with sand. The deck that works so well in St Augustine would be eaten alive by the tough seed heads and sand of Bahia. I know about changing blades from high lift to low lift to no lift. But still, sand blasting the underside of any deck will eventually do damage. That is one of the reasons I would not have a stamped deck. Break out the welder and do a fill when the deck has an errosion hole. With a manufactured deck I can weld in a new (stronger) patch or panel. My personal (home use) Sears Crapsman lawn tractor ate thru the deck in 400 hrs of use. Now I either have to weld the 6 holes and repair the three cracks or replace the entire deck for $1,000 !!
    Don't give me a hard time about my Sears Crapsman yard tractor, it's one that I use for around the house for quick small mowing and yard cart pulling. My wife also can jump on it and take it for a spin around her garden. My mower is a 2004 Ferris is5000 with a manufactured deck. We'll see how it does.
  4. Lumberjack

    Lumberjack LawnSite Member
    Posts: 180

    a few things to throw in the mix.

    Fabricated decks tend to stick to box like shapes where a stamped deck can be more free formed. If a study was done to determine the optimum deck shape I am sure fabricating it on an assembly line would prove difficult. Since there are also limits to stamping I suspect a third but more expensive choice of molding the deck would be needed to give absolute control over the shape and thickness.

    Steels do vary greatly in their composition but there is one that has high strength and resistance to corrosion but is very expensive. how about some stainless steel laminated to 1/4 inch high carbon?

    Just to add a topic why have side discharge at all? mulch it or bag it...
  5. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Because some grass grows so thick and fast that mulching just isn't an option. How about a half acre (or more) of solid crabgrass? The moisture content of crabgrass is about 10 percent higher than most other grasses. Even when it's dry on the outside (rare) it's still like cutting soaked grass because of it's high moisture content.
  6. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    You are quite right. But... It comes down to money and what something costs. A stamped deck can be built more economically to conform to the shape of the standard fabricated decks than a fabricated deck can be built to conform to the shape of most stamped decks.

    An additional consideration is does the manufacturer expect to make running changes to the deck design? Companies like Dixie Chopper and Hustler are making constant changes as compared to a company like Kubota that has a stamped deck. You see, with stamped deck manufacturing once the die is built (at about $1,000,000 plus) what you built is what you get. The die for the Gravely 50" deck is over 30 years old. And they're still using it. But when Gravely decided to revamp their lineup they couldn't do a thing with the die. They couldn't change the shape of the deck at all except for some internal baffling. Gravely wanted to go with a more conventional 48" deck and change the blade overlap. The deck die wouldn't accomodate any kind of changes like that.

    Now you take a company like Exmark. If they decide that a blade overlap or width change is in order they have their engineers come up with a design and then plug the new numbers into their computers. Bang, new deck.

    The main difference is in the blade overlap. The more overlap you can give a deck the less chance that blades of grass will be missed, especially on turns. The less overlap (the blades more in a straight lne) the further the deck will discharge the clippings and the deck should be able to handle higher volumes of grass.

    I don't know how that titanium thing will work out but there are already a few manufacturers that use timed blades in a straight line. Walker uses them as does Ferris in their new SD36 walkbehind.
  7. Lumberjack

    Lumberjack LawnSite Member
    Posts: 180

    I guess slowing down just isnt an option for some . :p
  8. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    With crabgrass it doesn't matter how fast or slow you go. It sticks to everything and you will be scraping constantly. I see people with mulching 21 inchers trying to get through the stuff. Cut 5 feet, stop and bang the mower on the ground, cut 5 feet, stall the mower out. You have to realize that grass isn't the same anywhere. Those of you above the transition zone really have no clue.
  9. Lumberjack

    Lumberjack LawnSite Member
    Posts: 180

    It is indeed the worst case scenario that separates good designs from bad ones.

    BTW I grew up in MD. I spent a few summers sweating with a 21 inch mower all for the price of a mere quarter..... :cry:

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