The lawnmower man

Dave Wilson goes to mow a meadow, but finds that the developers of his mower could have paid more attention to Design For Manufacturing.

‘One of the rarest things that a man ever does, is to do the best he can.’ – Josh Billings.

This morning, I received an email from one Karen Donovan at the Providence, RI-based Parker Group informing me that her client Boothroyd Dewhurst had produced a new white paper on ‘Design for Manufacture and Assembly’.

Thanks for that, Karen. But I’m not the one that needs it. Fortunately for you, however, I think I know some engineers that do.

The folks in question work for a lawn mower company. And my knowledge of them has come about purely by association, having tried and failed to use their Horrid Hovering Product (HHP) over the weekend.

It all started when a friend and fellow gardener asked me over to her house to take a look at the mower in question. It didn’t work and she wanted to know why.

We turned it on and it made a noise, but the blades refused to rotate. It was clear that the fan belt had come off. So I decided to take it apart to fix the problem.

First off, I removed the blade and then tried to pull apart a snap fit two-part section to access the belt and the motor. But I couldn’t get to it. Then I attempted to remove the motor housing. But I still couldn’t get to the fan belt. Finally after another four screws had been removed from the belt housing, I thought I was in business. I wasn’t. There was something holding the housing onto the machine that I just couldn’t figure.

After a lot of head scratching, I decided to clean the base of the unit to discover if there were any hidden fasteners that I hadn’t removed. And bingo! There it was – a hidden screw. But sadly, there’s no happy ending to this cheerless story, dear reader. Because the head of the screw in question had been exposed to the wet grass for more than two years, it had rusted and now resembled a rivet. There was no getting it off.

Resigned to my fate, I spent the rest of the afternoon sipping beer and reflecting upon why such a design had been passed into production in the first place. Why were the blades driven by a belt? And why was the pulley so flat that it couldn’t keep the belt on? Surely, even a simple tensioning system would have solved the problem? But worst of all – who would use a screw made from material that would rust once exposed to nature?

Titled ‘How to use Design for Manufacture and Assembly (DFMA) to slash manufacturing overhead, make products competitive, and bring new efficiencies to the manufacturing process,’ the paper from Boothroyd Dewhurst is available for download at http://www.dfma.com/dfmawp.

For those designers of the lawnmower, you might like to know that DFMA will allow you to systematically analyze your design with the goal of reducing manufacture and assembly costs, improving quality and speeding time to market. Not, I should add, reducing manufacturing costs simply to produce an ineffective low cost product.