This summer, after years of using a gas-powered rotary mower, I impulsively decided to go green and buy a manual push mower for my small, urban yard. The Fiskars mower I bought claimed to be the best in new technology, and the floor model that I pushed around at the store certainly seemed both well designed and well built.
Of course, some assembly was needed, but with the clear instructions, the mower was soon together. I checked out the blade adjustment, and it was right on. The fit and finish seemed very good. I tried it on the grass and it cut beautifully. Above all, it was silent. In fact, my wife commented on how odd it was to see me walking back and forth in silence after years of pushing a loud power mower.
I finished mowing the front and back yards, then came back and decided to cut the backyard shorter. And there is was -- a squeak. Then another squeak. Suddenly, the mower had a persistent squeak. Annoyed, I looked the machine over, and in a few minutes decided that it was the front guiding wheels making the noise. Both of them.
The solid, plastic wheels were each attached to the mower frame with a through bolt and nut. After removing the bolt and sliding the wheel out, the monkey work was apparent. The bolt clamped a steel spacer between the frame cheeks and set the end play, while the wheel ran on the spacer as an axle. Both spacers were coated with a moderately thick layer of soft rust! No lubrication of any kind was evident.
A few minutes with a Scotchbrite pad and the rust was gone. I then reassembled the mower, using silicone brake grease as a lubricant, and the squeaks were gone.
Why a brand new mower got assembled with corroded spacers, or what situation allowed just the spacers to corrode while the rest of the mower appears pristine, is something only the monkeys know, I guess.
—This entry was submitted by Vern Klukas and edited by Rob Spiegel.
Tell us your experiences with Monkey-designed products. Send stories to Rob Spiegel for Made by Monkeys.
It seems a shame that they couldn't include a little grease or at least a note to add some, since there may be hazardous shipment laws about including grease in the carton.
Good point, Tekochip. However, if they decide not to include grease before shipping, it would make sense to be very clear to the buyers that this needs to be added before usage. Including a package with grease would help as well.
No it won't. Not unless you have a thorough understanding of the plastic involved. Nylon, for example, is formed of long, twisty molecules that intertwine with one another, resulting in a mostly-ridgid, somewhat flexible, self-lubricating solid. But if you use any lubricant, it allows the twisty molecules to disengage one another, resulting in a soft, mushy material unsuited for most uses.
Now, as I get it, this application doesn't use the commonly used shoulder bolt, a bolt with increased diameter for a region starting at the head and supporting the wheel, with a smaller diameter threaded region opposite the head. These bolts need only a nut as additional hardware, but obviously need the shoulder to be just a bit longer than the wheel's axle bore.
Instead, this application uses a bolt of constant diameter, with an added sleeve to perform the shoulder function. This situation gives an additional point of friction. Is the wheel rotating on a tightly-clamped sleeve (plastic on metal) or are the wheel and sleeve rotating on a tight bolt. This latter condition would result in a metal-on-metal contact which definitely should be lubricated.
My guess is that it's the former situation--the sleeve is tightly clamped when the bolt is sufficiently tight. There should be no noise from a plastic on metal contact. I wonder about end contact. No one has discussed the question of thrust. I'm wondering about either end of the wheel hub rubbing on the bolt head outboard or the mounting plate inboard. If there's a metal washer at either end, sticking to the wheel and rubbing against the underside of the bolt head or the mounting plates inboard, it certainly makes sense to lubricate these metat-to-metal contact surfaces.
Thanks for the comments, guys. Funnily enough, moments after this blog story went live I got a Linkedin note from a engineer at Fiskars, wanting some more info. So I'd say Fiskars is stepping up to the plate here.
Just to respond to the comments, I don't think the design was intended to be lubricated.
The spacer is a sleeve, not disk like. The wheel's end thrust is taken direcly by the frame cheeks, which are wider than the wheel hubs, which the bolt & sleeve clamp.
The sleeve doesn't rotate, so the running surface is plastic on metal. I think the squeak was the result of the soft rust being compressed and then torn away in a stick-slip manner by the action of the wheel. The wheels have substancial running clearances, both axially & end float.
The wheels could be nylon, but I think not. The material seems more like a high density polyethylene or possibly a polyurethane.
I had a similar experience with a green lawn spreader with the name of one of the most respected manufacturers of turf products. It's wheel bearings were simply a steel shaft in a plastic bushing. After its first use, I followed the operating instructions and cleaned the bearings with a garden hose to remove fertilizer and lime. I even went beyond instructions by blowing air into the bearings to remove water and dry. Next, a liberal application of WD40 and a couple spins of the wheel Fast forward a year and time to fertilize again. Both bearings were locked from rust, making the device inoperable. Even WD40 would not penetrate and loosen the bearings. My initial thought was why someone would make a product to be used in a wet environment that would be succeptable to rust? I complained, got a refund check, bought a different brand, maintained it the same after use, and have been using it for ten years. It had the same basic bearing design, but maybe the materials were different.
That's interesting, Bob, that the second lawn spreader didn't have the same problem, especially since it had the same plastic against metal setup. On the first spreader, I wonder whether grease would have been a better solution than WD40. Out there on the forums, there is anecdotal evidence that WD40 can hurt some plastics.
@Larry M. I read your comments about nylon with great interest, but came away a bit puzzled. I have fishing reels with some nylon components. I have used these for over thirty years and at the end of each season I dismantle, clean and oil all of them. I have never noticed any degradation in the nylon. I am sure that there are numerous grades of nylon so maybe your scenario only pertains to a select grade. Also in my reels the mating parts are usually brass, so that may be a factor. I know very little about nylon so I would appreciate any explanation.
@Larry M: What you're talking about (reducing the amount of molecular entanglement and allowing polymer chains to slip relative to each other) is called plasticization. Polymers can be plasticized by solvents that are chemically similar to themselves. So non-polar solvents, such as the hydrocarbons that make up many lubricants, will tend to plasticize non-polar polymers. But nylon is a polar polymer. This makes it resistant to non-polar solvents. (On the other hand, it is plasticized by water; it readily absorbs water out of the air, and the higher the moisture content, the lower the strength and stiffness).
Vern, while there should have been grease on the part, it may have just been left off of your unit. Sometimes when you get into a new car the dealer will tell you that there may be coat of rust on the brakes, since they have not been used. This is not a problem. A few applications of the brakes and the rust is off. Most uncoated metal parts will acquire some surface rust. It would be interesting to know, from either the store or the manufacturer, if this was a problem others had reported.
From your description, the steel spacers sound like they were disc-like in appearance to provide a smooth plane for wheel rotation-? (to eliminate wheel wobble-?). If that's the case, I would have used polycarbonate (Lexan, or other PC) in the design. Much more water-friendly moving thru a wet lawn.
My guess - the designer specified stainless steel spacers, the manufacture didn't check the quality of the material at incoming inspection. The (won't mention country of origin) spacer manufacturer got paid for 18/8 stainless, supplied sub-standard parts, and kept the change. Our company has had a similar experience with a split-pin supplier.
I bought a bunch of hydraulic type stainless fittings to go on a boat. I asked if they were available in 316 grade. The supplier said that they could get them marked as any grade, but reckoned that they were all the same. Guess which country of origin !
Through the years I have been involved in making dozens of parts for lawn mowers and similar consumer products. But due to material costs, I can count on my thumbs the number of times I have been asked to make those parts from stainless steel. It is much more likely the parts were expected to be zinc plated.
One problem we run into quite often in producing stamped parts is intolerance for lubricants. In days of old strips were oiled as they ran through the press and the parts produced also had an oil film. Hence they were not so likely to rust between operations. Some were washed and then plated or painted according to use etc. Therefore, no matter what, there was a natural barrier to rust for a time. Today, our customers do not want any oily parts and OSHA has dictated that many of the stamping oils we used are hazardous to somebody's health. Today virtually all of our stamping compounds must be water soluable and so are very vulnerable to humidity, particularly with changing temperatures. The same conditions that cause dew on your lawn encourage rust on unfinished steel parts, even in warehouses. Just think of how many times you unpack steel parts today and somewhere in the packing material you will find a pack of silical gel, treated paper or something similar. If oxidation starts it will just be covered by painting or plating, unless it is removed beforehand. Eventually the rust will surface. So that rust may have been in place long before the assembled lawnmower was shipped.
I would have used thin grease and I do not make it a habit of spraying water into bearing surfaces.
The problem with using that stuff, WD40, is that it is a good solvent for removing whatever was used to lubricate and prevent rusting. It is fine for removing dirty hardened grease that is keeping something from working right, but it is worthless for preventing rust in the long term. cheap gear oil is a better choice, or anti-corrosion grease, or even anti-rust grease, which is probably hard to find today. My 5 pound can of it is very old.
While plastic bearings may not need lubrication to function correctly, the steel part of the assembly certainly needs something to keep it from rusting. Probably the ones who designed the mower didn't know that. IT is one area of details that don't seem to be mentioned in engineering classes any more. Even good plastic bearings will usually benefit from a bit of the propper lubricant. Sometimes findin out which lubricant is the best choice is a challenge, though.
I have used WD40 for a multitude of lubrication applications, usually with good short term results, but as you say light grease will perform better in the long term. However, as a rust preventative I have found it works well, unless it is physically removed. The product was originally developed to displace water in electrical applications (WD = Wire Drier and this formulation was the fortieth attempt), so it is not water soluable.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
0 
