Many of the nylons used for gear service are glass filled. As soon as the resin skin wears through, rapid mating gear wear occurs due to glass fibre ends rubbing on the mating part. Also, certain nylons / polyamides have naturally forming crystals in the resin which will also wear mating items. Nylon can flex away from the mating part, much more so than the mating part, if it is steel. So, by nature it will not wear as fast as a mating steel part. Any dirt or filings near the system will also become embedded in the nylon which makes it an excellent lap. Lubrication will actually worsen this, as it traps dirt and spreads it around. B&D of course do not want their appliances to last forever - if you get five years out of a hedge trimmer these days you are doing well. Then you buy a new one and make B&D happy. Luckily their stuff doesn't cost an arm and a leg. OT - anyone heard from Wilfried Vermeiren these days? Cheers, Jeff Dayman Waterloo Ontario Canada ----- Original Message ----- From: "alanjstepney" <alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Wednesday, August 11, 2004 8:22 AM Subject: [modeleng] Gear wear > As I am sure many of you have discovered, once friends and neighbours learn > that you know which end of a screwdriver to hold, along comes a steady > stream of "could you just look at this" type jobs. > Yesterday I had a hedge trimmer passed to me, as, "it only made a noise and > didnt cut". > > It is a Black & Decker, with their usual arrangement of a spiral gear formed > into the armature shaft, running on to a larger nylon gear wheel. > > The gear on the armature is worn down almost to the root of the teeth. > The nylon gear appears unworn. > > I checked, and the shaft is VERY hard, and yet has worn far mroe than the > nylon. > I have seen this happen before. > > Logically the nylon, being softer, would wear faster, but the reverse is the > case. > > Any explanations anyone? > > alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > www.alanstepney.info > Model Engineering, Steam Engine, and Railway technical pages. > > > MODEL ENGINEERING DISCUSSION LIST. > > To UNSUBSCRIBE from this list, send a blank email to, > modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line. > MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.