Tuesday, September 27, 2011

Failures MTBF and MTTF

The OCB has had a tough week so far. The OCG's koi fish pond pump impeller failed. The log splitter shreaded a Lovejoy spider. Our M-60 tank proof front gate has taken one too many hits by turnarounds. It was also attacked by a burglar that unsuccessfully tried to disconnect the mechanism. My smallest chainsaw gave up the ghost after 14 years after I tried a new batch of saw gas with a systhetic oil. That batch of gas also killed my brand new saw and I had to replace the carburator.
It is all Bush' s fault. It's all Obama's fault. Or, if the truth were known, It's all my own fault.
The pump failure was for a Savio solids pump that was supposed to stand up to some pond solids. I don't know if this includes the odd cottonmouth water moccasin and a few young Koi. Still the Savio company does not advertise repair parts and a local pond maintainer is going to try to get a new impeller. Easy to replace - unscrew the old one and screw on the new on.
The log splitter failure was on a very reliable OLD Montgomery Ward splitter. The cylinder hold downs kept failing and letting the hydraulic cylinder push back or to the side. This engineering genius got tired of this and put a block of 2" x 4' behind the cylinder. When the hold downs failed, the cylinder pushed the hydraulic pump shaft out of alignment and the Lovejoy coupling spectacularly failed. Of course, I found out about this when the OCG, who was splitting wood, told me she didn't think the splitter was working.
The chain saw had been kept running by squrting a little oil into the cylinder and cranking away. After a little smoke it ran just fine for a while. Please note, I have a 30" He-Man saw, a 22" alpha male/female saw, a 16" girly saw, and a 14" OCG saw. All Stihl! I've had the other junk and they are good for a season, maybe. Well, my daughter-in-law, an alpha female, was using one of the girly saws to cut a dead pine tree when she (not her but the saw) ran out of gas. I put in the newly made up sawgas with the synthetic oil and it would not even begin to start. I gave her the next larger girly saw and noted that it only had half a tank. I gassed it up with the new mixture and it ran for about two minutes before quitting, not to start. She then picked up the 22" alpha female saw and finished the job toute suite. The next day, the Stihl dealer said "you did what???!!!" Of course, me being the honest and competent engineer that I am, I blamed it on the OCG.
Now we get to my tank-proof gate. It seems that in Oklahoma, drivers don't know how to make a U-turn at the end of a road without hitting things - like my mailbox and gate. I have had a couple of celebrating young high school girls drive off my almost cliff, being caught by the attached trees. Of course, they had no trouble getting back up to the road with a bunch of boys around with hormones flowing.
Over the last couple of weeks, my gate had been hit hard enough to knock the reflective eyes off my bull head cutout. (great sight for a night-time turn around).
When this happens, my gate, driven by a GTO Mighty Mule opener gets out of "time" and has to be reset. Eventually, the whole mechanism deteriorates badly. This is my third mechanism, and I have talked to the factory repair people about a fix on damaged components. They tell me that they don't really don't try to repair them. If they are in warranty, they just replace the card or mechanism. Of course, that is a hell of a problem if it is not in warranty. One of my local dealers has tried to get someone qualified to repair normal illuse and abuse as occurs on a farm. I need to check back and see if they found anybody. I do think the GTO Mighty Mule company needs to take more responsibility for after-market problem, not in warranty. I am ambivalent about recommending this product to others just for this reason. I do admit that is seems to be a good product, but it was designed by engineering idiots.
Which brings me to mean time between failure (MTBF) and mean time to failure (MTTF). None of these equipments failed through normal use, but we have all had items fail, typically, one week out of warranty.
I think all electrical or mechanical devices, costing over some minimum amount (say $500 - $1000) ought to be required by the Federal Trade Commission (FTC) or a consensus trade organization (ASTM, IEEE, NEMA, ...) to have published MTBF and MTTF data, along with their uncertainty and confidence levels. That would put Consumers Reports out of business. Your automobile should have MTBF or MTTF figures published. We could have laws (bite my tongue!) that base warrantys on failures before MTTF, with all the costa reimbursed for products failing two sigma before MTTF.s

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