Tom Gardner - Why 750 Hours?

Jul 01, 2011 3 Replies


> Ok... I know some are going to say its just the wrong tool for the job,


>> but I get a lot of use out of the little Bosch Colt routers as a high
>> speed spindle for detail cutters on aluminum. I've got one that is due
>> for new bearings, and overall I am not unhappy with the stock bearings.
>> I get hundreds of hours out of them. I have found there are lots of
>> possible replacement bearings. The stock ones are only a few dollars and
>> I may go that way, but if a hybrid or ceramic might last longer it might
>> be worth paying a little more. They have to be able to handle continuous
>> speed upto about 35000 RPM. Actually free spin at max according to my
>> tach is a little higher, but I always back it off just slightly from
>> max. My brushes last 2-3 times as long when I do that. They have to
>> handle both axial and radial load. Most of the time they are shaving
>> thousands at high feed rates with little side load, but once in a while
>> on an aggressive cut/plunge with a bigger cutter I can actually hear the
>> motor slow down for a moment. I don't want to spend more on bearings
>> than the whole spindle is worth only to have them turn to ceramic powder
>> the first time I push them a little too hard. Suggestions? Ideas? >>
>
> We use a bunch of Hitachi 1/2" VS routers...probably very similar. We get
> about 250 hrs on a set of bearings, but we beat the crap out of them. We
> use the stock replacement bearings and usually have to pitch the router at
> 750 hours. For me, better bearings probably isn't worth the cost.

Thanks Tom. I was hoping somebody who beats on routers the way I do would answer. After posting I realized I had about answered my own question. The stock bearings are satisfactory and dirt cheap. If I find a good replacement interval for bearings and brushes its pretty cheap to keep them going. I have a question though. Why are you pitching them at 750 hours? What is wearing out that isn't easily replaceable? Not that $99 for a whole new router (today's price for the 20 series Colt at The Box) is a lot of money to just replace them. I bought one today so I would have a spare to use while rebuilding others. At that price if they'd had more than one I would have probably bought three or four of them.

Wa mount a 1-1/2" Rabiting carbide cutter and are cutting kiln-dried Beech. At @750 (I just go by how many per year) they are pretty beat up internally and externally. They are so cheap, it's not worth a mechanics time to replace castings, armatures and such.

Ok, Thanks Tom. That's what I wanted to know. So far I am just wearing out brushes and bearings. It only takes about 15 minutes to replace bearings and seconds to replace brushes so it is cheaper for my time than buying a new one. I will carefully check armatures, castings, and plastic parts when servicing and follow your lead if any of those are cracked.

For some reason little shavings of fine cut steel wire get into everything. Commutators on brushed motors get mangled and can only be dressed a couple of times. The other enemy of machines and tools is careless people...they just don't care, it's not their stuff. I cringe every time I have to bring any of my personal tools or equipment to work.

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