I recently got a bunch of portable power tools that were destined for the scrap bin. Among them were seven fairly recent Porter Cable 3701 laminate trimmer routers. This would be easy enough, I thought, until I took them apart and found a disturbing and unfamiliar construction detail
The top (commutator) bearing was inserted in a soft rubber cup. This cup is inserted in a socket in the plastic body. Is normal construction for portable power tools these days?
When side pressure is put on the bit, the top of the armature is going to deflect one way and the bit is going to deflect the other. Clearly the armature is not rigidly held in the housing like all of the routers I’m familiar with. Besides the performance issue, this condition imparts alignment issues with the larger fan bearing.
While this construction seems to make a little smoother feeling at idle, it does little to keep the bit perpendicular to the base when cutting.
What got me is that some of the other tools (not routers) I took apart also had that rubber cup on the armature bearing. Coopfab’s recent problem with a full depth mortise cut wandering horribly got my attention. That isn’t supposed to happen with a what I thought was a well built router. I checked the parts illustration for his router and sure enough, there was that rubber cup holding the top of the armature.
There seems to be a lot of experts on routers here, so I’m hoping to hear from someone else that has seen this rubber cup bearing holder. I’ve rebuilt a lot of routers over the last forty years. All I have ever seen had the commutator bearing in a solid housing. My deficit here is that I haven’t rebuilt any newer version routers or other newer portable power tools.
Any illuminating comments?
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