I just purchased an old black and decker industrial 7616 (dewalt) router. It is the Dewalt 610 620 type router with rack and pinion.
The thing gives excessive spark. I have another similar router, 7620, that runs OK. I’ve swapped brushes and there is still excessive sparks.
Is there a common fix for universal motors that give excessive spark? Does one use very fine emory cloth or sandpaper to smooth out the contacts on the rotor?
Replies
sounds like you need to dress the commutator a wee bit (the copper segmented piece that the bushes contact against).. the copper wears too, just a bit slower than the brushes. Eventually you reach the point where the mica insulators between the copper segments are just a tad proud of the copper causing the sparks you see as the brushes are lifted fractionally off the contacts by the mica.
The fix is pretty straight forward. Start by removing the shaft, then carefully sanding the mica flush with the copper. To even out the wear it's best to try to do this by spinning the shaft in a lathe (an upright drill might be able to handle it) and sanding with some fine wet n dry paper. If the brushes have slightly eroded the copper segments, they'll tolerate a smidge being removed from them just to even out the wear a little, but don't go too far.
Once the mica is flush, the next bit needs to be done with handraulics.. you need to slightly undercut the mica between each segment. Last time I did this I fond the best tool for the job was a junior hacksaw blade (tape applied over one end to improvise a handle). That said, you'll need to assess the required tool width for yourself; not all motors are created equal. All it takes is a gentle sroke or two between each segment; you only want to remove a couple of thou at best. Mark one segment with a felt tip pen, use that as your start point and gradualy work around the shaft till you're back where you started.
When you're done, thorougly rinse down the shaft with some electrical contact cleaner to flush away any filings and swarf created. Check the bearings for wear while you have the shaft removed too.
If you're at all uneasy about doing this yourself, any good motor overhaul shop should be able to take care of it for you. Rocket science it aint.. just takes a gentle hand and a bit of patience..
Mike Wallace
Stay safe....Have fun
Don't use emery. It conducts electricity and will increase sparking I use a fine file and grasp the armature in my drill press's revolving chuck.
When ever removing, or re installing carbon brushes, note the orientation of the brush as it is removed. Since the comutatator revolves mostly clockwise, a worn in brush aquire's a 'hooked' edge. When re installed, the hook digs in and chips and wears rapidly
Even New brushes will'seat'better, if first releived ,(chamfered) of the sharp edge using a fine file. Steinmetz.
Edited 4/17/2006 11:17 pm ET by Steinmetz
Woody, excessive sparking can be caused by worn brushes-as they become shorter there is insufficient pressure from the spring.
It is also caused by dirt (greasy carbon dust) on the commutator.
And it is caused by a worn commutator where the insulating separators are proud , causing arcing.
Sounds as though the commutator needs skimming-I have had one of those B@D models for 30years-who says they were not good?
Unless you have the faclities I suggest you let a motor specialist do it, as the way to do it properly is to machine the commutator between centers in an engineers lathe , copper requires a very sharp tooland the resulting finish should be smooth enough to not require sanding-which is verboten anyway for this application.Trying to Macgyver it in a drill press etc can lead to grief-the insulated windings are there just waiting to be nicked-if just one wire shorts out the armature will burn.
You also need to clean out the mica as Mike has said-grinding a hack saw blade to suit.One microscopic piece of swarf bridging
commutator segments will lead to smoke! While you are at it bearings may as well be replaced.
This is the sort of thing that is easy to do when one has knowledge and some experience-but I would hesitate to say it is easy for the run of the mill modern woodworker.Sorry to be at odds with other advice here, but I do speak from experience.Philip Marcou
Edited 4/18/2006 6:17 am by philip
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