Reply to thread

Message: <blockquote data-quote="Argus" data-source="post: 1576113" data-attributes="member: 42">If I recall, universal motors with an armature, commutator and brushes, the brush contact faces need to be curved to the same arc as the commutator, clean and of the correct dimensional widths so that no more than two adjacent segments are bridged at any one time. Often overlooked when brushes are replaced..... a bit of judicious sandpaper, usually.The comm segments also need to have a small recessed gap between them. Look closely with a mag glass. Sometimes,  over use, this gap fills with powdered waste carbon and this can add to the resistance of the contact and produce an arc. In extreme cases it can lift the brush clear of the comm surface so that there is effectively an open circuit. Excessive arcing can produce high frequency interference, which you'll hear on radios etc.You don't see big DC motors much, these days, if at all but on bigger DC motors with large armatures, it was a customary practice to get a piece of pointed wood to scrape all this kratzenkrud out of the inter-grooves, however this may be difficult on very small diameter comms., but a stiff brush stroke may do the trick. It's essential to stay away from any varnished windings behind the comm with sharp bits, though! Be careful.Basic stuff, but hope that it helps.</blockquote>

Join the conversation!