Electric drill runs poorly forward, but OK in reverse (fixed)

[PStechPaul]

I was using my Black and Decker 3/8" 4.5A corded electric drill model DR300, and it began running poorly in the forward direction, but seemed OK in reverse. It ran about half speed, and smelled like something burning. My guess was that it might be worn brushes. So I opened it up:



Sure enough, the brushes were worn more on one side than the other, which effectively caused the brushes to be misaligned. The forward/reverse lever actually shifts the brush holder about 30 degrees.

Sorry about the poor focus. I used a round file to restore the correct shape to the brushes, and cleaned the commutator with contact cleaner spray and Scotch-Brite pad.

It runs almost like new now.

[Willy]

Good save Paul!
Can't believe the looks of the gear set, dry as a bone but they look almost pristine, not even any residual dust inside the case from their use.
Wonder what their composition is, powdered metal with a graphite or molybdenum content?

[loose nut]

Use left hand drills.

[rjs44032]

Good Job!

Several years ago I had to do a repair on my Craftsman hand drill. It had started making terrible noise like a growling when you killed power. I opened it up to find that the back bearing (plain bearing) was gone. At the time I had picked up some router spacers with 1/4" ID bearings. Grabbed one and it fit perfectly on the shaft and in the housing. Been using it like new ever since.

Also did the same thing with my 5 Gallon shop vac.

Best Regards,
Bob

[PStechPaul]

It looks like this drill was pretty well designed and manufactured. I think it was made in USA.

[PStechPaul]

Well, this repair didn't last very long at all. Soon after thinking it fixed, the same problem returned, and I put it aside until now. I tried filing the brushes flat, but there was no real improvement, although it seemed to have the same problem in both forward and reverse. I might try installing new brushes, but they are listed as "not available" on ereplacement parts, and the places which seem to have very similar brushes do not show them as fitting my DR300 drill and the part numbers are different. My brushes measure about 5.8 x 5.8 x 9 mm whereas those I found,176846, are listed as 6.25 x 8 x 13 mm.

http://carbonbrush.com/blackdeckerbrush.htm

https://www.ebay.com/itm/271832040035

It very well could be that the brushes have worn to where they are too short and the spring does not have enough tension to make a solid reliable contact with the commutator. I guess I can risk $6 for a new set, although for that money I can probably get a working drill at a yard sale.

[nickel-city-fab]

Just as a suggestion for odd brushes -- I've found all sorts of "close enough" brushes NOS on ebay, intended for various models of Kirby vacuums, and Singer sewing machines. All I had to do was file them down to length.

[J Tiers]

I've filed (or more usually, sanded) down brushes many times. That makes them fit and normally all is well.

There are actually a whole lot of compositions of brush material for different purposes, different motor voltage, etc. Some of them can cause problems in the wrong application.

If you get brushes from a similar sort of product, they will likely work OK. But it is possible to find a brush that fits, but has different enough characteristics that it may overheat, or cause commutator wear, etc. And they may not look a lot different from the real ones.

[plunger]

Well, this repair didn't last very long at all. Soon after thinking it fixed, the same problem returned, and I put it aside until now. I tried filing the brushes flat, but there was no real improvement, although it seemed to have the same problem in both forward and reverse. I might try installing new brushes, but they are listed as "not available" on ereplacement parts, and the places which seem to have very similar brushes do not show them as fitting my DR300 drill and the part numbers are different. My brushes measure about 5.8 x 5.8 x 9 mm whereas those I found,176846, are listed as 6.25 x 8 x 13 mm.

http://carbonbrush.com/blackdeckerbrush.htm

https://www.ebay.com/itm/271832040035

It very well could be that the brushes have worn to where they are too short and the spring does not have enough tension to make a solid reliable contact with the commutator. I guess I can risk $6 for a new set, although for that money I can probably get a working drill at a yard sale.

How are you getting on.?

[reggie_obe]

Take the brushes to a electric motor shop.

[PStechPaul]

I cut and shaped a couple brushes from a larger brush that came from the ruined B&D mower. But still no joy.





However, I discovered that the bushing on the rear (commutator end) of the motor was badly worn. I found a ball bearing of the exact right size (8x22x7) and that fixed it just fine!


On the right is an old bronze bushing that I considered using, but it would have needed modification.

[nickel-city-fab]

Are they bouncing on the commutator? How round is it? Yeah I've had that before.....

[darryl]

Looks like what you really need is to restore the commutator- one important thing is going to be clearing the slots between segments.

I would be using fresh sandpaper, nothing coarser than about 150. Cut some strips wide enough to cover the length of the segments, then pre-wear them by dragging them back and forth over a piece of steel rod. This is to knock off the loose grit, and knock off the high spots of the abrasive. Might as well prep some 400 grit strips at the same time. Ideally you would remove the armature and mount it in the lathe. Put a sandpaper strip around the comm and pinch the ends together while letting it align itself. Run the lathe and move the strip side to side a bit. Reverse direction often during this 're-surfacing' operation.

If you see the black disappearing more or less evenly, then you won't have to turn the comm. This is very handy since it lets you avoid having to make a precision alignment. The sanding will follow the original alignment. If lots of the copper comes bright, but dark hollows remain, you might have to re-think turning the comm instead of just sanding.

Before you switch to the finer paper, clear out all the slots then use the coarser paper a few more times before switching to the finer grade. Clear the slots again, then go a few more rounds with the fine paper again, going both directions. I like to follow this with regular paper strips just to burnish the copper a bit. Don't use clay-filled paper, like high grade printer paper- just use cheap printer paper. For this last part, don't use the lathe- just pinch the paper around the comm with your fingers and do a lot of back and forth rotation.

The only time this method has failed me is when the comm is so badly worn that you can't get back to full shiny copper quickly. If you can't get the darkened spots out fairly quickly, then the comm needs turning, not just sanding.

If you're still with me at this point, the next step is to form the face of the brushes to the comm by putting it all back together and using the sandpaper again, but with the grit side facing the brushes. You'll have to pull the paper back and forth until you've worn the face of the brushes so the arc covers the full front to back of the brush.

At this point you have brush surfaces that are almost fully touching the comm segments. It's a really good idea to run the armature back and forth several times, cleaning the comm with something like lint-free paper often until the rate of carbon coming off lessens. You can use a cordless drill to turn the armature for this process. Afterwards you can run the drill under its own power to complete the brush bedding process. If you don't go through this bedding process, you'll be making burns on the brushes and the comm by running it under its own power- especially if you're driving screws or using larger drill bits. If you do take the time to go through the complete process, your drill will probably have thousands of hours left in it. Much depending on the state of the bearings of course.

[PStechPaul]

I appreciate the detailed procedure for renovating the commutator and brushes, and I might go to the trouble if this were a more expensive and needed tool. But it works well enough now - replacing the sloppy bronze bushing with a ball bearing really turned the trick. I have not tried it under heavy load, so perhaps that may show more need to do a better job.

I also have a motor from a Homelite string trimmer. It runs very well after removal from the housing, and it's a pretty hefty motor. I found it would start up and run strongly with as little as 25 VAC, probably at a few thousand RPM. At full voltage it might reach 15,000 RPM or more, and probably should be connected to some sort of load. Now I wonder how I might make use of it. I suppose I could try to retrofit a new trimmer head, although those that are available seem to be only for gas powered tools. And I do have a three-pronged steel blade that was on my old gas powered Homelite, but I have little need for heavy brush cutting, and my walk-behind string trimmer does the job away from a source of AC power. As usual, I will probably just put it aside in my pile of unfinished projects.