# Router Rotation Direction



## Cobra (Aug 21, 2016)

I am using a small laminate trim router as the motor for a tool post grinder.
I have a speed control for the router to keep the RPM reasonable.
I would like to change the rotational direction of the router.
My understanding is that swapping the wires that go to the brushes will change the direction.
Before I started taking things apart, I thought I would check with the forum.
Thanks for the help.
Jim


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## T Bredehoft (Aug 21, 2016)

Just off the cuff, I wouldn't bet on it.  In most cases you can reverse the plug (ignoring the third prong) and it won't change rotational direction.


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## Billh50 (Aug 21, 2016)

As far as I know routers are made to run in one direction only and can not be reversed. But why would you want to change the direction anyway ?


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## Cobra (Aug 21, 2016)

I would prefer the grinding wheel to be pushing grit and metal down instead of up.


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## David S (Aug 21, 2016)

Jim it is a universal motor and you can indeed change the direction of rotation.  Unlike some tools which are designed to run in both directions this router will likely have a leading commutator brush angle which gives it better performance in the normal direction.  If it is reversed you may notice a bit more sparking at the commutator, although it should not be excessive.

These motors have two field coils and the armature.  Power comes into one field coil (#1) terminal out of that coil (#1) to a brush(#1).  The other brush(#2) goes to the terminal of the second field coil(#2) and finally the other terminal goes to neutral.

You essentially want to swap the two terminals going to the brushes.  So field coil #1 goes to brush #2 and field coil #2 goes to brush #1.

I am at the rv park enjoying a rainy day and don't have access to make a sketch.

David


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## Tony Wells (Aug 21, 2016)

Can't just grind on the far side of the ID?


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## Cobra (Aug 21, 2016)

Tony Wells said:


> Can't just grind on the far side of the ID?



My concern was more when grinding an OD


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## Tony Wells (Aug 21, 2016)

I would have thought that the most common setup would have thrown the swarf down, with standard rotation. Have a pic of your setup?


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## Billh50 (Aug 21, 2016)

With the back end of the router pointing toward the tailstock the router should be turning in the right direction to throw sparks and grit downward when grinding an OD.


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## David S (Aug 21, 2016)

When I made my tool post grinder out of a surplus rotary tool I only had room on the lathe to mount it behind the workpiece.  It does throw stuff up in that location.

David


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## John Hasler (Aug 21, 2016)

David S said:


> Jim it is a universal motor and you can indeed change the direction of rotation. Unlike some tools which are designed to run in both directions this router will likely have a leading commutator brush angle which gives it better performance in the normal direction. If it is reversed you may notice a bit more sparking at the commutator, although it should not be excessive.


Also see if the brushes are angled.  If the brush angle exceeds 20 degrees reversing the motor may break the brushes.


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## Billh50 (Aug 21, 2016)

I had forgot about mounting the motor behind the toolpost. That would make it turn the wrong direction. That's why photos of a setup are always better.


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## David S (Aug 21, 2016)

I am not quite sure what the brush angle of 20 degrees means.  In all my years of designing power tools the brushes were perpendicular to the commutator, but the "brush angle" was the amount that they were rotated with respect to the field neutral position.  It could be mechanically by moving the brush gear around the comm..or by shifting the comm during the armature pressing process.

My experience is mostly with fractional hp universal and PM motors.

Could you clarify your comments so I don't lead anyone astray.

David


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## John Hasler (Aug 21, 2016)

David S said:


> I am not quite sure what the brush angle of 20 degrees means.  In all my years of designing power tools the brushes were perpendicular to the commutator, but the "brush angle" was the amount that they were rotated with respect to the field neutral position.  It could be mechanically by moving the brush gear around the comm..or by shifting the comm during the armature pressing process.
> 
> My experience is mostly with fractional hp universal and PM motors.
> 
> ...


In some DC motors the brushes are not perpendicular to the commutator.  I've seen this in treadmill motors and some older industrial motors (all integral horsepower).


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## David S (Aug 22, 2016)

The other consideration would be cooling.  Usually incoming air comes over the much hotter commutator / brush gear then as much as possible drawn through the armature air gap and around the field.  For reversing motors we would use a straight radial fan, which would "suck" in both directions.  However if the trimmer uses an axial fan it may not cool very well due to reverse air flow.  This may not be an issue if the tool post grinding loads are much smaller than as a laminate trimmer.

David


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## John Hasler (Aug 22, 2016)

David S said:


> The other consideration would be cooling.  Usually incoming air comes over the much hotter commutator / brush gear then as much as possible drawn through the armature air gap and around the field.  For reversing motors we would use a straight radial fan, which would "suck" in both directions.  However if the trimmer uses an axial fan it may not cool very well due to reverse air flow.  This may not be an issue if the tool post grinding loads are much smaller than as a laminate trimmer.
> 
> David


Good point.  You also don't want to be sucking air into the motor from anywhere near the stone.


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## Billh50 (Aug 22, 2016)

I did not understand that the router was DC and thought it was an AC motor.


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## John Hasler (Aug 22, 2016)

Billh50 said:


> I did not understand that the router was DC and thought it was an AC motor.


It's undoubtedly a "universal" motor which is actually a series motor.  It's called "universal" because it works on both AC and DC.


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## Cobra (Aug 22, 2016)

Billh50 said:


> I had forgot about mounting the motor behind the toolpost. That would make it turn the wrong direction. That's why photos of a setup are always better.



Hey Bill, not at a physical presence as yet.
This is a sketch of the proposed grinder.  It will bolt to the toolpost stud through the hole in the centre.
This sketch shows the OD grinding spindle; there will also be an ID grinding spindle.


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## Keith Foor (Aug 24, 2016)

Because of the speed involved in that type of motor.  There may be a timing issue with the brushes.  Advancing the brush timing can make the motor faster in one direction.  Since the motor would normally never be reversed.  So it may turn slower when you reverse it.  Now, the other issue with that is the current draw and heat will also go up in the motor is run with the brushes retarded.  If you reverse it and it seems slower.  It probably is and shouldn't be run in that configuration.    If the motor seems to run the same RPM it will be fine to be turned backward... the only thing you may notice is increased brush wear.


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## Cobra (Aug 26, 2016)

David S said:


> Jim it is a universal motor and you can indeed change the direction of rotation.  Unlike some tools which are designed to run in both directions this router will likely have a leading commutator brush angle which gives it better performance in the normal direction.  If it is reversed you may notice a bit more sparking at the commutator, although it should not be excessive.
> 
> These motors have two field coils and the armature.  Power comes into one field coil (#1) terminal out of that coil (#1) to a brush(#1).  The other brush(#2) goes to the terminal of the second field coil(#2) and finally the other terminal goes to neutral.
> 
> ...



Thanks for the directions David.  I got at it today to give it a try.
First time effort to reverse a motor.  Electrical is not my comfort zone!
Got the motor apart fairly easily and could see the field coils and the brush wires.
I was thinking that I was going to have to unsolder the brush leads and move them but when I took a closer look, the brushes were spring attached to the brush housings.





Unscrewed the field coils from the frame, popped the leads of the brush holders moved them to the opposite side and reassembled.  Easy right?  Not so fast.
Must have flipped the field coils over when I was messing with the brush attachments.  Damn thing is still going the same direction.  They good thing was that it still worked!








Took it all apart again and got smarter this time.  Marked the orientation of the coils, swapped the brush leads and re-assembled.
Worked!  Rotating in the opposite direction.  Seems to run just as smooth as original, no sparking on the brushes.
The speed is exactly the same as the original orientation.  Settled in at 32,000.

Thanks again David.  Your directions were spot on.

Jim


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## David S (Aug 26, 2016)

Jim thanks for closing the loop.

I worked designing power tools for the largest consumer power tool company in the world for 30 years.  Universal and DC motors were my thing..among myriad other awesome things.

I am glad it worked out.  Did you notice what kind of fan it had?

David


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## Cobra (Aug 26, 2016)

David S said:


> Jim thanks for closing the loop.
> 
> I worked designing power tools for the largest consumer power tool company in the world for 30 years.  Universal and DC motors were my thing..among myriad other awesome things.
> 
> ...



The fan is a cast aluminum piece that seems to work just as well in the other direction.


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## David S (Aug 26, 2016)

Jim do you happen to have a picture of the fan so we can show the difference between axial and radial fans for future discussions.

David


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## Cobra (Aug 26, 2016)

I didn't take one today but I can get a shot tomorrow.


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## Cobra (Aug 27, 2016)

David S said:


> Jim do you happen to have a picture of the fan so we can show the difference between axial and radial fans for future discussions.
> 
> David



Hey David.  Got a chance to take it apart again this morning.
Here's a couple of shots of the fan.








Thanks again
Jim


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