Thread: Ryobi Cut Off Saw has sped up?

My two bobs worth is in agreement with China's comment earlier:
The commutator needs to be trued up in a lathe and undercut after machining, not just cleaned with glass paper, prior to installing new brushes.

My experience with an angle grinder was the new brushes lasted about 15 minutes so I learnt the hard way prior to truing up the commutator. My AEG drill also gave grief but that time I had missed a piece of copper bridging two commutator bars -- hence the need to undercut after the machining.

As always BE CAREFUL with anything sharp and electrical - power unplugged and off if dismantled, all covers in place prior to energising etc etc. get someone to help/check if any doubt and even as good work practice.

from one who is still learning!

Thanks HavinaGo, very useful information there. I've got as far as removing the outer shell of the motor exposing the armature. I'm not sure how to get the armature itself off as it's obviously hooked into a gearbox of some sort. I googled some places in Brisbane that machine armatures... I'll ring one tomorrow to get a ballpark $$$... unfortunately it might turn out to be "cost prohibitive" verses replacing the whole saw

But I've got this far.. might try removing the armature.. any suggestions how?

Here's a photo of the exposed armature (all power disconnected! Safety first)

Looks like the other electric gurus have got you covered, never hear of something running faster myself. As you sure the blade is not blunt which is why it throwing sparks and making you think it's running faster? It may have gotten blunt with the last few things you or someone else cut with it.

I do agree the armature could do with a clean up, then use a hack saw blade or something similar to cut scrape down between them to clean it out.

I see someone mentioned measuring the speed it's going, on ebay the have cheap non contact digital laser tachometers for around $$12-15 posted to you from China. I bought the contact/non contact SFM, MPM model but it's was up in the $30 range, so getting pricey for just this job. The non contact part on mine is just the same as the cheaper $15 ones and works fine.

They are a good toy/tool to have around for the odd job that needs it. They are also good for checking things like drill presses and other machinery to see if the name plate is actually true or not.

Dave

HI,
You have a real Puzzler there. I don't know why its sped up - I don't think that its the Brushes though. Looking at the Picture of the Commutator on the Armature it certainly need Cleaning - it should only need Machining if its not worn true. It is actually better to use a Clean Flat File (not a coarse one) to Clean the Commutator. Sandpaper tends to leave debris behind which can get stuck in the Comm's Grooves and cause problems. If You are going to use Sandpaper use Wet & Dry.

Once You have Machined or Cleaned the Armature then as Dave J said get a Hacksaw Blade and clean out the Commutator Grooves. The Hacksaw Blade will need to be prepared (reduce the blade thickness) - You can do this by holding the Blade against the side of a Bench Grinder Wheel (carefull not to grind your fingers) or uniformally Grind it with a Angle Grinder or even a Sander. Oh yeah leave the Teeth intact you need them. Once You've Cleaned the Comm give it a Spray with some Electrical Cleaner and a Blow of with some Compressed Air.

Just My 2cents worth. Good luck with it.

I've not done this with a motor, but lots of times with generators (mostly old ones that cannot be replaced anymore): I gently used abrasive pads to clean the commutators mounted in a lathe spinning slowly. That way they get cleaned with minimal material removal, but you can then see very clearly if anything has been discoloured, worn unevenly or deteriorated for other reasons. You can then run an indicator (armature between centres) and make a decision if material actually needs to be removed. If not, the pad will not have even raised an edge on the commutator.
Cleaning out the gaps with a thinned sawblade is good, but there is no need to remove much or any of the insulator material - again, you just want to see that it hasn't been burnt to coal. anywhere.
If you accidentally raise burrs along the edge of the segments, another brief touch with the abrasive pad will remove them.
Just my 2 Cents' worth.
Joe