Skil Worm Drive Pops and Shoots Flames

[Wamsutta]

I'm hoping it's just the armature bearings. I haven't even used that much.

It's one of the last USA made worm drives, so throwing it away is not an option.

Label Says:

SKILSAW HD77M
7-1/4’’ (184mm) Worm Drive Saw F012HM7700
120V 60Hz 13A no load speed 4600/min
SN 78315 HH344112
Assembled in USA

 

[The Cobbler]

flames from the brushes?
shorted armature is my guess

 

[Wamsutta]

Flames from somewhere else besides the brushes. Flames shooting out from between the motor cooling fins.

I don't think the brushes are worn out. I haven't used the saw that much. Still looks somewhat new.

I'll take it apart tomorrow. I'm hoping it's just worn armature bearings allowing the armature to float around too much.

 

[Rusted Nut]

Flames or sparks? I’ve used Skil 77’s for years, if you use them in a dark area, you will see some sparks, not flames though.

 

[Wamsutta]

Sparks. I'm being a little bit overly dramatic by saying flames.

 

[Wamsutta]

Well I took it apart and put it back together. I followed the instructions in the video. I couldn't find anything wrong. The armature itself looks fine and so does its bearing. Brushes have tons of life left. The saw doesn't sound right when it's running. It still has a muffled pop ever so often. I'm going to take it to the shop on Monday. I tried and put in an honest effort.

 

[Wamsutta]

I've had it after today. I'm taking it in tomorrow. The saw runs perfect until you put it under load. Start pushing it through the material and it'll pop a flame out the left rear side of the motor housing.

 

[Olafur]

Could be shorted armature. One of the windings shorted, lost efficiency.. Difficult to measure.

 

[ChevyEFI]

Sparks. I'm being a little bit overly dramatic by saying flames.

We know.

 

[Wamsutta]

I turned it in to the repair shop today. I feel guilty for leaving it with total strangers.

My fear is that someone there will say it got lost because of it being one of the last USA made saws.

 

[IndyGarage]

I have an old 77 I bought many years ago that does the same thing. Probably 80's vintage. It throws sparks from the brushes.

I was going to take it apart and try and figure it out, but ran across an identical old one for $12 at a yard sale and although it was very well used, it works perfectly. Typical me, I haven't parted with the one that throws the sparks yet.

 

[Wamsutta]

I took it to a place called Ideal Saw Works. It's a place that sells wood working equipment and has a blade sharpening service. I wish I could've spoken to the technician directly instead of just the receptionist. I don't see how they can possibly verify the issue unless they try to cut something with it. I don't think they're going to find the problem. I'm having second thoughts about taking it in. I should've tried replacing the gear set and all the bearings. Now I'm worried about the saw getting lost. I can't replace it because they don't make them like that anymore.

 

[nadogail]

When the smoke leaks out, they are officially dead; but they can often be brought back to life with a parts transplant.

 

[duneslider]

I think you are needlessly worrying. I have had to take my bosch version of the mag77 in and they fixed it up good as new.

 

[Wamsutta]

I went and got it out of the shop today. They haven't even looked at it yet. They were having a hard time finding it. I was on pins and needles the whole time they were looking for it. Oh well, it's not fixed but at least I have it home.

 

[dr_clyde]

I can't tell if you just want attention about this or if you have some sort of weird, unhealthy obsession. You're treating this tool like it is a child or a pet and frankly, that's very very strange.

No one is going to steal it, its a broken saw FFS. Even if it was working, no one is stealing old corded circular saws. MOST people who use a saw don't care in the slightest about where it was made. They just want to cut stuff.

The way I see it, you have four options. Option 1, send the saw out for repairs. Option 2, buy the parts and fix it yourself. Option 3, chuck the broken saw in the bin and buy a new saw. What option you choose is totally up to you, but those are the options that lead to a useable saw. The 4th option is to do nothing and be weird about it on the internet, which is what you're doing now and that does nothing to fix your saw issue.

 

[Lassen Forge]

I went and got it out of the shop today. They haven't even looked at it yet. They were having a hard time finding it. I was on pins and needles the whole time they were looking for it. Oh well, it's not fixed but at least I have it home.

Over a saw? Unless it is serial number 01-0000001, and in collectable condition, seriously, it's just a saw. Use it, break it, fix it, use it, break it, have it fixed, then eventually s#!tcan it when it's dead.

If you're taking a broken saw to a saw shop to get your saw fixed, and it's not gone 48 hours and your freaking out over it beign in the saw shop for repairs, you may have other issues that either a saw shop or anyone here can help with...

Sorry, but I just don't get it.

OTOH if the shop takes your saw in and 48 hours later "can't find it", that's the kind of FBN shop I hopefully avoid.

 

[Wamsutta]

Over a saw? Unless it is serial number 01-0000001, and in collectable condition, seriously, it's just a saw. Use it, break it, fix it, use it, break it, have it fixed, then eventually s#!tcan it when it's dead.

If you're taking a broken saw to a saw shop to get your saw fixed, and it's not gone 48 hours and your freaking out over it beign in the saw shop for repairs, you may have other issues that either a saw shop or anyone here can help with...

Sorry, but I just don't get it.

OTOH if the shop takes your saw in and 48 hours later "can't find it", that's the kind of FBN shop I hopefully avoid.

Are you trying to say I need a power tool psychiatrist?

 

[dogdog]

You should have jus my re-groove the commutator or as the other pro says “undercut” it

 

[Wamsutta]

You should have jus my re-groove the commutator or as the other pro says “undercut” it

I got the thing totally disassembled. Everything is perfect except one of the bearings that the armature shaft goes through feels a little rough.

I'm thinking maybe the armature is getting some "bad harmonics" from that bearing.

 

[dogdog]

I got the thing totally disassembled. Everything is perfect except one of the bearings that the armature shaft goes through feels a little rough.

Bearing don’t spark or shot flames unless you bend or have it hitting something like metal to metal rubbing. But that would have obvious signs. Shorted winding would give sign of burn. Open winding would not spark but you should be able to map out the contacts. It is always 180 deg apart I think…
The commutator gap is usually the culprit on these brushed universal pmcs, dc motors that uses the brush and commutators….

It’s easy to do, just google up undercutting commutator or me I only remember regroove…. No special tool needed. Just some sand paper and a knife or hacksaw blade. Maybe a block of wood for holder or make your jig

 

[Wamsutta]

It’s easy to do, just google up undercutting commutator

You mean like this?

 

[Wamsutta]

ok I found this information

Very interesting. They're saying the mica insulator between the copper segments don't wear down as fast has the copper segments. They say the mica insulator is supposed to be .050" below the top of the copper segment.

So I guess running a toothpick between the copper segments don't cut it then.

 

[The Cobbler]

I used to use a mica armature undercutter whe I worked in the automotive electrical place. i wonder if you could do the same with a dremel tool, being very careful.

 

[dogdog]

You mean like this?

Just use a hack saw blade break in half with sharp point or a knife, awl what ever fits. no need for fancy pantie tools if you are not doing it daily or professionally. You are basically digging the groove and prevent the carbon build ups that could be conductive path for arcing between the two pads. And don’t cut the wires. You are not digging to China lmfao on that groove. A light depth. So don’t bring out the gorilla in you.

 

[dogdog]

ok I found this information

Very interesting. They're saying the mica insulator between the copper segments don't wear down as fast has the copper segments. They say the mica insulator is supposed to be .050" below the top of the copper segment.

So I guess running a toothpick between the copper segments don't cut it then.

Yes and no for existing dirty commutator. It’s the carbon buildup on the grooves that is causing the problem. You know the carbon from the carbon brush or dirt in the air that caught up in there over time.

I used a 200 grits or 250 what ever to clean the copper then about 1000 grits to make sure it is smooth copper and not going to file the carbon brush with those pits made by course sand paper.

You can use water to wash dirt off NBD just make sure it is dry from fan or a blower

 

[Wamsutta]

Yes and no for existing dirty commutator. It’s the carbon buildup on the grooves that is causing the problem. You know the carbon from the carbon brush or dirt in the air that caught up in there over time.

I used a 200 grits or 250 what ever to clean the copper then about 1000 grits to make sure it is smooth copper and not going to file the carbon brush with those pits made by course sand paper.

You can use water to wash dirt off NBD just make sure it is dry from fan or a blower

How do I measure the grooves so that I can verify they're .050" deep?

I can sink my finger nail down in there but I don't know how far that is.

 

[The Cobbler]

I can sink my finger nail down in there but I don't know how far that is.

if the grooves are clean that's not your problem then

 

[Wamsutta]

if the grooves are clean that's not your problem then

Well I guess the idea is is if the grooves are gone because the commutator is worn so far down, then the copper segments can short together. The armature I'm dealing with looks brand new like in the pictures at the parts houses. I can't figure out what is going on and I don't think a repair shop could either. Repair shops are used to dealing obvious failures like if the blade won't turn because the gears are fried.

 

[Wamsutta]

ok I went to electric motor school YouTube. I'm trying to figure out how this things work.

 

[dogdog]

Well I guess the idea is is if the grooves are gone because the commutator is worn so far down, then the copper segments can short together. The armature I'm dealing with looks brand new like in the pictures at the parts houses. I can't figure out what is going on and I don't think a repair shop could either. Repair shops are used to dealing obvious failures like if the blade won't turn because the gears are fried.

Maybe a pic of that part ? And see if some one that have worked at a motor shop can give you a better advise. Otherwise people are shooting in the dark. You have eliminated communator gaps and carbon tracking issues, and the brushes are good? Then maybe a pic of that spark area. Some one might be able to help.

 

[The Cobbler]

good repair shops , or at least old time repair shops would diagnose the problem easily. today's throw away society, maybe not . but the technology is there to fully diagnose .

 

[redmondjp]

I'm with the others above - I picked up a Mag77 (the red-handled one) that has this same issue, and it's a partially-shorted armature. When I looked up how much the armature costs several years ago, I shelved it (literally). Maybe if I come across another saw that is cosmetically beat that I can part out, I will fix it someday but I doubt it. Just bought a brushless 18V Ryobi (under $100) 7 1/4" circular saw, and I still have the heavier Skil non-magnesium case worm drive for when I have a big job to do.

 

[dogdog]

How do I measure the grooves so that I can verify they're .050" deep?

Well I guess the idea is is if the grooves are gone because the commutator is worn so far down, then the copper segments can short together.

purpose of that groove is not rocket science... It's just there to break electrical contacts between pads. Over time it gets filled by dirt from environment / carbon buildups or grease / oil. It's the carbon on the tracks that conducts, and also it's not the AC, is the back EMF I think that is what is it called... there is another name for this don't remember.

and a little spark is expected on brushed motors.

 

[Wamsutta]

purpose of that groove is not rocket science... It's just there to break electrical contacts between pads. Over time it gets filled by dirt from environment / carbon buildups or grease / oil. It's the carbon on the tracks that conducts, and also it's not the AC, is the back EMF I think that is what is it called... there is another name for this don't remember.

and a little spark is expected on brushed motors.

I ordered a new armature for it, but I can't understand why I had to. The original armature looks excellent.

 

[nadogail]

Well I guess the idea is is if the grooves are gone because the commutator is worn so far down, then the copper segments can short together. The armature I'm dealing with looks brand new like in the pictures at the parts houses. I can't figure out what is going on and I don't think a repair shop could either. Repair shops are used to dealing obvious failures like if the blade won't turn because the gears are fried.

I believe that when commutator segments get badly worn the Mica needs to be undercut.

 

[i4ni]

I had a hound thatI put Nitro methane in his water bowl and he would shoot flames out his ****. He sure was fast though

 

[dogdog]

I ordered a new armature for it, but I can't understand why I had to. The original armature looks excellent.

That is when a pic is needed there really not much area that can spark. Unless your saw is slowed down with very dry grease then still no spark but probably a very hot saw

 

[Wamsutta]

That is when a pic is needed there really not much area that can spark. Unless your saw is slowed down with very dry grease then still no spark but probably a very hot saw

I'll probably go ahead and put the saw back together with the original armature because it'll be at least a week before the new armature gets here. At least I was able to inspect the gears and just like I thought, they're perfect with zero wear. I'll be installing a new bearing that I picked up today for the armature. You want pictures? I can take pictures of it if you think it'll help.

 

[KnurledNut]

You want pictures?