Oh Dear, I've blown the chop saw...

I strip down and repair several chop saws every month, mostly wood working saws. The field coil in the picture does look a bit burnt but can look dark under certain light due to the way light is dispersed by the varnish.

Only way to check is to strip it down and look at all of the parts. If doing so, I'd suggest taking out the brushes first as they may get damaged when the armature slides out of the housing.

Ed.

second the Rage metal chop saw....

better yet, get that and bandsaw.....that sort'a size will eat the chop saw tipped blades....and plenty of hot chips...

tho cheap at Screwfix...

as I'm always cutting heavy metal I invested in a 12" bandsaw, (with coolant) the biggest Rage chop and circular metal saws...

a lot of money BUT

never looked back......hardly ever use abrasive cutting disc's anymore....

Failure could also be due to a mechanical part, such as a bearing or a gear. This will make the rotation stiff or eccentric or both, and can overload the fuse. That was certainly the case with my Aldi angle-grinder, now repaired.

Cheers, Tim

Thanks for all the comments.

Unfortunately, my budget doesn't stretch to a replacement at the moment. Certainly not a bandsaw, though I would like one and should probably have jumped at the Aldi one when it was available. However, my shed is pretty much packed as it is and I would struggle to find somewhere to store it.

I will disassemble the chop saw and see what I can see.

I do have a (fairly old) circular saw - would that do the trick if I got the right blade?

Iain

Before the chop saw, I used 10" x 1/8" cutoff discs in the 3/4 Hp circular saw for cutting through steel plate. You had to be careful not to set the workshop on fire with all the sawdust around !!

Cutting speeds for wood tend to be far higher than for metal, so most are not appropriate. OK with a cutting disc as SB5 indicates.

I've taken the saw to bits and extracted the motory.

One of the bushes is chipped on one edge.

The armature was dirty and there was carbon between the copper.

I scraped this with a small knife and then brushed with isopropyl alcohol.

I measured the resistance between the copper rings. Adjacent rings had a resistance of about 1 ohm. each successive ring added about 0.1 ohm - so copper on opposite sides of the armature had a resistance between them of about 2.2 ohms. I didn't test all of the pairs but all I tested seemed to show the same.

The resistance between live and one of the bushes was about 4.3 ohms and similarly between neutral and the other bush.

I don't know if this is normal or not.

I have pictures, but I didn't see anything untoward - if they would be useful then I can upload them.

Iain

Check between the comm bars and the armature spindle for leakage, preferably with a megger, armatures usually fail to earth when they overheat and the varnish melts. also check continuity through the field coils, and to the metal laminations of the field coils.

Before you consign the chop saw to the scrap-head, don't forget to retrieve all the useful bits (bearings, gears, shafts, and anything else that might come in *handy* one day).

I don't really know what I'm doing here, but I checked various resistances and capacitances and it all seemed OK. So I thought I would put it back together and give it another go - who knows, it might work.

When re-assembling I noticed this

It's not the best photo in the world, but the windings are clearly burned and the shell has also been burned.

So it's bye byes for this little chap.

I will pop into Aldi and see if they can do spares. The interweb appears not to.

Iain

it's unusual for the field coils to fail. You may find a reader who has a set of coils as it is usually the armature which fails when they overload the motor/ saw. These devices such as angle grinders,and table saws need the speed to keep them cool. John

Field coils can be rewound......not too much trouble...

But I stand to be corrected by more knowlegeable folk.....

Edited By John Rudd on 26/05/2019 19:21:39

Thanks, All.

Guy (and others) - the Rage range of chop saws look good. I know you said that it would go through solid bar, but the pictures only show tube. I'm a bit concerned that I will blow one of these as well - though at least spares exist. Will it really cope with that thickness of solid steel?

Also, the size range is up to (say) 65mm and I'd like to cut some bar thicker than that. In this case I have some 90mm cast iron which I got in the minimum length and need to cut in half. It's not that long so I anticipate needing to make some jig to hold it, but will if fit under the blade of one of these chappies?

And yes I will take the bits out that are useful - i have boxes of bits which might be useful someday!

And, John. I don't think rewinding field coils for this beasty is within my competence or skill level. Sad, really.

Iain

It could be that when that coil was wound the magnet wire got chafed or the insulation coating cracked. Also could be the protective insulator paper or plastic sheet between wire and coil laminations was not placed correctly or was split. After a bunch of hot / cold / vibration cycles the conductor became exposed and the distance between wire and laminations got short enough to allow an arc to start. It can happen. Some years ago people were having exactly the same fault on Weed Eater brand line voltage grass trimmers. Must have had the fault in many thousands of them during a production run - there were hundreds brought in for service and hundreds more visible at the curb on garbage day for months.