Thread: Table saw motor problemthmi

With the humidity we have had this last few months it's likely. I had a bandsaw that used to fill up the switch box to the point the contacts would be blocked. Never shorted but I was aware that it might so at regular intervals I would blow it out.
Regards
John

Did you try and run the motor no load while it was still full of dust? If it was causing problems on the workbench by itself and only to be sorted once you pulled the sawdust out, I'd say you've just solved your own problem.

If it behaved the same on the bench before and after, then one of the caps associated with the start/run system is probably stuffed. Most likely the start capacitor, but your comments about it tripping breakers and only moving a little before stalling also hint at a dodgy run capacitor (assuming it's a two cap motor).

Alternatively, if you tear the motor apart (as in, take the end caps off), you may find that the ends are full of sawdust and that it is interfering with the operation of any centrifugal switch associated with the start/run system. The switch is normally on the opposite end of the motor from the output shaft extension.

If the caps aren't what's dead, then most likely something to do with their connection to the motor windings is - like a loose or burnt away connection. This is far less likely as the caps are normally what blow first.

In my experience, winding failures normally present as smoke coming out of the motor or flashovers.

Originally Posted by themage21

Did you try and run the motor no load while it was still full of dust? If it was causing problems on the workbench by itself and only to be sorted once you pulled the sawdust out, I'd say you've just solved your own problem.

If it behaved the same on the bench before and after, then one of the caps associated with the start/run system is probably stuffed. Most likely the start capacitor, but your comments about it tripping breakers and only moving a little before stalling also hint at a dodgy run capacitor (assuming it's a two cap motor

I cleaned the terminals box & the start & run capacitor boxes before starting the motor on the bench. I suspect it might be an intermittent fault in the start cap. I decided it was too difficult to reassemble into the cabinet on the assumption that I had inadvertently fixed the problem so I opted to send it to the experts.

I'll be sealing the covers with PVC tape before refitting the motor, that's for sure. The dust extraction out of the cabinet leaves a lot to be desired.

mick

I don't think its the cap, when a cap blows you'll know about it, plenty of smoke and the smell is unmistakable.

Dust wouldn't cause it to fail either, as the capacitor is a separate unit and is sealed. It sounds like you've made the right choice sending it to a motor winder. Having said that like others have said that capacitors are generally the first things to go.

The dust build up does pose a host of other issues which most likely lead to the motor failure and I suspect the actual cause is build up of heat due to the lack of ventilation causing the windings to fail.

Regular cleaning/maintenance inside the cabinet will be the best option imo

Originally Posted by Glider

I'll be sealing the covers with PVC tape before refitting the motor, that's for sure. The dust extraction out of the cabinet leaves a lot to be desired.

mick

Depending on where the terminal box is on the motor, I find that more dust gets in between the box and the motor where they meet. The better motors have this junction all closed up with a well-designed casting. Cheaper motors tend to have a plastic box screwed on to the shell of the motor sitting above the fins, generally because their cases are an aluminium extrusion. Hi temp gasket goo silicone can be used to close up this gap. Otherwise, periodic maintenance is probably the better path - if, as you say, the cabinet is bathed in dust most of the time, you'll always get dust into any motor that is not rated as intrinsically safe.

Originally Posted by themage21

Depending on where the terminal box is on the motor, I find that more dust gets in between the box and the motor where they meet.

The terminal box is pressed Al and fitted metal to metal against the casing. Induced negative pressure inside the box is the only explanation for the amount of dust found inside. A fair warning for all Carbatec users.

Given the issue is intermittent and causing fuse tripping, I'm thinking it's either a short between terminals or a dodgy cap. Anything else probably means a new table saw.

mick

Originally Posted by Glider

The terminal box is pressed Al and fitted metal to metal against the casing. Induced negative pressure inside the box is the only explanation for the amount of dust found inside. A fair warning for all Carbatec users.

When the saw runs for a while the motor gets warm-hot, the air inside the terminal box heats up and a small amount of air is pushed out of the box. When the saw stops the box cools down and draws air back in. If there is any dust hanging around the outside near the it can get pulled back into the box. Over the years this can build up to more than enough to cause the switch to fail.

RedShirt Guy's recent post reminded me of something. When my power fuse tripped, the earth leakage device did not. In my inexperienced mind this means there was a current overload contained within the circuit. Had the dust caused it, I think it would have transferred to the earth wire and/or the cabinet itself and tripped the safety switch.

mick

Originally Posted by Glider

RedShirt Guy's recent post reminded me of something. When my power fuse tripped, the earth leakage device did not. In my inexperienced mind this means there was a current overload contained within the circuit. Had the dust caused it, I think it would have transferred to the earth wire and/or the cabinet itself and tripped the safety switch.

mick

It depends where the conductivity pathways develop within the saw dust.
Dry wood dust is a good insulator so it's only when a connective path develops within the dust that electricity can travel and start to do things.

The most conductive path depends on conductivity and distance.
If conductivity is relatively constant in the dust the distance between the neutral (N) and active(A) is usually the shortest path and electricity along this track may rapidly create an even more conductive pathway that preferentially carries more current.

If the earth(E) -A is closer a preferential pathway may start up between A and E and trip the RCD

In the case of my sawdust choked powerpoint the A-N conducted enough current to start the sawdust smoking and only once this had taken off and affected the whole PP did the RCD trip.

OK, the final wash up. The motor winder called today and told me there was nothing wrong other than dust contamination inside. He cleaned it out and it runs perfectly. I'm not looking forward to reinstalling the motor.

Time to convert the outlet from 100mm to 150mm and upgrade to a grunty dust extractor.

mick

Hi Mick,

Before you go about cutting holes in your table saw (its a good idea none the less) and spending more money on things you may or may not need. I don't know your setup, but from my experience, the stock ~100mm dust port should be more than suffice to clear majority of the dust your table saw produces. Especially most of the big stuff, dust only builds up in the corners right next to the dust port but never high enough for me to believe its of concern. Thats with me sticking my head in there every 6 months or less with regular usage.

The only time i notice it build up slightly more than usual is when I was too lazy to hook up the dusty (one too many times) and clogged the port.

Some things I suggest that may cause your dust build up are:

- Are you running a zero clearance insert or have sealed up all the gaps? As widening the port will do little to nothing if no air can get into the cabinet
- Is your dusty efficient? see 2hp dusty modification sticky if you're unsure what an efficient dusty looks like.
- When was the last time you cleaned your filter bag/pleated filter?
- Is your stock dust port still got the grate on it? if so remove it
- Are you running the dusty for a short time after your last cut (i normally run it for 5-10 mins) to clear everything, this will also help your motor cool and reduce the effects of dust being sucked back into the motor.

In regards to cutting holes in your cabinet, I found its much easier and more efficient to leave the stock port and cut a new port on the back side of the cabinet. This way the port is situated much closer to the source, and directly opposite the opening on the front of the cabinet. This also reduces the amount of dust that spits out the front of the table saw too.

Good luck with the reinstall.

A 100mm port and ducting, with sufficient air into a cabinet, may well clear the visible dust from a TS but it simply won't clear the fine (invisible) dust generated by this machine.

To grab all that fine dust around 800 - 1000 CFM needs to be removed at the source of the dust making. Even with a powerful DC only around 425 CFM gets through a 100 mm port and duct setup.
You absolutely have to use 150 mm ducting to get those higher flow rates.

Even using 150 mm ducting, just sucking on the cabinet is not be that effective either as most TS blade guard collection is also pretty ordinary and a substantial amount of fine dust escapes from above the table.
If a 150 mm ducting is used its worth using a 150-100 mm Y connector and use the 100 mm to suck on the blade guard and direct the 150 to the cabinet. Even a shop vac on the guard is better than nothing.

And don't forget if either the shop vac and DC are located so the vent inside your shed you will be constantly bathed in fine dust anyway.

My Carbatec saw didn't come with "over the blade" extraction. I'll drop into their Sydney shop and see if there's anything they can offer.

In addition to changing to 150mm outflow, I am now inclined to try a major modification to increase the airflow through the cabinet because the points of ingress only serve to reduce the internal pressure and create little effect on airflow versus something which will create a directed flow towards the dust port.

The plan is to induce the Benoulli effect with an extra port opposite the existing outflow and away from the motor.

Has anyone tried this?

mick

Originally Posted by Glider

My Carbatec saw didn't come with "over the blade" extraction. I'll drop into their Sydney shop and see if there's anything they can offer.

In addition to changing to 150mm outflow, I am now inclined to try a major modification to increase the airflow through the cabinet because the points of ingress only serve to reduce the internal pressure and create little effect on airflow versus something which will create a directed flow towards the dust port.

The plan is to induce the Benoulli effect with an extra port opposite the existing outflow and away from the motor.
Has anyone tried this?

Adding more vents to get more air generally into a machine cabinet has been around for a while.

Adding an opening such that it is on the opposite cabinet wall to where the the main outlet is located, and as much in line with the dust source as possible, has also been used and there are some good examples on this forum.

If you mean using the "Bernoulli effect" to try and drag more air though the blade table slot then you wont get much joy out of this. At best only a few CFM moves through the blade slot under the influence of a DC. The greatest mover of air though the slot is the blade itself. The back of the blade pulls fine dust ladened air from underneath the table to able the table and the front of the blade pulls the same amount of air from the top of the table to the underside
BUT
In between crossing from the back to the front the blade sprays air and fine dust into the shed. This is the fine dust that needs to be collected by the OH guard.
Thats why the main opening on a blade guard should be at the back of the guard to work with the action of the blade to drag that fine dust towards the front of the guard where the collection port will help pickup chips as well.