Problems with my Festool saw, aaarrrgghh!

[Aragorn]

Woody
Looks like a trend is developing here! That's 4 Festool saws (I think :?) that perform like yours (or very similar).
I think this thread has made most of us Festool saw owners a bit anxious. I would expect a tool of this price and quality to last way longer than 8 months even with high level everyday use.
My little Bosch drill "retired" after 10 years of very heavy use. I would expect a similar performance from the Festool, frankly :|

Alf... I don't see why you have to be funny about it, as i wasn't asking you for anything. :?

Really, Woody, Alf wasn't being funny about it. There's just no reason to believe that a question from me or Chris will elicit any more response than from you or a complete newbie. Don't we pride ourselves on that here at UKW? Mine (and Chris'?) response were rather tongue-in-cheek, but HEY! let's hope a few more Festool saw owners get a chance to check out their saws in the next few days.
Hopefully Festool themselves will clear it all up for us anyway.

 

[Manny]

I would expect a tool of this price and quality to last way longer than 8 months even with high level everyday use.

My thoughts also.

John

 

[tim]

As a potential purchaser of one of these bad boys I was surprised to hear about the noise level, pulsing and play.

Looking forward to hearing what Festool have to say about this.

T

 

[Ian Dalziel]

i checked mine at the weekend and yes it does the same at speed one through to 6.

I also went to the scottish woodwork show where festool were demonstrating and guess what it...theres was the same as mine.. i asked the question and the guy just said 'its the way they all are its something to do with the electronics' not really a suitable answer but it was busy and the guy was under pressure from the crowds. I also asked about the drifting of the blade and he replied he had never heard of this. i left it at this because of the amount of people around
As for johns problems with it moving i can only assume that it has ran a bearing on the motor shaft which has allowed the blade to drift. not what you want to hear after only 8 months of use.
I know you said John that it gets a lot of use but that is why you pay a premium to get something that should last, for me that shouldnt even raise a question..to expect something to underperform after only 8 months use i would well pi**** off. If any of my LN had to warp of of square so badly i too would not be a happy bunny. not because fear or replacing but because i need the tool at the time and running away to dealers etc is time consuming and usually ends up with me arguing with someone. not good for the bp
I am dissapointed to hear than the new one has recut more of the rubber strip. Part of festools selling point is that its range of tools is interchangeable with other tools for its guiderail in its range how offputting would that be if you were a 1mm or so out because they 'werent interchangable'. I will be interested to hear what Festools reply is. there guiderails are expensive enough and handy to be interchangeable but not if there is going to be discrepencies

FWIW.I have had problems with some of my festool stuff but they change it or repair it without any questions,

Ian

 

[RogerS]

Regarding the 'pulsing' on low settings....being devils' advocate here...I realise that the sound may be disconcerting but if the cut is still OK then probably that's the way it is.

Dredging through my memory circuits from my electronic days there are IIRC only a few ways to alter the speed electronically and it depends on the motor design. If the motor is synchronous then its speed could be controlled by the frequency of the driving circuitry. I suspect that in this case it isn't and so the only way to slow it down is to reduce power...either by slicing chunks out of the mains frequency sinewave (like thyristors and dimmer circuits) or by pulsing the motor with complete sinewaves....and relying on the blade and motor rotor to give some degree of flywheel action to smooth out the pulses. It sounds as if this is the case here.

Now waits for Tony to shoot my theory down :wink:

 

[Neil]

Hi Woody,

I haven't been able to get to the workshop since you asked about the pulsing, but I'll have a chance tonight and I'll let you know.

Cheers,
Neil

 

[Philly]

You lot have got to be worried! :wink:
Glad I haven't bought one yet........
Stirring it,
Philly :lol:

 

[Waka]

Philly

I'm still here lurking and placing orders. Its better doing it from a distance because I don't have to consult with HID's.

Come on take the friday off and join the spenders at Yandles.

Regarding the festool saw, I used it a lot last time home and have to admit that I didn't experience what JE is going through, mind you I haven't run it on any speed but 6 yet, still getting perfect cuts and at right angles.

I will give it the once over when I get back, but hopefully by then the answers to all the question will be available.

I'd still buy another.

 

[Woodythepecker]

As i have said Festool claim that "The MMC electronics with 6 regulation and control functions retains a constant preset speed to allow optimum processing of a wide variety of materials"

Now i know nothing about electronics, but would i be right in thinking that this "pulsating" is the saw motor slowing down and speeding up again? If this is the case then the tool is not retaining a constant speed, and if it is not retaining a constant speed then it must be a fault. That is the conclusion i would have come to if it was only my saw, but this is not the case and so far all but one of them have this pulsating noise. So what are the odds that all these have a fault? Is it just a quirk, or is there something wrong?

I am even more confused now. I will let you know what Festool have to say.

Aragorn, Ian, Philly, Waka, Neil, Roger, Tim and John. Thank you all for taking the time to reply.

Regards

Woody

 

[Neil]

Stirring it,
Philly :lol:

You just watch it, Philly! That reminds me of something - I was reading the other day about a new strain of wood worm which is partial to cast iron. At the moment, it is confined to the Dorset area - so no worries for most of us :wink: The effects are devastating, I believe - they can reduce a Unisaw-clone to iron filings in a matter of months... :shock:

Cheers,
Neil

 

[Adam]

Right, I think the only replies needed from now on should be on-topic.

Adam <mod hat on>

 

[froglet]

Woody I think you might be worrying overmuch about the pulsing. It is probably just because the saw is running without a load. The saw's electronics will be designed to monitor the speed of the blade and apply more power as the blade is slowed by the cut to maintain the blade speed within a narrow range. Equally if the blade is running too fast the electronics will cut power and allow the resistance of the cut to slow the blade back to within the desired speed range. With the blade freewheeling and at the slowest speeds it probably doesn't take much power to get the blade up to speed and if it ends up running a little fast there is nothing to slow it down. Under these conditions the motor controller is probably having to remove power for long enough to bring the speed down that you notice the little pulse in the power.

Of course somebody may come along in a minute who really knows what they are talking about and tell me I am talking rubbish.

Graeme

 

[Jake]

I instinctively agree with Froglet, but Tony or someone with the requisite knowledge will hopefully come along. If it wasn't an electronically maintained speed, the motor would increase its speed under no load, and slow down under load. The hunting you seem to be describing sounds as if it is the electronics doing exactly what it is supposed to be doing - albeit that with no load perhaps the feedback can't quite keep up with the very rapid changes in speed which are going to happen with little friction or inertia to counteract the changes in input to the motor from the electronics. It is the speed under load you need to be listening for, I think.

Having said that, we are all guessing becasue we can't hear the noise you are describing - it could be far worse than I'm imagining!

 

[Anonymous]

I was going to keep out of this but for what it's worth:

Speed control of a DC motor (I know you plug it into mains AC but it is still a DC motor) is best accomplished by Pulse With Modulation (PWM). This is a method of sending 'packets' of electrical energy to the motor in rapid succession. If the packets are small, then the speed is low and if the packets are large, then the speed is fast.

Typically, we would hold the frequency (repetition rate of the packets) constant and the duty cycle (ratio of on-time to off-time - or the 'width' of the energy packet) adjusted between 0 and 100%. If the chosen frequency is suitable for the motor, then the mechanical inertia (resisitance to a change of speed) in the load AND the electrical inertia (Inductance = resistance to a change in current) of the windings should smooth out the pulses of energy to the motor quite nicely. Result = smooth running and very good speed control with good torque characteristics. If the duty cycle is VERY low, then the pulses of energy might not be fully smoothed out and one might see some 'pulsing' in the motor.

I would have to say that there is not likely to be any speed monitoring on the saw (I do not know this to be true but expect that Festool would see no need for this extra expense) and so it is running 'open loop' Well, any open loop system will be affected by variations in load etc., especially at low duty cycles (speeds) when the power developed within the motor is significantly reduced

I would not expect to see any pulsing of the saw speed UNLESS the speed was set too low; or the frequency of the PWM signal was set too low for the motor (design error - not likely in Festool kit).
To quantify 'too low' for the speed, I would say that if the saw cuts without stalling at a speed setting of 1, then the duty cycle is not set 'too low' and the saw should not pulse.

I would feel inclined to email Festool if it were me

 

[johnelliott]

Well, quite a lot of stuff going on here. hadn't expected that.

Anyway, tried my saw on the irrelevant and unecessary speed one this am, and it was definitely pulsing. The way I see it, maybe it would behave oddly if I ran it upside down too. So what. Mine is always on speed 6 and there it will stay.

As to the saw only lasting 8 months, well, mine started misbehaving at that age, but perhaps I shouldn't have said that if it only lasted 8 months it was still a good deal (or words to that effect). The reason is that it is guaranteed for 3 years, and whatever the problem is, the retailers and/or Festool themselves are going to have to put it right, so the question of it only lasting 8 months doesn't really arise.

I haven't heard from the repair people yet, if they don't ring today then I will ring them tomorrow, and will, of course, report back here

John

 

[froglet]

Tony it is a selling point of the saw that it maintains a constant speed and I don't see how you could achieve this with an open loop system. Surely some sort of feedback is required or else how can the motor controller respond to the changes in load? This isn't however my subject and I am ready to be told I'm talking rubbish again

Graeme

 

[Anonymous]

Graeme

I have never considered buying any Festool kit and am unfamiliar with their claims in advertisements.


Your point is quite reasonable Graeme.
However, I see no logical reason to implement feedback control in a circular saw but Festool may indeed have done so.

If they have, then there is no reason why the speed should vary at all. if it does, then there is some fault, whether design or manufacture

A circular saw by its very nature is simply a motor with an inertia disc attached and the unloaded speed of this can be very easily controlled using open loop PWM control - DC motors and loads is very well understood. If the motor generates a lot of torque, then this open-loop speed control will translate to steady speed of rotation during light cutting quite nicely

 

[Jake]

This is counter-intuitive, for me. Am I imagining that the torque demands of a saw are more than they really are, or underestimating the torque of a dc motor?

 

[Anonymous]

Jake I do not understand your question.

I stated that IF the motor generates high torque (it will do so regardless of load), then the speed of rotation will not alter significantly under light cuts, surely this is not counter-intuitive?

The torque that a motor can generate depends on it's electrical design and speed of rotation

T= (Z*phi*I)/(2*pi) in Nm

Where
Z = total number of armature conductors (copper wires in rotating section)
phi = the magnetic flux per motor pole (how strong a magnet we have)
I = current flowing in the armature which is speed dependant

 

[Jake]

I'm probably just exposing my ignorance, Tony.

I just didn't imagine that a dinky electric motor would have enough torque to maintain a constant speed without more trickery than you are describing. I'm not doubting you, it's just the assumptions in my head that are wrong. So it is counter-intuitive, to me. My intuition being fallible.