Thread: SAWSTOP fires off again!

I think the Sawstop rep is feeding you a load... and throwing you off looking for whatever might be the real cause, unfortunately. If the sawstop couldn't cut ply or MDF I'd be getting a refund. I'm only a hobbyist user but I've made many a cut on my PCS through MDF, veneered MDF, pre primed MDF, structural pine ply, marine ply, melamine chipboard, some plastics, and aluminium. The aluminium was in bypass mode but everything else was with the safety engaged. No drops in 4 years. Both with the regular cartridge and the dado cartridge.

Not that I'm trying to victim blame but rrich could be on to something, could there be some aspect of your workflow that's causing unknown contact?

Originally Posted by Alkahestic

I think the Sawstop rep is feeding you a load... and throwing you off looking for whatever might be the real cause, unfortunately. If the sawstop couldn't cut ply or MDF I'd be getting a refund. I'm only a hobbyist user but I've made many a cut on my PCS through MDF, veneered MDF, pre primed MDF, structural pine ply, marine ply, melamine chipboard, some plastics, and aluminium. The aluminium was in bypass mode but everything else was with the safety engaged. No drops in 4 years. Both with the regular cartridge and the dado cartridge.

Not that I'm trying to victim blame but rrich could be on to something, could there be some aspect of your workflow that's causing unknown contact?

Thanks for your input. Can't fault the rep, he's been great and really wants to help. I rang CARBATEC the next morning and they sent the rep out that same morning. He's scratching his head as he can't see any issue with what I'm doing, how I'm doing it outside that I may be using a too long of an extension cord. So, I've got the election coming out to put another power point in right next the saw. See if that helps. I don't think it has anything too do with my work flow or the MDF..... I use the saw every day with the same sled (and others). The key point I thought strange was that all of the firings happened when using a sled, and they where 3 different sleds at that! 2 marine ply and one MDF. They are all sleds that seen a lot of use on the PCS before having a "firing".... got me scratching my head! I keep everything clean, neat, and tight. If it goes again in the future, I'll let you all know, I'll try and get some better images of all the contact points next time.

In the U.S., there have been reports of problems with more recent supplies of MDF out of China that have a high-ish content of metal as part of the filler. One user went through six "firings" before finding out the his supply of MDF was the problem. Apparently not a problem with older stocks of MDF.

The Sawstop technology has the potential to save a finger when it operates correctly , but also to cause a heart attack when it operates incorrectly.....

Swings and roundabouts I suppose.

Be interesting to ask the rep if multiple firings have an impact on the integrity of the saw. I can’t imagine it being too healthy for the machine to have multiple breaks happens.


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Prior to Covid, I had free access to a commercial shop with a large Altendorf slider (for most work) and a sawstop for little jobs. They had multiple false firings og the Sawstop. They have identified some, but not all, causes of the false firings.

First, they do a lot of laminating and steam bending work, using timber dried to 20-25% moisture content. Green wood is mildly conductive and triggers the system.

Second, they work with celery top pine (Phyllocladus asplenifolius), a timber which, uniquely, is mildly conductive and also causes false firings.

Third, they suspect that Tasmanian golden sassafras (Atherosperma moschatum) has similar properties.

Fourth, they suspect that resin pockets in some eucalypts may be a factor. Or the machine was just being perverse.

They say the real cost of these false firings in a commercial shop were:

• the down time of having an idle machine,
• the cost of replacing saw blades,
• the contempt that their craftsmen have for the equipment,
• replacement cartridges is a relatively minor cost.

Originally Posted by GraemeCook

Prior to Covid, I had free access to a commercial shop with a large Altendorf slider (for most work) and a sawstop for little jobs. They had multiple false firings og the Sawstop. They have identified some, but not all, causes of the false firings.

First, they do a lot of laminating and steam bending work, using timber dried to 20-25% moisture content. Green wood is mildly conductive and triggers the system.

Second, they work with celery top pine (Phyllocladus asplenifolius), a timber which, uniquely, is mildly conductive and also causes false firings.

Third, they suspect that Tasmanian golden sassafras (Atherosperma moschatum) has similar properties.

Fourth, they suspect that resin pockets in some eucalypts may be a factor. Or the machine was just being perverse.

They say the real cost of these false firings in a commercial shop were:

• the down time of having an idle machine,
• the cost of replacing saw blades,
• the contempt that their craftsmen have for the equipment,
• replacement cartridges is a relatively minor cost.

Which adds some weight to my suspicion that the Northern Silky Oak may be the cause.

(long one - read on if interested)

A SawStop has been on my purchasing radar for a long while as I believe the safety concept is good.

However, I have had reservations about,

• the technology, - capacitance.
• how reliable the technology is,
• how much of the perceived safety benefits are hyped by marketing gurus,
• what is not disclosed – i.e. what causes false activations?
• what research SawStop has to back their claims.

Being “battery operated” (a defib / pacemaker) I must consider any additional potential hazard/s that may be associated with any new tool, machine, or process that I adopt.

I asked SawStop directly about

• how does the technology work? A. “Our technology is similar to that used in "touch" lamps that turn on when you touch them.” (Capacitance)
• could it pose a risk of inducing an "inappropriate therapy" - a full defibrillation shock from my defib? A. “the signal and voltage we use are so very small, there is no concern it would cause problems with the device described. We have customers with similar devices who have never had any problems at all.”
• Has the SawStop technology been evaluated & what research is there available to support their claim? A. “We don't have any data or research to supply you, unfortunately.”

My research indicates that the SawStop technology is based upon a “change in capacitance” to trigger the safety mechanism. The technology truly is remarkable, however like all technology it comes with caveats – it may not work as intended in some specific scenarios.

False activations, imo, are an inconvenience for the reasons Graham listed above, but you get to keep your fingers.

If it doesn’t work????? There is data that shows considerable time delay in some activations, well above SawStops claimed “triggering time” – so it saving a finger amputation / injury may not always be the case, but it will certainly lessen the damage.

My suspicion is that “false triggerings” are caused by a combination of

• higher MC’s nearing the fiber saturation point,
• a particular species of wood that has more unique electrical properties,
• natural inclusions that are not always present that modify the “typical” properties of a species,
• foreign contaminants. (CCA, LOSP, Borax, Salt, fertilizer etc?)

Most experienced wood workers are familiar with moisture content, moisture gradients in drying timber, and the EMC – Equilibrium Moisture Content of wood. They also may be aware of the differences between “pin” (measure resistance) and “pinless” (measure capacitance) moisture meters and their pros and cons.

“Pinless” (measure capacitance) moisture meters are generally considered the most accurate method of measuring MC however they must be “calibrated” for wood species and density and can be affected by surface roughness etc.

As the SawStop uses similar “sensing technology” surely it must be affected by wood species, density, MC, inclusions, and other potential chemical contaminants on or in the wood passing through the saw?

My suspicion is that SawStop’s technology is not that unique and that it employs “frequency-dependent polarization/diffusion capacitance” to monitor “blade contact.”

The electrical properties of wood (i.e. resistance, impedance, capacitance, conductivity) have been researched extensively to monitor wood drying, prevent drying degrade, and improve commercial returns.

“Electrical Conductivity
The electrical resistance of timber varies greatly with its moisture content, from many thousands of megohms when very dry to near zero at the fibre-saturation point; electric moisture metres utilise this properly to measure the moisture content of timber.

In the moisture ranges where timber is a good insulator (poor conductor), moisture metres are reasonably accurate. However, timber becomes a good conductor at and above the fibre-saturation point, meaning that resistance moisture metres cannot be used in this range with accuracy. Other metres, based on electric capacitance, can be used in these cases.

As a conductor, timber can be heated by subjecting it to a high-frequency electrical field. Some adhesives can be heat-cured by this process during laminated timber or plywood manufacture.

Seasoned timber is normally regarded as a non-conductor for most practical purposes. Note however, that timber containing high levels of water-soluble salts from some preservatives and fire-retardants or through prolonged contact with seawater, may undergo an increase in conductivity when the moisture content exceeds about 12%. “ (NAFI - TIMBER SPECIES AND PROPERTIES)

“The frequency-dependent polarization/diffusion capacitance provided the most consistent correlation with moisture content. Changes in the dielectric properties indicated that substantial shrinkage in the pit aperture occurred as the drying process traversed the fiber saturation point.” (Characterizing Moisture Content and Gradients in Pinus radiata Soft Wood Using Electrical Impedance Spectroscopy)

The fact that SawStop make available the “option” to over-ride the sensing / triggering circuitry is an acknowledgement that there are flaws in the application of their technology in particular scenarios, which imo aren’t that uncommon!

The reported "false triggerings" when MDF, or plywood are suspected may have some truth (residual MC, changed EMC??) given that "As a conductor, timber can be heated by subjecting it to a high-frequency electrical field. Some adhesives can be heat-cured by this process during laminated timber or plywood manufacture."

If any moisture present at all in the air or timber let alone close proximity an unseen arc will form. An example is try using your touch screen very lightly slowly lowering finger you'll find you don't need contact at all. Same goes for arcing to Sawstop

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Really good summation, Mobyturns.

Rather than just say: "This is what I think." could I suggest that you broaden your research to include a couple of inter-related issues.

First, the inherent safety record of Anglo-American type saw benches versus Continental sliding top saws.

Second, the system being developed by a European consortium that detects proximity of flesh and then retracts the blade before contact. No need to touch blade and blade not buggered. Can restart in 20 seconds.
Altendorf's "ASA" safety assistant - Altendorf

Your response may independently confirm (or refute) the research that I have done, which is why I am being coy.

Please remember that most statistics show that 60-65% of saw injuries are from blade contact and 35-40% are from flying materials. And there are cultural differences: I suspect that the Swiss and Germans are more diligent in reporting accidents that Americans or Australians.

Very interesting post Mobyturns. There is only one statement that I would have an issue with

Originally Posted by Mobyturns

False activations, imo, are an inconvenience for the reasons Graham listed above, but you get to keep your fingers.

false activations don't involve the possibility of losing fingers. Many, many woodworkers use table saws on a regular basis over decades without ever coming into contact with a spinning blade.

Although I'm happy to acknowledge that there are many workshops where the SawStop technology is virtually a must (schools, men's sheds, anywhere there are multiple users - especially if they're inexpert) there's not much likelihood of one getting a guernsey in my workshop. I'm just heading out to the shed now to 'touch wood' in the hope that I'll never need it.

Originally Posted by GraemeCook

Really good summation, Mobyturns.

Rather than just say: "This is what I think." could I suggest that you broaden your research to include a couple of inter-related issues.

Already been there.

Its a shame that we await the expiration of SawStop's patent protection (from Aug 2021 and on, unless extensions are granted) to see further developments in similar technology from competitors.

I may be cynical but I have strong reservations about the "worth" of a "safety device" that is so assertively protected. But that is not what this thread is about.

I would like a bit more transparency about "false activations" before I commit. I've survived near 50 years using power tools with all digits intact, though I've had a few close encounters, enough to make appreciate the value of protection systems similar to SawStop etc.

Originally Posted by aldav

Very interesting post Mobyturns. There is only one statement that I would have an issue with

false activations don't involve the possibility of losing fingers. Many, many woodworkers use table saws on a regular basis over decades without ever coming into contact with a spinning blade.

Although I'm happy to acknowledge that there are many workshops where the SawStop technology is virtually a must (schools, men's sheds, anywhere there are multiple users - especially if they're inexpert) there's not much likelihood of one getting a guernsey in my workshop. I'm just heading out to the shed now to 'touch wood' in the hope that I'll never need it.

My point is that only machinery is harmed in a "false activation" - not fingers!

Now IF there is an over reliance on the technology to "save the fingers of operators" in situations like you describe and it doesn't trigger in the claimed "activation time" OR the technology is "disabled" and the operator has not checked that its is operational ?????

It is not idiot proof! Like any "protection system" that relies on any "human element" for it to work - there is always a "better class of idiot" who will find someway to circumvent the "protection system."

I agree that there are plenty of well trained operators of table saws who have a very healthy respect for machinery. I have grave reservations about the "need" for SawStop like technology. The issue is more about giving inexperienced, poorly trained, and unsupervised "operators" access to machinery in "community workshops." We digress!

Originally Posted by Mobyturns

... It is not idiot proof! Like any "protection system" that relies on any "human element" for it to work - there is always a "better class of idiot" who will find someway to circumvent the "protection system."

So true; idiots are extremely creative.

Originally Posted by Mobyturns

... I agree that there are plenty of well trained operators of table saws who have a very healthy respect for machinery. I have grave reservations about the "need" for SawStop like technology. The issue is more about giving inexperienced, poorly trained, and unsupervised "operators" access to machinery in "community workshops." We digress!

We don't digress, Mobyturns. The key issue is saw safety, and we are raising a few more issues.

The saw safety figures for continental Europe are significantly better than for the "Anglo" countries. I think part of the difference is cultural (less gung ho) but a major factor may be that the continentals mainly use sliding top saws and the Anglos use saw benches.

Second, does the SawStop create a false sense of security?

Finally, apparently when a sawstop fires there is a lot of noise, a lot of smoke, and then silence. One of the machinists I mentioned above said that the first time he triggered the sawstop it "frightened the bejesus out of me", and then "all the b***s accused me of breaking the saw."