In the Firing Line

I recently met with a new owner of the SawStop, and took them through some of the specifics of the machine, including some of the basics of safe operation of a tablesaw.  As they were an experienced operator, the focus was certainly around the brake mechanism.

Six months later, and I get a call.  Turns out the SawStop mechanism got tested for real.  Scared the bejesus out of him – not only when it activated, but more fundamentally, that it happened at all.  So we are going to have another session, and this time running through the A, B, Cs of tablesaw use.

Had my own experience last weekend.  Not of the SawStop mechanism, but a reminder of basic safe operation.

I try to ensure that I am not standing directly in line with the blade when it is cutting.  That isn’t always possible, but it is a good practice, and this time was no exception.  I was standing to one side while ripping a piece of timber, and a piece of the offcut splintered from an unknown internal fault in the timber.  It got spat out by the blade, and sailed right past my ear.  Close enough for me to hear it pass by.  Close enough that I felt it brush the ear.

Reinforces why I like standing to one side while cutting!  Even if it had hit, it is unlikely to have done any damage, but it is a good reinforcement why we practice safe use.  And why eye protection is mandatory.

I finished off the cut – nothing wrong there, so the technique was fine.  It really came down to a weakness in the timber.

As much as I was out of the line of fire, it was a full-depth cut.  And while having the riving knife fitted helps protect against kickback, having the full dust guard fitted when it was appropriate for it to be used would have prevented this happening at all, at least as far as having a small missile launched in my general direction goes.

You Can’t Beat the Physics of Kickback – Fine Woodworking

A really important look back at a kick back article/video on Fine Woodworking.com by Ed Pirnik

You Can’t Beat the Physics of Kickback – Fine Woodworking.

Picking one comment from the article, which goes to the crux of the matter:

Here’s the KickerWhat floored me wasn’t the fact that the kickback occurred, or how violent it was but rather, the fact that despite the fact that this fellow knew the kickback was coming, and was prepared to pull his hand away at that fateful moment, the momentum of the blade was simply too much to fight against. In his slow motion replay at minute 4:20 we clearly see that despite his efforts to pull his hand away from the blade, it still gets sucked right towards it. By my estimate, his left hand was pulled in to within 1/2-in. of the spinning blade-again, this despite the fact that he was intentionally pulling his hand AWAY from the danger zone.

Just goes to show, you can’t beat physics, no matter how hard you try!

When you see the video again, in light of the quote reproduced above, you can see no matter how good an operator you are, if you get yourself unintentially in a kickback situation then you are in harm’s way no matter how experienced you are.  I’ve had a couple of situations over the years where I’ve found myself standing very still re-evaluating the situation after something violent and unexpected just happened, visually checking extremities and looking for claret.  Fortunately, on the rare occasion it has happened, nothing untoward has been found (other than some dramatic scars cut deep in the timber when it is found flung somewhere in the workshop).  Luck.  I don’t like relying on luck.  I like being in control of the situation, and if I can’t be in control, I want the equivalent of “airbag technology for the car” on my tablesaw.  And that is why I’m getting a SawStop.

Burl meet Torque

Another burl found itself being flattened at the hands of the TWC at Ballarat last weekend. This one had quite a curvature, with over 1″ from edge to centre on the cut side.

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For a thicknesser, this would be a nightmare. For the TWC this was a piece of cake.

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You may be able to see the separate passes in the photo- this is because at the time of the photo, I was working on maximum material removal (4-5mm per pass, to the full width of the cutter). This means the grain on adjacent passes got cut in the opposite direction to the previous, resulting in a different reflective surface- you can see the passes, but it still feels flat.

The final pass is done with very little material removed 0.5mm depth of cut, and maximum 1/2 the cutter width max, so all the grain is pushed in the same direction.

Either way, a few passes with the ROS (random orbital sander) removes any minor irregularities.

The problem for the thicknesser is both the tortured grain – in all directions so tearout is likely. The cutter direction on a thicknesser makes this even more likely, with the cutter scooping the material up, out of the surface.

Secondly, stabilising a burl to pass through a thicknesser is also tricky. With drive rollers pushing down before and after the cutter, the chances of the burl shifting and getting a massive kickback from the thicknesser is pretty high.

On the Torque, the cutter direction is horizontal, the amount of material removed each pass can be minimal, and is not over the entire burl width simultaneously, and there are no feed rollers to potentially destabilise the burl during the cut.

Thicknessers obviously perform a very useful role, but when their idiosyncrasies work against you, the Torque Workcentre takes over!

Continues….

Today was very much more of the same – I broke down the last 2 sheets of 2400×1200 MDF (one 12mm, the other 16mm) using a circular saw and a guide.  I really have a very low opinion of circular saws – dislike using them at the best of times.  The real danger comes with kickback, and unlike a tablesaw where the kickback results in the piece of timber being thrown, when you are using a handheld circular saw, and it tries to kickback, it is the saw that jumps and bucks, and tries to rip out of your hands.  It doesn’t take much to cause that to happen either.  The blade only has to bind just a little in the cut for the blade to stop doing what it is meant to, transferring the power of the motor into the cutting tips of the blade, and instead transferring the motor power into a rotational force that your hands and arms have to resist or risk a runaway saw (and potentially serious damage).  Even if you get away with it, your large sheet can incur some significantly horrendous scars.

I hate circular saws.  It kicked back more than once on me – each time I twisted the blade slightly during the cut.  It was a moderately powered saw – 1800W with a thin kerf blade, so I don’t know what was contributing to the (user caused) problem.  Was it that the blade was thin, so could distort under incorrect loading easier and therefore bind? Was it the saw itself was too powerful vs its weight? Not powerful enough, so it stopped cutting when conditions were less than ideal?  Whatever the cause, there is an underlying cause – I didn’t cut perfectly straight.  I got past that task, but I’ll be happy if I never have to use a circular saw handheld again (and with the imminent arrival of the Torque Workcentre, which has a circular saw mount and can cut a full 1200 wide panel, I’m hoping it means I will never have to).

You might ask why I am using a handheld saw if I dislike them so much, when I have a large tablesaw?  Simple answer – I might have a big saw, but a small shed – I have to break the sheet down smaller to be able to handle it in there.  There is another reason – single-handedly managing a sheet that size through a tablesaw can still result in twisting the sheet (and having the sheet stop contacting the fence), and there is every potential of a kickback in that situation too.  In future, if I have to do it by hand again I am going to take Marc Spagnuolo’s approach, and have the sheet resting on the ground, with a sacrificial board underneath (he uses polystyrene) – it will take more of the variables out of the picture and result in more ability to focus on, and control the saw through the entire cut. (I found I was overreaching near the end, and that is when things were going pear-shaped).

Despite the couple of….issues during the breakdown, things were pretty productive and I got both fridges made, as well as all the doors and tops cut.  Now they are getting close to needing the finer details made and fitted – taps, knobs, handles and the small things that take the build from the ordinary just up to the next level.

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All coming together

Some of the additional details I want to add include the fridge door- adding a shelf (on the inside obviously, like a real fridge), and an egg holder shelf.  It is little, easy details like that which will elevate the overall build to a level I will be happy with giving these to friends.  I still need to cut the stove elements, and the sink cavity, make the stove knobs, door handles etc etc – now that hard work (not necessarily the heavy work) begins.  I’m really looking forward to this part of the project – when it comes to life.

While I was working today, I found myself using one tool (other than the Domino) a number of times – one I find really useful.  It is the Black & Decker PowerFile.  I’ve had it for a number of years, and it is great for getting into areas, minor shaping, quick hinge mortising etc.

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B&D Power File

It is a belt sander, running a finger-wide belt with an exposed end.  Not very clear in the photo, but the notch seen here in the MDF to fit around the cabinet upright was cut on the bandsaw.  I then needed to round the edge, and that is where the power file came into its own.

SW09 – Preventing a Kickback

As discussed in the previous article, a kickback is when a blade stops cutting, and instead transfers the machine’s power directly into the workpiece, propelling it with incredible force.

Not getting in the way is a really good option when it happens.  However, we are talking about something coming at you at 200km/hr is hard to dodge.  Only having less than 1/100th of a second to not only realise something is flying at you, and get out of the way kind of suggests that if you are in the way when a kickback occurs, you have already been hit.  Hard.

Ok, not everything is going to be accelerated to the full tip speed of the blade.  A full sheet of MDF will not find its way to 200km/hr.  It will still find itself winging its way towards you, and given its mass, and the power of the tool that threw it………

So hopefully we have determined that being out of way before the kickback is a really good idea.  Staying out of the “fling zone” is a really good start.  For example, on a tablesaw, don’t stand directly behind the blade, or stand to one side, and reach across the line of fire to push the work through (dumb on a number of levels).  Position yourself where you can fully and safely control the workpiece AND stay out of the fling zone.  Body armor is not a bad idea either.  If you can’t get some of this, a leather shop apron is a great idea (and is not budget breaking either)

Anti Kickback Suit

Anti Kickback Suit

So that takes care of what happens when it happens.  Now let’s try to prevent it happening in the first place.

Tablesaw:

Ensure the fence is parallel to the blade.  If you can’t be SURE it is parallel, it is better to toe out than toe in (in other words, angled away from the back of the blade rather than towards it).

NEVER crosscut using a mitre gauge AND the fence.  You have trapped the workpiece solidly between the blade and the fence, and given it is a crosscut if it has any chance to twist at all, it will bind and kickback.  I have commented in the past about how I use the fence for accurate measuring before completing the crosscut, but note even my method leaves a good 40mm for the workpiece to move into so it can’t get trapped.

Have some form of holddown (if possible) at the back of the blade.  It doesn’t have to do much, but if it resists the workpiece floating up with the rear teeth rising, lifting it then this will minimise the likelihood of it being thrown.  In saying that I took the holddowns off my saw – they were too strongly spring loaded.  My blade guard does a reasonable job anyway.

Use a splitter and/or riving knife.  As a piece of timber is cut, internal forces are relieved and you can get significant amounts of timber movement.  If that happens to be in the direction to close up the kerf, the timber can attempt to bind on the back of the blade = missile.  Also, this helps prevent an offcut coming into contact with those rear teeth (remember I said I had some evidence 12 months after a kickback – it was my gut that got in the way, and it was an offcut that was the missile).

Riving Knife

Riving Knife

This riving knife (which also carries the fence (not show)) rises and falls with the blade, and is removable with a quick release.  It is kept pretty close to the blade to prevent an offcut getting in between and being kicked.  It also acts as a splitter, holding the kerf apart so it cannot close and pinch the blade.

Never use the saw without either a mitre gauge or fence (ie never freehand cut).  If you twist the piece even slightly, see above result.

Even better is to also use featherboards, to hold the workpiece snugly against the fence.  I use the term deliberately, as a featherboard can be snug without being so tight as to really make it difficult to slide the workpiece.

These featherboards from MagSwitch are my favourite, as they can be positioned anywhere (and are not dependent on the location of the mitre slot).  And the really nice aspect I think, is that it can almost be an afterthought – you are all set up for the cut, and you remember that you’ve forgotten the featherboard (heh), it is a simple matter of bringing it in and locking it down, wherever it is needed.

MagSwitch Pro Featherboard

MagSwitch Pro Featherboard

You will notice it is positioned just forward of the blade.  Once the blade has begun cutting, I don’t want anything pushing that offcut back into the blade.

Storage of the MagSwitch is also easy, and ensures it is right onhand whenever needed.

MagSwitch Storage

MagSwitch Storage

Pushsticks are also a great idea (obviously). Not only do they keep your fingers away from the blade, but a good one, a good design will also assist in preventing a kickback.

You can easily make a pushstick, and if you want to there is no reason not to.  If however, you never get around to things, there are some good designs on the market, such as this one by Kreg:

Kreg Multipurpose Pushstick

Kreg Multipurpose Pushstick

This one is from Carbatec, costs all of $30 or so.  The reason why the design works so well, is it pushes the work through (thanks to the lip on the back of the pushstick), but because of the position of the handle, effort is both forward, and downward.  Because of the large leading edge, the workpiece is held down well onto the surface of the table.  A kickback caused by the workpiece floating during the cut is virtually eliminated by this design.

Ensure the blade is sharp.  Dull blades = accidents.  Some blades also come with an antikickback design.  These have a tongue of the sawblade body out of the back of the preceding tooth so you can’t (theoretically) overfeed the blade, and the blade has less opportunity to pick up bits of waste etc.  Not sure how effective these are, but it doesn’t detract from blade performance.

Antikickback Tooth Design

Antikickback Tooth Design

Router Table:

Ensure you use the correct feed direction.  Normally right to left when using a fence (but don’t have the workpiece passing between the router bit and the fence).  Climb cutting has its place, but the vast majority of cuts, you should feed the workpiece in the opposite direction to the spinning bit.

If freehand routing (with a router bit with a bearing) always use a starter pin.

This can be as simple as a brass pin screwed into the tabletop near the router bit, or as complex as this freehand router guard from Professional Woodworkers Supplies (and Woodpeckers)

Freehand Router Guard

Freehand Router Guard

This one has been adapted to include the convenience of MagSwitch for positioning and mounting onto the router table.

When you are dealing with smaller pieces, a router table also benefits from featherboards, both horizontal and vertical where possible.  Again I’m using the MagSwitch Pro Featherboard as an example, with the optional vertical attachment.

MagSwitch Featherboards on the Router Table

MagSwitch Featherboards on the Router Table

If you are wondering about the colouring, the one on the right is the current colour scheme, but the functionality is identical.  I have 2 mounted here, as it is a really good idea to have both an infeed and outfeed holddown on the router table (unlike the tablesaw).  You can also use a fence-mounted vertical featherboard if you have a fence that can take one (this can), and own one (I don’t!)

Other things to avoid for kickbacks – don’t try to take off too much material in any one pass, use sharp router bits, watch your feed direction, be particularly careful when first engaging the router bit – for example feeding a long piece in means the bit is first going to impact into the endgrain, and if it doesn’t just chip out, it could kick.  This is minimised by using bits with an antikickback feature.

Antikickback Router Bit

Antikickback Router Bit

You can see the large amount of body in front of the carbide.  This limits just how much of the carbide is exposed to the workpiece.  Most router bits these days incorporate this feature.  If it doesn’t, be very wary!

Jointer/Planer:

Again, adequate holddowns are the go, with pushsticks, and optionally a fence featherboard should be sufficient (and don’t try to take off too much in a pass)

Fence Featherboards

Fence Featherboards

Again, MagSwitch have featherboards particularly suited as they attach magnetically directly to the vertical fence.

Kickbacks do happen, and most can be prevented.  If you get a kickback, the first, second and third reasons you consider should all start with the term “User Error”.  Find out what you did wrong, and try not to repeat it!

SW09 – Kickback

kick-1There are all sorts of risks in the workshop.  But the one that really seems to give woodworkers the willies is kickback.

When a kickback occurs, it is always pretty startling, you find yourself with the deer in the headlights look, and once your wits start returning, you start looking for claret.

I’ve had some pretty impressive kickbacks, and I can guarantee you something in every single case.  User error.  (Of course I do have that router bit that seems to kickback no matter what I try, but let’s ignore that here).

I’ve had kickbacks from tablesaws, routers (table mounted primarily), thicknessers, bandsaws, lathes, drill press…….  Pretty much anything with a blade can kickback.  That list isn’t a badge of honour.  What is then, is that I still have intact bodyparts.  One kickback I had from a tablesaw a few years ago gave me a bruise/mark that took a year to fade.

So just what is a kickback? I tend to think a kickback is when the cutting surface (be that a tooth, a blade or whatever) fails to do its intended task, and instead propels the work instead (which more often than not is back towards the operator!)

I’m not covering prevention here- that will be tomorrow’s article.  This is looking at causes of kickback.

Tablesaw:

A kickback on the tablesaw can be a frightening experience.  This can be a 3HP machine, with a large diameter cutter (10″+) and given the speed they run, the blade tip speed can easily exceed 200 km/hr.  If a piece of work doesn’t cut, and instead is propelled, then that is the sort of speed it is going to come flying out at.

There are  couple of places on the blade that are most likely to kickback – the side (which then lifts the work to the top of the blade where it gets propelled with a large degree of rotation), and the back edge (where you get massive acceleration of the workpiece).

Tablesaws have been known to propel a piece of timber so fast back towards the operator that it has punched right through the wall of the shed.  You don’t want to be standing in the line of fire.  Ever!

A rear kickback is when the workpiece is lifted by the rapidly rising teeth, and propelled over the top of the blade.  This can happen when an offcut works its way into the back of the blade, or when a workpiece is not adequately restrained and floats (lifts) because of those rapidly rising teeth.

A side kickback is often when a piece is not restrained properly as it passes the blade, and twists, (which obviously is then wider than the gap between blade and fence (measure across the diagonal).  The blade then chucks the piece.  It can also be when the fence is not parallel to the blade, and angles towards the rear of the blade.

It can also be caused when the operator pulls the material back towards him on completion of the cut (or when the piece becomes trapped because of the non-parallel fence), and is pulling it in the same direction as the blade is trying to throw it.

Router Table:

A kickback here is generally parallel to the fence, and to the right of the table.  Less likely to be directly at the operator (unless you happen to be standing down there).

Causes are many and varies again.  Incorrect feed direction is a biggie.  Feeding from the left, (or feeding in from the right but to the wrong side of the router bit), so the feed direction is in the same direction as the cutter is spinning.  A router loves to accelerate and propel pieces, like a small spinning wheel (but one that is going up to 20000 RPM!).  Tip speed of the router bit tends to be around the 150 km/hr.  Climb cutting is rarely a good idea.

I’ve had some other instances when a kickback has occurred, even though everything seems to be correct, and these are freaky, as they are completely unexpected.  Some I still haven’t been able to determine the cause, and have put them down to the router bit itself (one that I have chosen to retire).

Feeding too aggressively is also possible, or when starting a cut, engaging the router bit at the wrong angle can all be causes.

What is really scary about a router bit kickback, is its tendency to pull the operator’s hand towards the cutter.  A few kickbacks I’ve had on the router table, I’ve come away ashen faced, checking the hand to see if it is all still there. (The shock of the impact is quite explosive, and can leave the hand feeling numb, so you can’t actually tell if you’ve been cut or not).  I’ve not, but they have been very strong reminders that extreme care is definitely needed on these machines – the consequences of getting it wrong can be dramatic.

Thicknesser:

Not a common machine to kickback, but it is possible.  I’ve only managed it once – cutting a resawn piece of timber where I had gotten the resaw cut way to uneven, and the blade had managed to catch, rather than cut.  It is also possible when cutting something too thin, which can twist, and rise (especially the leading edge) into the cutter, hitting it at the wrong angle.

Thicknessers tend to be pretty good – some have antikickback fingers, and there is that leading roller that helps constrain the timber so it is cut rather than propelled.

Bandsaw:

Has teeth, can kickback.  However, the cutting direction is vertically downward, straight into the table so the result is pretty much a non-event (from a danger to operatior point-of-view).  The highest risk then is breaking the blade.

Lathe:

This is unusual, in that the workpiece is rotating, and the tool is not moving (the chisel).  It can still kickback though, particularly if you get the angle of attack wrong (or the one I had was……the skew chisel).  Instead of the workpiece flying at you, the lathe propels the cutting edge towards you (mainly down).  The main one I had was the skew, and it was like a firework going off with a loud bang.  Took me a few seconds to realise just what had happened, and I couldn’t feel a thing – my hand and arm were so numb from the shock it took quite a while to complete checking to see if I was in one piece.

Drill press:

Again, a bit unusual – the drill bit can grab the workpiece, so instead of cutting the workpiece becomes a helicopter.  As it rotates around rapidly, it will hit anything in its path, including the operator.

So that is just a brief overview of kickback, and some of the machines that can cause it.

One of the scariest events that can happen for a woodworker, because it is so fast, and dramatic (and there are definitely potential consequences!)

The next article will look at prevention.

Productive Days

Been a couple of rather productive days, which always feels good, recharges the batteries, keeps the electron population down and generally results in piles of sawdust!

For those that have been asking – yes, the pen turning video (and CA finish) has been shot, and is “In-the-Can” as they say.

Had a few successes, and a few failures, but that is also acceptable as it hopefully means something learned, and therefore less likely to be repeated.

One of the failures was actually the router bit of the month back in November last year – the Linbide Flush Trim Bit.  I cannot seem to use this bit without some colossal grabs, and kickbacks, and I’m starting to feel surprised by the number I’ve had, that I haven’t had a body part pulled into the cutter.  I don’t understand what is going on with it, as I came to a conclusion that I probably will shelve the bit for a good while (at least until the heart recovers (bloody good thing I installed a defibrillator recently!!)) before giving it one last attempt, and the benefit of the doubt.  However, given the number of startling grabs I’ve had with it, I returned to my old pattern copying bit (or straight cutter with bearing bit, however you want to call it), and with the same material, same approach etc etc, I didn’t have a single grab or scary moment.  I was starting to doubt myself there for a while – thought I’d lost my touch (and was quickly loosing my nerve), but it is the bit I tells ya.

Ran some more material through the drum sander tonight – this time some cyprus pine that I had resawed aways back.  I’m steadily becoming more and more impressed with the machine- it is achieving exactly what I was hoping it could do (but didn’t know as never having seen, let alone used one).

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