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!

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