Table saws: is kickback feasible with a riving knife?

[sploo]

I've just bought my first table saw (an Axminster TS-200) and whilst I've been using a variety of tools and machinery for years, I've no prior experience with table saws.

Obviously a good percentage of the info out there on the web is US centric; which tends to mean no riving knife, and the blade guard "removed for clarity" (*cough*). I've read (and watched) plenty about the perils of kickback, but I've not seen a single instance of someone claiming they got a kickback with a riving knife present.

I suppose it might just be possible (especially if you tried to induce it), but, assuming your fence is acceptably parallel, the blade isn't wobbling, and the knife is correctly installed, is there a scenario where kickback may occur? The only one I can think of would be for material to pinch the rear side of the blade before it gets as far as the knife, but I assume that'd require extreme movement from the material being cut.

On a mildly related subject; with the guard installed on the knife on the TS-200, you can't get a full depth of cut. Other than the simple fact the blade would be exposed, are there any particular extra dangers of removing the guard (but not the knife) in order to do a full depth cut? I'm thinking of something other than the obvious extra load on the machine due to the depth - i.e. are issues of kickback (or something else) more likely?

Finally, if I were to modify a riving knife so that it was about 1mm below the top of the blade (such that I could cut thin dados or box joints) are there any particular extra safety issues? (other than the fact there would be no guard, and there would be a tiny amount of the top of the saw that was not being shadowed by the knife)

Advice from people with both the full compliment, and fewer than the full compliment, of fingers greatly appreciated :wink:

 

[Rhossydd]

if I were to modify a riving knife so that it was about 1mm below the top of the blade...are there any particular extra safety issues? (other than the fact there would be no guard,

It is possible to guard such situations with various solutions.
I posted details of how I worked round it alternative-guarding-for-ts200-when-tenonin-t80835.html and it has worked well for me in the last year.
Not a perfect solution, but in an amateur workshop used by just one person it helps.

 

[blackrodd]

The timber, being cut on you're saw will not necessarily bow or distort in an even fashion, it will, and can, clip or pinch the saw blade commonly at each end of the timber being sawn and anywhere else, along it's length too!
Always stand to one side, when sawing and allow no person to be behind you, effectively"in the firing line"
It doesn't happen very often, but it makes the old pump go.
And it can be a bit scary.
If you can't hold the piece, Just Hit the red button!
Then you can hang on or let go, either way, as you will be in a safe situation.
Regarding the riving knife, you will probably, at some stage be using smaller or different blades, so no, I don't think it is safe to cut the riving knife. make smaller ones, to suit different blades.
I treat each alteration as a "Setting up"and as such always return to original and safe standard set,
HTH Regards Rodders

 

[SteveF]

i remember a long time ago cutting some ply
knife was in place
it "kicked" back at such a force my testicles were black for weeks
never did work out what happened or what i did wrong..if anything
so yes it can happen

Steve

 

[sploo]

if I were to modify a riving knife so that it was about 1mm below the top of the blade...are there any particular extra safety issues? (other than the fact there would be no guard,

It is possible to guard such situations with various solutions.
I posted details of how I worked round it alternative-guarding-for-ts200-when-tenonin-t80835.html and it has worked well for me in the last year.
Not a perfect solution, but in an amateur workshop used by just one person it helps.

Nice idea - thanks. I have thought about adding a guard on an arm that comes down from the ceiling. It occurs to me that a guard attached to the riving knife would be very difficult for a kickback to lift off completely (allowing the material to ride over the top of the blade), whereas one hanging over it would move more easily. However I'm assuming the guard is mostly there to stop you accidentally getting your hand on the blade from the top or side, so either design should fulfil that purpose.

...Regarding the riving knife, you will probably, at some stage be using smaller or different blades, so no, I don't think it is safe to cut the riving knife. make smaller ones, to suit different blades.
I treat each alteration as a "Setting up"and as such always return to original and safe standard set,
HTH Regards Rodders

Yep. It's my plan to buy several riving knives (assuming Axy will sell me them as spares) and make a few for each application. I suspect that 99% of the time I'll have the standard knife on (plus guard). With a knife that's been ground to just below the height of the blade (for cutting over the top of the blade) I'm struggling to think of any scenario where you'd ever need to completely remove the knife (which is a good thing).

I suppose there's Matthias Wandel's idea of running plywood over the blade from the back of the saw (http://woodgears.ca/shop-tricks/tearout.html) to mimic a scoring blade, before setting a full cutting depth and ripping. However, he was talking about only doing a 1mm deep cut, so I guess even that could work with a ground knife present.

 

[RobinBHM]

Yes kickbacks can occur, solid timber can have a lot of tension and bow in towards back edge of saw blade even with a riving knife. The likelihood of a severe kickback on the rear of the blade is very much reduced with a riving knife, Ive found severe pinching can tighten up on the riving knife so much it takes a hammer to get the wood off.

A riving knife wont stop wood getting trapped between blade and rip fence and flying back like an arrow. Less likely if the rip fence stops in line with the gullet of the saw blade at the front.

Ive found osb board quite lively when cutting so even man made boards need care.

 

[blackrodd]

I suppose that the lesser of two evils would be to have the riving knife HIGHER, than the saw, but allowing for the guard to be bolted just "in the clear" of the top of the saw, but in the normal fashion.
Then you have the benefit of the base of the guard still stopping the piece from "hinging" and hitting you in the face, but it would allow for any cuts as maximum height to be easily made, if this is an issue.
we should also remember that various blades, made for specific materials, are, sometimes different thicknesses, so in effect using the wrong thickness riving knife, which is also a potential hazard.
Regards Rodders

 

[worn thumbs]

There is a reason why riving knives have to be in place when professionals use saws.Even they still suffer minor kickbacks with riving knives and without riving knives the power of a professional saw can kill.Americans,bless them,are immune to the laws of physics and appear to regard the use of riving knives and guards as an admission of unmanliness.But they do obsess about the brand of fence and never have applied the same effort to developing riving knives and crown guards.They also seem to regard woodwork as an excuse to buy tools-but only tools with switches.

 

[Rhossydd]

Yep. It's my plan to buy several riving knives (assuming Axy will sell me them as spares) and make a few for each application

I'd be surprised if Axi had any significant stocks of riving knifes as spares. I just bought some steel plate off eBay and cut my own. Easy if you have a jigsaw with a metal cutting blade.

 

[Ed Bray]

I bought some brass plate the same thickness as my blade to make a replacement riving knife. Used a metal gutting blade in a coping saw and then filed it down and used my bobbin sander to match the patten, I also used the scrolling trick of sticking thin plywood to each side to protect the brass whilst cutting.

 

[heimlaga]

Theese are my safety precautions. The saw is fairly powerful with 5 hp three phase motor and 400mm blade.

-An overarm guard that is easily adjusted in height.
-A riving knife that does not protrude above the blade. This because any guard that has to be removed for certain operations has a tendency to not get replaced for "only this cut". I know myself and have to make precautions according to that knowledge.
-An emergency stop that is easy to reach.
-A pusch stick that is made from plywood so it doesn't splinter.
-A short fence attachment used when resawing or ripping any wood that seems to have a lot of stress in it. I also use it together with the sliding table when I maker shoulder cuts on tennons. This prewent the offcut from being pinched between the blade and the fence. Some newer saws have a fence rail that can be slid back for this type of cuts.
-A guard which encases the blade below the table.
-A brake to stop the blade after sawing
-A special wrench to lock the shaft with when tightening the blade nut. I don't feel good jamming something against one of the brittle carbide teeth.
-When ripping heavy stock I always set the blade as high as possible in order to decrease the vertical force on the wood. Then I lower the guard around it.
-Our vocational school teacher (rest in peace) told us that a man who stands in the direct line of fire when ripping two inch slabs does not need his testicles anyway because he will be too stupid to function as a husband and father.
I am trying my best to prove that I belong to the more intelligent of the two cathegories :roll:

This is my way........ others do things differently..... and the Americans seem to rely on good luck and small motors to reduce the damage. Our present European safety standards tend in my oppinion to rely a bit too heavily on CE-markings and manufacturer's own apporovals and declarations of conformity.
I find certain approved guards like for instance the riving knife mounted self destructing plastic crown guards to be too risky for my taste....... but that is just me.

 

[marcros]

I bought some brass plate the same thickness as my blade to make a replacement riving knife. Used a metal gutting blade in a coping saw and then filed it down and used my bobbin sander to match the patten, I also used the scrolling trick of sticking thin plywood to each side to protect the brass whilst cutting.

Is brass a suitable riving knife material? I always believed not, but may have been mislead...

 

[Rhossydd]

Is brass a suitable riving knife material? I always believed not, but may have been mislead...

It wouldn't be (wasn't) my choice.

 

[blackrodd]

Theese are my safety precautions. The saw is fairly powerful with 5 hp three phase motor and 400mm blade.

-An overarm guard that is easily adjusted in height.
-A riving knife that does not protrude above the blade. This because any guard that has to be removed for certain operations has a tendency to not get replaced for "only this cut". I know myself and have to make precautions according to that knowledge.
-An emergency stop that is easy to reach.
-A pusch stick that is made from plywood so it doesn't splinter.
-A short fence attachment used when resawing or ripping any wood that seems to have a lot of stress in it. I also use it together with the sliding table when I maker shoulder cuts on tennons. This prewent the offcut from being pinched between the blade and the fence. Some newer saws have a fence rail that can be slid back for this type of cuts.
-A guard which encases the blade below the table.
-A brake to stop the blade after sawing
-A special wrench to lock the shaft with when tightening the blade nut. I don't feel good jamming something against one of the brittle carbide teeth.
-When ripping heavy stock I always set the blade as high as possible in order to decrease the vertical force on the wood. Then I lower the guard around it.
-Our vocational school teacher (rest in peace) told us that a man who stands in the direct line of fire when ripping two inch slabs does not need his testicles anyway because he will be too stupid to function as a husband and father.
I am trying my best to prove that I belong to the more intelligent of the two cathegories :roll:

This is my way........ others do things differently..... and the Americans seem to rely on good luck and small motors to reduce the damage. Our present European safety standards tend in my oppinion to rely a bit too heavily on CE-markings and manufacturer's own apporovals and declarations of conformity.
I find certain approved guards like for instance the riving knife mounted self destructing plastic crown guards to be too risky for my taste....... but that is just me.

I was taught that When cutting, the saw blade should be as low as possible so as to have as many teeth sharing the work, and therefore cutting smoothly.
Also when the saw blade is higher it can gather some awesome power to heave the timber back at you, where as when the saw blade is lower, forming a lower arc and therefore, the power, is lessened. you can see both the principles with the aid of a matchbox and a two pence coin.

A saw bench of that size will likely have a pin about 1 1/4" above the blade centre especially when left hand thread, to stop that nut turning!
when fitting a new blade, believe it or not, the prescribed method is to gently push the blade against the pin, fit large washer, which also covers the pin, and then the nut, fit the really large ring spanner on the hand tightened nut, and belt the spanner with the wooden mallet or club, band sawn for this very purpose while just holding the saw. A clean bolt or piece of 2"x !/2"in the gullet, would hold the smaller saw, a pencil will hold an 8" bladefrom the gullet!
Regards Rodders

 

[sploo]

A riving knife wont stop wood getting trapped between blade and rip fence and flying back like an arrow. Less likely if the rip fence stops in line with the gullet of the saw blade at the front.

I must admit I've felt uncomfortable about using a shorter fence when ripping a sheet - simply because of the risk of the stock twisting against the non-existent fence. How do you prevent the sheet turning towards the fence as you feed the last bit in (when there's now very little material running along the fence)?

I suppose that the lesser of two evils would be to have the riving knife HIGHER, than the saw, but allowing for the guard to be bolted just "in the clear" of the top of the saw, but in the normal fashion.
Then you have the benefit of the base of the guard still stopping the piece from "hinging" and hitting you in the face, but it would allow for any cuts as maximum height to be easily made, if this is an issue.

That would make a lot of sense, and I assume the reason the standard knife isn't high enough on the TS-200 is because it wouldn't allow it to drop below the table for transport. Though you obviously need to remove the guard in order to do that, so you're having to find a spanner anyway (though that is granted easier than removing the riving knife).

I'd be surprised if Axi had any significant stocks of riving knifes as spares. I just bought some steel plate off eBay and cut my own. Easy if you have a jigsaw with a metal cutting blade.

Just ordered 5 :wink: (not all for me, a few are for someone else with the same saw)

I plan to cut a slot by the guard mounting hole so I can more easily lift the guard off for full depth cuts; more specifically, it's then trivial to put it back, so you don't do "just that one cut without the guard" when you didn't need to. I also plan to grind one so it's a couple of mm below the blade height, so it's possible to do (an admittedly thin) dado. Might be useful for box joints, though I've no immediate plans in that regard.

I was taught that When cutting, the saw blade should be as low as possible so as to have as many teeth sharing the work, and therefore cutting smoothly.

That's always been my understanding - the minimum height necessary to make the cut. In fact, that's one of the criticisms of the TS-200 guard mount - because it fouls the top of the blade you always need to have the blade quite a bit higher than you would if the guard wasn't attached to the knife. I guess a separately mounted guard would solve that. Or fabricate your own (taller) guard.

 

[blackrodd]

The riving knife thickness should be a smidge less, than the saw kerf, should you have different blades for different materials, most seem to be able to get away with using two different thickness of riving knives.
Some saw benches, are supplied with two riving knives for this reason.
As I said earlier a riving knife made and used with the guard bolted on top and enough clearance under to allow maximum cut, thus removing the "need" to use the saw without adequate guarding in place.

Do try and allow the teeth gollet to "clear" the stock being sawn when at all possible as this can cause the blade to heat up and as the sawdust cant get out quick enough, and, in reality a lot more dust is produced!

The rip saw blade, should have the fence just stopping at the "root" of the blade at the gullet and at the same time, the fence should slightly "lead" towards the saw blade, thereby stopping the blade under cutting stock, by size, as there is a gap between the stock and fence, on the other extreme.
And a longer fence can be used for sheet material, again sometimes supplied with the machine.
Regards Rodders

 

[sploo]

The riving knife thickness should be a smidge less, than the saw kerf, should you have different blades for different materials, most seem to be able to get away with using two different thickness of riving knives.
Some saw benches, are supplied with two riving knives for this reason.

All the blades I've seen for the TS-200 are 2.2mm kerf (either 200 or 205mm dia). I suspect the saw doesn't have enough grunt to run anything thicker - though that at least makes the knife selection trivial.

The extra knives have arrived, and whilst I haven't tried them they look ok - bare instead of painted, and the hole for the guard is drilled in a slightly different place, but the important stuff (the curve, height, and slot to fix to the machine) are identical. Thickness is the expected ~2mm.

As I said earlier a riving knife made and used with the guard bolted on top and enough clearance under to allow maximum cut, thus removing the "need" to use the saw without adequate guarding in place.

Yea, that's a good point. I don't have any suitable steel (or metal working gear, other than a 9" angle grinder) but I suppose I could probably get something and fashion a taller knife. Problem is I'm planning on incorporating the saw into a larger table (that will also be the router table). I'll need to be able to drop the blade + knife under the table for some router operations, so a standard knife would be better. Perhaps an overhead ceiling mounted guard would be in order.

Do try and allow the teeth gollet to "clear" the stock being sawn when at all possible as this can cause the blade to heat up and as the sawdust cant get out quick enough, and, in reality a lot more dust is produced!

Understand gullet, but trying to visualise what you mean by "clear" the stock? Do you mean that the teeth should come out of the top of the stock sufficiently that you'd just see the gullet of those teeth?

The rip saw blade, should have the fence just stopping at the "root" of the blade at the gullet and at the same time, the fence should slightly "lead" towards the saw blade, thereby stopping the blade under cutting stock, by size, as there is a gap between the stock and fence, on the other extreme. And a longer fence can be used for sheet material, again sometimes supplied with the machine.

By "lead" I assume you don't mean "at an angle" (i.e. the fence is still square to the saw)?

 

[blackrodd]

Sploo, the finer teeth saw kerf, mainly for man made materials will probably be less than a rip saw, though, much depends on the maker and price.

Can't you use one of the riving knives you already have and just bolt the guard to the top of that and adjust the saw clearance?
Yes, the saw will perform best when the saw blade gullet just clears the stock, and the most teeth are cutting, many saws instructions will advise this. but if you're guard is in place, should be difficult to see.

The fence should should lead, as in, head in the direction of the saw blade, just enough to keep the saw effectively cutting a straight line, possibly in the same token as the to-in of a car's steering.
when you can cut a piece of timber,parallel, without any back sawing at the riving knife, and no gap at the fence, That's it! Regards Rodders

 

[Jacob]

Theese are my safety precautions. The saw is fairly powerful with 5 hp three phase motor and 400mm blade.

-An overarm guard that is easily adjusted in height.
-A riving knife that does not protrude above the blade. This because any guard that has to be removed for certain operations has a tendency to not get replaced for "only this cut". I know myself and have to make precautions according to that knowledge.
-An emergency stop that is easy to reach.
-A pusch stick that is made from plywood so it doesn't splinter.
-A short fence attachment used when resawing or ripping any wood that seems to have a lot of stress in it. I also use it together with the sliding table when I maker shoulder cuts on tennons. This prewent the offcut from being pinched between the blade and the fence. Some newer saws have a fence rail that can be slid back for this type of cuts.
-A guard which encases the blade below the table.
-A brake to stop the blade after sawing
-A special wrench to lock the shaft with when tightening the blade nut. I don't feel good jamming something against one of the brittle carbide teeth.
-When ripping heavy stock I always set the blade as high as possible in order to decrease the vertical force on the wood. Then I lower the guard around it.
-Our vocational school teacher (rest in peace) told us that a man who stands in the direct line of fire when ripping two inch slabs does not need his testicles anyway because he will be too stupid to function as a husband and father.
I am trying my best to prove that I belong to the more intelligent of the two cathegories :roll:

This is my way........ others do things differently..... and the Americans seem to rely on good luck and small motors to reduce the damage. Our present European safety standards tend in my oppinion to rely a bit too heavily on CE-markings and manufacturer's own apporovals and declarations of conformity.
I find certain approved guards like for instance the riving knife mounted self destructing plastic crown guards to be too risky for my taste....... but that is just me.

The only thing missing is a second push stick! I always use two - one to hold it in and the other to push it along. After a bit it becomes second nature. It also makes you more dexterous - they are like arm extensions and give you extra reach and a longer pass without having to change hand position.

 

[Graham Orm]

Yes. It's happened to me. Kickback happens very fast and with a lot of force. Assume it WILL happen EVERY time you use the saw riving knife or not.