Table saw riving knife

[user 19915]

just a quick question should the table saw riving knife be the same highs as the blade or above or below ??? better safe than sorry
ALAN

 

[Steve Maskery]

You do have a bit of leeway on this, but it should be at least as high as the wood you are cutting. If it's higher it does matter. Obviously if you are making any kind of a non-through cut, then it must be fractionally below the top of the cut, otherwise the wood will hit it. (This practice, although historically commonplace, is no longer approved by the HSE, I believe)

The clearance between the blade and the RK should be in the range 3 - 8mm.

S

 

[Wizard9999]

Obviously if you are making any kind of a non-through cut, then it must be fractionally below the top of the cut, otherwise the wood will hit it. (This practice, although historically commonplace, is no longer approved by the HSE, I believe)

Steve

I have often wondered about fitting a knife that is below the top of the blade. My logic is that if I can make non-through cuts without removing the knife there is less risk that I will take it off and not put it back on - I know, I know, but I am at least realistic about what I might end up doing. However, I have alway puzzled as to whether there is actual benefit to having a riving knife in place, would be interested in our and the toughts of other experts.

As an aside, I think we have the same saw (older model Xcalibur) and I wondered if you have any idea on a source of spare parts. Buying a riving knife and cutting it down is the easiest way I can think of ending up with a shorter riving knife.

Terry.

 

[RobinBHM]

When cutting timber the saw blade must higher than the timber by a reasonable amount so as long as the riving knife is higher than the timber being cut it should still be acting as a safety device to prevent the timber closing up over the blade.

Some timbers have a large amount of tension which can result in significant binding on the riving knife. Ive had situations where the timber has tightened so much its taken a club hammer to get it off.

 

[Steve Maskery]

I have always puzzled as to whether there is actual benefit to having a riving knife in place, would be interested in our and the thoughts of other experts.

Terry, I don't want to sound rude, I really don't, but if you don't understand the importance of a RK then you should not yet be using your tablesaw. Get some proper training. You are almost certainly putting yourself at unnecessary risk in the way you are working. Short fences for ripping, pushsticks, featherboards. The RK is just one of an armoury of bits and pieces which help to keep me safe at my saw.

As an aside, I think we have the same saw (older model Xcalibur) and I wondered if you have any idea on a source of spare parts. Buying a riving knife and cutting it down is the easiest way I can think of ending up with a shorter riving knife.

I made mine from a piece of tool steel gauge plate. I did film it for my TS Safety DVD, but the footage did not come out and I did not have time to re-do it before being evicted. So unfortunately it is not on there.

I basically drew round the original, sawed it out and filed it to shape. You do have to be careful not to let it get hot, otherwise you can't work it. If I were to do it again I would put a polystyrene tray in the freezer, filled with water then when I cut out the new RK, put it on the block of ice and go at it with a jigsaw.

Don't be tempted to use mild steel, you'll never keep it flat, and once it is bent it is useless.

 

[user 19915]

Thank;s for that i can put my mind to rest now
Alan

 

[custard]

Obviously if you are making any kind of a non-through cut, then it must be fractionally below the top of the cut, otherwise the wood will hit it. (This practice, although historically commonplace, is no longer approved by the HSE, I believe)

Do you have a link for that Steve?

I'm surprised in that pretty much every Suva guarded saw I see in commercial workshops is set up that way, and I guess you could argue that Mitre Saws are effectively set up the same in order to allow trenching cuts.

I also see Felder (who are generally scrupulous about adhering to safety guidelines) are still marketing their "submerged cut" riving knife/splitter,

http://uk.feldershop.com/en/Sawing/Acce ... mm-FE.html

 

[Steve Maskery]

Hmm. I can't find it, which means I may be mistaken. I could have sworn I had read that tablesaws should not be used for none-through cuts. But the current HSE document only talks about not being used for STOPPED rebates. Maybe it was that and I misunderstood. If so, then apologies all round.

 

[custard]

Okay, you may still be right, the HSE aren't always as clear as they could be.

 

[Sgian Dubh]

just a quick question should the table saw riving knife be the same highs as the blade or above or below ??? better safe than sorry
ALAN

The answer really is ... it depends on the riving knife and blade configuration. In some saws the riving knife has the crown guard attached to it, e.g., the Hammer brand (Felder's lesser offerings), meaning the riving knife must sit higher than the blade in order to hold the crown guard. In the case of other manufacturers, e.g., Altendorf, the crown guard mounts on a separate arm, and the riving knife is set to just a hair below the tangent of the circle described by the rotating blade. So, again, it depends on what type of saw you have, and how the riving knife and crown guard are configured, and also depends on how closely you wish to follow HSE recommendations for safe table saw use. Slainte.

 

[Wizard9999]

I have always puzzled as to whether there is actual benefit to having a riving knife in place, would be interested in our and the thoughts of other experts.

Terry, I don't want to sound rude, I really don't, but if you don't understand the importance of a RK then you should not yet be using your tablesaw. Get some proper training. You are almost certainly putting yourself at unnecessary risk in the way you are working. Short fences for ripping, pushsticks, featherboards. The RK is just one of an armoury of bits and pieces which help to keep me safe at my saw..

Not rude at all Steve, but it was a spectacularly badly phrased post on my part .

What I meant to say was that I am puzzled by is the benefit of a riving knife when making a non-through cut. I see that SawStop supply a knife that sits below the blade and given they trade on a safety USP I have concluded there must be a benefit, however, instinctively I can't help thinking that as the timber is not cut through by definition in a non-through cut the normal benefit of a riving knife may be negated. However, as I say, I can see that a tangential benefit is that you would not be removing the riving knife for the non-through cut,so there would be no temptation to make subsequent cuts before it was fitted again.

Ultimately I am sure I can learn how to be safer in using my table saw and as mentioned on another post I fancied Peter S' machinery course, but it runs infrequently and is full until Easter next year now. However, I do understand the principle behind the use of the riving knife for through cuts, always use push sticks and feather boards when appropriate. I confess my biggest safety sin is not using a fence of appropriate reduced length when ripping. Any other recommendations on machining courses covering the usual suspect machines but excluding a spindle moulder.

Thanks for the info on making the riving knife. I also wnet for the obvious answer staring me in the face and dropped Alan at Woodford an email earlier today to ask if he can help.

Terry.

 

[Steve Maskery]

Ah, OK, I see. Fair enough.
Right, so why use a RK for non-through cuts? Well if the cut is shallow, I don't suppose it is doing anything at all, really. But if you were doing a non-through cut at full height, 3" say, (and that would scare me a bit, if I'm honest) I suggest that there would still be the possibility of the wood closing up on the RK at table level. As Robin has said, it is quite common for wood to close up on the RK (which is why we have them in the first place) or spring apart, pushing the workpiece away from the fence and into the blade (which is why we use a short fence for ripping).

 

[Wizard9999]

Ah, OK, I see. Fair enough.
Right, so why use a RK for non-through cuts? Well if the cut is shallow, I don't suppose it is doing anything at all, really. But if you were doing a non-through cut at full height, 3" say, (and that would scare me a bit, if I'm honest) I suggest that there would still be the possibility of the wood closing up on the RK at table level. As Robin has said, it is quite common for wood to close up on the RK (which is why we have them in the first place) or spring apart, pushing the workpiece away from the fence and into the blade (which is why we use a short fence for ripping).

That makes perfect sense Steve. Guess I never really think about non-through cuts of that sort of depth, I am usually thinking of something of just a handful of millimetres, but I can see exactly what you are saying about something if it were that deep. I guess the other factor is how deep the cut is relative to the depth of the item being cut, the closer it is to a through cut instinctively I would guess the greater the risk as there is less 'meat' holding the shape of the wood.

Thanks again.

Terry.