Replies

1. 
   JohnWW | Mar 27, 2007 04:31pm | #1

   You probably mean "pawls", those curved and toothed spring loaded parts on either side of the splitter.  They are there to prevent wood from being kicked back, which is primarily a problem that occurs when ripping.  The splitter, with or without the pawls, serves little to improve safety when crosscutting unless the piece being crosscut is especially large. 

   So the answer is yes, you can remove the pawls without significantly degrading your safety when crosscutting with a sled. BUT with the pawls removed, the chances of a kickback increase when you are ripping unless you reinstall the the pawls on the splitter after you have finished using the sled.

   John White, Shop Manager, Fine Woodworking Magazine 

1. 
   woodman2263 | Mar 27, 2007 04:46pm | #2

   John,

   If I have the splitter in there without the paws, doesn't it make it darn near impossible to kick back with the splitter acting like a riving knife?  I know you have to proceed with caution on this subject, but I would believe that the splitter acting like a riving knife would make it impossible for the material to catch the back of the blade?

   Isn't that your thoughts?

   Jeff

1. 
   JohnWW | Mar 27, 2007 05:17pm | #3

   Jeff,

   This is the critical difference between an American style splitter and a true riving knife.  Your splitter doesn't shield the teeth on the back and the top of the blade nearly as well as a riving knife.  This is especially true when the blade is set at just an inch or so of blade height, which is most of the time when cabinetmaking. 

   At low blade heights there can be several inches of space between the blade and the splitter, more than enough for a piece of wood to swing into the rear teeth of the blade and then grabbed and thrown at the operator or pulling a poorly positioned hand into the blade. 

   With a riving knife, the space between the knife and the blade is under 1/8", no matter what the blade height, and it is almost impossible to get a high speed kickback since the blade's teeth just can't get enough purchase on the wood.

   I know that when looking at them, there doesn't seem to be much of a difference between a riving knife and a splitter, but a riving knife is a significant safety improvement over a splitter.  It is a shame that it is only now showing up on machines other than high priced European saws sold in the U.S.

   John White 

1. 
   SgianDubh | Mar 27, 2007 08:28pm | #4

   "With a riving knife, the space between the knife and the blade is under 1/8", no matter what the blade height, and it is almost impossible to get a high speed kickback since the blade's teeth just can't get enough purchase on the wood."

   The riving knife is not usually set quite that close John. Regulations over here in the UK say the knife should be within (I think) 8 mm of the teeth.

   To back up the latter part of your quote above, I can vouch from personal experience that a riving knife will not prevent every kickback. Occasionally a piece of timber will pinch so tight that not even a riving knife will save you. However, cutting a piece containing such serious stress within it means it usually pinches on the blade very early in the cut, but not always.

   With such a strong clue given that early in the cut no experienced worker proceeds. But inexperienced ones sometimes do, to their soon to follow  trouser located (sometimes)double sphincter loosening experience, ha, ha. Slainte.  Richard Jones Furniture

1. 
   JohnWW | Mar 27, 2007 09:36pm | #5

   Mr. Jones,

   "Within 8 mm" means that the 8 mm is a maximum, and less is allowable.  The Sawstop manual calls for a gap of only 2 mm, just slightly more than 1/16".

   John W.

2. 
   SgianDubh | Mar 27, 2007 10:37pm | #6

   Very true John. Less is allowable as you say. In practice riving knives often don't exactly match the curve of the blade.

   For example, most of the saws I've used would, or will, accept sawblades ranging in a diameter band somewhere between about 250 (10") and 450 mm (18".) A typical range of saw blade diameters fitted to machines I'm familar with is between 300 mm and 400 mm (12"- 16"). The inside curve of a single riving knife can't match the curve of  all the blade diameters the machine will take.

   For instance, if the 'normal' sawblade fitted to a SawStop is of 10" diameter the standard riving knife may have been made to match that circumference precisely. But what happens if the user fits a 9" or 8" diameter blade? Or a 12" diameter blade assuming one will fit on a SawStop, something I freely admit I don't know?

   The riving knife would have to be fitted as best it could to the blade profile, which usually results in a bigger gap than 2 or 3 mm in places. After my last post I checked the UK regulations, and the maximum gap permissible at table level is 8 mm. The OSHA regs in the US might specify something different.

   Anyway, all I'm saying is that it is rare in my experience that a riving knife can be fitted to a bench saw where the inner curve precisely matches the curve of a sawblade, so I suppose this is why a bit of wiggle room is possible (in the UK regs). On the other hand a bespoke riving knife could be fabricated to match the diameter of every blade fitted to a saw. I don't think I've ever seen anyone go to that length, but I suspect someone has made an extra riving knife or two for their machine. Slainte.

   Richard Jones Furniture

   Edited 3/27/2007 3:39 pm by SgianDubh

3. 
   JohnWW | Mar 27, 2007 11:16pm | #7

   Slainte,

   The Sawstop is limited to using only 10" saw blades since a smaller blade wouldn't engage the brake cartridge properly.  The electronics of the saw will detect a smaller than 10" blade and lock out the power, so cheating isn't allowed.  The arc of the saw's riving knife is a very close fit to the blade's circumference over the full arc, so in comparison to the Euro machines it may offer better protection.

   The Sawstop does accept an 8" dado set with a matching brake cartridge but there is no need for a riving knife when using a dado set.

   John W.

4. 
   SgianDubh | Mar 29, 2007 12:56am | #11

   That clears that question up then John. The riving knife on a SawStop saw only has to match one blade diameter. Thanks for clearing that up for me. Slainte.Richard Jones Furniture

2. 
   BarryO | Mar 27, 2007 11:33pm | #8

   FWIW, the pawls on the Biesemeyer splitter are easy to remove and install; I take them off and put them back on as needed.

1. 
   Elcoholic | Mar 28, 2007 12:13am | #9

   Not me I cut them off completely.John O'Connell - JKO Handcrafted Woodworking

   The more things change ...

   We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized.  I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.

   Petronious Arbiter, 210 BC

1. 
   SARGEgrinder47 | Mar 28, 2007 04:43pm | #10

   It is my opinion that neither a riving knife or a splitter offer the maximum safest operating conditions when they stand alone. There purpose is to aid stress stock staying separated avoiding closing past the cut that would pinch the blade. As RJ stated, that could happen earlier in the cut if enough stress and that stock should be avoided.

   But under normal circumstances, if kick-back does occur.. what feature does the riving knife or splitter offer that stops the stock from being launched upward? I have never seen a splitter or riving knife that extends to at least center point of the blade.  I personally think that to be a short-coming in maximum protection considering under the most ideal conditions, kick-back can still occur.

   And.. you have not maximized in what you can do to block stock by limiting the directions it can be launched. The riving knife or splitter has not covered "upward" launch. So the pawls act as a block and keep it from riding up!

    But... but.. after having a pawl drop on my finger and almost sever it (the saw was off and the plastic shield raised to change blades) I will not use them period. I've marred some good stock with those sharp pawls and another reason I condemn them.

   The problem IMO can be solved simply enough with either a riving knife or splitter (considering that the splitter is wide enough) by drilling two holes in it and adding a crown guard to block stock in kick-back from launching upward. Anyone that is capable of making a piece of furniture should be able to make such a simple retro-fit addition. And worth the time I feel. I'm sure there is a piece of hard-wood scrap in your short bin at the moment that is just waiting to serve this useful purpose. If you don't have a crown guard, I would persoanlly ask why not?

   Regards...

   Sarge.. jt

    

   
1. 
   SgianDubh | Mar 29, 2007 01:06am | #12

   Sarge, riving knives come in two common patterns here in the UK.

   The first is the classic tapered dagger shape. A crown guard sits over it mounted on an arm that is attached somewhere off to the right of the machine as seen from the infeed end.

   The second type of riving knife has a large top with bolt holes to which an integral crown guard attaches. This resembles the pattern you created. This type is shown in the attached image. Slainte.Richard Jones Furniture

   
1. 
   SARGEgrinder47 | Mar 29, 2007 07:11am | #13

   Morning to ya, Richard...

   Thanks for the photo. I do believe it may be the one I saw you posted several years ago that got me interested in crown gauds to begin with. You had a pic of you standing behind that "monster" TS (a Wadkins 12 HP if I remember correctly) ripping what appeared to be 16/4 stock in your former shop in Houston.

   Same scenario with the Euro short fence which you notice I built and retro-fitted over a Biesemeyer in that same photo-graph. Easy to make and retro-fit IMO and I won't operate the saw anymore without either as both are a better way to proceed as I see the world turn.

   As with many things.. change takes time. But with time things change....

   Regards...

   Sarge.. jt

   Edited 3/29/2007 12:13 am ET by SARGEgrinder47