Riving Knife Height

[woodshavings]

Is there any reason why the riving knife has to be higher than the blade?
On my W650, it's about 20mm above the top of the blade. I want to modify it so it is level with the blade and not have to remove it when trenching.
I asked Charnwood why it was above the blade, they said it was because of H&S.
I cannot see why it will be any less safe, there really a safety issue?
John

 

[jimi43]

Did it have a guard attached to it? How is your guard fitted?

 

[Anonymous]

no reason apart from H & S laws.

In America they use a stub like riving knive on a lot of machines i have seen.

 

[devonwoody]

I have adjusted my riving knife fitting so that it can be both above or below blade level.

However this does give rise to safety issues. It means that if the knife is not at its supplied position you are at greater risk of getting kick backs.

 

[Jeff Gorman]

Fig 5 of the HSE Information sheet at http://tinyurl.com/pywalm shows the riving knife just level with the crown of the saw.

I think we can take this as sound and authorative advice based on the experience of Factory Inspectors through the years.

Jeff
www.amgron.clara.net

 

[jasonB]

Fig 5 of the HSE Information sheet at http://tinyurl.com/pywalm shows the riving knife just level with the crown of the saw.

I think we can take this as sound and authorative advice based on the experience of Factory Inspectors through the years.

Jeff
http://www.amgron.clara.net

Thats provided the saw has an SUVA type overhead gaurd as if the gaurd fixes to the knife it will need to reach above the blade.

Also just below Fig 6 it states that at all times the blade should protrude above the top of the work and then goes on to say a table saw should not be used for rebating & grooving. You should not take one bit of advice and ignor the other.

J

 

[Steve Maskery]

I see absolutely no reason whatsoever why it has to be 20mm above the blade to be an effective RK. It may, of course, need to be 20mm above the blade to support the blade guard, depending on the design of the guard arrangement.
I've scrapped the RK and guard that came with mine. I use a thin-kerf blade a lot of the time, anyway, so the RK that came with the saw is incompatible. And I have a selection of guards for different operations. I usually use my SUVA-style guard but have a magnetic free-standing guard for times when the SUVA gets in the way. My tenon jig has guarding built into it.

I'm currently making a film about tablesaws and it's interesting looking at RKs and guards from different manufacturers. The RK hasn't changed much in decades, as far as I can see. I see the fact that new saws in the US now have to have a proper RK as fantastic news. I think it will mean an improvement in design which will trickle down to us. I mean, Good Grief, they'll be using guards next!

Cheers
Steve

PS Jason, whilst I agree with you, the same document clearly shows rebating being done with Shaw guards:
"unless the blade is effectively guarded".

 

[woodshavings]

Did it have a guard attached to it? How is your guard fitted?

The guard is attached to the riving knife. This detaches without tools (a knurled knob retains it) and would need to be removed for grooving/trenching.
My plan is to replace it with a shop made overhead guard, magnetically attached to the bed, when trenching.

Steves forthcoming video about tablesaws sounds very interesting - look forward to seeing it.

John

 

[jimi43]

Did it have a guard attached to it? How is your guard fitted?

The guard is attached to the riving knife. This detaches without tools (a knurled knob retains it) and would need to be removed for grooving/trenching.
My plan is to replace it with a shop made overhead guard, magnetically attached to the bed, when trenching.

Steves forthcoming video about tablesaws sounds very interesting - look forward to seeing it.

John

Well, that's the reason why the guard did protrude above the blade....not for any other reason than to hold that type of guard. There is no need for a riving knife to protrude above the blade to work.

As Steve says...the SUVA guard is a fine design but I would keep the riving knife in place...to prevent kickback.

Jim

 

[Steve Maskery]

Ah, Jimi, when I said I scrapped the RK that came with mine, I meant that I'd replaced with a separate one. I didn't mean I don't use a RK....

S

 

[jimi43]

Ah, Jimi, when I said I scrapped the RK that came with mine, I meant that I'd replaced with a separate one. I didn't mean I don't use a RK....

S

I though that a tad strange Steve, given your view on safety in general but I thought maybe the epic journey into video production again must have addled your grey cells slightly and that I better clarify the statement for the OP in case there was a temptation to chuck that away as well!

Looking forward to seeing the video.

Jim

 

[woodshavings]

Many thanks guys - very useful....
The RK design could continue to support the guard but still allow adjustment downward when needed. Of course, the guard would be removed and swapped for a alternative one when using this configuration.
John

 

[jimi43]

You probably know already John but I will tell you anyway just in case...

The riving knife for your saw would have been designed for use with the blade that came with it.

A riving knife should be of a thickness that falls between the thickness of the blade kerf (the cut) and the land (the body of the blade at the thinnest part).

This means that when the stock is cut it will pass by the riving knife but if it were to close up, it will pinch against the riving knife and not the body of the blade...the main cause of kickback.

It then stands to reason that if you put a thin kerf blade on...it will not pass the riving knife and if you put a thicker bodied blade in the closing stock will close on the body of the blade and not the riving knife...rendering it useless with such a blade.

Also...if you are making a riving knife...make sure the leading edge is double bevelled so that the cut is guided into the knife easily and ensure that the mounting bolts are firm and have spring washers to prevent vibration loosening the knife.

Jim

 

[Steve Maskery]

Lots of good advice

S