Thread: Jet JWCS-10 Riving knife

Aluminium can makes good thin shim material, especially beer ones.
A few help the thought process sometimes
H.

Margarine containers and similar plastics can be used to make spacers, easy to cut with scissors or craft knives. Another good source of spacers and shims is old Xray films, very useful in the workshop.

Alan...

when I bought my contractor saw about 5 years ago there was a thread about making one that fitted and worked with the existing rise and fall, If I remember correctly the fellow that designed and made it would provide a printed template. It was made for a Hare and Forbs saw and looked like it would be OK I never went any further with it but if you scroll back through the threads you mite get some ideas.

Cheers. Rick.

I have done a bit of searching and found it, good photos and details. Retrofit Riving Knife for the Hafco SB12

Originally Posted by Rick47

I have done a bit of searching and found it, good photos and details. Retrofit Riving Knife for the Hafco SB12

When I look at this post there's no link, but if I click 'Reply With Quote' the link is there. That's weird.

Ahh, the link has been added after I opened the page.

Retrofit Riving Knife for the Hafco SB12

Originally Posted by aldav

When I look at this post there's no link, but if I click 'Reply With Quote' the link is there. That's weird.

Ahh, the link has been added after I opened the page.

There wasn’t a link originally, just a date, page no and username, so I went and found it and then edited with a link

Originally Posted by Rick47

when I bought my contractor saw about 5 years ago there was a thread about making one that fitted and worked with the existing rise and fall, If I remember correctly the fellow that designed and made it would provide a printed template. It was made for a Hare and Forbs saw and looked like it would be OK I never went any further with it but if you scroll back through the threads you mite get some ideas.

Cheers. Rick.

I have done a bit of searching and found it, good photos and details. Retrofit Riving Knife for the Hafco SB12

Although I applaud his ingenuity there's an awful lot of work involved in fitting the riving knife. Leaving aside fashioning the various components you have to pull the entire saw apart to fit it and putting it back together necessarily involves realigning the saw blade to the mitre slots. For anyone who has never had to do this on a contractor saw I can assure you that it is a complete PITA, once done you never want to touch it again. Although I'm happy to acknowledge that you get a superior result if you fit the riving knife I'm unconvinced that it's sufficiently better to encourage me to forsake the splitter attached to the rear trunnion alternative, which would appear to be quicker and a hell of a lot easier. I guess it's horses for courses.

I got my 12" contractor saw in 2006 and removed the stock splitter/OH guard a few months later as I wanted to improve OH dust extraction. I replaced the guard with a stock Big Gulp Hood on a stock Dust Picker arm. I also added a 1mm thick Polycarbonate (PC) shield to the hood so that it fully covered the blade and slo I could see what was going.
IMG_4864.jpg

For the decade or so I had this setup, the lack of a riving knife meant that the blade did sometimes grab the workpiece, there would be a loud bang and teh hood would shake violently but when the guard was fully covering the blade no serious kick back out towards the operator eventuated. This is probably because a blade fully covering the work piece prevents the workpiece from rising up to the highest point of the blade above the table. Its at this point that maximum forward thrust is generated and what makes kickback so dangerous

If the piece was short enough so's it was not held down at the back of the blade by the guard, when the workpiece grabbed and did manage to rise to the top of the blade the hood still aways managed to contain the workpiece. On one occasion the workpiece did slam into the inside front of the shield so forcefully it rotated the hood so that the back of the PC shield did make contact with the blade and it cut a neat 50mm long vertical slot in it. This is why PC is one of the best transparent materials to use as using something like Acrylic could shatter.

In ~2015 I started doing air flow tests on hoods and found that opening up the back the hood allows more air to enter the hood and extract more dust I made several hoods with fully open backs. This open hood back does not hold the workpiece down on the table as well as the old hood did so it became possible for the workpiece to rise up further on the blade and increase the seriousness of kickback. This effect is counteracted by the fact that the hood is somewhat heavier than the old hood and the back angled hood front and swing arm hood action actively prevent the workpiece from taking off. Provided my hood is in contact with the workpiece it can be very difficult to pull the wood backwards out of the cut and I have to reach fwd and push the guard towards the blade (usually with a push stick) to release the workpiece so I can pull it backwards.
TSguard1.jpg

Despite the open back of the new hood I have not experienced increased kickback compared to teh old hood. Some of this is because I don't use my TS was much as in the past and when I do use it I tend to use it more to cut Al than wood.

FWIW I still advocate using a riving knife especially if no (or flimsy) hoods are use, or in places like mens shed etc.

I finished up with 3 MDF model riving knives cut on band saw, appeared to be OK, so now good wife steps in, makes 4 acrylic copies on her laser cutter, will try them out and dont mind loosing them to breakage testing, unfortunately the laser wont cut metal so hoping there is a business in town I can get to do the finished job for me.

yes pictures not happening at this stage. stay posted, but will be having a well deserved time away for couple of weeks

Originally Posted by Tonyz

I finished up with 3 MDF model riving knives cut on band saw, appeared to be OK, so now good wife steps in, makes 4 acrylic copies on her laser cutter, will try them out and dont mind loosing them to breakage testing, . . . .

If the knife breaks and fall onto the blade you could end up with a high speed projectile headed your way. My guess is, with a high surface area to weight ratio a piece of acrylic riving knife travelling at blade speed probably won't kill you but it will be most unpleasant if it were to strike you in an eye. Suggest using a full face shield when testing.

BTW I usually wear a full face shield when using a TS anyway.

yeah maybe acrylic is not a good idea after all, I'll get her to tidy up MDF ones on her laser then try them.