Making riving knife: a few questions

[SpoonsbySven]

Hi Folks,
Time in the workshop has been limited for the past few months, so progress on my Kity 419 table saw has been glacially slow. I’ve pretty much finished the modification to the tilt mech (will do a separate thread about that).
Anyway, I’ve started on the riving knife(s), and would really appreciate some feedback from more experienced TS owners.

I’ve made a template out of polycarbonate, traced from the on the Sketchup model that Robert MP posted here: http://www.ukworkshop.co.uk/forums/my-ts-200-fettling-and-saw-rt-bench-build-thread-t40316.html for his Axi TS200.

So my questions are:
1. Does this look OK? Could/should I make it thinner by removing more material from the spine (follow black line on template?). I’ve done a test mount, and the current shape seems to be OK for staying level with the top of the saw blade when it’s in place.
2. Mounting to the TS: I know it’s safer to have mounting holes (or a closed slot), but an open slot would make for much easier changing. I guess the answer is “it’s up to me”, but I’m interested to know what the collective view is.
3. At the mounting end, it only needs to extend say, 20mm past the bottom mounting bolt, right? I’ve drawn a black marker line on my template where I think it could end. It’s just that the one I traced off is much longer.
4. I bought a set of 3 Parkside saw blades from Lidl the other day for a tenner. Unfortunately, they’re 210mm diameter: a bit big for my saw. However, I’m pretty sure they will fit (still in the packaging in case it’s a bad idea), and I’m fairly sure I could make the riving knives such that the inside edge is within the recommended 4-8mm clearance on both a 200mm and 210mm blade. Are the other problems with using a slightly bigger saw blade? I realise that it will put more strain on the motor, but given that the increase in diameter is only 10mm, I reckon this will be negligible?
NB: it’s taken as read that any opinions offered are just that, and anything I decide to do will be entirely my decision and responsibility.
Questions 1 and 3 are really due to the fact that I’m keen to make the most efficient use of the pieces of 01 tool steel I bought (so that I have more left over for other projects!)
Very grateful for any advice or opinions.
Cheers,
Sven

 

[Steve Maskery]

It's all up to you, but my riving knife has a closed end. Just how much trouble is it to remove on the rare occasion that yo have to?
If it does come loose and it hurtles towards you...Why take the risk?
S

 

[SpoonsbySven]

Steve,
Many thanks for your reply. It's an excellent point-I certainly want to avoid flying riving knives!
Having only owned one table saw which only had one blade, I'm interested to know how much blade changing people do. My experience of using a tablesaw so far is that I do a real mixture of ripping and crosscutting. My "new" table saw has a general purpose blade and a crosscut blade which unfortunately are different thicknesses, so I imagined that changing blades (and therefore riving knives) would be a fairly frequent exercise.

I know that doing something frequently isn't an excuse for having an unsafe system, but I suppose I imagined getting into the getting into the habit of being really careful to ensure the mounting bolts were tight, and possibly using some thread lock (and possibly a spring washer?) to reduce the chances of them working loose.

Cheers again.
Sven

 

[blackrodd]

I would look at the original roving knife and copy that, the "open" slotted ones are fixed just as well as the closed ones,
and when bolted up correctly will not, in my experience, come in contact with the saw blade.
What is just as important is matching the riving knife to the saw blade in thickness,
A riving knife, too thick will be just as useless and dangerous as a thin one.
Try and keep you're ripping blades and finishing blades as equal in saw kerf thickness as possible,
This was the reason for two riving knives being supplied on the better saw bench models in days gone by
I'm not sure that two knives are supplied now.
Regards Rodders

 

[SpoonsbySven]

Thanks Rodders.
I should have said that the reason for making a new riving knife is that the previous owner had lost the original. When I got the saw he "was sure he still had it somewhere", and promised to look it out, but after multiple nudges, I've given up. I put up a post asking if any Kity 419 owners could post a photo or scan of their RKs, but didn't have any luck there. Looking at the Sketchup drawing RobertMP did for his TS200 riving knife (link in my original post), it has an open-ended slot, which was partly what started me wondering.

I've read that the RK should be slightly thicker than the disc of the saw blade, and slightly thinner than the kerf, so so I understand that multiple RKs are necessary if you're using different thickness saw blades.

The saw came with a thin, general purpose Freud blade, and a thicker crosscut Freud blade (can't remember the exact thicknesses offhand). I'd like to be able to use both, hence the plan for two RKs of different thickness.

Cheers,
Sven

 

[blackrodd]

Have you seen this from August 1012,--
There are pics as well.
mounting-riving-knife-to-a-kity-419-t63252.html
Either 2.5mm, or 3mm thick depending on the blade you are using, I would suggest.
HTH Regards Rodders

 

[SammyQ]

Rodders? "Have you seen this from August 1012,"......I'm all for the Romans'n'so on, but internet..... way back then?

:lol:

Sam

 

[blackrodd]

Rodders? "Have you seen this from August 1012,"......I'm all for the Romans'n'so on, but internet..... way back then?

:lol:

Sam

Well spotted Sammy, another sign of rodder's ageing. :shock:

 

[SpoonsbySven]

Ha ha, thanks Rodders and Sammy :lol:
Cheers for the reminder of that thread- impressive memory (despite your apparently advanced years)- I referenced that thread in mine on Kity 419 mods, but had forgotten that it contained pictures and info relevant to my query in the original post.

Thanks again to Eric the Viking for the excellent work there.

Riving knife MkI is done, just been working on the spacers and retaining plate this eve. Of course I didn't have any plate of the right thickness, so had to use 2 rectangles cut from an old saw blade a mate gave me, and will now have to think of a way of taking one of them down by about 0.6mm in thickness. That'll be fun. :?

Thanks again.
Best,
Sven

 

[SammyQ]

Rodders, dignity (and the certainty it would put you off food for some time) forbids me from sharing with you and our august woodworking brothers exactly what MY "signs of... ageing" are.

Sam