Table Saw Riving Thing

[Hugh M.]

Hi All. I was given a very cheap table saw. I haven’t used because:

1. It scares the willies out of me.
2. I noticed straight away that it was missing the riving knife.

It has sat unused whilst I try to cut everything on my bandsaw and try to avoid eye contact with it. As I think I understand it, the riving thing stops the material being cut closing and pinching the blade which in turn causes kickback? This I know has the potential to be very bad.
I have a task that calls for the table saw right now. I have a short length of wood that I need to cut grooves across the grain. I only need shallow (say 3 or 4mm) grooves right the way across; not even a third of the way through the thickness. The 2mm kerf offers the perfect groove width.
I am thinking a mitre slide and hands and fingers as far as possible from the blade. I will flip it over to facilitate distance from pinkies to blade.

Safe? Or, will I end up not being able to count to ten?

 

[Agent_zed]

If you aren't cutting all the way through and only shallow at that, it's unlikely that anything untoward will happen. If it doesn't have a riving knife though does it have a blade guard? Most hobby saws have a riving knife that holds the guard.

It shouldn't be that hard to make a riving knife, it is at the end of the day a bit of flat steel with a bit of a curve, there should be some mounting holes. I'm not sure of the thickness though, as that is the important bit, hopefully someone can confirm.

If you don't have guard, you should either get one or make one. I'm looking to make one that is held from the side. This means a riving knife can be used and still allows cuts that don't go entirely through. The guards on the riving knife prevent this.

Something like this https://ctpowertools.com/wp-content/uploads/DELTA34-976DeluxeUniguardTableSawBladeGuard.jpg

 

[ChaiLatte]

Think about if you were doing the same cut using a (sliding compound) mitre saw.

That does not have a riving knife.

Cutting cross grain partial depth is unlikely to lead to pinching. It is only when you do a long rip cut that the material will try to close up on you.

If the factory riving knife extends above the top of the blade (perhaps to hold the factory guard), it could not make a cut like you want and would need the machine altering in any case.

If the piece of material being cut is small, the mitre slide will only help if the piece is secured to that slide. You could have a slide that is 2' square but if you are holding the stock 1" from the blade, it does nothing.

You could similarly double-sided tape the piece you are cutting to a large offcut of 6mm plywood (9mm overall cutting depth), then your hands will be nowhere near the blade.

You are starting from a poor position saying you are scared of it. Fear makes us do stupid things. Eliminate the fear by educating yourself on the dangers of the machine so you treat it with the appropriate degree of respect and exercising appropriate caution in using it.

You know the fundamentals: keep fingers away from blade. Develop a mode of work that systemises that (i.e nothing ad hoc, make it up as you go along in front of a spinning blade) and the discipline to follow that system.

Do a dry run with the blade lowered below the table so you know your hand positions before, during and after the cut. With the machine switched off and unplugged, put your hands in the place they are going to be and draw around them with a marker pen (like in the films with dead bodies). When it comes to the real cut, make sure your hands go back to that position and no other.

 

[meccarroll]

As above.

Pinching if the wood being cut generally occurs when ripping through the full depth of the timber.

Tensions in the timber can cause the cut wood to close on the open end of the cut which in turn results in the wood pinching the sides of the blade and acting like a clamp then kickback occurs. It can be very serious when it happens.

Crosscutting wood does not seem to invoke the same problems as ripping wood and consequently the vast majority of mitre saws intended for crosscutting do not have or need a riving knife. It is VERY VERY important to note that most blades sold for crosscutting on mitre saws will use a negative rake or have very littk angle on the teeth to reduce the posibility of the teeth snatching the wood.

For the operation you intend doing you should make a jig to hold the wood being cut and also ensure the saw blade is never exposed enough for your fingures to engage the saw blade while making the cut. A sort of tunnel is the idea so your fingers can never get near to the revolving blade even if the wood snatches and pulls you in.

My best advice to someone who is unsure is to leave well alone and try to borrow a mitre saw for the job or buy one. It will be a lot cheaper and safer than having a few weeks of work with fingers missing.

 

[Hugh M.]

Thanks everyone. Yes, I was confident in the theory that it wouldn’t grab and indeed, it didn’t even hint that it was thinking about it.

I think if a table saw is required, it will be a new one that I get. This one probably isn’t worth spending money on.

It is a mighty Pingtek Blueline and the blade is probably very blunt. I had to plug it into the house as the switch kept flipping in the garage. No hint of that in the house main and none of my other tools do that. The sudden demand and lack of a soft start function maybe?

Anyhow, the job is done (bat ladder) and I can return it to the shelf!

Thanks again.