Riving Knife and sheet goods

[Kent Adams]

Ok....so I managed to do something I never thought I would do, stop the blade on my 5hp PM2000. I was cutting 5ft long 1/2" BB with a Forrest Duraline HI-A/T Thin Kerf (bought when I had a contractor TS with only 1.75hp). What caused the binding was a full kerf riving knife. I removed the riving knife and the sheet good went through like butter. Lesson learned.

Now, I have just two questions:


Did I just damage something with my TS by making the blade bind and stop?
Is it safe to run full length sheet goods through the TS without a riving knife? I don't think it is, because kickback could still occur. However, to mitigate kickback without a riving knife, I'm also using Jessem's TS stock guides which have an anti-kickback feature to them, which I'm thinking mitigates the lack of a riving knife for something like sheet goods cut lengthwise through an entire panel.

[Jamie Buxton]

You didn't likely damage your saw.

Get a full-kerf blade.

[Prashun Patel]

1. No. Binding a blade may at most cause the saw to trip off, but it wont (or at least hasn't for me) caused any kind of damage after you reset.

2. My RK was also too thick for think kerf blades. IMHO, the right solution is to grind down your RK or to use a full kerf blade. I think plywood has a reasonable risk of kickback because the rip cuts can be wide and prone to twisting. Second, thinner plywood (1/4") can be prone to lifting.

[Kent Adams]

1. No. Binding a blade may at most cause the saw to trip off, but it wont (or at least hasn't for me) caused any kind of damage after you reset.

2. My RK was also too thick for think kerf blades. IMHO, the right solution is to grind down your RK or to use a full kerf blade. I think plywood has a reasonable risk of kickback because the rip cuts can be wide and prone to twisting. Second, thinner plywood (1/4") can be prone to lifting.

Thanks Pashun. I don't, at the moment, intend to buy another blade like this with full kerf. I did buy a stabilizer to use with it for the more powerful TS. The Jessem TS guides prevent the plywood from lifting up from blade to fence and at a 5 degree angle toward the fence, I think should eliminate the stock from getting twisted back into the blade. I'm thinking the Jessem TS guides eliminate the need for the RK.

[Peter Quinn]

I don't see the relationship between right knife, tk blade and stopped saw. If the blade is thin, the plywood hits the thicker knife behind the blade and pretty quick it stops the plywood, blade continues to spin in the kerf it's made while you try to find a way to stop the saw roughly 8' away from the switch with most of a sheet of plywood in your hands. My guess is the binding happens when you start reacting to the situation and shift the plywood. I doubt any harm has come to your saw, these things are made tough. Sheet goods can definetly come back at you. I'd check to see if Sawstop can provide a thin kerf riving knife for use with your thin kerf blades, probably cheaper than a new blade. It's unlikely that a full sheet would kick back, but the knife is still nice to keep things from drifting away from the fence.

[John TenEyck]

You should always use a RK or splitter; bad things can and do happen w/o them. If you can't get a thinner RK and aren't up for making one, then make a ZCI out of BB plywood and install a wood splitter behind the blade.

John

[Erik Loza]

No firsthand experience with your particular machine but IMO, go back to full-kerf blades on a 5HP saw. Save the thin-kerfs for jobsite tools. Can't tell you how many customers I have had who put the thin-kerf on their sliding table saw and it vibrated, made noise, sub-par cut, etc. Freud and other good blades, not contractor junk. I personally think you need a blade with more mass once you get into the heavier machines, 5HP, etc. Hope this helps,

Erik

[Von Bickley]

I don't buy thin-kerf blades anymore.

[Rod Sheridan]

Hi Kent, I would purchase a full kerf blade for your saw, they work much better than the thin kerf models.

You can also buy a different thickness riving knife for your saw if you want to run thin kerf blades.

No, it isn't safe to make any non through cut without a riving knife of splitter..............Regards, Rod.

[Mike Heidrick]

I'm thinking the Jessem TS guides eliminate the need for the RK.

Your off cut can go into the blade very easily.

[Andrew Pitonyak]

You should always use a RK or splitter; bad things can and do happen w/o them. If you can't get a thinner RK and aren't up for making one, then make a ZCI out of BB plywood and install a wood splitter behind the blade.

John

Yes yes yes. I had a nice kick back many years ago. It was probably the first piece of wood I ever ran through a table saw. I turned off the saw and did not use it for a week while I was reading up on how to safely use a table saw. That table saw did not have a riven knife. At this point, I am not likely to use a saw without one. I did exactly what John recommends and I used an aftermarket splitter that went into the ZCI.

[Jason Beam]

I'm thinking the Jessem TS guides eliminate the need for the RK.

What good do they do for the other piece that's cut off?

[Rich Engelhardt]

Run to Woodcraft and pick up this - MJ Splitter (http://www.woodcraft.com/Product/146178/MJ-SPLITTER-KIT-THIN-KERF.aspx?gclid=CjwKEAiA64uyBRCVmKyT2vuAjzgSJADfIN B6JrqtSOn4GRyh74lxkm8TcpKMz1wuaiPuNNs-xz04cRoCQNrw_wcB).
They work great with a ZCI.

[Jim Dwight]

This won't help the OP but for anybody considering a thin kerf blade I would skip it regardless of your saw. I think it is a bit of a myth that they help underpowered saws. I use a Ryobi BT3100 which has a 15A universal motor. So it is less power full than a saw with a 15A synchronous motor (due to the lower effiency of the universal motor (has brushes)). I have both thin and regular kerf blades. For full depth (3.5 inch) rips, I like my full kerf 24 tooth Freud ripping blade. I can cut hardwood with it full depth but I have to use a fairly slow feed. I have a thin kerf one too and it doesn't allow a significantly higher feed rate. I have all around blades of both types too and again I see little to no difference.

So I think full kerf blades are the way to go regardless of your saw. They have more carbide and are stiffer so they have other advantages. Any gains in cut speed are minimal and not worth the disadvantages of greater flexibility and smaller teeth inherent in the thin kerf blades.

If you have a problem with feed rate, I think you need to be sure that you are using the right type blade for your cut and that the blade is clean and sharp. Those are the important variables in my experience.

Now a minor bit for the OP, I use a riving knife I made that is slightly thinner than a thin kerf blade and I arrange it so that it for sure doesn't protrude towards the rip fence. I use this for all blade types. I have no problems with this setup. I think you should look for a thinner riving knife until you use up your thin kerf blade(s).

[Justin Ludwig]

Is it safe to run full length sheet goods through the TS without a riving knife? I don't think it is, because kickback could still occur. However, to mitigate kickback without a riving knife, I'm also using Jessem's TS stock guides which have an anti-kickback feature to them, which I'm thinking mitigates the lack of a riving knife for something like sheet goods cut lengthwise through an entire panel.

Yes.

I don't use a RK, splitter or anything on my PM2000 (3hp). I do use full kerf blades. I rip and crosscut full sheets of 3/4 ply by the bundle on that puppy, no problems. I did throw away the UHMW fence and replaced it with MDF and formica. SO much better IMO. I had one kick back 8 years ago on a Delta Unisaw crosscutting a 1/4 sheet of hickory bead board, it hit me in the butt. It happened because my head was up my butt (luckily the sheet missed my head while it was up there :D)

If my worker uses the saw, I put the riving knife in.

[John Sincerbeaux]

IMHO a riving knife is a totally unnecessary training wheel for a table saw. If you push ANY size wood across the blade with the proper direction/pressure in relationship to the blade/fence, you will not get a kickback.

[David Kumm]

I've never had sheet goods that were unstable enough to close up on a kerf. If should also be remembered that for a riving knife or splitter to work, it should be properly sized to be somewhere between the thickness of the blade plate and the kerf, and no thinner than the plate. Lots of talk about riving knives, but the same knife doesn't always work when you change blades. Dave

[mreza Salav]

IMHO a riving knife is a totally unnecessary training wheel for a table saw. If you push ANY size wood across the blade with the proper direction/pressure in relationship to the blade/fence, you will not get a kickback.

It's a matter of time only to get situations where properly fed (direction and pressure) wood has caused a kick back, which are typically nasty.
Even if you do everything correctly by the book, you can't predict how the wood you are cutting is going to react once it is cut; it is quite common for pieces to have internal stress and once cut the two pieces pinch the back of the blade and there starts a kick back.

[Erik Loza]

....you can't predict how the wood you are cutting is going to react once it is cut; it is quite common for pieces to have internal stress and once cut the two pieces pinch the back of the blade and there starts a kick back.

This ^^^^^....

I have had this happen a number of times while ripping on a bandsaw. You can almost feel the wood pop as the tension is released. The same would apply to straight-lining or ripping on the table saw. I suppose it's less of a possibility with sheet goods but I cannot think of any good reason to not use the riving knife if the machine has one.

Erik

[Kent Adams]

Frankly, I think everyone advising about a RK skipped over the use of the Jessum TS guides, either because they aren't familiar with how they work or they just reacted and mentally skipped forward to the lack of a riving knife. As I view it, the Jessum TS guides are just a manual form of a power feeder. They guide the cutoff stock toward the fence at a 5 degree angle and the bearings do not turn backwards.

Generally speaking, I won't run my saw without a RK, however, in this circumstance, the guides are serving to guide the cutoff stock away from the blade.

[Prashun Patel]

I think you are right, Kent. Most of us probably have never used the Jessem TS guides.
Also, we do tend to proclaim that the 'best' way to do something is the 'only' way to do something around here.

One poster mentions that the guides don't control the cut off though. Is that correct? here is one place where a RK may be excel - even though that's not the question.

Point taken.

[mreza Salav]

"... I'm thinking the Jessem TS guides eliminate the need for the RK."

For using with plywood, maybe; in general I don't think so. I've had situation that the internal stress of the wood (once cut half-way through) was so large that I could barely open the kerf using a screwdriver as wedge. It pinched the RK so hard it became difficult to push the piece. I highly doubt that the guides would be able to keep the piece from pinching the RK.

[Kent Adams]

Hi Prashun,

If you're referring to Mike's comment, he's somewhat wrong. The off-cut can't go back into the blade under normal operation, unless you purposely try to strong arm it into the blade.

[Kent Adams]

"... I'm thinking the Jessem TS guides eliminate the need for the RK."

For using with plywood, maybe; in general I don't think so. I've had situation that the internal stress of the wood (once cut half-way through) was so large that I could barely open the kerf using a screwdriver as wedge. It pinched the RK so hard it became difficult to push the piece. I highly doubt that the guides would be able to keep the piece from pinching the RK.

The question I had was around plywood. I wouldn't trust going RK-less with hardwood even with the guides.

[John Sincerbeaux]

It's a matter of time only to get situations where properly fed (direction and pressure) wood has caused a kick back, which are typically nasty.
Even if you do everything correctly by the book, you can't predict how the wood you are cutting is going to react once it is cut; it is quite common for pieces to have internal stress and once cut the two pieces pinch the back of the blade and there starts a kick back.

Assuming the blade is sharp, I still stand by the ... the blade does not cause a kickback. I have operated a table saw on an almost daily basis for 40 years. I bought my first table saw before I could drive. I have cut every type of wood from every corner of the world. I know very well about wood stress. I have experienced a few times when a board starting clamping down against the blade. My technique is to hold the board/piece firmly where it is, turn off the TS and let the blade stop in it's track.

I have said on this forum before that when I was in high school shop (Southern California), we learned how to properly use all the "industrial" class equipment safely and properly and neither of the huge Rockwell table saws had a blade guard, RK, or auto blade stop. And 14 year old kids could use this equipment daily.