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Plywood kicking back

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Forum topic by tengallonhat posted 10-08-2013 04:05 PM 1188 views 0 times favorited 41 replies Add to Favorites Watch
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tengallonhat

79 posts in 444 days


10-08-2013 04:05 PM

Topic tags/keywords: question

I have an older table saw and I have now had 3 seperate kick backs trying to break down small pieces of plywood.
This is my saw:
http://vintagemachinery.org/photoindex/detail.aspx?id=16047

There is no splitter or riving knife. The fence is generally solid and square, but I believe the first kickback actually threw the fence way out of alignment from the force. Being out of alignment likely made it more prone to kicking back the other two times.

I’m starting to think the cuts I’m making are just a bad idea, even though I see it done all the time.
I always start with no more than quarter sheet (48”x24”) and the kickbacks occur when I’m “crosscutting” these to a shorter length. In this case I was crosscutting a 15”x24” piece off between the blade and the fence. The more I think about it, this is probably a really bad idea. Is my suspicion right? My fence isn’t long enough to make this cut on the outside of the blade.

Assuming the fence is aligned and the blade is square to the table, is this a safe cut to make?

The result from the kickback looks like this:

Scary. It has happened the same way each time. As soon as the blade comes through the back edge, the piece catches, lifts up, lands on the blade (leaving the arc and teeth marks) and throws. Luckily I’m not hurt aside from a couple small bruises and a dent in my car(yikes).

I’m using a “Freud Premier Fusion 1/8 kerf blade

I also think the twist and force on the blade actually caused the teeth the bite into the stainless zero clearance insert. There are no noticable chips in the blade, but the gouge in the insert and the red Freud streaks on insert tell another story. Even though the blade doesn’t look damaged I think I may replace it to be on the safe side.

What else can I do? I spent all of last night re-squaring the fence. I believe this old fence may actually have enough play in it that I need to square and verify after every fence adjustment.

1) I will likely add a splitter.
2) Should I look into a modern fence that won’t require squaring with each cut?
3) Stop making these cross cuts on the Table saw? Use a jig and circular saw instead?

Would this kind of kickback be prevented with a riving knife? The option I hate, but am considering, is getting a different saw with a guard and riving knife.

Any thoughts or advice would be appreciated.

Thanks.


41 replies so far

View Loren's profile

Loren

7734 posts in 2336 days


#1 posted 10-08-2013 04:09 PM

There’s a knack to locking those old style fences square.

-- http://lawoodworking.com

View Bill White's profile

Bill White

3497 posts in 2648 days


#2 posted 10-08-2013 04:25 PM

Cross cutting between the blade and the fence is an invitation to kickback.
Mark the cross cut dimension, cut without making the work piece contact the fence.
You absolutely need a splitter of some sort, and after those kick backs, ya might even want to recheck the blade, blade alignment, etc.
An aftermarket fence like a Biese clone would be a plus.
I have the Shop Fox Aluma Classic on my Grizz. It is a great fence for the buck.
You have a fundamentally sound saw. Gonna take some tweeking and add-ons to make it a really good and safe saw.
Just my thoughts.
Bill
Bill

-- bill@magraphics.us

View tengallonhat's profile

tengallonhat

79 posts in 444 days


#3 posted 10-08-2013 04:37 PM

Thanks. I don’t have any experience with after market fences. Does it typically take modifications to the saw to add them? I am very happy with the saw (besides this problem). Would a new fence like the Shop Fox stay square or do I still need to check it with every cut? I assume they stay square.

I have a bunch of zero clearance inserts I cut from 1/2” ply that I will finish and add splitters too and probably replace the blade.

I would be pretty happy to add a new fence and eliminate the squaring issue as opposed to ditching the saw for a newer one. Given it’s a beautifully constructed and HEAVY saw.

I did check the blade and blade alignment after I realized the fence was out. Everything seems to still be in alignment I just had to readjust the fence.

Thanks for the input!

View Loren's profile

Loren

7734 posts in 2336 days


#4 posted 10-08-2013 04:47 PM

Any of the currently available aftermarket fences will be
a big improvement. You can cut wood with the fence
you have but the new ones adjust quicker and lock
consistently square.

-- http://lawoodworking.com

View CharlieM1958's profile

CharlieM1958

15706 posts in 2906 days


#5 posted 10-08-2013 04:50 PM

Generally speaking, what you are trying to do is not a good idea because the weight of all that material to the left of the blade tends to pull the leading edge of your work piece away from the fence as you make the cut. A miter gauge with a wide fence would be a better option.

Having said that, I have done it myself. But first I make sure my fence is aligned to the blade, and then I push through the cut very slowly, making sure I keep the edge tightly against the fence.

-- Charlie M. "Woodworking - patience = firewood"

View DaddyZ's profile

DaddyZ

2414 posts in 1729 days


#6 posted 10-08-2013 05:21 PM

Sounds like you need the saw & fence both tuned up.

I set my fence almost parallel to the blade, the end of the fence(part farthest away from me) is a fine hair wider away from the blade, that way there is no way I can pinch anything between the fence & the blade.

http://www.newwoodworker.com/basic/tsalign.html

-- Pat - Worker of Wood, Collector of Tools, Father of one

View MrRon's profile

MrRon

2860 posts in 1932 days


#7 posted 10-08-2013 05:30 PM

What do you mean by “crosscutting” when you are using the fence to guide the plywood. Crosscutting is done using the miter gauge, not the fence. It sounds like your fence is not long enough. You should get a new after market fence, like a Biesemeyer or one of their clones. Your blade is probably set too low. It’s interesting that it’s a left tilt saw fo such an old machine.

What is a “stainless” zero clearance insert?

View CharlieM1958's profile

CharlieM1958

15706 posts in 2906 days


#8 posted 10-08-2013 05:45 PM

MrRon, what he means is that the piece he is cutting is wider from left-to-right than it is from front-to-back.

-- Charlie M. "Woodworking - patience = firewood"

View crank49's profile

crank49

3458 posts in 1659 days


#9 posted 10-08-2013 05:47 PM

You said it. This is a crosscut and therefore should not be depending on the fence at all.
Cutting a 15” x 24” piece off a 24” x 48” is exactly what needs to be done with a crosscut sled.
Most miter gauges can’t guide a 24” wide (front to back) piece because the blade to table edge is usually 12” or less.
But a sled can be build that rides in both miter slots and overhangs the table edge a foot or so.
I built my sled specifically to handle things at least 25” wide.

Just be sure the blade is still in alignment with the miter slot first. This is a prerequisite for accurate work anyway.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

View tengallonhat's profile

tengallonhat

79 posts in 444 days


#10 posted 10-08-2013 05:49 PM

By crosscutting, I mean I was running a piece of plywood through that was wider than long against the fence. Which is dumb but I see people do it with plywood all the time. I’ve finally realized that this probably isn’t smart and need to stop.

My zero clearance insert is machined stainless steel designed for 1/8” kerf blades. Here is a picture of it on the table.

I suppose technically it’s not zero clearance since the kerf of the blade didn’t make the cut through the insert, but it is close. I think the blade must have flexed and hit the steel when it kick backed. I don’t see any visual damage to the teeth of the blade, but I have to believe hitting steel is not going to be good for carbide teeth.

I am definitely thinking a new fence is going to be the answer. I am looking at ordering this Vega setup.

Or else this Shop Fox system.

Any thoughts on these two options?

View tengallonhat's profile

tengallonhat

79 posts in 444 days


#11 posted 10-08-2013 05:52 PM

Thanks Crank49, I do have a crosscut sled, but it wasn’t built quite big enough for these cuts. I am planning on cutting the 15” wide pieces to final length on the sled since they will fit. Now I have a reason to build a bigger sled.

View PurpLev's profile

PurpLev

8476 posts in 2337 days


#12 posted 10-08-2013 06:03 PM

That’s a nice saw. things I would consider:

1. adding a riving knife like a BORK (bolt on riving knife) – not sure if there is one available for your saw, but I would check !

2. readjust your saw, blade to miter gauge and fence to miter gauge to make sure everything is parallel and straight

3. use a crosscut sled to make those cuts, or some other miter-slot jig to securely pass the plywood through the blade

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Loren's profile

Loren

7734 posts in 2336 days


#13 posted 10-08-2013 06:09 PM

That kind of cut works better if the material is over 12” wide
but also works better with an outfeed table. I cut 12” squares
now and then using a fence on a table saw with no problems.

I think maybe the physics of it are that if the back of the material is
cut before the front is clear of the back teeth, then you’re
in trouble.

-- http://lawoodworking.com

View shipwright's profile

shipwright

5087 posts in 1486 days


#14 posted 10-08-2013 08:07 PM

That is not an optimal way to make the cut you are attempting, but it is also not a particularly difficult or dangerous one if good technique is used.
All the additional bits and pieces mentioned above will help in one way or another but I think you need some guidance on the general principles of controlling your stock.
I learned in an old school industrial workplace and wouldn’t recommend my methods to others but in my mind that kickback would never happen if you had proper control of the piece, extra parts or not.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Ralph's profile

Ralph

164 posts in 821 days


#15 posted 10-08-2013 11:24 PM

Would some feather boards holding the stock against the fence be any help???

-- The greatest risk is not taking one...

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