Thread: Ripping banana-shaped lengths particleboard

Have you checked the fence and blade for parallel to mitre slot in the table? If they are not then that is your problem.
Another possibility is too much pressure sideways onto the fence which will swing the fence out of parallel.

From your photos it looks like the ends are different measurements? Or is it the centre that's narrower/wider? If it's the ends of the cuts that are different is the measurement under or over at the out of spec. end and is it the feed in or out end that's not the spec. width?

Woodturning?

Originally Posted by rwbuild

Have you checked the fence and blade for parallel to mitre slot in the table? If they are not then that is your problem.
Another possibility is too much pressure sideways onto the fence which will swing the fence out of parallel.

I've been through the full setup of this saw in the past and just checked the front and back teeth of the blade against the fence--which is out by about about .002" or .05mm if I'm converting correctly. I suppose over 2400mm that may be enough to make a difference?

Don't understand the crook shape though... starts off okay, then dives inwards and comes back out okay. It's as the board is rotating around the fence as it travels along.


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Originally Posted by michhes

It's as the board is rotating around the fence as it travels along.

Sorry, other way around I meant! Starts off okay, twists around the fence and then straightens out again. Hump in the middle.


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Originally Posted by aldav

From your photos it looks like the ends are different measurements? Or is it the centre that's narrower/wider? If it's the ends of the cuts that are different is the measurement under or over at the out of spec. end and is it the feed in or out end that's not the spec. width?

Yep, the centre widens--to look at it. But if I actually measure the board at multiple points along its length, the width measure is off by no more than 1mm. Which is baffling!!!


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This is almost certainly the fence moving away from the blade as you push through the cut. Does the fence lock effectively at the front so that you are unable to move it sideways even with excessive pressure? If it does lock effectively then the problem is at the rear. If you can't adjust the rear locking to improve it can you clamp it? You could then do a test cut to confirm that this is the problem. Is the fence fairly substantial or just a light weight aluminium extrusion? The fence that came with my saw was pathetic.

Originally Posted by aldav

This is almost certainly the fence moving away from the blade as you push through the cut. Does the fence lock effectively at the front so that you are unable to move it sideways even with excessive pressure? If it does lock effectively then the problem is at the rear. If you can't adjust the rear locking to improve it can you clamp it? You could then do a test cut to confirm that this is the problem. Is the fence fairly substantial or just a light weight aluminium extrusion? The fence that came with my saw was pathetic.

The fence is the pretty sturdy Biesemeyer clone that came with the saw but it does only lock at the front and it's bloody clunky sometimes. Might try clamping it at the back. Was actually thinking about rigging up some sort of alternative fence (e.g. something longer that I can just clamp to the saw table).

Mich, clamp a jointed, true 100*50 or 4*2 hardwood to act as the fence. Check the measurements at the front and rear of the blade.

I have found with some fences that there is the faintest of kicks, whereby the piece between the fence and the blade gets a nip on the way out, I then have to recut ever so slightly and almost stop the blade with the work piece next to the blade to prevent. The fence isn't locked at the tail end and seems to get caught by the back of the blade.

to combat this I slide the fence back so that the end of the fence is in line with out a inch before the back of the blade, so that the piece is total free of the fence when the last part of the cut has been made, there is no pressure from the fence to kick the piece back onto the blade.

this maybe happening with you but on a larger scale.

Have you checked the alignment of the riving knife (assuming you use one) with the blade. If it is slightly closer to the fence than the blade it will bind, but if it is slightly further away it will pull your timber away from the fence therefore creating a hollow in the blade side of your timber. When I say slightly, it only needs to be a few thou outside the line of the blade teeth and can cause problems.

Originally Posted by Treecycle

Have you checked the alignment of the riving knife (assuming you use one) with the blade. If it is slightly closer to the fence than the blade it will bind, but if it is slightly further away it will pull your timber away from the fence therefore creating a hollow in the blade side of your timber. When I say slightly, it only needs to be a few thou outside the line of the blade teeth and can cause problems.

Good thought, one thing that's been niggling but that I haven't checked. I'm actually using a replacement Carbatec riving knife which I had ground down to use as a low-profile knife without the blade guard but I've never been 100% satisfied with the alignment.

Thanks for all the help and ideas, I've improved the situation considerably after doing a couple of things:

1. Clamped the end of the factory fence so it can wiggle--I noticed it would shift a bit if sufficient side pressure was applied
2. Added a *thick* extension fence (clamped to the face of the factory fence). It's made of five strips of particleboard glued together and held in place with the little side clamp thingies
3. Installed the factory riving knife in place of the low-profile knife I was using (also from Carbatec but alignment always seemed slightly off with the shark fin). I think the alignment is still out a tiny bit so room to improve there, maybe.
4. Adjusting side pressure as I feed, pressing more towards the end of the fence closest to me.

In the end, my 2400mm test piece was off by about 3mm after implementing the above. Still with a hump and still with consistent measurements along the length (which continues to baffle me).

Given the length, I think I can live with 3mm but I will adjust the knife further.

WP_20180819_001.jpg

I'm surprised you couldn't get a better result than that. 3mm is still a huge amount of run off over a 2400mm length, something funny going on there. Have you checked the saw arbor mechanism for play? With the zero clearance plate in place any variability in the rotation of the blade should show up fairly obviously in the alignment and width of the saw cut in the plate.