Riving knife alignment changes with blade height

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Kicked Back

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Merry xmas.

Santa brought me an Axminster AT254LTS table saw. Everything was going so well. Cast iron table is perfectly flat. Fence, blade to mitre, etc. were super easy to set up perfectly. Then came the riving knife...

I seemed to be going in circles for a few hours, messing around with the four set screws that allow you to adjust the plane with respect to the blade. Then it hit me. The top of the riving knife can be set directly in line with the top of the blade when the blade is set to around 10mm cutting depth. But as the blade is raised to its maximum depth, the top of the knife moves out of square... Having had a look inside, i see there's some kind of mechanism to allow the riving knife to maintain its height with respect to the blade, and my best guess is that it rotates on a slightly different plane to the blade rise/fall. I don't think there's anything for me to adjust.

I don't know how much of an issue this is. With the current setup, it just means that on cuts near to max capacity, the top of the riving knife might apply a tiny bit of side pressure into the fence (to the point that pushing has a little more friction). But the wood stays happily on the fence. I think this is a better option than pushing the piece away from the fence?

Thoughts?
 

baldkev

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If the knife moves independently in some way, maybe one of the machined faces isnt 100% parallel to the blade.... that'd be the block the knife must bolt to?
But if the blade rises and the knife moves independently in some way, is it being caught by something and being deflected? My riving knife on my multico is further from the height pivot point, bolted behind the blade on a block, meaning as the blade rises, the knife rises faster, so the pivot must be forward of the arbor.

Do you have a photo?
 

Doug71

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The riving knife on my saw leans very slightly towards the fence but this is caused by the weight of the extraction hose hanging off the crown guard, it doesn't affect the cut at all though, if I remove the hose everything is in line.

If you can feel it when pushing timber through it does need sorting out.

Does that saw have one of the easily removeable riving knives? I'm not familiar with them but it does sound like one more thing that can go wrong.

Hope you get it sorted, those saws do look like a nice bit of kit.
 

doctor Bob

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The riving knife should be in line, if it leans it may not affect the cut to much, if you use a short fence (level with centre of blade) as recommended then often you will get a slight wobble on the cut at the end of it. Some may not notice due to being very small but invariably it will affect it.
 

Kicked Back

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Attached a screenshot from the manual showing the riving knife assembly. The riving knife sits on an arm that pivots around the arbour as the blade rises and falls. Having 4 grub screws means there's total control over the riving knife position with respect to that arm. But it's like the arm doesn't pivot on the exact same axis as the blade so as it rotates, it ends up deviating laterally (by around 1mm). So the grub screw adjustments can't help.
 

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Kicked Back

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I measured the distance between the riving knife arm (attached to the arbour) and the blade during the rise and fall. It moves by 1mm. So any adjustment of the grub screws is pointless. Simply optimising for a particular blade height.
 

Sandyn

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Really irritating when you get something new and you have a problem like this. Especially on something so expensive. Contact Axminster. You might have have to suffer them saying you set it up wrong and it's withing tolerance etc, etc but there is a general video from them on setting a knife, in particular, they say check the alignment of the blade and knife by setting a straight edge on two teeth and check they are aligned and corresponding gaps on either side, i.e. not 1mm to one side.
Can you set the knife at mid position, so you split the error between top and bottom?
As @doctor Bob says it will affect the cut. It would be really irritating to cut a bit of MDF, then flip one half and mate the two cut edges and find there was a gap.
What accuracy can you expect from a trade saw? They do say "A compact yet capable saw, offering complete accuracy with every cut" whatever 'complete' means
 

Kicked Back

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Really irritating when you get something new and you have a problem like this. Especially on something so expensive. Contact Axminster. You might have have to suffer them saying you set it up wrong and it's withing tolerance etc, etc but there is a general video from them on setting a knife, in particular, they say check the alignment of the blade and knife by setting a straight edge on two teeth and check they are aligned and corresponding gaps on either side, i.e. not 1mm to one side.
Can you set the knife at mid position, so you split the error between top and bottom?
As @doctor Bob says it will affect the cut. It would be really irritating to cut a bit of MDF, then flip one half and mate the two cut edges and find there was a gap.
What accuracy can you expect from a trade saw? They do say "A compact yet capable saw, offering complete accuracy with every cut" whatever 'complete' means


I thought I'd dodged a bullet when I immediately checked the table for flat before unpacking. I've never had completely flat cast iron anything before, so I thought it was a good sign...

Unfortunately due to the magnitude of the movement (~1mm) and the difference in thickness of blade kerf and riving knife (<0.5mm?) - there's no way to position in order to achieve a reasonable compromise. The best I've been able to achieve is a slight bit of pushing away from the fence on ~20mm cuts, which causes snipe when you can no longer push with your left hand into the fence near the end of the cut and the riving knife springs out.

Then with the same settings, at ~70mm depth, the top of the knife pushes thicker pieces into the fence, creating friction (although not much). If I change it such that there's no pushing away from the fence on lower cuts, the friction on the deeper cuts is insane.

If I were to use a shorter fence (which, since I'm working with timber, I really should be doing), then I'd expect the into-fence pressure would result in pivoting around the back of the fence and pushing the front into the blade....

TLDR: I'm screwed... but I've bought a lot from Axminster and their customer support is the best around IMO.
 

Oakay

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On some saws riving knives need adjustment by a combination of slight bending and shimming with washers or card packing. A shame when new equipment isn't setup right from the factory.
 

Kicked Back

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Latest update. Spoke with the Axminster service team (different from the normal support), who were excellent. They had their guys try to replicate the issue on their end and have decided that it's a replacement jobby since it would require a bearing press on-site which isn't going to happen.

The good news is that they'll set up, and verify everything on the new one at their end so I won't get another lemon delivered.

Thumbs up for Axminster in the end.
 
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