Thread: Blade cut is wider than blade kerf

Originally Posted by Chief Tiff

Does the needle swing evenly and smoothly or is there a definite “hump”? A hump can be rectified in situ but if it’s even then there is a possibility that the arbor is actually bent or there is some sort of bearing eccentricity. I would repeat that test but at 90 degrees, such as on the ground section of the arbor where the blade sits. That should be practically zero run out. Any further diagnosis probably requires the arbor to be removed entirely and set up between centres and/or vee blocks. For something that small; one and a half thou runout on that flange is appallingly bad manufacturing. Hell; as an apprentice I could file by hand to within two thou…

Just re-measured using the "flat" gauge tip of the gauge against the face of the arbor flange, I get 0.0015" runout and it is an even swing - so no hump.

Using the "pointy" tip on the ground section of the arbor, I get 0.0005" runout (or 0.02mm).

Originally Posted by Chief Tiff

But; in the greater scheme of things will fixing a 0.25mm run out at the blade tip improve your woodworking? As I stated earlier I don’t regard a table saw as a precision tool anyway; to me they’re just convenient tools for rough dimensioning.

Yeah I'm too inexperienced to know. Mobyturns reckons yes if doing inlay banding (which I don't do...yet . Either way, if this is acceptable for a saw at this price-point, fair enough. But if it should be better, then I want to know.

I also didn't start with the gauge. I actually first noticed that when spinning down, I could just see the blade "wobbling", but didn't think too much of it. Then when I built the cross-cut sled I noticed the width of cut in the sled base was noticeably wider than the blade. So then I did that test cut of raising the blade into a bit of wood and got the 3.55mm width of cut. Only then did I get on here and start using the alignment gauge. In short, it is "noticeable" with the naked eye from the artefacts of using the saw. Whether that is a problem in practice, seems the answer depends on who I ask

Originally Posted by lemerv

Using the "pointy" tip on the ground section of the arbor, I get 0.0005" runout (or 0.02mm).

That’s not as good as it should be so I suspect your arbor is either slightly bent (possible but unlikely) or is sitting eccentrically in the bearings. Could be crap Asian bearings or the way the arbor is mounted in them. Do you have an exploded parts diagram for the saw? If the arbor is locked into the bearings using grubscrews that can cause the issue and may be able to be “tweaked” into alignment.

Originally Posted by Chief Tiff

That’s not as good as it should be so I suspect your arbor is either slightly bent (possible but unlikely) or is sitting eccentrically in the bearings. Could be crap Asian bearings or the way the arbor is mounted in them. Do you have an exploded parts diagram for the saw? If the arbor is locked into the bearings using grubscrews that can cause the issue and may be able to be “tweaked” into alignment.

Thanks. Should it basically be 0.00mm?

Exploded diagram is pg25 of this doc: https://www.carbatec.com.au/document...ual%202018.pdf

Not sure exactly what I’m looking for in terms of grub screws. Are you able to take a look?

Appreciate your help.

Edit: yeah can’t see any grub screws. Looks like it is bolted in from behind??

Shaft run out in close fitting ball bearings should be almost immeasurable… so yeah there’s a bit of an issue. I’ve looked at the drawings and the bearings are standard single row ball bearings. It’s possible that one of the bearings was fitted slightly cocked; either on the shaft or more likely inside the housing. Or the shaft could have been machined slightly undersized in the way of either bearing and the run-out is the effect of the shaft not being truly concentric with them.

Unfortunately there is no way to determine where the issue is without stripping the assembly down. I would recommend seeing what Carbatec have to say; you can throw the runout figures back to them and claim that these are well outside expected manufacturing tolerances but the only fix available to them will be to replace the saw so obviously there will be some reluctance to accept that.

Originally Posted by Chief Tiff

Shaft run out in close fitting ball bearings should be almost immeasurable… so yeah there’s a bit of an issue. I’ve looked at the drawings and the bearings are standard single row ball bearings. It’s possible that one of the bearings was fitted slightly cocked; either on the shaft or more likely inside the housing. Or the shaft could have been machined slightly undersized in the way of either bearing and the run-out is the effect of the shaft not being truly concentric with them.

Unfortunately there is no way to determine where the issue is without stripping the assembly down. I would recommend seeing what Carbatec have to say; you can throw the runout figures back to them and claim that these are well outside expected manufacturing tolerances but the only fix available to them will be to replace the saw so obviously there will be some reluctance to accept that.

Thanks for all your help Chief Tiff, appreciate it. I'll have to reach out to Carbatec and see what they say.

Out of interest, what's your background. How do you know so much about this stuff!? It's quite the rabbit hole for a novice like me.

Cheers

Originally Posted by lemerv

Out of interest, what's your background. How do you know so much about this stuff!

Hah! My “trade” as such was a Marine Engineering Artificer in the Royal Navy. I usually describe it as akin to being a cross between a tradie who understands thermodynamics and an engineer who can use a spanner without inflicting self-injury. At the end of the day all machines from an electric motor to a supercharged V12 racing engine all follow a fixed series of “rules” regarding how the parts are made and how they are fitted together; there are only so many ways you can achieve each individual goal and system complexity is all down to how many diferent options you apply to each sub-system.

Woodworking machinery is pretty basic and I get plenty of practice fixing the machines at the Bundaberg Woodworkers Guild. Today I finished putting back together a Hafco 14” bandsaw that was donated in a bit of a shocking condition; I still need to replace all the guide roller bearings but after rebuilding it and setting up all the various adjustable elements I finally powered it up and proceeded to cut my standard test piece; a 1mm thick veneer slice from a 3” thick lump of camphor laurel.

Originally Posted by Chief Tiff

a cross between a tradie who understands thermodynamics and an engineer who can use a spanner without inflicting self-injury

Haha this is great! I come from an industrial design background so I tell people I know how to make form and function be friends.

Thanks again