Wonky sawblade?

jm51 · Post by **jm51** » Mon Feb 13, 2012 9:33 am

An 8" plywood blade just arrived (America -> UK) so had a quick try on some 12mm (1/2") BB plywood.

This is my first go on a table saw, SS or otherwise. First thing I noticed was that one arbor wrench isn't enough off the machine but I only had one wrench. Fitted the sanding disk to the back of the headstock, then 1 wrench was ok.

The thing doesn't seem flat. Could be runout in the headstock but a mounted sanding disk seems flatter to me. Any way to flatten it?

Did a few tests and just a tiny bit of feathering top and bottom which can be fixed by gently scraping with another piece of ply.

The biggest problem is the shape of the kerf, it is wedge shaped and thicker at the bottom of the cut than the top. I can get a glue ready joint from it but one side only as a 90' cut on one side is 87' on the other side.

What's likely to be the cause of this?

pennview · Post by **pennview** » Mon Feb 13, 2012 9:46 am

I'd expect that the arbor you're using is the source of the problem. Inspect it carefully for any burrs or bumps that might cause the blade to be mounted improperly. Check the inside of the bore on the arbor as well.

On the other hand, you can warp a blade if you get it really hot, but that is rarely the case. A new blade should be flat, but I'd guess it could be damaged in shipping. Check the flatness of the blade by laying it on something flat. The sanding disk should be flat enough to check this.

dusty · Post by **dusty** » Mon Feb 13, 2012 10:29 am

jm51 wrote:An 8" plywood blade just arrived (America -> UK) so had a quick try on some 12mm (1/2") BB plywood.

This is my first go on a table saw, SS or otherwise. First thing I noticed was that one arbor wrench isn't enough off the machine but I only had one wrench. Fitted the sanding disk to the back of the headstock, then 1 wrench was ok.

The thing doesn't seem flat. Could be runout in the headstock but a mounted sanding disk seems flatter to me. Any way to flatten it?

Did a few tests and just a tiny bit of feathering top and bottom which can be fixed by gently scraping with another piece of ply.

The biggest problem is the shape of the kerf, it is wedge shaped and thicker at the bottom of the cut than the top. I can get a glue ready joint from it but one side only as a 90' cut on one side is 87' on the other side.

What's likely to be the cause of this?

I am not sure that I know what a "wonky" saw blade is but I am going to pretend that I do and suggest a way to verify whether or not yours is wonky.

With the power off and the power plug removed from the wall outlet:

Mount a miter gauge and install an allen wrench as shown in either of the two attached photos. The allen wrench should just barely touch the saw blade.

Manually rotate the blade and watch (listen to) the blade as it turns. If the blade is wonky - you should see proof of that by doing this.

The same test can be done by laying a ruler or small stick, pencil or screw driver on the table top - touching the blade in the same manner.

[ATTACH]16231[/ATTACH]

[ATTACH]16232[/ATTACH]

Repeat the test with the allen wrench close to the arbor (center of the blade). There should be the same relationship there.

All the allen wrench is doing is providing a visual point of reference that will allow you to see what the blade might be doing.

Side comment: I did some photos similar to this a couple days ago and while viewing them I became aware that I had a saw tooth that was missing the carbide.

wa2crk · Post by **wa2crk** » Mon Feb 13, 2012 2:02 pm

JM51;
If you can post a couple of pics it would help a lot. If you rip a board along its length will the kerf close up if you put the two cut edges back together? They should. I can't see how one wall of the kerf is being cut at a different angle. Pennview suggested that you check the arbor and I agree but I would also suggest that you make sure that you are using a saw blade arbor and NOT a universal arbor. If the board is not flat but cupped when you cut it, then it is possible that the cut line will not line up if the stock is put back together along the cut line. There will probably be a space at the bottom of the kerf. Is this what you are seeing?
The teeth on most saw blades are wedge shaped but this does not produce a wedge shapped kerf because only the tip of the tooth does the cutting and the tip traverses the full depth of the kerf. In a non through cut the top of the kerf will be "V" shaped and that is normal.
A picture is worth a thousand words.
Bill V

JPG · Post by **JPG** » Mon Feb 13, 2012 2:29 pm

wa2crk wrote:JM51] If the board is not flat but cupped when you cut it, then it is possible that the cut line will not line up if the stock is put back together along the cut line.[/color] There will probably be a space at the bottom of the kerf. Is this what you are seeing?
The teeth on most saw blades are wedge shaped but this does not produce a wedge shapped kerf because only the tip of the tooth does the cutting and the tip traverses the full depth of the kerf. In a non through cut the top of the kerf will be "V" shaped and that is normal.
A picture is worth a thousand words.
Bill V

Add to that a table not exactly 90 degrees to the blade and it adds up if the 'cupping' is concave downward.

If not, wonky is an accurate description. A warped blade or cocked arbor(burr or whatever) will not produce the different side angles.

Far fetched, but if the blade is 'flexing' while passing through the workpiece, a tapered wall might be produced. That would imply the blade is oscillating.

wa2crk · Post by **wa2crk** » Mon Feb 13, 2012 3:00 pm

One other thing came to mind that is a bit far fetched but possible. If one of the teeth on the blade was brazed onto the blade body at an angle then it could produce results similar to yours. One tooth angled to the right, as an example, would be sufficient to cut one wall of the kerf at an angle. This is assuming that it is a carbide tipped blade. Inspect the blade's teeth very carefully.
Bill V

jm51 · Post by **jm51** » Mon Feb 13, 2012 3:06 pm

It isn't quite flat when laid on a piece of BB ply, almost 1.0 mm out but seems worse when doing the test suggested by Dusty.

Wouldn't surprise me if everything was wrong, from table alignment to the blade itself. I just wanted a quick cut to see the quality, I don't trust the setup as is to do more than take test slices off a 4" wide strip of ply.

Need to find my SD card for pics. Failing that I'll dig the awkward Kodak software to get pics onto the laptop.

e2a: It's a Shopsmith branded 8" plywood blade, no carbide.

beeg · Post by **beeg** » Mon Feb 13, 2012 6:17 pm

Does it wobble as it turns?

dusty · Post by **dusty** » Mon Feb 13, 2012 6:33 pm

beeg wrote:Does it wobble as it turns?

How do you test one to determine if it wobbles?

JPG · Post by **JPG** » Mon Feb 13, 2012 9:58 pm

dusty wrote:How do you test one to determine if it wobbles?

By observing the wobble!:) The sides appear to be waving!;) No, no numbers, just observing it is >0.