Neat little trick to check bandsaw for perpendicularty

bobgroh · Post by **bobgroh** » Thu Sep 12, 2013 11:20 am

Just caught this little video from a link from an eNewsletter from Wood Magazine. It shows a (IMHO) rather neat way to check your bandsaw to make sure the blade is truly perpendicular to the table:
http://www.wwgoa.com/video/000329_squaring-your-blade-to-the-band-saw-table/?sssdmh=dm17.692085&esrc=nwwood091213

Well, at least it seemed neat to this guy!

algale · Post by **algale** » Thu Sep 12, 2013 11:29 am

Thanks for posting. I do think that's nifty.

dusty · Post by **dusty** » Thu Sep 12, 2013 11:37 am

Yes, that is a neat trick but think about it a little bit. That does not apply to just the band saw.

You can, with some minor changes, confirm table saw table to blade in much the same way.

You can also confirm the miter gauge is square to the blade the same way.

SDSSmith · Post by **SDSSmith** » Thu Sep 12, 2013 12:52 pm

I believe their logic is flawed. I believe trigonometry would reveal that the cut lines would be parallel even if the blade is not square to the table using their technique.

Now if you made a cut all the way through the board, rotated it 180 degrees around the vertical axis, made a second cut. The cutoff will have parallel sides if the blade is perpendicular to the table.

reddog5362 · Post by **reddog5362** » Thu Sep 12, 2013 1:40 pm

SDSSmith wrote:I believe their logic is flawed. I believe trigonometry would reveal that the cut lines would be parallel even if the blade is not square to the table using their technique.

Rob is correct. If the cuts aren't parallel all you've proved is that the opposite edges aren't parallel.

dusty · Post by **dusty** » Thu Sep 12, 2013 3:09 pm

It sure sounded like a neat trick!

I was convinced but after going to the shop to verify what Rob reported, I am instead embarrassed.

With my math background, I should have seen that immediately.

charlese · Post by **charlese** » Thu Sep 12, 2013 4:13 pm

SDSSmith wrote:I believe their logic is flawed. I believe trigonometry would reveal that the cut lines would be parallel even if the blade is not square to the table using their technique...

Even plane ol' plane geometry.

Maybe we (someone) should write to Wood Magazine. Maybe someone who subscribes to their eNewsletter.

jimthej · Post by **jimthej** » Thu Sep 12, 2013 4:43 pm

No, it's correct. The caveat is plainly stated that the edges of the board must be parallel.

heathicus · Post by **heathicus** » Thu Sep 12, 2013 4:57 pm

Someone should leave a comment to the video explaining it. I would, but I didn't see the problem and had to test it myself using a post-it note (as the wood), a business card (as the blade) and my desk (as the table) to verify! I don't want to steal someone else's smarts, but a comment should be left there.

terrydowning · Post by **terrydowning** » Thu Sep 12, 2013 5:00 pm

It might also be a good idea to verify the cuts with a known good square.

Which is tested pretty much the same way.

Using a jointed, trued edge to reference from, scribe a line, flip the square and scribe another line next to the first. If the lines are parallel, you're good.

The proviso is clear though. The edges of the board must be dead flat and parallel to each other.

I use a square against the blade If I need a cut to be more square than that, I'll shoot it on a shooting board.