Neat little trick to check bandsaw for perpendicularty

[bobgroh]

Ouch - I guess the technique is deeply flawed - as in, it won't work. I made a pass at this using geometry and have to concur.

One thing that we could do is cut the vertical in the board (presumably perpendicular) and then check that cut vertical that using an accurate square (which, thanks to a great estate sale find, I actually have). We can also, with a little geometry, actually calculate just how many degrees the blade is off (of course, all of us are dead on!).

[beeg]

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

So if the edges are parallel. The table at 89°, the cuts will be parallel?:rolleyes:

[bobgroh]

So if the edges are parallel. The table at 89°, the cuts will be parallel?:rolleyes:

The answer is yes. Unfortunately.

[greitz]

A common procedure to check that a scroll saw blade is perpendicular to the table is to make a shallow cut in a block of wood (like the first cut shown in the video), then rotate the block 180 degrees on the table, without lifting the block from the table, and check to see if the back of the blade fits smoothly into the slot in the block of wood. If it fits, the blade is perpendicular to the table.

Should work the same way for the bandsaw.

(Also described on the Shopsmith site under "basic scroll saw techniques:)

http://www.shopsmith.com/academy/scrollsaw/021003.pdf

Gary

[dusty]

So if the edges are parallel. The table at 89°, the cuts will be parallel?:rolleyes:

But I do hope that they are not perpendicular to the table.

[JPG]

The slide around to the back side of the blade procedure eliminates two problems with the 'video'.

1) Using two different edges and assuming them to be parallel.

2) The problem Rob identified.(a straight line crossing parallel lines does so at common angles, but not necessarily 'normal' to the parallel lines).

FWIW a technique similar to the 5 cut procedure with the table saw would be more accurate. The fifth cut would not need to be a through cut. A tight holding against a miter gauge would be required to be effective(maintains cut edge to blade angle). That seems like too much trouble though! Also likely to be affected by :eek:blade drift:eek:.

[jimthej]

Ok, I was wrong. The swing around the back is correct. Someone posted a comment pointing out the error on the WGOA website.

[forrestb]

Couldn't help myself. Rather than off-setting my bandsaw table I offset my square by several degrees and used a 'perfectly' parallel board (well, perfect within 1/128) and did the WWGOA trick. Obviously wrong, both lines are parallel and at the angle of my square>
Forrest
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