What causes a blade to have mind of it's own?

[jackal]

Hi my home made saw has a habit of cutting in a direction not guided by me. The saw has a new clamp to the top but I have my original prototype clamp to the bottom which is a screw type clamp. I will be making a new bottom clamp but would like to know the potential cause. I keep making slight alterations to my prototype scroll saw and each time it seems to improve the functionality of the fret saw. Any ideas would be a help

[mtnman]

Jackal, With most blades, you have to aim to the left of center to cut a straight line. How far to the left depends a lot on the blade. Different blades cut differently, but even on fairly expensive commercially produced saws, you have to adjust to how the blade wants to cut. Also, if cutting with the grain, I find that the blade wants to follow the grain rather than my line.

I like your upper clamp. Keep showing your improvements.

[kofte]

Sometimes a blade may get twisted just slightly while making a turn. After that the blade may start drifting at a different angle. Especially infuriating if you haven't realized you twisted the blade. Grrrrrrrrrr.

[wood-n-things]

Another answer is that there is not enough tension on the blade allowing wood grain to dictate where it travels.

[3_M]

Yes Mike I have to agree with you about tension. Also the blade might be slipping out of the clamp.
mtnman, is talking that the blade will cut to the right. Most blades have burr on the right side and will cut to the right. You have to move the wood some degree to the right to stay on the line.
However most likely it is the tension. The blade should not move more than 1/8" side ways and that is almost too much.
FD Mike

[CanadianScroller]

I agree with all the comments so far.
I see from the pictures you have the tension set by the upper clamp. Rotating the handle moves the upper clamp away from the lower clamp.
Is there any sort of a cam operation to adjust tension too.
I would recommend that for speed of blade change and for the ability to repeat the tension settings.

[Xray]

Are you confident the upper & lower clamps are perfectly aligned ?

[Terry Jay]

How thick is the wood you are cutting, and what is the species?

Everyone's comments above are accurate and appropriate, but species grain and thickness can make it really bad.
Terry

[dgman]

I agree with Mike and mike about not enough tension!

[jackal]

Cheers for the replys I have now made a new lower clamp and it is better aligned with the top and the blade change is easier. The turning has stopped to the degree it was before. The old clamp was hole with a set screw and it didn't manage to hold the blade straight.

Cheers for the comment it was most helpful in finding the solution

Jackal