What's wrong with this sawblade ?

[Andy Dingley]

of mine showed me this at the weekend. It's a 7 1/2" CMT thin kerf sawblade, used once in a Hitachi C78U. Both of these are pretty decent kit and shouldn't be causing problems.

As reported, the blade was used once for sawing some MDF (and it was in the right way round). The cut wandered and so my friend was trying to steer it back into line. Sideways rubbing led to the overheating you can see, which is hardly surprising on a thin kerf blade.

But why should the overheating be confined to two opposed spots, rather than a ring ? Is there some mounting-induced warp that I've not noticed ? Runout (by eye) seems negligible.

[Eric Johnson]

I saw a high speed video at the Milwaukee ww'ing show last spring that showed that exact problem, vendor was selling blade stiffeners. Anyhoo the blade when it starts to distort takes on a potato chip shape as it actually starts to run in two separate planes. I guessing those hotspots are where the distorted plane was beginning and ending. I'm also guessing that they eventually would work around in a full circle with continued use. But hell I've been wrong before... could be just a flaw in the steal or machining.

EJ

[TeamCasa]

I agree with Eric, the real problem is between the handle of the saw and the outlet it plugs in at. Tell you friend that saws, unlike cars, boats and airplanes are not to be steered back on course.

Dave

[George]

Two weakened spots - the holes - flex, and the part in contact at max deflection would be where the burns are?

[Old Nick]

On Tue, 14 Sep 2004 03:08:46 +0100, Andy Dingley vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

I hyave used an old non-tunsgten blade to cut steel. In too-thick steel it gets very hot and starts to warp. When it cools down it's straight again. So you check the blade, and find that it's OK when cool.

The wandering is probably because the blade is not parallel with the foot(?) on the saw. So if you cut with a fence, the saw wanders. You then have to push sideways to maintain the cut and bingo.

***************************************************** I know I am wrong about just about everything. So I am not going to listen when I am told I am wrong about the things I know I am right about.