Guide pressure

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Guide pressure

Postby kingcobra » Wed Dec 14, 2011 3:00 pm

I'd like to hear some opinions. All the material i've seen in regards to guide pressure shows the top and bottom wheels having a common centerline (the wheel faces are plumb) or that the top wheel is set "back" from the saw line to create giude pressure on the top guide. In ther first arrangement top and bottom guides are off set to create pressure. In the second arrangement the guides are in a plane parrallel to the bottom wheel face and the op wheel is rolled "back".

My question is - in a bandmill where the top guide adjusts according to depth of cut is there any special consideration given to top wheel position and guide offset?

The guide travels at a fixed offset but the angle the saw leaves the top wheel changes. The lower the guide position the lesser the angle it leaves the wheel. The higher the guide moves the greater the angle becomes.

I'd love to hear any thoughts on this matter, Thanks!!!
kingcobra
 
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Re: Guide pressure

Postby thinkerf » Mon Dec 19, 2011 1:06 pm

My procedure is generally:

1. Set the guide pressure for the bottom guide.
2. Move the top guide up so that it is in the position for your larger logs. Don't set it for the occasional monster log or for the top of the slide if it never goes there.
3 Now adjust the top guide so it is plumb to the bottom guide. Also check the knee to saw distances top and bottom.
4. Move top wheel back or forward to get the same guide pressure as on the bottom.

For cuts where the top guide can come down, there is less pressure on the top guide, but this is ok since the depth of cut is smaller.

While you're at it, check that the guide slide is plumb, otherwise the top guide will move laterally as it goes up and down. Some movement can't be avoided because the blade is bent over the guides, so span between the guides is never straight and the amount of bending depends on the guide span.

5. Tilt the guides so that the blade touches the top and bottom edges of the guide block. This greatly reduces guide wear and the bending stresses in the blade, which will reduce the likelihood of cracking.

6. Use a spider to check for cross-line in the guides. If you can do this for the up and down position of the top guide, that will also show if there is a problem with the guide slide. You can also use the spider to check for cross-line between the guides and the wheels.
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