Measuring for Miter Cuts

[dkammer]

Hello,

Definate newbie question here:

OK...so my rip fence is set up perfectly. My cuts are exactly the width they should be...when the blade is at zero degrees.

When I change the angle of the blade...will the long side be true to the scale? The short side will (obviously) be shorter and by how much will be dependant on how thick the stock is. If the long side is not true to the scale then is there a rule of thumb as to how much you lose per angle or do you just have to make a cut and measure to see?

Thank you!
Darren

[WEG]

Hi Darren;
First of welcome aboard, secondly, that's a great question! I don't have a clue, I always measure, but sounds to me like you need to be real careful cutting those angle cuts with the saw blade tipping into the rip fence (if that's what you are doing...). You are setting yourself up for a possible kickback or a bad accident with the blade and you during the "push through"...be careful please. Don't have too much blade above the stock. If you can try cutting those on the other side of the blade so the blade tilts away from the fence.

Back to your question, I would think it all depends on where the saw/motor "pivots" in relation to the top and how much blade you have above the top. I bet it's not constant but changes with the blade height... I'm thinking here as I'm writing, always a dangerous thing
WEG

[LCHIEN]

quote:Originally posted by dkammer

Hello,

Definate newbie question here:

OK...so my rip fence is set up perfectly. My cuts are exactly the width they should be...when the blade is at zero degrees.

When I change the angle of the blade...will the long side be true to the scale? The short side will (obviously) be shorter and by how much will be dependant on how thick the stock is. If the long side is not true to the scale then is there a rule of thumb as to how much you lose per angle or do you just have to make a cut and measure to see?

Thank you!
Darren

when you tilt the blade the width depends upon where the arbor is.
As you raise the blade, however, the blade stays in one plane so the
cutoff width does not change with elevation.

I suggest you watch how the blade moves as you elevate and tilt it (with the power off, of course).

[Pappy]

quote:When I change the angle of the blade...will the long side be true to the scale?

Short answer, no. This would only be true if teh blade could rotate (tilt) at the point it cleared the throat plate. There is no formula for this that I am aware of. I mark the piece to ce cut, move the fence to the left, and sneak up on the cut line.

[LarryG]

I used the same method as Pappy. Mark the piece, get it roughly in the right position (but pretty close) with the saw not running, make a test cut to see where I am, adjust as required. Actual measuring, either on the saw or on the workpiece itself, is done only as a last resort.

[JimD]

I've never had great success in dialing in the width of a piece ripped at 45 degrees. I generally test on scrap. The rip fence scale is accurate on a relative basis, however. In other words if you rip and you are 1/8 over (nicer than 1/8 under) if you move the rip fence the necessary 1/8 you will be where you need to be.

I also do not like the fact that the BT3100 angles the blade towards the rip fence when tilted so I generally move the rip fence over to the left of the blade - so the tilt is away from the fence. This would make the small dimension closer to the 90 degree setting of the rip fence. A zero clearance plate that sits flush with the top helps. You have to put a angled slot in the plate but I have several that I use for this. Then you can measure from the rip fence to where the blade passes through the throat plate to get the initial rip fence setting. That gets me close. A micro-adjuster is also handy for moving the rip fence a little to get the rip exactly where you want it.

Jim

[skipwill]

quote:Originally posted by dkammer

Hello,

Definate newbie question here:

OK...so my rip fence is set up perfectly. My cuts are exactly the width they should be...when the blade is at zero degrees.

When I change the angle of the blade...will the long side be true to the scale? The short side will (obviously) be shorter and by how much will be dependant on how thick the stock is. If the long side is not true to the scale then is there a rule of thumb as to how much you lose per angle or do you just have to make a cut and measure to see?

Thank you!
Darren

Darren,

What I do is take a piece of scrap, clamp it to the SMT and cut it at the angle that i want. I then shut down the saw, slowly pull back the SMT with the scrap still attached to the SMT and make a pencil mark at the front of the saw, near the plate that indicates the point where the blade will make the cut, using the cut piece of scrap as an indicator. I then use that mark to line up future cuts, knowing exactly where the blade hit.

I do that for 45 as well as the normal 90 degree blade angles.

Skip