how to measure a board that is to be sliced

[elizabeth]

Hi, Guys:

I meant to ask this before. Actually, every time I have to do it! ;D

I want to cut a board that is at 45* into equal slices. Because my measuring is off, I end up with many un-usable ends of different lengths. I can cut a rectangular board into equal pieces and even do the figuring to compensate for the kerf. A board at 45* eludes me.

I spent two hours measuring and figuring to cut a new blank into equal pieces. I drew it out on paper first, like you suggested. I accomplished it, but the slices are narrower than I wanted. This is what I did:

After doing the math, I set the miter gage at 45* and measured the distance from the out feed side of the kerf cut in the auxiliary fence to where I "wanted". Placed a mark on the fence and a stop block. I'm cutting from right to left, with the fence coming towards me, and the offcuts are my keeper pieces. I measure the board, and place the stop, after the first miter cut is done.

No problem, except that I soon realized my pieces were about 1/8th narrower than I wanted. The mitered edges were the exact dimensions I set up for, but that's no help! I won't waste the board, but it would be nice to know how to set-up for these cuts so I get the right size slices.

This is got to be a variation to the rise, run, slope you have labored with me. I haven't been able to resolve this on my own and I sure can use your help.

Thanks!

[Ruffnek]

I just woke up from a nap but I'm having trouble visualizing your set-up or what you are trying to accomplish.

Would it be too much trouble to take a picture of your set-up with perhaps a simulation of the cut you are attempting?

[Beezlebub]

I would just cut a waste board until you have the set up right.

[Knotty_Pine]

I'd almost be certain the 1/8" you're losing is the width of your kerf. You must allow for that wastage. As the saying goes, it's impossible to cut a 8' board into two exactly 4' pieces, they'll either be one 1/8" short, or both 1/16" shorter.

TJ.

[TDHofstetter]

'Lizabeth, I'm not quite clear on exactly what you're doing either... but I suspect this might be a good time not to MEASURE, but instead to FIT something. Like... cut a piece of scrap so-and-so wide or long, then use it to lay out your cut. I'm not sure that made any sense at this point, not knowing for sure exactly what your cutting setup looks like.

[elizabeth]

Gotcha. I'll take photos and post next day or two. Have a storm coming and need to turn the PC off.

Happy Memorial day!

[dburkhart]

sure sounds like that is the width of your saw blade,just add 1/8

[elizabeth]

Storm is past for a bit. May have to shut down again.

In a gist: When I'm cutting a blank at a 45*, into slices, I'm having difficulty calculating how many slices I can get out of the length of the board. For some reason, I can't do the math, and when I think I've got it, I end up with either too many pieces, or worse, too few. I've measured the teeth of my blade. It's 3/32.

In my math, I've added 3/32 to the desired width since I'm keeping the off-cut pieces. I've set the stop block to the desired length. I've scribed lines on the board to guide me. The first cut (after the initial miter of the end) is on target, and I set my block with it. None of the succeeding cuts, thought equal in width as the first, correspond to the lines I've drawn. When I'm reaching the end of the board I'm holding my breath hoping that I'll have enough wood left to get the number of pieces I need.

See pics:

This first pic shows a measurement at the diagonal? Ended up not wide enough, but it's what the math determined. I had set the stop at 9/16 from the outside of the kerf cut on my fence. What I wanted was a 9/16 wide piece. Didn't get it.



A sample on how I set my stop block at 18/32 (thereabouts)




Ended up with 13/32 when I wanted 18/32




Cut slice:



Glue up:



I made two different width chevrons today. What I did on the one you see was to lay my combo ruler across the board at the 45* and then rested a straight ruler on it's end, against the 45* to determine a width of cut (triangulation?). In spite of this and the subsequent pencil lines, I was so off mark on the succeeding cuts I thought I was going to be out of wood !

Obviously, there is a method I am incapable of thinking of on my own.

Please let me know if I've clarified matters, or need to try again.

Thank you for your patience.

Your Agee!

[Ruffnek]

The reason you are measuring 13/32" is because that end is still at 90 degrees. If it were angled at 45 degrees, it would measure 18/32".

To get a slice that's 18/32" at 90 degrees to the long axis, you will have to set your stop at ~23/32".

Gert some scrap to practice on until you are able to repeat the dimension you want.

BTW, I love your set-up. I've been worried about your methods and your safety but I see that you are doing things perfectly safe. Good girl.

[elizabeth]

Oh, Yeah! Safety first. It's the first thing you all drilled me in. Thanks!

But: Yes, I can practice. But isn't there a formula I can use that would be repeatable, depending of the different dimensions I want, instead of making numerable test cuts? Without it, I won't know if I have enough board!

Ie: How did you KNOW I needed my stop at 23/32 to achieve a slice of 18/32?

[Ruffnek]

May 31, 2010 19:32:51 GMT -6 elizabeth said:

Oh, Yeah! Safety first. It's the first thing you all drilled me in. Thanks!

But: Yes, I can practice. But isn't there a formula I can use that would be repeatable, depending of the different dimensions I want, instead of making numerable test cuts? Without it, I won't know if I have enough board!

Yes, it can be calculated but not by me! I'm mathematically challenged, also. Dave Carter is pretty good at this stuff. Perhaps he will chime in.

[elizabeth]

[/quote] Yes, it can be calculated but not by me! I'm mathematically challenged, also. [/quote]

I don't buy that. You somehow knew that I needed my stop at 23/32 to get a 18/32 slice! How did you figure that?

[Ruffnek]

May 31, 2010 19:49:54 GMT -6 elizabeth said:

Yes, it can be calculated but not by me! I'm mathematically challenged, also.

I don't buy that. You somehow knew that I needed my stop at 23/32 to get a 18/32 slice! How did you figure that?

I figured it by subtracting the 13/32" measurement from the 18/32" measurement and then adding that amount (5/32") to the 18/32" measurement.

Trust me, I am not mathematically inclined.

[TDHofstetter]

Elizabeth - remember that magic number, 1.414 and its partner 0.707. They work all SORTS of places where you've got 45-degree angles. In this case, your pieces came out 0.707 times as wide as you wanted them to - you needed to measure 1.414 times as large as you wanted to be right on the button.

Funny numbers, 0.707 and 1.414.

0.707 x 1.414 = 1.000.
1.000 x 1.414 = 1.414.
1.414 x 0.707 = 1.000.
1.000 x 0.707 = 0.707

0.707 x 2 = 1.414.

The hypotenuse of a 45-degree right triangle is 1.414 times as long as the other sides.
Each of those sides is 0.707 times as long as the hypotenuse.

[elizabeth]

Thank you! I knew it had to do with what you've taught me but didn't know how to apply it. Now I can!