smorgasbord
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- Jan 7, 2022
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I just watched a couple years old video from Spencer Lewis in which he made an interesting observation about his DeWalt SCMS that he uses to his advantage when cutting 45º trim to fit inside of wainscoting he built:
He saw that for his setup, the vertical pivot axis is the right side of the kerf where it meets the front of the factory fence. So, he has his measurement fence/stop block running to the right of the saw blade, and he's able to make both the 90º cuts for the vertical frame members of the wainscoting as well as for the 45º inside miters for the molding that goes inside with the same setting - as long as he does so to the right of the saw blade.
That struck me as odd: I would have thought the vertical pivot axis would be in the center of the kerf where it meets the factory fence. So I set about finding where it is on my Bosch GSM12SD "knuckle" SCMS:
1) Got a pretty flat board that is taller than fence, and clamped it to the fence on both sides of the blade.
2) Cut a 90º all the way through.
3) With a sharpie, marked the back of the kerf's edges:
[attachimg=1]
4) Then cut a right 45º down just enough to reach the top of the factory fence:
[attachimg=2]
As you can see, it cut off the sharpie, and actually cut about 1/32" more of the stock at the back.
5) Then cut a left 45º part-way down:
[attachimg=3]
Maybe you can see it just grazed the sharpie on the left (Looks like the right since this is taken from the back looking forwards).
Here are the boards pulled off the saw:
[attachimg=4]
Left board is on the right and right board is on the left, sorry, with the back sides up.
I'm running a CMT thin-kerf (2.5mm) blade on my Bosch, which has the arbor open side on the left. So, a full ⅛" kerf blade would cut about a 1/32" more off the left hand board. That would be good in that it would be (close to) centered, but in practice bad since the length of my boards using the ruler/stop block to the left would be off on angled cuts. As it is now, it's perfect for me: cut with the stock to the left mostly and the ruler/stop black will always give me the dimension to the stock at the back of the fence (which is usually the long run on angled cuts).
Attaching an auxiliary fence to the factory fence would mean the pivot axis isn't anywhere on the stock anymore, so the length you cut would change based on the angle being cut. That got me to thinking that if your saw doesn't have its pivot axis where you want, you might be able to move the factory fence forwards or back. The 45-90-45 cut test I shown above should give you enough information to figure that out, should you be as anal as I am about these things.
He saw that for his setup, the vertical pivot axis is the right side of the kerf where it meets the front of the factory fence. So, he has his measurement fence/stop block running to the right of the saw blade, and he's able to make both the 90º cuts for the vertical frame members of the wainscoting as well as for the 45º inside miters for the molding that goes inside with the same setting - as long as he does so to the right of the saw blade.
That struck me as odd: I would have thought the vertical pivot axis would be in the center of the kerf where it meets the factory fence. So I set about finding where it is on my Bosch GSM12SD "knuckle" SCMS:
1) Got a pretty flat board that is taller than fence, and clamped it to the fence on both sides of the blade.
2) Cut a 90º all the way through.
3) With a sharpie, marked the back of the kerf's edges:
[attachimg=1]
4) Then cut a right 45º down just enough to reach the top of the factory fence:
[attachimg=2]
As you can see, it cut off the sharpie, and actually cut about 1/32" more of the stock at the back.
5) Then cut a left 45º part-way down:
[attachimg=3]
Maybe you can see it just grazed the sharpie on the left (Looks like the right since this is taken from the back looking forwards).
Here are the boards pulled off the saw:
[attachimg=4]
Left board is on the right and right board is on the left, sorry, with the back sides up.
I'm running a CMT thin-kerf (2.5mm) blade on my Bosch, which has the arbor open side on the left. So, a full ⅛" kerf blade would cut about a 1/32" more off the left hand board. That would be good in that it would be (close to) centered, but in practice bad since the length of my boards using the ruler/stop block to the left would be off on angled cuts. As it is now, it's perfect for me: cut with the stock to the left mostly and the ruler/stop black will always give me the dimension to the stock at the back of the fence (which is usually the long run on angled cuts).
Attaching an auxiliary fence to the factory fence would mean the pivot axis isn't anywhere on the stock anymore, so the length you cut would change based on the angle being cut. That got me to thinking that if your saw doesn't have its pivot axis where you want, you might be able to move the factory fence forwards or back. The 45-90-45 cut test I shown above should give you enough information to figure that out, should you be as anal as I am about these things.
