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Why would bevel angle change with change in miter angle?

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Forum topic by LiveEdge posted 09-12-2014 08:45 PM 1092 views 0 times favorited 10 replies Add to Favorites Watch
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LiveEdge

486 posts in 1085 days


09-12-2014 08:45 PM

I’m attempting to make some very accurate cuts that have both a horizontal angle (I’ll call that the miter) and a vertical angle (I’ll call that the bevel). I started out by truing the blade of my DeWalt compound miter saw to 90 degrees both horizontally and vertically. I make a test cut. Looks good measured by my bevel T-square. I then tilt the saw to 20.9 degrees to make my bevel cut and measure. Looks pretty good as well. Finally I rotate the saw to 30 degrees to make the miter cut. When I do this the cut of the bevel on the wood measures 113ish degrees instead of 110.9. It repeatedly does this so it isn’t an inaccuracy of my T-square.

Why is this happening? Is this something coming from “the math” (ie. the angle actually changes because I’m not making a square cut in the other dimension)? or is it something coming from a problem with my saw?


10 replies so far

View Jim Finn's profile

Jim Finn

2412 posts in 2386 days


#1 posted 09-12-2014 08:50 PM


Why is this happening? Is this something coming from “the math” (ie. the angle actually changes because I m not making a square cut in the other dimension)?
- LiveEdge


Exactly! that is the issue. I have found on line instructions on how to compute this and even a chart for it. I do not remember where it was but a search should find it for you. I have found that if the bevel angle is five degrees or less one can ignore the issue.

-- "You may have your PHD but I have my GED and my DD 214"

View Loren's profile

Loren

8307 posts in 3112 days


#2 posted 09-12-2014 09:04 PM

Compound miter saws can wander a bit in more extreme
cuts. The blade plate can flex and if it is a slider play
in the sliding mechanism may affect the cut.

If you’re trying to cut staves for a tapered sort of
cone, which I have done, the best I can suggest
is keep notes, make jigs and use trial and error
test cuts to get the bevels to match up.

View LiveEdge's profile

LiveEdge

486 posts in 1085 days


#3 posted 09-12-2014 09:10 PM

I’m trying to cut hexagons that will go together to make a sphere (think soccer ball with only hexes and no pentagons). It’s amazing how much you get out of whack as you build with a small error in the cuts.

The problem with actual test cuts is you have to make a minimum of five to put into a ring to see how close you are. I’ve been measuring with my bevel T-square, but so far my attempts are not close enough.

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Loren

8307 posts in 3112 days


#4 posted 09-12-2014 09:16 PM

Pattern cut them on a table saw. This will at least allow
you to go back, reattach the pattern, and make the
bevels steeper. Still trial and error. You are not
going to succeed in closing the form without significant
fiddling.

View ksSlim's profile

ksSlim

1204 posts in 2354 days


#5 posted 09-12-2014 10:19 PM

+1 for loren. Make a pattern, cut verticals, use router table for bevels.
I had to make a jig for the router table as the only bevel cutter I own is made at 45 deg.
Man adjustable jig and use a straight cutter.

-- Sawdust and shavings are therapeutic

View cutmantom's profile

cutmantom

389 posts in 2499 days


#6 posted 09-13-2014 12:31 AM

on a compound cut, both angles relate to each other, if you change one you most likely have to change the other, search for compound angle calculator

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LiveEdge

486 posts in 1085 days


#7 posted 09-13-2014 03:56 AM

Ok. I really like the idea of cutting the hexes out first with no bevel and the making a jig to cut the bevel on each edge. The only question in my mind will be how much wiggle the jig will have and will that throw things off. I’m out of town until Monday but I’m going to try this when. I get back.

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LiveEdge

486 posts in 1085 days


#8 posted 09-15-2014 03:50 AM

Can I just update and say that changing my plan of attack to have the hexagonal cuts on the chop saw and the bevel cuts on the table saw (thus separating the two) has made all the difference in the world. I have 10 of the 20 pieces gluing up and they went together with hardly a fuss. Amazing!

View ksSlim's profile

ksSlim

1204 posts in 2354 days


#9 posted 09-15-2014 04:14 AM

Here’s a calculator explanation if you’r like to set bevel and slope on a miter saw.
http://www.pdxtex.com/canoe/compound.htm
Took me a few tries to make it work.
That’s why i cut vertical and bevel the mating angle.

-- Sawdust and shavings are therapeutic

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LiveEdge

486 posts in 1085 days


#10 posted 09-15-2014 05:22 AM

Two shots of the work in progress. No sanding. No glue removal etc. I’m hoping to finish the other 10 panels tomorrow. I didn’t even want to breathe on the saws for fear of getting the angles off. :)


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