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cutting a 50 degree angle

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Forum topic by daddywoofdawg posted 11-19-2017 01:38 AM 1442 views 0 times favorited 19 replies Add to Favorites Watch
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daddywoofdawg

1022 posts in 1407 days


11-19-2017 01:38 AM

I know there is a answer,but I can’t figure it out I’m making 1×2 christmas trees See photo,It calls for a angle cut at 49 degrees. On my miter saw it’s marked as 0 (90) – 45.So my thinking is 0 is 90 and then 49 would read 41 on the saw.(let me know if this is the wrong thinking) but My issue comes when I place the boards as required together (one end calls for 20 and the other has the 49), when I put them together I get a gap of anywhere from a piece of paper to a business card gap at the joints,I have checked the cut and they are even,checked the measurements and they are right on,check the angles they are right on,tried angles from 48-51 and still get same results.yes know big deal on these I can and do putty them,but projects like this I use as honig a skill projects. can any see what I maybe doing wrong or how to fix? arrows point to joints.


19 replies so far

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jbay

1848 posts in 732 days


#1 posted 11-19-2017 02:02 AM

I come up with 49 @ top and 20.5 on the 2 others at the bottom.

On your miter saw you would use 41 deg. if your piece were 90 deg (perpendicular) of the fence.

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

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daddywoofdawg

1022 posts in 1407 days


#2 posted 11-19-2017 02:15 AM



I come up with 49 @ top and 20.5 on the 2 others.

- jbay


That .5 degree could be the reason for the gap. is it even possible to get 20.5 on a miter saw, or should try to get the angle on the table saw?

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Dark_Lightning

2908 posts in 2941 days


#3 posted 11-19-2017 03:07 AM

This is a time when you should consider using a shim on one end of the wood. A little trig, and you’ll have the angles right where you want them. When I made my cross cut sled, I used a feeler gauge set (carefully cleaned- I use them for mechanic work, too) to get the front board square to the blade. It is dialed in to the the wiggle of the blade. People may think that that is overkill, but when one is making a small box, the joinery has to be right on. Just use a little math and shim an end so that when you run the wood through the saw, that it is dead on. I’ve even made shims from masking tape, for cuts that need to be close.

-- Random Orbital Nailer

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jerryminer

798 posts in 1274 days


#4 posted 11-19-2017 06:20 AM

20-20-49 does not make a triangle.

20.5-20.5-49 will do it, or 20-20-50.

Lots of possible causes for the small error:

lengths slightly off
Blade deflection
wood not perfectly straight
Miter scale slightly off

-- Jerry, making sawdust professionally since 1976

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daddywoofdawg

1022 posts in 1407 days


#5 posted 11-19-2017 08:30 AM

I was thinking the info was off. so on a miter saw that is marked 0-45,would 40 be the same as 50? i.e 45 is 45 but wouldn’t 0 be 90? so 45+ 1 degree =46, etc to 90 or zero on the scale?

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Loren

9602 posts in 3480 days


#6 posted 11-19-2017 08:36 AM

90-20=70
90-50=40

70+70+40=180

Triangles with straight sides always add up to
180 degrees at the corners.

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jerryminer

798 posts in 1274 days


#7 posted 11-19-2017 09:05 AM

Right. Your triangle would have 70 degree angles at the base, and a 40 degree angle at the top.

The miter saw settings would be 20 at the base, and 50 at the top

-- Jerry, making sawdust professionally since 1976

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richardchaos

517 posts in 212 days


#8 posted 11-19-2017 10:14 AM

I just heard THIS GUY is turning in his grave…

-- “In a time of universal deceit, telling the truth is a revolutionary act.” ― George Orwell

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Tootles

808 posts in 2334 days


#9 posted 11-19-2017 10:22 AM

If you cut the bottom piece with your miter saw set at 20°, the the top angle must be cut with the saw set at 50° – which you cannot do directly. When I have done something like this before I did the following:
  1. Clamp a piece of wood against the fence of the saw. The wood needs to be quite wide – about 5” and laid flat.
  2. Make a cut with the saw set at an angle of 45°
  3. Set the saw to a 5° angle (to make a 50° cut)
  4. Place the piece of wood that you need to cut onto the saw using the 45° cut of the wood clamped to the saw as a fence
  5. Make the cut – being EXTREMELY careful of where your fingers are.

In cases where I had a number of these cuts to make, I made a jig based on the procedure above that allowed me to place the pieces more consistently and that better allowed me to keep my fingers away from danger.

But the angles and dimensions that you list do not quite add up. With a 20° angle at the base, a triangle that has a base with of 12” will have a vertical height of 16 1/2”. If you want a 12” base and a height of (approx.) 24”, then the easiest is to make the base angle 15° in which case the angle that you set the saw at for step 3 above also works out to be 15°. This will give a vertical height of 22 3/8”.

-- I may have lost my marbles, but I still have my love of woodworking

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Tootles

808 posts in 2334 days


#10 posted 11-19-2017 10:29 AM

I’ve just has another thought. If you cut the top angle with your saw set to 45° and your base angles with the saw set at 22.5° (most saws do have a positive stop at this angle), then the angles of the triangle will add up to 180° as required. Unfortunately, however, the triangle will be even more squat than with the base angles set at 20°. It depends which is most important to you – height / shape or ease of manufacture.

-- I may have lost my marbles, but I still have my love of woodworking

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jerryminer

798 posts in 1274 days


#11 posted 11-19-2017 06:38 PM

If your saw won’t swing to 50 degrees, you can fab an acute angle jig like this:

-- Jerry, making sawdust professionally since 1976

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bandit571

18600 posts in 2516 days


#12 posted 11-19-2017 07:23 PM

Just did a very ROUGH mockup….used my Langdon 75 set at 40 degrees, and at 20 degrees…...all depends on which side of the saw blade you cut from. Need to cut better miter cuts, as there wasn’t any stops at 40 and 20.

Used just what scraps I had on hand…....might need the sizes the OP was going to use, to make a better one….

-- A Planer? I'M the planer, this is what I use

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Kelly

1821 posts in 2777 days


#13 posted 11-20-2017 05:34 PM

Keep it simple, for those of us who don’t even know what trig is – Everything boils down to a circle. That is, it has to tie to 360 degrees. As such, a square needs four ninety degree joints to avoid gaps, a hexagon needs six sixty degree joints, a pentagon needs five 72 degree joints and a triangle needs three 120 degree joints of variation.

In the end, the pattern is obvious – it has to add to 360. You can take some off one joint, but you’ll have to add it elsewhere to keep things real.

Of course, it remains the cuts are half the joint angle (e.g., a 90 degree joint needs 45 degree cuts, a 120 degree joint needs 60 degree cuts, a …...).

Sometimes, you have to goof with the numbers to get to what you need. For example, my table saw cannot cut the 60 degrees I need for a perfect triangle. Because of this, and, again, not knowing anything about that trig stuff, I had to experiment. I knew 90 degrees was, for whatever reason, an important number in the scheme of things, so I shout for it and tipped a board on end and went for that, via the balance (60 from 90) and my saw made a 30 degree cut just fine.

Whatever. Maybe that ninety and the thirty tied in there somehow to give me the 120. Maybe it tied to the 30 being half the sixty. Anyway, it worked and I got my triangular planter by playing with common circle numbers, and a few guesses.

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jonah

1441 posts in 3131 days


#14 posted 11-20-2017 07:16 PM

^^ That might be the most bass-ackwards explanation of geometry I’ve ever seen.

Try getting a protractor and a piece of paper and playing around with different angles if you’re having trouble visualizing what angles affect other angles in triangles.

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Kelly

1821 posts in 2777 days


#15 posted 11-20-2017 07:49 PM

It might be, but what would you do if the Net didn’t exist and you had never taken geometry or trig?


^^ That might be the most bass-ackwards explanation of geometry I ve ever seen.

Try getting a protractor and a piece of paper and playing around with different angles if you re having trouble visualizing what angles affect other angles in triangles.

- jonah


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