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Need help in determining the angles I need to cut

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Forum topic by Angela posted 1132 days ago 1627 views 0 times favorited 15 replies Add to Favorites Watch
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Angela

205 posts in 1530 days


1132 days ago

Topic tags/keywords: question joining tablesaw mahogany design designing math formula

I’m designing a stand for my TV. I figure there must be a math formula I could use to determine what angles I need to cut. There are the two side pieces which will be at an angle and the rear side piece will be at an angle with the back piece. I figure that once I can determine the angles, then I can determine the dimension of the front.

I added the image because there’s no way I can explain what I’m talking about. It’s not the best image but I didn’t know I’d be posting it online.

Thanks
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's


15 replies so far

View drewnahant's profile

drewnahant

218 posts in 1723 days


#1 posted 1132 days ago

I can figure this out quickly for you, but I need to know how you are laying out the front, do you have a width you need, a depth from the widest point to the front, or an angle. you just dont have enough info there to determine.

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drewnahant

218 posts in 1723 days


#2 posted 1131 days ago

I drew it up with the front sides at 45* to the horizontal of the drawing. though bentlyj’s suggestion seems good to simplify things.

View Angela's profile

Angela

205 posts in 1530 days


#3 posted 1131 days ago

Thanks so much I’m going to have to study your drawings but thanks I didn’t know I’d get such great answers. So the 16-5/16 isn’t set right? If that is changed then all the others would change. Is that what you ment about missing info? Instead of the 16-5/16” I would like the depth to be 22” or somewhere around there.

Thanks again I’m at awe with your guys drawings.
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

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Angela

205 posts in 1530 days


#4 posted 1131 days ago

After looking at my diagram and looking at the TV I have I think I’m going to have to change the dimensions. I would like the total depth 25”. After looking at the sizes of the sides I have would make the angles pretty severe. If you guys would be so kind, I would like to get better measurements then ask you about the angles.

Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

View auggy53's profile

auggy53

159 posts in 1314 days


#5 posted 1131 days ago

bentlyj ,,,,,,,,,,, you sure are a nice guy

-- rick

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gul

398 posts in 1597 days


#6 posted 1131 days ago

Oh God,this is so complicated :/

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Angela

205 posts in 1530 days


#7 posted 1131 days ago

OK I’ve made a pattern and good thing or it wouldn’t have worked but here’s the final design with measurements. I hope I provided all the ones you need.
Thanks again
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

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Angela

205 posts in 1530 days


#8 posted 1131 days ago

I took a stab at it. I indicated the miter setting and not the angle. But I was wondering if I’m even close.
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

View Tootles's profile

Tootles

690 posts in 1136 days


#9 posted 1130 days ago

Angela

Why are you making the cabinet this shape (i.e. six sides)? Is this to go into a corner of a room? If so, the angles given to you by Bentlyj in post #6 are essentially correct as they will give you two sides parallel to the two walls, to sides at right angles to the walls and two sides (the front and back) across the corner at 45° to the room.

If you then accept that those angles are correct, all you can do to dimension the unit to fit the TV is decide the width of the front, the depth of the sides perpendicular (or at right angles if you prefer) to the walls and the depth of the unit (with some trade-off between size of the perpendicular sides and the depth).

Hope this helps. I’m sure I could explain further if you need me to.

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

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Angela

205 posts in 1530 days


#10 posted 1127 days ago

Bentyj – Thanks for your help. I’m interested to see how everything comes out.

Tootles – Thanks for the info but it’s not going into a corner. Anyway that would make this too easy and I’m ready for a challenge.

Thanks everyone
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

View Tootles's profile

Tootles

690 posts in 1136 days


#11 posted 1126 days ago

That’s great Angela, a challenge is always a wonderful thing.

Calculating the angles mathematically, I get one angle a little different to Bentlyj – I get 129.3 instead of 127.8 (and so the 121.9 becomes 120.4) but, when I plot it on Sketchup, my dimensions come out entirely wrong and I agree wiith Bentlyj’s numbers – so I’m a touch confused as to what’s going on there.

That suggests a third method might be even better for marking out and measuring, which works something like this:

1. Mark out the front line (36 1/2 “)
2. From the centre of the line, draw the 23” depth at 90°
3. Mark out the back line (33 1/2 “) parallel to the front and having its centre on the 23” line
4. Using a compass (you could even use a pencil tied to a piece of string if necessary), draw two arcs with a 7 1/2” radius from the ends of the front line
5. Using a compass, draw two arcs with an 18” radius from the ends of the back line
6. Measure that the two intersection points are 46” apart, and that the line betwee in parallel to the front and back.
7. Measure your angles from there. You might not even have to actually measure using a protractor, it may be sufficient just to set a sliding bevel.

Alright, enough said. Go enjoy your challenge!

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

View helluvawreck's profile

helluvawreck

15627 posts in 1501 days


#12 posted 1126 days ago

For anyone that is interested, there is an excellent CAD program that is not very expensive yet has a lot of features. It’s called Turbocad and at $129 it is a bargain. It will give you professional looking drawings and will help you perform mathematical problems. Plus it comes with all kinds of symbols that can be used in drawings. I use it at home and in the machine shop at the plant. It also runs a CNC router that we use at the plant to make templates that we use to grind our molder tooling with. I’ve never needed any other CAD program and we occasionally build special machines for the plant.

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

View Angela's profile

Angela

205 posts in 1530 days


#13 posted 1124 days ago

Tootles I also got 129.3 for the measurment but I figured Bentlyj was more exact so I went ahead with his measuements and so far so good. Everything fits together nicely. My next step is securing the miter corners. I first thought of biscuits but then after doing some reading I settled on splines. I’ve use biscuits before but never splines. I’ll also be using dowels or tenons for some of the other joints. I haven’t used either so far in a project so each step is new for me and I thank everyone for posting their comments and helping me.

Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

View Tootles's profile

Tootles

690 posts in 1136 days


#14 posted 1123 days ago

Bentlyj, I agree, I could come up with no sensible explaination why Sketchup should be wrong. On the other hand, I could come up with no reason why the answer calculated using trigonometry should be wrong either. As both an engineer and a future maths teacher, that worries me. Fortunately, although it took me a while, I do have an answer.

I worked off the following 6 dimensions:
- Front = 36.5”
- Back = 33.5”
- Distance front-to-back = 23”
- Distance point-to-point =46”
- First angled edge = 18”
- Second Angled edge = 7.5”

Put simply, these dimensions cannot all be achieved if the front and back are parallel – only five of the six are achievable. Plotting the shape using the angles I caclulated using trigonometry results in the distance front-to-back being about 3/8” short of 23”. Plotting it as I suggested using a compass rsults in the distance point-to-point being about 3/4” short of 46” (according to Sketchup). And plotting it as you did in Sketchup extends the length of one side by 1/4”. Any one of these solutions is viable, it’s Angela’s choice which dimensions are most important and which one she doesn’t mind altering.

So Angela, you have done the right thing by just picking one method on the basis that you don’t mind the side being that 1/4” longer and running with it. In fact, since Bentlyj’s method is the only one that enlarges the shape overall, I think you made the best choice. Bentlyj, not that you didn’t have this already, but let me say publicly that you have my respect.

Angela, keep on having fun and good luck with the joints. I wil be keeping an eye out for the project when you get it done.

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

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Angela

205 posts in 1530 days


#15 posted 1121 days ago

Bentlyj I did use your angles and they worked great. I see in the drawing you have 18 and not 18-1/4” which you mention in a later posting. It’s interesting because I ended up using 18-1/4”. I’ll have to check the other side measurement because I can’t remember if it’s 7-1/2” or 7-3/4”

I thank everyone for their help. I’ve started a blog regarding the problems I’ve had so far with this project.
Angela

-- www.WoodWorkersWebsite.com - Helping other woodworker's

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