Cutting a mitre

As a carpenter designer , in many ways I use sketch up as I would timber on site eg , I can cut one rafter then use it as a pattern to cut a whole load more once I have checked it fits – in sketch up obviously cut means draw /make component /cut more ctrl C then ctrl V
One thing I commonly do on site with complex shapes eg handrail with a curved top is cut ends at 45degrees to form a mitre joint , I have never worked out an effective way to do this with sketchup components containing curves
Any Ideas – A mitre saw extension would be great :slight_smile:

Draw a rectangle and position it where you want the cut, imagine it is a saw blade, then use Intersect Faces with… to make the cut.
I’m not at a computer just now so can’t make a demo.

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Hi Box
That is perfect thanks! :slight_smile: , I had done the drawing the rectangle at an angle part before but never realized what intersect could do - I had worked out a much clumsier way of doing it by drawing a square putting the profile face on it using follow me then doing a lot of deleting - your way is so much easier and more versatile

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Mike: mean compound miter cut???

FWIW, if you are putting a 45 degree miter on a rectangular prism, a board in your case, you could also select the waste corner edge and move it along the length the same distance as the board is wide. At least for 45 and 22.5 degrees, it’s pretty easy and fewer steps.

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Hi Dave

handrails.dae (106.3 KB)

Hi Dave
Thanks for that one I did try previously but it doesn’t work with more complex shapes - as attached pic
the intersect works beautifully – I am going to play with it more – I may see how making a “mitre box”
With standard angles, pre-marked on a “baseplate” works – I am thinking about using the same to address Macs question about compound mitre - unless there is a smarter way to do that as well! :slight_smile:

You’re right, Mike. Moving the edge doesn’t work for more complex shapes but it’s a handy one to know for simpler shapes.

You can make the “miterbox” if you want. I’ve never seen the need for one. It’s so simple to set up a single face at the required angle and use it as a cutter.

Another option is to draw the molding or rail using Follow Me and then divide it into sections at the joints. In the example below, I drew a miter line on the bottom face to divide it and then made components of each part. This will work for compound miters, too.

If you have common miter angles and common profiles, you could just make components that can be reused. No need to cut the miter every time. So for example, you could make a couple of crown molding components. One with an inside miter and one with and outside miter and you’d be all set for any 90 degree corners.

Hi Dave
I found the follow me works ok , ans I initially though perfect make a few standard ones then use push pull for lenghts but actually demands multiple ones when you start to look at all the possible combinations of what you might want at each end eg point to point opposite mitrw ,point of mitre to flat end left or right etc etc
Again the intersect works more flexibly
I just drew a rough first go at a “mitre Box” as you say its real use is to copy the face required then paste/move that onto the point I want to cut at - first attempt I have a 45/34 degrees compound mitre - perfect :slight_smile:

Whatever works for you is the way you should do it.

Make sure you are correcting face orientations as you go.

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Say Dave, is it important to orient the faces correctly, even if you aren’t going to render the scene? I just export images and have never noticed anything wrong with them.

Joe, there are other issues related to face orientation other than just rendering. From my experience of modeling and helping others with their models, I can say that’s part of clean modeling and clean models are much easier to work with.

There are many miter calculator ie Compound Miter Saw Calculator
in this they use SU to show the illustrations for the angles

Hi Joe
Thanks for the interest , I have to agree with Dave re the orientation of faces , I do a lot of drawings with multiple components - sometimes quite complex curved shapes set at specific angles that I copy and paste into their relevant positions to produce a large model - for example a house -eg’s below , w
My experience is that drawing them in the correct orientation is much easier than trying to get hold of them to rotate them afterwards
This exchange is actually a much needed kick up the behind me to learn the solid tool functions :slight_smile:

e built the outdoor kitchen (including the structure it sits under) ,stainless balustrades, and fixed the seawall here
What is your favourite rendering package?

I have to revive this subject…and I apologize.
I’ve been using SU for a few years and I’m struggling with mitering some moulding.
I get the intersect faces, I’ve used that before but I’m stuck on the simplest thing.
“draw a rectangle” Draw it where? I can’t just draw a rectangle in open 3D space, and how at 45 degrees? I drew one on the baseline, tried to rotate it but the top has no width, can’t get the rotate handle to grab onto anything.

So, I’m stuck on “draw a rectangle”. It’s probably SO obvious, I just can’t see it.

Thank you all.

Draw the rectangle where you want the miter. Think of it as the edge of the saw cut if you were cutting the molding on the CMS. If you share your SketchUp model file, it would be easier to give you specifics.

You should be able to use the parts of the model you’ve already created as reference for drawing the rectangle.


Thanks for your example, it’s going a little fast.
mitre.skp (24.9 KB)

There’s not much to upload. I’d love your comments from here…

Did you make the rectangle a component?

It looks like after you draw the rectangle, you CUT, but when I cut, it deletes the face of the rectangle and not the edges. Maybe you are making it a component, but I don’t see that you do.


No. The molding pieces are components but the rectangle is loose geometry.

Notice that I selected both the face AND the edges (double click on the face with Select) Again, I’m not making it a component.

Here it is again. This time I dragged a left to right selection window around the rectangle.

The only way to make the rectangle CUT like that is if I make it a component (G), otherwise it CUTs the face and leaves the outline. SO… I make it a component.
Then CUT, edit component, paste-in-place etc…
Then when I erase the extra corner, it leaves an open hollow end.