Making mitered corners with a trim saw

On my Facebook page, one user mentioned that he wanted to make stone boxes but he could not figure out how to make mitered corners with his trim saw.  Since this is not all that uncommon of a project, I figured it would be relatively easy to find a tutorial on it.  However, after some searching, I found no such thing.  So, I created my own.  This will be the first part of the tutorial - making the miter cut.  Later, I will actually make a box and will post about that process. 

Remember in all you do - measure twice, cut once :). 

Tools used:

1.  Wood miter saw or miter box
2.  Rock trim saw, preferably with a rip fence or other guide to keep your cut straight
3.  Block of wood at least as thick as the stone you want to miter
4.  Enough stone slab of equal thickness to make the size box you want
5.  Tape measure
6.  Sharpie
7.  Cheap 5 minute epoxy
8.  Strong, preferably waterproof epoxy
9.  Rubber bands
10.  Second block of wood, preferably as large as the slabs you are trying to connect

Ok ... you are ready.  Note that my regular little trim saw is dead, so I am using what I normally use to cut slabs.  Same concept though. 

1.  First, you need a guide that will guide the slab through the saw at a 45 degree angle.  Use your first block of wood for this and a miter saw.  Set the miter saw to a 45 degree angle.  Cut the edge of the block of wood to forty five degrees.  If you have a longer piece of wood, it doesn't matter so much where you cut it, you just want to make sure the cut goes all the way to the bottom of the wood.

2.  Set the miter saw to zero degrees.  Cut the tip of the 45 degree angle off.  Ideally, you will want the thickness of the par you cut off to be equal to the cut angle of the slab (the red line in the figure below).  You can calculate this if you know the thickness of the slab, and you know you are cutting a 45 degree angle, using the cosine of the angle.  If this ia a foreign language to you, you can also just measure it.

Also, if you are going to be using the block for more than one slab, they may not all be the same thickness.  It is not critical that this measurement be the same, as long as it is equal to or greater than he thickness of the slab when it is cut.

3.  Your result will be a block with a 45 degree angle with the tip cut off.  

4.  Next, measure the size of the slab that you want the outside of the box to be, the side that is not mitered.  Keep in mind that the inside of the box will be approximately 1/2" less due to the miter.  

 5.  Cut the slab to size, being sure to cut straight.  Use a rip fence or guide to help keep the slab straight.  For reasons described below, you may want to cut the slab a little bit bigger than the size you want it to end up.

6.  At this point it is best to glue the slab to the wood using a cheap 5 minute epoxy.  This will ensure that the slab doesn't move when you are cutting it.  It may say "5 minutes", but really you want to let it cure competely.  A few hours or even over night would be ideal.  For this reason, you may want to have more than one block, so you can cut all the pieces at once.  

Here, if you cut the slab to the exact size you want, you will need to cut the slab so that the mitered edge, just hits the bottom tip of the slab.  If you cut the slab a little bit bigger, you need to align it s that the saw hits the bottom of the slab at the point you want the outside of the box to be.  The benefit of the latter is that if you cut it too big, you can still trim it down.  

7.  Once you have determined where you need to cut, adjust your rip fence of guide so that it holds the slab straight at that position.  As this saw does not have a rip fence, I used a block of wood pushed against the side of the saw so that the gap between the wood and the saw blade positioned the slab where it was needed.  

8.  Once you have mitered the corners of your slabs, you will want to smooth them down so they fit tightly.  Use whatever lapidary means you available to make the mitered edge smooth and straight.  It does not need to be polished, no one will ever see it.  Finally position the two mitered slabs together.  Ensure they fit well, then use a high grade epoxy, preferably a waterproof one, to hold the slabs togher.  

9.  You will need to hold the slabs together while the epoxy dries.  If you happen to have an angle clamp, great - use that.  If you don't - position a block of wood in the corner so the two slabs are tight against the wood.  Make sure the mitered corner does not come apart.  Then tightly wrap rubber bands or string around them to hold them in place.  Allow them to dry for 24 hours.  

Onc you have mastered cutting mitered corners, you will be on your way to making a box!  In a later blog, I will actually make a box.  Stay tuned.

Dr. Janet Bertog, Ruby Mountain5 Rocks

** a special thank you to Stanley Bertog for providing advise on construction ideas, such as how to hold the mitered corners together while they dry.