# Machining a trapezoid?



## TwoSkies57 (Feb 23, 2009)

Got a question for you CNC guys out there. Is it possible to cut multiple trapezoids from the following: 

1 1/4" thick "END GRAIN" stock (the end grain facing up)
size of material provided can vary depending on equipment capacities. 
Looking to maximize stock used. 

each piece would be. 1.730 wide x .750 thick with two 60 degree sides. the 4th side would end up at 0.87".

Tolerances are only +/- a couple thousandths. 

Plan B would be cutting the trapezoid from flat long grain 3/4" stock in 14" lengths....

any help would be appreciated.

thanks
bill


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## 4DThinker (Feb 16, 2014)

Easiest and most efficient way would be to use a table saw with blade set to 60 degrees. On a CNC you can do what you want a few different ways:
Use a 60 degree V-bit to run down both sides. One or more passes depending on how large your V-bit is. 
Or use a 3D extruded model or the Moulding tool path in Aspire/V-Carve to create the 60 degree sides and cut them using a ball end bit that steps down the slope in small increments. 


4D


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## MEBCWD (Jan 14, 2012)

Bill is this what you had in mind? It is doable on a CNC but if I were doing it I would do it on my table saw with sliding table of sled.


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## Cherryville Chuck (Sep 28, 2010)

Bill are you describing an isosceles trapezoid? Parallel base and top and equal angles tilted in? If so they should nest against each other so that would maximize material. If the vertical height of the trapezoid is .75 and you want end grain I don't understand why you would be using 1.25 thick material.


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## MEBCWD (Jan 14, 2012)

Looks like a cutting board project fixin to happen.


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## TwoSkies57 (Feb 23, 2009)

Yep...cutting boards. I did a couple "test" boards and had em sold for big bucks before the wax dried, even though I wasn't thoroughly pleased with either one. Used the tablesaw with resulting cuts being less than ideal IMHO. Looked at a 60* router bit, would have to go thicker to take advantage of the bearing, then drum sand down. Definitely an option, but a good bit will run 80 bucks with a 1"+ cutting height. 

Mike, that is exactly what I'm looking to do with end grain up.. I thought if I could farm this out to CNC I would get the spot on accuracy I"m looking for thus eliminating alot of the fussing around that seems to be assoiciated with using a TS. With the table saw I"d have manageable lengths that would need to be sliced up. With the CNC concept, I'd have alot of individual pieces needing assembly. However, with the CNC I can also work a couple of different patterns. 3 pieces are required to make up 1 piece of the puzzle...

I should ad, that the results achieved with the tablesaw were due to an old saw that has just about run its course....and NO, I don't see that saw being replaced anytime soon....


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## Cherryville Chuck (Sep 28, 2010)

Is the problem the saw or the blade? I've often found that the problem is the blade is not stiff enough, particularly at an angle. A sled and blade with stiffeners might fix that. A saw will be a lot faster in the long run.

I've been cutting out cabinet doors from ply the last few days and I was getting a little bit of wobble when I would change feed rate (I think that's when the wobble happened) and it was just enough to show when I glued some solid banding on. I added stiffeners to the blade and no more wobble marks.


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## TwoSkies57 (Feb 23, 2009)

thinking its a bit of both...wear on the saw and perhaps to some extent the blade. I do use stiffeners all of the time. Don't cut without em...feed rate was something of a problem. I ran short lengths, 14"s and was just breezing them thru the blade... not giving the blade enough time to evacuate all of the chips, this would cause the blade to choke from time, depending on which side of the blade the piece was, it would cause the blade to weave to one side for just a moment..enough to ruin the run.


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## MEBCWD (Jan 14, 2012)

Bill I think I would still use the table saw with a sled for any straight cut parts like these.

When you get into boards made up of curved parts then I would us a CNC machine but you still have a problem when cutting different woods, parts may end up slightly smaller or larger depending hardness of the wood. On a good machine the parts should be close enough to make your board without much touch up/repair. On jobs like this I try to do the assembly as soon after the parts are cut as possible to limit the change in sizes due to humidity. A board made something like this picture


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