Problem setting radius in Fusion 360

I build acoustic guitars. I have programmed F360 to cut x-braces. I have specified a radius of 300" for the bottom of the brace, but F360 keeps reverting to a radius of 168". Where am I going wrong?

I assume this is a radius in a sketch. I have no problem setting the diameter to 600 inches.

That’s a big guitar.


You can try using a three-point arc and only constrain the endpoints. The dimension (radius or diameter) will place the center point. If you are having issues you may have a hidden constraint somewhere. This often happens when an errant snap happens.

I hope this helps. I build acoustic guitars too!

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Found it, simple mistake. I was specifying radius and the program was asking for diameter.

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Mike, how are you using your CNC in your acoustic building? So far I’ve only used mine to cut out braces, but I’ve only had it two weeks. I plan to do compound fretboards, bridges and rosettes. And later on archtops.


I have yet to receive my machine but plan on using it to make forms, fixtures, and templates to start. I build mostly acoustic instruments so I can see in the near future headstocks, bridges, and rough profiling necks.

I’m mostly excited about how quickly I’ll be able to explore new or prototype models of what I’m currently building.

How is yours working out for you?



I’ve built about 45 acoustics thus far, including one weissenborn and a couple of archtops, a bunch of ukuleles and several electrics. I originally bought the CNC to cut my logo in MOP. I had a guy at the local community college doing it for me, but he became unreliable. CNC is totally new to me and I’ve been working my way through Fusion 360’s learning curve. I’ve almost finished my own F 360 program for making compound radius fretboards. I’ve played around making some boxes with v-carve inlays, but I’m finding out wood with different hardness’s require different feeds and speeds and require a lot of experimentation to find the sweet spot for each tool. I haven’t tried cutting any MOP yet. I spoke to Ron Reed the owner of Precise Bits. I purchased a 0.010” diameter end mill from him specifically for cutting pearl. He told me before I do anything I need to measure the total runout of my collet. I had purchased what is supposedly a precision 0.125” collet from Elaire. Ron said that if the run out is greater than 0.0007” I’ll break the bit. I plan on checking that this evening. His website has a wealth of information. If the run out is to great I’m afraid my only option is to ditch the Makita and buy a spindle. Thus far the 1F has been great for cutting out braces.


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