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PostPosted: Wed Jul 05, 2017 9:23 am 
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Brazilian Rosewood
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I am upgrading the controller on my CNC before I set it back up after almost three years sitting in the corner of our current garage. I have requested that the new controller be capable for a 4th axis as I was thinking that a small rotary table (much like a lathe) may be good for carving necks. Any thoughts on this?

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PostPosted: Wed Jul 05, 2017 11:57 am 
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I've carved over 50 necks (most for a charity giveaway, but a dozen or so for my instruments) on a three axis machine. I think Andy Birko runs his business on a three axis machine.

I don't think there is any need for an "A" rotary axis. That said, I love experimenting. I've been toying with adding one too just to see what I actually can make with it! So don't let me discourage you.


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These users thanked the author rlrhett for the post: Dmaxwell (Wed Jul 05, 2017 11:30 pm)
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PostPosted: Wed Jul 05, 2017 3:32 pm 
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Ya I was just thinking of using a straight bit, rather than a ballnose and then you might be able to keep the neck blank surface square to the bit. And like you, it would be a bit of experimenting for sure.

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PostPosted: Mon Jul 10, 2017 6:43 pm 
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I've been wondering about this for years and hope to experiment with it some day.

But I'm still with the ball-nose bit & 3-axis method for now.

If you do any experiments in this direction I hope you'll post about it :)


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PostPosted: Thu Aug 31, 2017 9:51 am 
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I thought about this strategy too but, everything works so well with 3 axis.

The thing that I'd worry about is on thinner necks, you'd probably see a lot of vibration when cutting around the middle. Some sort of trunnion table could eliminate the vibration but it's also eliminates the possibility of machining the whole neck in one setup - which is kinda the goal of using 4 axis

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PostPosted: Thu Aug 31, 2017 12:16 pm 
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I don't see vibration as an issue if you have a solidly machined, indexed, and very stiff holder for the neck blank. Don't forget, the 4th axis wouldn't need to move fast (although Andy would want it going at 1000 IPM, I'm sure), it just needs to be really solid. The spindle does all the work, but even then it will mostly move in just two directions, depending on the code and toolpath you choose. I would still want a ball-nose cutter since we're talking about tapered cuts, unless you build the taper into the jig, but that would be difficult since you're not cutting a round object, but typically an elliptical one.

I've also thought a lot about it, and nearly started to work on one. But as Andy said, doing it on the 3-axis machine works so darned well.

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PostPosted: Thu Aug 31, 2017 11:13 pm 
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Don Williams wrote:
I don't see vibration as an issue if you have a solidly machined, indexed, and very stiff holder for the neck blank.


That's the point I was making though - if you have a "very stiff holder for the neck blank" - you have a trunnion style 4th axis which necessarily prohibits machining access to one of the work faces. So, If you can't chuck up a piece of wood and have the machine cut all 4 sides, what's the point in even going 4th axis? Only disadvantages over 3 axis IMNSHO ;)

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PostPosted: Tue Sep 05, 2017 11:52 pm 
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Andy Birko wrote:
Don Williams wrote:
I don't see vibration as an issue if you have a solidly machined, indexed, and very stiff holder for the neck blank.


That's the point I was making though - if you have a "very stiff holder for the neck blank" - you have a trunnion style 4th axis which necessarily prohibits machining access to one of the work faces. So, If you can't chuck up a piece of wood and have the machine cut all 4 sides, what's the point in even going 4th axis? Only disadvantages over 3 axis IMNSHO ;)


These are great points.

What about using a trunnion with a slot in it for cutting the truss rod slot? So you could still cut the whole neck in one clamping.


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PostPosted: Wed Sep 06, 2017 9:33 pm 
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Durero wrote:
What about using a trunnion with a slot in it for cutting the truss rod slot? So you could still cut the whole neck in one clamping.


It probably wouldn't work for me because I establish the tenon or dovetail mating surface from the fretboard side as well as cut the profile of the neck. The profiling step could possibly be skipped but I find it helps with tear out in some spots on the back.

Doesn't mean that it wouldn't work for you though. Give it a shot and report back!

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PostPosted: Thu Sep 07, 2017 8:39 am 
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Just a thought here, but not every operation is necessarily done best or more efficiently on the cnc.

Just sayin'...

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These users thanked the author Don Williams for the post: Andy Birko (Thu Sep 07, 2017 2:47 pm)
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PostPosted: Thu Sep 07, 2017 2:47 pm 
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Agreed!

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