[John Coloccia]

I attached a file. Using a .25" bit. Depending on settings (especially step-down) I get lots of different behavior. With some settings, it does strange things with the ramp/radius setting, and sometimes just plunges. With a larger stepdown setting, the ramp sometimes starts on the wrong side and actually collides with the model.

[JOM]

One problem is when setting the stepdown larger than the total "Box" height. If the total depth is 0.3 inches, the stepdown shouldn't be set to 1 inch. The z-level finishing is meant to be used for multiple cuts.

The plunges depends on the safe clearence. For a 0.25 inch cutter, the default safe clearance is 0.125 inches. If the cutting depth is set to 1 inch, it will make a rapid approach of 1 - 0.125 = 0.875 inches.

I think the best result would be to set the stepdown no more than the total depth which would be 0.3 inches in this case. When using a large stepdown, the best would be to make a ramping approach without any radius lead-in. Set the radius lead-in = 0, ramp angle = 10 degrees and ramp depth = 0.3.

Thank you for sharing this and you have a point here!
For the next servise release, it will be a message box that will popup and warn the user if the stepdown depth is set larger than the total depth.

/Joakim

[John Coloccia]

Thanks for the clarification, Joakim. It's no big deal, really. The original step down was large because I was playing around with different toy models trying to find the best machining strategy for my real parts and I thought you'd want to know about it. Here's what I was trying to do and you'll understand why I was doing what I was doing.

I'm trying to make an angled pocket...think about the neck pocket in your guitar video, but angled instead. Since it's angled, I can't use a 2.5D pocketing....at least I don't think I can. Anyway, my strategy was to rough out the entire pocket, leaving may .05". Then I wanted to do a planer finishing pass to get most of the pocket down to finished depth, leaving perhaps .01" by erecting some walls. Then follow it up with one full depth Z-level pass for the final cleanup of the edges. One edge is very thin an needs to be handled gently.

Maybe I should just do the whole thing with a planer finishing passes and just erect walls to limit the cutter so that I can do one final cleanup with another planer pass. Then I could knock it out in one shot without re-cutting each time when Z drops. I really want to have a radiused lead in for that final clean up pass, though.

I'm really not sure how to get what I want.

[John Coloccia]

So let's forget about the Z ramp. It doesn't really matter. What I really want to do is make this pocket. This isn't the real pocket...it's just a toy model. The key is machining the edges so that they have good tolerance, and machining the open side of the pocket so I don't blow out the wood there. I want to machine the open side of the pocket first...very gently. That edge needs to be good. I want to machine left and right sides of the pocket gently. What happen in the middle I hardly care about. It need to be a good fit, but it doesn't have to be perfect as the edges have to be.

I'm starting to think that the proper way to do it is to make my own tool path to rough the front (open edge) of the pocket and the sides of the pocket, and then let the standard roughing tool path hog out the area in between. Then follow up with my own tool path to carefully machine the sides and open edge to final tolerance, and then let the planer tool path hand the rest in the middle. Is this correct? The key is this is in wood, not metal. I need to have the critical cuts backed up with material at all times so that I get a crisp line instead of big chunks of wood breaking off and making a mess. I don't think there is a standard tool path that reliably gets me that, and maybe that's why I'm having so much trouble.

[JOM]

I am not sure, I am more used to metal working, but this is what I would do.

1) Select your region curve.
2) Make a planar finishing with contouring option.
3) Make a pencil tracing toolpath. You can use raise Z for multiple cuts and set the stepdown if needed.

/Joakim

[John Coloccia]

Oh, I see. The pencil trace will get me the edges without having to draw my own paths. I never would have though of that. I'm so used to thinking of pencil tracing as almost a poor man's re-machining step, it never would have occured to me to use it to control the toolpath.

[dotmkr]

John
Do you have a five axis machine? If not then how are you making an angled cut for your neck?


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Ken

[John Coloccia]

John
Do you have a five axis machine? If not then how are you making an angled cut for your neck?


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Ken

Just a three axis machine. What angled cut are you talking about?

[dotmkr]

Neck angle john. I thought the guitar body needs to be set at an angle before the route similar to using a pin router. Is there a way in the tool path to make a cut with a slope at 4 or 5 degrees?


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Ken

[John Coloccia]

Neck angle john. I thought the guitar body needs to be set at an angle before the route similar to using a pin router. Is there a way in the tool path to make a cut with a slope at 4 or 5 degrees?


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Ken

Sure. You just use the 3d tool paths. The only problem is the front of the cavity has an undercut. There are several ways of dealing with that, but the simplest is to cut it straight and then either put the angle in the heal of the guitar on the CNC, or just do it by hand. It just takes me a couple of seconds on the disc sander to put in the angle by hand.

The other option is to cut the neck pocket straight and angle the guitar heel. I do that do, and usually that's how I do it, actually. I'm not going to get into why because it's hard to visualize if you're not familiar with it, but it looks better

And a 3rd option is to simply angle the body in a fixture and cut it straight. That works too. The angle is only 4 degrees, so it's pretty trivial to fixture it like this if you want.

Does that answer your question?

[dotmkr]

Yes. 100 percent!

Thanks john


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Ken