Official Luthiers Forum!

Hola,

Reaching out to the collective expertise here for some help. I have a nagging issue with splintering/chipping in one area of the toolpath that I use for thinning a fender-style headstock and creating the transition curve up to the fretboard. I've tried various strategies but still more often than not it's a problem.

At this point in the game, I have the fretboard attached to the neck and the neck is face up on the table. The perimeter cut around the entire neck has been done but the fretboard is not yet radiused or slotted and the headstock is not yet thinned.

I generally do a roughing pass with a 1/2" carbide ball end mill (new, hopefully not dull) with a 25 or 50% depth of pass and a stepover, leaving .02" or so for the finishing pass. Same end mill on the finishing pass. I've tried zig zagging in the X direction, in Y. Or more of a pocketing/facing style operation. Doesn't seem to matter. The chipping always occurs in the pink circled area (what will ultimately be around the bass side of the nut slot) on the finishing pass.

40-60 ipm, 20k on the router.

How would you approach this cut? What would you do to try and eliminate the chipping?

Thanks in advance!

Pink circled area? No joy.

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"Act your age, not your shoe size" - Prince

Chris, if you look closely (open the attachment) you can see a light pink circle at the bass side of the nut area.

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Jim Hansen

Are you running this before or after you do the outline of the headstock?

After - the whole perimeter shape is already done at that point. It's my last step before radiusing and slotting the board...

Thin the headstock first, then profile.

If that's impossible clamp a spoil stick to the edge of the neck to support the edge as it's being machined.

+1 on the spoil piece, or profile last. Maybe try a climb cut vs conventional.
MK

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I'm outside looking in, just farther from the window than most.

Thanks for the ideas guys. I will have to think hard to try and incorporate either thinning first or a spoil stick...hmm...

The thing that chaps me is that I've done this in the past without the chipping but I can't for the life of me remember how. It was simply a matter of the toolpathing though because I've always thinned last and after the perimeter cut. I need to take better notes!

Was it with the same kind of wood? Some species chip and splinter more than others.

I did a couple maple necks this summer. I left about the same amount of wood for the finish pass as you, and only went back and forth in the direction of the length of the neck which is my Y. I didn't go back and forth x then Y or Y then X to thickness it. I've only done 3 necks like this and found that I got a better result when I cut the perimeter first and then did contouring and the neck shaft carving.

Guess you could rough machine that area first with left hand cutter.

Is the bit you're using an upcut? Downcut may fix the problem...maybe.

I'm having the same problem with my fretboards, only in ebony though, roughly 50% of the time. I am using a downcut but, because my vacuum jig is universal and the fretboards I've cut have various dimensions, there's a little gap under the fretboard at that point so it's un supported at that point so I'm often getting a splinter from changing directions and conventional cutting there. I went to a downcut because the upcut was causing a problem when I was doing too aggressive a cut. The thing I'm going to try is to re-order my operations.

Right now I radius first and then profile with the downcut. I'm going to try to profile first with an upcut which may result in chipout on the top of the board but then I'll radius which should machine out the splinter. Hopefully the radius will still have a nice sharp edge.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

This is in maple or rosewood... Doesn't seem to matter much.

I may isolate just the curved/ramped area and drop my stepover from .03" to .01 in that area. The increased time would be worth it for a clean cut.

I think it is an upcut spiral...

Mike,

Can you give a step by step process? This might help with solving the issue. For instance, are you starting your cut on the inside of the board and working out, or starting on the outside and working in? On a fretboard, I would always choose the following strategy. Climb cut first and foremost. Second would be to start my tool path on the outside edge of the part letting the path work it's way to the middle. If the software will only choose the inside out option, then I would make a couple passes on the outside path by manually building the path if necessary, then I would let the software do the path to finish. After that, I would cut the outside path, and I prefer to make a mlti step depth cut, with a single full depth skin cut of about .020" for my finish outside cut.

What software "package" you using..... pun intended!

Mike

As others have said, contour second. Contouring first is removing the 'support' material on that part of the headstock.

Alternate is to run another path that cleans up that area with a tiny cutter, or use a bottom to top constant surface step over tool path (called scallop in Mastercam)

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

rough it out with chisels and then finish it the old way, using a 1.5" drum sander, and/or pipes wrapped with sandpaper... ? thats how i do it. kinda time consuming though

MadCAM of course!

An abbreviated step-by-step goes something like this:

1. Neck blank face up on cnc, cut overall neck perimeter and truss rod slot.
2. Off cnc, install truss rod, attach fingerboard, flush trim fingerboard to perimeter.
3. Neck face down on cnc, carve back side.
4. Neck face up on cnc, thin headstock, radius and slot fretboard.
5. Sand, fret, finish.

Needless to say it's frustrating to get a good piece of wood all the way to near completion only to lose a chunk. We've all been there, I'm sure...

I did a test and got better results with what I described before, by doing a very, very fine finish pass (.01" stepover) on the ramped part of the headstock, zig zagging parallel to the frets (my X) starting at the fretboard top and sloping down to the headstock face. I always do a climb cut but I suppose I should at least try a conventional cut.

I like your idea Mike of forcing a toolpath around the perimeter first, then going back and cleaning out the middle, essentially. I will investigate that.



I've been scratching my head over how best to do it. I suppose I could simply cut the whole thing oversized in my step 1 process.



That's exactly where I'm headed if I lose too many more. Although in my case it was bandsaw then sanding drum. Come to think of it, it's a lot faster too. I will admit to trying to do too much on the cnc sometimes. A solution looking for a problem...

Now you've given me pause lol....

Well, I thought you used Madcam but could not remember for sure. Send me the model and let me tinker with it a little. I am going to be calling Joalkim here in a little while, assuming I can make contact with him, and will ask him what he considers the best strategy. Since it is Madcam though, I can help you.

Mike

I didn't read the whole thread but I will add that this problem is generally solved by making your first cut....prior to surfacing the fretboard or headstock....a 3D contour cut along the entire outside perimeter at finish height. I don't know if your software can do this though.

This cut needs to fall on top of the perimeter lines....no left or right compensation.

Usa a 1/2" ball....maybe 3/8".....as large as the geometry allows but not too much smaller than 3/8".

If you can successfully program it...all subsequent material removed off the face of either the fretboard or headstock cannot tear out at a corner because all material that creates the leverage to rip out the grain in a tiny, localized crosscut is now missing.

In the worst case scenario (lightweight....splintery woods) I'll attack that area with a left turning ball mill using the same technique....but you probably won't need to take extreme measures to get this.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Nice! I've used that technique on other parts, but never even considered using it on necks.

That's the best method I've heard of, so take heed!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Mike I talked with Joakim today and we discussed this problem you are having. He said you can rough it in, then select planar finishing using the contour method and it allows you to select start from the outside. You can of course project curves and cut the perimeter passes like was mentioned earlier. Contact me via pm if you need additional help. That is what I do for Madcam........

Mike

Thanks mike but I have the entry level version. Unless something changed the contour planar option isn't there...

No worries though, I already created the outer contour toolpath per the suggestions here. I'll have another chance to test in the next few days.

Thanks all!