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verhoevenc

Looks Like I Joined the Club

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So I've had the thing for awhile but I've mostly been telling myself, "You can't play with your new toy until you finish up a few things." Well I did so I've finally been playing! Over the last two days I have cut out what I'll refer to as my first "guitar-shaped object" aka: GSO. It's just pine and for testing, but boy was it a bunch of fun! Before this all I've ever cut out was an E and a small sign with a word on it.

It'd say for a first go at a GSO and my first go at 3D cuts (using the MeshCAM trial right now and quite happy) the learning curve hasn't been ass big as I'd feared.

Here's the various pieces I needed:

cuts.jpg

2D top cuts went smoothly!

top2d.jpg

As did the arm bevel cut with a very fine step-over on the finishing pass:

top3d.jpg

On the back I for some dumb reason told the cutter to cut inside the profile instead of outside, GAH! But so far this is the only mistake:

back2d.jpg

I figured why let that slow me down so I also did the 3D cuts on the back for fun and tried it with a less fine step-over on finishing:

back3d.jpg

Don't get me wrong... this took hours of generating and re-generating my tools paths until I was happy. Also took several smacks of the emergency stop when I saw the cutter heading the wrong direction hahaha. But I feel like in the end everything except that back 2D cut went really well and I went from 0 confidence to like 70%!

Best,

Chris

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Actually, I'd be curious to know what you think of MeshCAM. I'm looking for a standalone CAM application to simplify generation of toolpaths from CAD.

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So far I'm having a hard time finding anything I'd want to do on a guitar that MeshCAM won't handle in 3D. I'm still using VCarve Shotbot edition for all my 2D stuff simply cause:

1- It's so dang easy

2- I can string multiple operations together in a single file (which I'm yet to really figure out with MeshCAM unless I want to use the same speeds, etc. for all the operations).

Great thing about it is you get a free 15 day trial. I'm 5 days in and I feel I already have a very good grasp of it. It's made for ease-of-use CAM... but there's still a TON of features in the version I'm trialing (Standard, not even Pro) that are way beyond the detail I need.

As for confusion... that's disappearing much faster than I would have initially anticipated!

Chris

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I'm yet to do anything more than 2.5D milling, which at the moment suits my requirements sufficiently. My machine is arguably too small to machine 3D contours for bodies and necks anyway. I've got a CAD background, so I can wrap my head around most 2D CAD programs well enough to get things done, although AutoCAD is where I did the bulk of my original training.

3D stuff I haven't looked at for probably 16 years or more now, so I'm seriously rusty in that area.

Downloaded and gave MeshCAM a quick go last night, but it seemed reluctant to want to work with anything other than closed polygons. Opening a fret board drawing with the slots drawn as straight lines was apparently not kosher - surely they should be interpreted as a slotting operation?

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You know your way around G-Code so a fingerboard (even multiscale) slotting operation can be written manually. I'm sure that you could script the output from FretFind2D into a basic G-Code program, then run a loop of light passes which lower the cutter each pass. That could accumulate errors if any steps are missed of course. A good stress test for the CNC! :thumb:

Chris, now you've gone and done it then I am sure that it's going to get a whole lot crazier given what you can manage already!

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Yes, I haven't cracked MeshCAM's secret on why it only respects surfaces and polygons... not lines. One thing I'd really like to do is mill constant-depth fret slots the follow a radius. Therefore, I need to do it in MeshCAM... but I've had the same experience there as you. I plan to play around with that particular issue a bit more so I'll keep you posted.

Chris

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Yay! More tests! Building a fully functional guitar from cheaper materials will be the true test of my knowledge IMO. I did this last night. The only issue is my cuts from the back were slightly off... Nothing I can't salvage and save the build from... But before real builds happen I need to figure out why! Something up with my index pegs? Zeroing of the Y? Who knows.

image.jpegimage.jpegimage.jpeg

The nub you're seeing at the edge isn't the off-cut from flipping, it's the 1/4" I left that held the body to the blank which was bolted down. That'll get routed off in one quick pass.

Chris

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See I knew you'd end up doing some crazy stuff. I guess you've see that Ernie Ball Music Man CNC rout a binding channel into a blank and then pour in liquid binding? I bet that if you could eliminate voids and bubbles, making a binding liquid out of Alumilite and various dyes/powders, etc. would be very very sweet. Especially the high-content metallics.

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It would even allow binding to do some crazy things that you simply cannot achieve normally, such as dipping into cutaways and splitting into different paths.

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Off by how much? That looks like quite a step. More than what misalignment of positioning pegs might add in.

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Prostheta, read the bit under the pictures. I left 1/4" in the center of the body that I'll route off by hand later. That kept it attached firmly to the rest of the blank while milling which is where the locator pins were. The misalign is not what you're seeing in the last pic. You're seeing that 1/4" left area that I just band sawed to detach from the rim once done CNCing.

Chris

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I get you Chris. It was last thing at night so I did my skim reading thing! It's more apparent now you point it out, especially TheSentence! :lol:

My skim reading consists solely of numbers and colours I think.

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Well I'm onto testing out neck cuts. So far I'm really happy with my results! The one thing I'm not happy with is their fit into the neck pocket. Neither neck, despite being from the same drawings I'm 99% sure, will fit in the pocket I milled into that body!? One neck is full size exactly, one neck I undersized by .010" to see if that helped. It didn't. Granted, this is the same body that had the weirdness where it didn't line up 100% after "the flip over." But what still strikes me as weird there is that the pocket was milled in one operation... I can't see how the issues I had with the sides matching up perfectly could possibly cause that. I guess tomorrow I'll mill a bunch of pockets and see if that changes things?

CNCdNecks.jpg

Best,

Chris

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Slight mismatch between the cutter diameters and your generated G-Code, perhaps? Heels and pockets will quadruple any discrepancy. Beware of operators that re-sharpen their carbide and keep the working diameters in their head.....!

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HI Chris, when you did the flip in your software did you flip the pegholes as well? If not then that is your problem. Your center is not exact and the peg holes need to flip with the entire project.as a complete unit.  :) I tend to always use my closest pin location to my home location as x,y zero.

Mike

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That's what my original thought was @MiKro, but the index holes were purposefully placed equidistant from the center line so as to avoid that issue. I'm going to re-try it here again soon... but right now I'm thinking it was probably some user error or something... maybe something I did to set the XY zero off or something.

As for the cutter... it's a brand new cutter from the Shopbot folks' starter pack. That'd be pretty BS if they send out off-sized cutters to new users in their starter pack (which is supposed to help folks by being easy!)

Chris

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That's cool Chris, Another thing is make sure that you home the machine after a setup change and then go back to your G5x position for zero form home. If by chance you stopped the machine at  home and turned it back on, you should always move out some then rehome the machine. That way you get no stepper offset when powered after a power down.. I assume you are using a G55 or something for code for your zero. If not the standard G54 will do but you will always need to rehome .and then use a go to command to get to your work zero and rezero the machine for the workpiece from the machine home zero. 

 

added: Gawd it's been awhile since I had to think this hard LMAO!!!! Need to get my head out of my arse and get back to building, Have a cool reso electric build in my head. :) It will require me to totally rethink how I machine stuff LOL!!

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So this is weird. I did some tests with both the 1/4" endmill I got with the Shopbot starter pack, as well as one I bought elsewhere. The shopbot bit is definitely not as exacting as the other bit... pretty disappointing since they sell that as a bit kit to help folks starting out...

However, even with the other bit I can't mill the neck and pocket to be exact matches! I'm finding... and yes I realize this is going to sound huge cause I think it sounds huge... that a .010" offset (aka: .020" total difference in neck width compared to pocket width) gets me a tight fit. In my head this sounds like insane amounts of slop for a CNC machine... but the odd part is it's not slop, it's the "exact milling" is TOO tight!?

Am I missing something here or do other folks experience this too?

Chris

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Have ShopBot Tools responded to any feedback on this as of yet? I'd like to hear what their take on it is, especially if 10 thou is acceptable slop with their machine. Have you measured the end mills yourself to see how out of spec they might be?

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No, I have not reached out yet. However, this isn't slop; it's TOO tight. Also, I bought both the machine and bit kit (although the kit was unopened) used... So it's a little different.

i have no mic'd the end mills, which I should probably do. Although admittedly I'm not 100% how to do that on something that isn't a solid circle shape and still get accuracy to the thou.

Chris

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Mic the width of a pass cut with the bit. Also, I'd do that in wood, which can compress instead of cut to a small degree and do it again in acrylic or something similar that and see how the measurements compare. Try it with both bits and see what you learn.

SR

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Good idea Scott. I wonder if tool pressure might be deflecting the bit? Is there a final light finishing pass?

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There is no light finishing path. But I've tried this with both actual wood, and 1/8" Luan ply and get the same result. Something tells me faux little pockets and necks in 1/8" Luan don't need a final finishing path.

Also, if CNCs require that... why isn't that the standard method of cutting as far as programs are concerned. That seems like I'd have to run two tool paths (PITA); one to cut the pocket, another at full depth with an offset vector.

Chris

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3 hours ago, verhoevenc said:

There is no light finishing path. But I've tried this with both actual wood, and 1/8" Luan ply and get the same result. Something tells me faux little pockets and necks in 1/8" Luan don't need a final finishing path.

Also, if CNCs require that... why isn't that the standard method of cutting as far as programs are concerned. That seems like I'd have to run two tool paths (PITA); one to cut the pocket, another at full depth with an offset vector.

Chris

Chris,

it is very common, even for machine shops to run what they call a spring cut. It is basically a final pass at true measurements. The first cuts depending on the accuracy of the machine (backlash) are done to within a few thousands of the the wanted final result, then the spring cut is used to clean up and finalize it. This takes away almost all possibility of any deflection caused by feedrate, tool cutter sharpness and other anomalies, it won't compensate for backlash though. and backlash should be calculated into your cuts at the beginning for all axis..

 

MIke

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