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Both cuts you can see are just purfling slots to give the fret board a bound look without having to actually bind the board. Sense we cut the fret slots on the CNC we have no need to bind the boards.

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Josh Garrett
Galloup Guitars CNC

Josh, What is your feed speed and depth of cut for your fret slots? Do you use compressed air to cool the bit and clear chips? What size bit are you using and what is your bit source for your fret slots?

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tim...
http://www.mcknightguitars.com

For fret slots I use a 0.023" 3-flute end mill from http://www.precisebits.com/products/carbidebits/ultrabit-soft.asp. Speed of 18000 rpm with a feed of 18 imp. Depth of cut of 0.015". I use compressed air to clear chips. There isn't enough heat generated in this operation to cause a problem, but the chips left in the slot are. These bite are very delicate, so you must be very careful. Hope this helps.

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Josh Garrett
Galloup Guitars CNC

Hey Josh,

How would you characterize the duration of the sharpness of your tooling at those numbers? I'm curious.

To cut fret slots I'm first running a .0625" ball to a depth of .01" lower than the surface...to make a little chamfer. Then I use a .023", two flute cutter at 15ipm and .01" depths at 4000 rpm....way less rpm. I'm cutting fret slots in rock maple but I've used the same cutter and numbers for tons of inlay cuts in bloodwood.

A wise old machinist once told me that cutters need something to do. He said a cutter will last longer taking out a bigger chip because larger chips carry away more heat. Applying his theory to plastics and wood...it seems true...maybe.

How has your .023" cutter held up using 18K rpm? If I did the math right on this your chip load is less than 1/4th of mine and it would appear you are making dust rather than chips. Does it seem to run hot at all? I can't come close to 18K rpm on my machine to test 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

Now this is good stuff right here. To have the cnc pros discuss feed rates, spindle speeds, type of cutters and the reasons behind all the decisions is great! Thank all you that have shared.

Mike

You can definitely push them. I've run them in production at 90K with a slightly higher material removal per rev than Stuart. I know I did a run of 50 boards with one of them. I don't remember when it eventually broke, so they last alright.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Tool life for the fret slot cutter varies for me. I have had the cutters last over over 75 Indian Rosewood fret boards. However the tools are so delicate they ofter break from improper handling or not using compressed air to clear the chips. With cutters this small I don't really see a degradation in cut quality before the tool just snaps off.

The theory of cutters need something to do is very true. What I have found with my 3-flute cutters is that any slower rpm or faster feed and the cutters are much much more likely to break. My theory on this is adding the extra flute takes away area for chip evacuation, so even though the cutting equations say I can move faster, the volume of chips made causes too much load on the tiny cutters and they snap. I have been experimenting with a feed of 20 ipm and it does seem to work well as long as I aim the air stream right at the tool flutes. After my next small run of boards I'll be making 20 ipm my standard and testing out 25 ipm.

I have never noticed any tool heat in the small cutters but that's probably because the compressed air cools everything down well or I don't use air and the tool snaps before any heat can build up.

Today's project is cutting electric guitar bodies for our students. I'll be doing all the back cuts then all the tops. I'm guessing I'll get through about 10 of the back cuts today.

Here's the Jig I use to cut the single cutaway body shaped guitars.


This is it with the second stage bolted to it.


And here it is with a body that has been back cut vacuumed down.


Finally, here's the machine in action cutting the profile in the back of the body.

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Josh Garrett
Galloup Guitars CNC

Man those fixtures make me envious. makes that crappy fixture I made look stone age. LMAO!

What is the gasket material used on the vacuum jigs and at what depth and type of cutter is used for the channel?

MK

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

Yeah....is that closed cell foam weatherstripping?

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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

I use this http://www.vaculok.com/Gasket_Material.html. It's specifically made for vacuum clamping. It's a bit more expensive than standard weatherstripping but it's much smaller. I use mostly the 1/8" width size unless I really need as much vacuum area as possible then I use the 1/16" width. To cut the phenolic jigs I use a single flute 1/8" (or 1/16") solid carbide end mill made by Micro 100.



Other companies make a similar product but these are available where I buy most of the tools I use. Today I'll be cutting a few necks for set neck electrics then continue and hopefully finish cutting the backs of the single cutaway flat top electric bodies.

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Josh Garrett
Galloup Guitars CNC

Bob, are you saying you were feeding in the neighborhood of 400 ipm? That's screaming fast!

Josh, what's the idea behind the second stage female perimeter fixture?

I'll take a guess that he uses that jig to locate on the perimeter of the body whereas in the earlier stages (usually when doing back cuts) you locate on tooling pin holes. That's the way PRS cuts stuff as well..

I don't think the heat removal logic applies to wood cutting - wood is a pretty lousy conducter of heat. Also, if the chips do heat up, then you can have some obvious issues...

With those tiny bits, runout is everything in terms of preventing breakage. You definitely want to spin them fast, but you don't want to run a high feed rate if your spindle has high runout (I would say more than a 1/2 thou or so).

You can run large ball mills (over an inch in diameter) at hundreds of inches per minute if you have enough horsepower to push it and the vacuum is strong enough to hold the part. Body top carves run pretty quick at those rates...!

Trev

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http://www.PeakeGuitars.com

400 ipm would be a mighty high feed rate, but with machining centers it's not out of the question.

For making the electric guitar bodies I first locate them on the jig locating only by centerline and markings on the jig itself. There I cut the back and profile. Then I add the female plate to the system, flip the body and cut the top operations. It's a very stable and very strong way to locate it on there. I have used other methods in the past but this has worked the best so far. I plan on making the plate out of phenolic soon, but for now the birch ply works great.

Heat removal through chips does apply to wood, but it is less significant than in metal. I do notice that when I have my feeds and speeds dialed in correctly, the fresh chips are warm and the tool is much cooler at the end of a part. That said, I've only noticed it with my cutters over an 1/8" diameter. And the larger the tool the more I notice it's importance.

The large tooling is the exact reason I would love a machining center like in this PRS video.

At about 6:45 the big cutter comes in. Also the video shows a similar type of vacuum jig to hold the bodies.

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Josh Garrett
Galloup Guitars CNC

Yep - that's my buddy James (aka "Jimmy Ducks"). Say hi to him for me if you ever run into him at the factory!

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http://www.PeakeGuitars.com

OT: what's that loud clunking sound as the ball passes over the horns in the PRS video?

Sheldon I watched the video yesterday, and to the best of my ability to remember that far back, it is the sound of the machine changing directions, or slowing down or speeding up quickly.

Mike

Mike is correct, when the machine changes directions that quickly it makes a clunk. Our machine does it sometimes as well.

I cut the last pass on a Galloup rosette today, but neglected to take pictures. I'll be cutting electric bodies for our students for the rest of the day sense I didn't get to them yesterday. 16 to go for back cuts then 24 to cut tops in. I may try a different approach when cutting the tops, using the first cutter and cutting all 24 then change to the second and cut them all then again with the third cutter. I feel like it will go quicker to change the whole part than to change cutters. If nothing else it should be less hassle. I guess time will tell.

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Josh Garrett
Galloup Guitars CNC

Hey Josh,
Can you post a couple of pics of your flexible compressed air nozzle set up and do you have a source for it?
Thanks...

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tim...
http://www.mcknightguitars.com

I've watched tons of Guitar CNC videos from professionals and one thing I've always been amazed at is the speed they run them at. I've been making guitars with CNC for years now, but it's a home built machine, all aluminum super strong and accurate, but it's not a Haas. The Haas' can cut at 400 IPM and have 720 IPM Rapid. It just seems with the high end bits, spindles and programmers they have they would be running those machines WAY faster. Maybe it's faster than it looks or going to extreme speeds leads to tons of tear out.

Most of Haas' current offerings can feed at 800IPM, but the spindles are the problem. When cutting wood, CNC mills are limited by their spindle speed and CNC routers are limited by their rigidity. If the chipload gets too big then the wood starts tearing and it leaves a really gross finish.

I've watched videos of my own toolpaths running and they definitely look slower on video than in real life. They seem to look slower if they have very few directional changes, as well (smoother paths look slower).

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

So Bob what you are saying is I look FATTER when on Video? Or is it I am slimmer in real life. LMAO!

I just had to mess with ya Bob. We all know that everyone always look worse in the cameras eyes. Now our machines look different?

AH! I know it's a time warp. Have a good one my friend.

MK

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

Oh camera fat...

http://www.bnet.com/blog/advertising-business/ralph-lauren-8217s-photoshop-addiction-a-fourth-slenderized-model-confirms-the-company-8217s-warped-aesthetic/5101

Could be worse...I think they needed an extra set of hands on this one:
http://www.tressugar.com/Photoshop-Anyone-324414

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

The air nozzle I use is called Loc-line. You can get it all over like MSC, PTS, or Grainger. I use the 1/4" kit and a valve.


I have found that tare out is one of the biggest limiting factors when it comes to speeding up my programs. I have run a 1/8" cutter at 100IPM with no issue except for the massive tare out where the cutter entered and exited the wood. I had to feed at less than half that to eliminate the problem.

I cut a few necks today for our Great Lakes acoustic guitars.


I'm starting to cut the first step it the tops of the student electrics now.

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Josh Garrett
Galloup Guitars CNC

Changing the entire part instead of the cutters was a success. It was far less hassle than changing the cutters and I think it was faster as well. I won't know until I actually get them all done but I'm pretty sure it will be worth it.

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Josh Garrett
Galloup Guitars CNC