What are the tolerances to expect?

2795 Views 15 Replies 8 Participants Last post by Nate Banton, Nov 11, 2019

Nate Banton

Discussion Starter · Oct 25, 2019

Hello,

I’m a bagpipe maker researching CNC routers. Using both for the typical CNC set up and also using a 4 axis set up. I’ve got a fair bit of 3D modeling experience under my belt, so I’m not afraid of that part at all, but I’m wondering what sort of tolerances I can expect?

For a machine, I only need something smaller. For example, something like the smallest Avid Pro, or the Shopsabre 23. (Though I haven’t ruled out building my own machine). When something is produced using a machine, how close to the 3D model do you get (I’ll be using very hard woods, mostly exotics like Ebony). .005”? .05”.? I realize there are a lot of factors that are involved, but I’m willing to do what I have to to get things as tight as possible.

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difalkner

· #2 · Oct 25, 2019

Welcome to the forum, Nate! Add your first name to your profile to clear the N/a in the side panel. Add your location, as well.

A good rigid machine can hold to 0.005" without much difficulty. You'll see manufacturers state better than that but 0.005" shouldn't be hard to hit. I built our machine and cut the EIR bridge on the guitar I built last year and the tolerances held were better than 0.005", so it's doable. Many boutique Luthiers cut fret slots in Ebony fingerboards and those really need to be 0.005" max in tolerance.

David

Reactions: 1

Cherryville Chuck

· #3 · Oct 25, 2019

Hi Nate and welcome.

MEBCWD

· #4 · Oct 25, 2019

Welcome to the Router Forums Nate.

An Avid Pro with an added rotary axis should be able to do it without any trouble. Avids rotary axis is a little pricy but any rotary unit can be used. That being said I do like how their rotary mounts to their system.

Just make sure if you buy an Avid Pro that you make sure you get the added driver in the electronics you choose so you don't have to do it later.

Reactions: 1

Nate Banton

Discussion Starter · #5 · Oct 26, 2019

Thanks for the warm welcome guys. I'll look into the first name and location thing when I'm on a laptop.

That's reassuring. .005" is a good goal. I'd be using the machine to do certain important tasks like drilling the tone holes (the holes the fingers cover) and .005" tolerance would work decently for that.

Good to hear about the Avid machine. That said, I've been worrying about the backlash that these machines have with their 4th axis rotary set ups. I suspect I'll end up buying the bulk of the machine from someone like Avid or shopsabre, but build the 4th axis part myself to try to get that backlash close to 0. Avid quotes 3 arcmin and shopsabre quotes 5 arcmin. I've never worked with a machine like this, but doing some math on what that might mean and I don't like it.

Nate Banton

Discussion Starter · #6 · Oct 26, 2019

Also, cool to hear from someone else working with musical instruments. I also play banjo, so in the back of my head I'm seeing building a banjo as a nice thing to do with my hobby time on the machine.

Reactions: 1

difalkner

· #7 · Oct 26, 2019

Nate Banton said:
Also, cool to hear from someone else working with musical instruments. I also play banjo, so in the back of my head I'm seeing building a banjo as a nice thing to do with my hobby time on the machine.

I haven't watched it in a while but here's the video I did of cutting the bridge -

David

Reactions: 3

Nate Banton

Discussion Starter · #8 · Oct 26, 2019

Awesome, David. That's very reassuring to see some of the procedures I'd also be be using done in rosewood.

What machine is that you're using?

Reactions: 1

difalkner

· #9 · Oct 26, 2019

Here's the full build thread - http://www.routerforums.com/cnc-routing/97721-2nd-build-first-cnc-router.html

David

gdonham1

· #10 · Oct 27, 2019

I have a Shapeoko XXL. It does not have the 4th axis but it is a reasonably priced machine. You can use Fusion 360 to turn two sided projects. Usually you have some sort of reference holes with pins to turn the project over and cut the second side. If you need the 4th axis you will be looking at $10k or higher to start with. It depends what you want to spend.

If you are a bag pipe maker and have a little Scottish in you check out the Shakeoko. If you want to spend more the pro models can be quite expensive.

If you want to know if someone has built bag pipes join the forums and ask and you will get suggestions about your specific topic.

There are forums on Carbide3d, Inventables and Openbuilds for the hobby class of equipment. There are many others and be sure to check out youtube.com to see if there are any bag pipe makers.

Nate Banton

Discussion Starter · #11 · Oct 28, 2019

I will definitely check out the Shapeoko. But 99% of what I make is round, so no 4th axis is a problem. I could maybe add one anyway.

marecat3

· #12 · Oct 28, 2019

welcome to the forum

BalloonEngineer

· #13 · Oct 28, 2019

Nate Banton said:
I will definitely check out the Shapeoko. But 99% of what I make is round, so no 4th axis is a problem. I could maybe add one anyway.

Not unless you replace the entire GRBL control system, GRBL is remarkable that it can run on a little arduino, but there is just not enough compute power there to handle 4 axis at once. Those who have added rotary either switch Y axis to control rotary or completely have another controller and switch out. Better off starting with something powerful enough to handle a 4th axis, as it is not stiff enough to hold the kinds of tolerances you desire anyway.

Same applies to software. The commonly used VCarve Pro or Aspire has somewhat limited rotary capabilities, what they call "wrapped rotary". The limitation is that the Z-axis cannot move off the centerline of the rotary axis, if you need an off axis hole, it cannot be done with this concept. You cannot have the Z-axis travel below the centerline of the rotary axis either (a capability required for a cabriole or ball and claw leg, for instance). There is other software out there like DeskProto and Rhino that I believe have more capable rotary toolpathing strategies. I believe that Fusion 360 may also allow this type of toolpaths, but do not have a rotary, and have not tried.

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Nate Banton

Discussion Starter · #14 · Nov 1, 2019

Thanks, Richard, that's very helpful to know. And I haven't even begun to explore software options. Looks like I better start!

Reactions: 1

jpbldr

· #15 · Nov 5, 2019

3

Nate,

Some pics of one of my projects, wing ribs for an RC sailplane... These are relatively small parts, less than 6"x1/2" for the largest. The smallest steps you see in the part, are around .020". The primary notch in the middle, where they are lined up on the ruler in one pic, has a tolerance of +/- .003 as cut, compared to the CAD drawing they came from. This is in balsa, using a .031" endmill.

Machine is a Probotix Comet, and I use Fusion360 for CAD/CAM. I know Probotix has an option for 4th axis, not sure on the tolerance differences when using that vs the standard 3 axis.

Brian

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Nate Banton

Discussion Starter · #16 · Nov 11, 2019

Brian,

I'm very impressed and encouraged by your work. Thanks, and I'll check out your machine as well.

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