Need Run-out and Accuracy ImprovementTips

So, my first post as I am new to the CNC/CAD world. I bought my Shapeoko XXL back in April and have been busy trying to learn my way around learning drawing software and running the machine to produce, mainly, guitar parts and pieces (would be happy to hear from other Luthiers using the products). I’ve made probably 25-30 guitars over the past 5-7 years (using templates and basic woodworking power tools, etc.) and thought that CNC would provide me with a way to streamline and standardize certain aspects of the process and, at the same time, improve the accuracy and detail of some work (particularly things like hole placement for bridges, inlay, and other precision operations). For the most part, I have been quite satisfied and feel the machine is living up to what I want it to do, and the biggest challenge has been learning a drawing software (I’m using Inkscape) that provides the accuracy needed for design and eventual milling.

The problem I am encountering is with, what I perceive to be, run-out. Last night, I was machining some inlay with some fairly small mills (1/16 and 1/32) and was having some trouble gaining tight tolerances. What I noticed was quite a bit of “wobble” in the end of the mills when placed alongside a fixed edge. I was not able to measure it, but it appears to be at least the diameter of the 1/32 mill. There does not appear to be much movement in the spindle itself, and I was using an insert in the standard 1/4 collet that came with the now standard issue Carbide 3d router spindle in order to reduce down to the 1/8" shaft of the mills. So here are my questions:

  • Would I benefit from some “upgraded” collets? I note that actual 1/8 collets are available rather than using an insert.

  • If upgrades are recommended, can someone suggest a brand. What specific type of collet fits the standard-issue Carbide 3D (are they interchangeable with, say, and Dewalt or Makita)?

  • Is there a way to accurately measure run out in order to build in compensation?

Any other tips and suggestions would be appreciate. I’ve read some other posts here, one in particular on cutting fret slots, that suggest a need to compensate for run out by using smaller mills and undercutting slots, but that seems to be a cut and test proposition.

Thanks

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Hi Everett,

You can:

  • drop the adapter and buy high-precision collets: Carbide3D’s or Elaire’s are the two options that pop-up regularly here. My understanding is that Elaire’s “Makita” collets would work fine on the CCR, since it’s basically a Makita, but you may want to double-check that, I don’t own a CCR and can’t confirm.
  • try the “tapping” method, there are some threads here from @Vince.Fab and I wrote a bit about this myself here (my own take on measuring runout is also covered there)
  • upgrade to a spindle. They generally have lower runout than routers, and possibly much lower runout if you purchase wisely.

This should get you a very low runout, and then you “only” have to care about deflection to get to really tight dimensional tolerances (I hear 0.0002" is within reach on a Shapeoko)

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Julien, thanks for the excellent information. The link is very comprehensive and gave me a lot of food for thought. I see that you have a number of topics outside of Dimensional Accuracy, so I will be doing some extra reading in the next few day. I’m going to try some high-precision collets as well as see if I can gain a little less wobble with a tap or two. As to a spindle, do you have any recommendations for something that will fit the XXL? Not sure if I’ll go that route right away, but it’s worth considering.

Thanks

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Any spindle will fit the XXL, but for the heavier ones (2.2kW) you will probably need to upgrade the Z axis (HDZ or similar), so if it’s only to benefit from the lower runout, an 800W spindle would be best suited (similar weight and diameter as the routers, works with stock Z axis). There are a gazillion threads on the forum about spindles, this one is probably my favorite.

But don’t go there, you’ll get gear lust as I did :slight_smile:

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LOL. As a musician and long-time guitar player (as well as my other interests in tools and equipment), I am all too familiar with Gear Acquisition Syndrome (AKA GAS).

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Here’s how to measure it and another source of precision collets and other useful information. Remember to minimize endmill and router stick-out as well as cutting forces.

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Gerald,
Thanks for the link. More good information and I see they also offer specialized luthier tooling.. Very cool.

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Gerald, by the way, I see quite a discussion in this article on the low quality and poor tolerances for inserts, which is how I was stepping the 1/4 collet down to fit my smaller mills. I definitely will be buying a more precision set of collets for my CC3D router to include an actual 1/8 collet.

They’ll run at up to 100 kRPM too and faster is usually better.

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Thanks to everyone for all the answers. To update, I purchased a couple “precision” collets (a 1/4" and 1/8") from the Carbide Store to fit the standard-issue Carbide router. There is great improvement with these, particularly with the 1/8 shank endmills as I was using a reducing insert previously. Have not had a chance to acquire a dial indicator to actually measure, but cut tolerances are much tighter and I note very little “wobble” when placing the mills alongside a fixed edge and rotating the collet by hand. This certainly was not the case before.

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