Starcadian - Second project, second mistake

I have one weekend worth of experience with CNC machines, and have still never used a CAD program. But for this second project I have a secret weapon. I’m not the reason why I bought the Nomad 883, my kid (Dallas) is a junior in high-school and is taking pre-engineering classes. Dallas has worked with a 3D printer, and has used a CAD program that the school provided (Autodesk Inventor) to do Engineering homework.

While this is our second project, you are only going to see photos from the final attempt. We burned through several of those 25 cent floor samples (see our first project for detail) getting to this point. The key lesson learned from all of these failures is related to physical limits on the designs. In retrospect it seems logical now, but it took us several failures to understand what we could and could not do.

Dallas and I found an indie-musician online we like his music, and we also like his logo. Starcadian’s logo was our second project. So no “CAD” design here, we were just taking the graphic image and loading it into MeshCam.

The logo looks like you’re looking through the small window of an old tape deck, but then it has a film strip running down the middle. I say this so when I say things like “the tape wheel” you (hopefully) understand what I am talking about.

Trying to using the above image we were not successful, the small details were lost. We were using the #111 0.625 ball cutter for the finishing pass, and here is what happened…

The squares in the tape wheels were etched on the left side, but not the right. The filmstrip running up the middle of the logo reached a point where things just got to small. I got out a caliper and determined the failure point within the filmstrip was when the boxes got less than 2mm thick. The kid pointed out that our bit was 0.625 inches which is roughly 2mm so this made perfect since. So we decided the logo needed to be “corrected” with this 2mm tolerance level.

Since I don’t know CAD, but I do know how to use Adobe Photoshop I reworked the original logo in Photoshop to make some of the elements within the logo bigger and eliminate the tolerance problems we were having.

While it wasn’t perfect, we were pleased enough with the results to consider this project finished…

What I learned here is that when milling into material (aka making a hole) the hole needed to be at least the size of the bit. I feel stupid making that statement, it seems so obvious to me now but with everything else we were trying to learn that fact got lost on me the first time. It also didn’t help that after nearly 50 years of dealing with inches and feet it wasn’t helping that my in-house engineer was forcing me to do everything using the metric system.

Our final result still has examples of this mistake. If you look at the small arc inside each tape wheel you can see that I didn’t leave enough of a gap. The CNC did it’s best to get in there and I’m sure if I would have cleared out just a little more room in the design it would have worked.

Also notice that the sprockets within the tape wheel are less than 2mm, and they are just fine. Because the bit can leave less than 2mm it just needs 2mm wherever it is going into the material.

@ColdCoffee - This is a really nice writeup. Remember, everything, after you have learned seems obvious in retrospect. We have all been there and can sympathize with what you’re experiencing. You’re doing a great job working through it.

One of the most important rules, you’ve already learned - you can’t have a feature that is smaller than your bit. So, you have two choices - you can either use a smaller bit, or make the features larger. And I think you understand that now.

The lessons you have learned will help you as you and your son move on to more and more projects. As you get more comfortable with the process, and begin creating your own designs, you’ll remember these ‘rules’ that you’ve learned and apply them as you are designing.

Keep up the good work.


If the bit actually fits in that feature, you could try lowering the tolerance to get a full cut in there.
Also technically ball mills and other non-flat mills can mill a hole or slot smaller than their full diameter (though a a reduced depth).