These are Hill Country CNC & Woodworking's biggest mistakes for CNC.
Let me start with, their are a billion things you can do wrong with a hobbyist CNC. But if you get the 17 biggest mistakes of CNC I have listed below, you will probably be doing pretty good. A quick quip about me, I started CNC a few years ago and have grown it into a full time business, that I love to wake up to. Making things on your CNC is not just satisfying, it’s actually really good for your brain in the problem sets and planning involved.
What are the biggest mistakes for CNC that I have seen?
There you go. I answered the question, now go away. NO! I’m not the best blogger. If you want to learn what I mean by each of these, stick with me as I explain it all. Read on!
Top 17 (in order of relevance – meaning how often and how bad)
- Not securing your work material properly to the CNC surface.
- Not properly tightening your bit properly.
- Loading wrong file.
- Not cleaning your collet!
- Tool in path of X or Y rails.
- Not setting Z height.
- Not putting away you Touch Probe.
- Improper Feeds and Speeds.
- Wrong bit for what you are trying to cut.
- Not understanding the material.
- Not understanding G-Code.
- Improper Set-Up or CNC maintenance.
- Not flat material OR not flat surface board.
- Not understanding Inlay depths.
- Not allowing for proper drying (epoxy/glue).
- Wrong type of bit.
- Running over the router / spindle power cord with the bit.
And my bonus… Not enough Coffee.
Mistake 1: Not properly securing you material to the table.
Let me start off with, my blog is geared toward the hobbyist and/or beginner CNC worker. If you have a $80,000 Laguna, some of these issues won’t apply to you!
Moving on. I consider this to be the big ol number 1. Not having your material properly secured to the table. It has really bitten me in the butt before, and most notably the picture above. That was a pretty expensive chunk of Texas Mesquite filled with Milliput Epoxy that I was commissioned to make.
The following is my list of hold down methods, click here, for a more in depth conversation.
- Vacuum Table
- T-Tracks and Clamps
- Blue Painters tape and CA glue
- Double Sided Tape
- Screw the material to the wasteboard
I didn’t really list them in my order of preference because it really depends on what you are making. Sometimes just screwing material down works, although it is my least favorite. Vacuum is definitely the way to go, but you need a good vacuum table and they are not cheap. At my home shop I use Double Sided Tape 90% of the time.
Mistake 2: Not tightening your bit properly.
This is a very common mistake that new CNC operators make and the problem is usually counterintuitive. You would say, let me just tighten the hell out of it, but that is in fact wrong.
When securing your bit in the router or spindle you want the bit to be tight. Overtightening or Undertightening will cause the bit to move during operation once torque is applied to horizontal movement.
Too tight and the front of the collet is pinched leaving the back of the bit loose. This usually causes the bit to slide inwards, which is not the worse thing in the world. You just have to recut.
Too loose and the bit slides down while cutting. Massive changes in depth usually cause bit breakage.
Don’t forget that on endmills, your bit is either pushing material down or pulling material up. Thinking about it that way helps me think about why the bits move.
Mistake 3: One of the biggest mistakes for CNC is loading the wrong file.
That should be enough said. If you choose the wrong file (and you will) it will likely be disastrous. Successful CNC work is truly about attention to detail.
Luckily for me I had a professor that over emphasized file management. This is an example of one of my files names.
Thats (what it’s for)+(what I’m doing)+(the size material)+(the depth of cut)+(the bit).
Mistake 4: Not cleaning your CNC Router or Spindle Collet.
This is a mistake that can easily cost you a bit and project. Your collet, how ridiculous as it seems, collects the tiniest amounts of dust from your cutting of materials. This dust does two things.
- The dust is on the inside of the collet when you are tightening your bit. The dust is in between the bit and collet. This caused both friction (heat) and a loose bit).
- The dust causes you collet to sit a micro amount out of center. This causes extra vibration on the tip end of the bit (that’s bad).
Mistake 5: Tool in the path of the X or Y rails.
This is one of those accidents that can actually cost you a lot of money. On my home machine there is a nice little inviting ledge on the right side that just begs for you to put something there. I did it once, and the results were not great. The tool bound on the X rail causing the stepper motor to slip (it could have destroyed the gears).
Easy fix. Just make sure you don’t have anything in the way of your CNC.
BTW, I have also pinched my hand in a rail while looking over the project. Let me tell you, I am not making that mistake again!
Mistake 6: The sixth beginner mistake for CNC is not setting the Z height.
I think this one goes without saying, but it happens alot. I see on forums all the time where someone forgot to set their Z height. The big issue here, dependent on what you are trying to do is that you will cut at the wrong depth. To high, you are good. To low and you break a bit.
Just make sure you check your Z!
Mistake 7: Not putting away your touch probe.
Since we are talking about Z height, we should mention the Touch Probe. This is another one of those mistakes for CNC that just comes from the repetitive actions we do in the CNC world. Some controllers have a warning “ensure you put away your touch probe,” but honestly the higher in price you go, the less you see that.
Starting a Router or Spindle with a Touch Probe still attached is nasty and will decimate the Touch Probe cable.
Mistake 8: Another of the biggest mistakes for CNC Improper Feeds & Speeds
There is so much to say here. The key is three fold, get the router/spindle RPM right, have the CNC reed rate right and have the speed right. Sounds so simple.
Here is what I will say, first most bits come with a feed and speed and you can look up your router/spindle RPM. This is not the sure fire way, but it really should get you close. Once you have used a bit a few times you will start realizing if it can go faster or needs to go slower.
Learn about what proper chips look like. Counterintuitively, your chips shouldn’t look like dust.
Also, you should know that many CNC bit makers have free databases you can download and plug into your software. I primarily use Vectric VCarve Pro and Fusion 360, both take the downloadable files from Amana Tools. It makes it very easy and is pretty dead on. I only tweak things based on material (hardness).
Mistake 9: Wrong bit for what you are trying to cut.
Yes. I said it! I see on forums all the time where people are complaining about really poor results on their project, when questioned about it they had a compression bit doing the job of a downcut. New CNC operators need to spend some time getting familiar with different types of bits, bottom line.
- Downcut- makes a clean surface cut, tearout at the top.
- Upcut- Rougher bottom surface, cleaner top edge cut.
- Compression- Kind of does both, because it takes the best qualities of both downcut and upcut. Arguably, unless you are cutting through your material in one pass, you probably just should go with the up or down cut.
- Bowl or Ball- Think a juice groove on a cutting board
- Radius- To make your edges rounded over.
- Drill- To drill a hole, straight down and then back up.
- Keyhole- Makes a great little keyhole for hanging pictures.
There are way more, but you get the idea. Learn about them to minimize accidents!
Mistake 10: Not understanding your material.
This is another one where you just need to learn about what you are doing. Cutting MDF is nothing like cutting Mohagany. The differences in hardness (learn about the Janka Scale) will significantly change how you cut something.
The charts for most bits ARE NOT designed for wood over 2,000. You significantly have to change you feeds and speeds to prevent bit breakage.
Mistake 11: Not understanding G-Code.
With most of our CAD (Computer Aided Drafting) software directly programmed with our CAM (Computer Aided Manufacturing) many CNC operators leave this step out. They “forget it” because truthfully programs like VCarve Pro or Fusion 360 do a great job at programing the G-code and understanding the line by line seems pointless.
What you should know though is the basics. Knowing that you are missing your M3 code (turn the spindle on) will definetely save you a bit.
And accidents like that happen, they just do. Programs are rarely perfect. If you want to learn more about G-code, here is another article I wrote.
Mistake 12: Improper Set-Up or CNC maintenance.
Another simple error that is easily preventable. You need to check (I do it weekly) All screws & cables. Your rails need to be clean (everytime) and lubricated (weekly). Make sure that your CPU is away from sources of static and that your power cord is grounded. Also check all cables at the CPU.
I recently moved a box next to my CPU and guess what. I noticed as the X & Y were moving the Y cable would sneak out. It didn’t do anything because of what I was working on, but if it was something more complicated… Ouch.
Make yourself a maintenance routine, it really will help.
Mistake 13: Not flat material OR not flat surface board.
Not having a flat surface is probably one of the most frustrating things to me. So much so that I really take time to ensure things are flat first.
The bigger concept here is that if your material or spoilboard are not flat, your bit will cut flat and that will make the end product look uneven.
I always flatten my spoilboard and materials with the Amana Tool RC-2265. I think it is the best surfacing bit out there for a 1/4″ collet.
Mistake 14: Not understanding Inlay depths.
As mistakes for CNC goes, this is a small one, but worth mentioning. If you are doing inlays, they really shouldn’t be shallower than 3/16″. I’m sure I will get some grief over that- but I am telling you, go less and you will inevitably have a problem.
Mistake 15: Not allowing for proper drying (epoxy/glue).
Patience. Everything with proper CNC is patience.
I know how long it takes epoxy to dry, and you can figure that out exactly. My best practice is to calculate the cure time, and then give it another night. So if cure is 16 hours and that ends up at 10 am, give it another night.
My rule isn’t always needed. Tiny filler won’t take that long, but to be sure, that’s what I do.
What happens if you don’t? Not the worse mistake for CNC work, but it is messy, nasty and just something you don’t want to clean off your bit and dust collection.
Mistake 16: One of the biggest mistakes for CNC is using the wrong type of bit.
I’m not going to go terribly far into this one, but!
- Drill Bits ARE NOT CNC bits!
Likewise, I really feel you are pushing your luck using the $20 nine piece router bit set from Walmart.
Mistake 17: Running over the router / spindle power cord with the bit.
I am so embarrassed, but I have done this one. It sounds so strange that you could run over your power cord, but with many CNCs the cord isn’t specifically run into a channel or they don’t have cable management. When I was starting with my home (hobbyist style) CNC that is ridiculously different from my professional shop CNC I was surfacing my spoilboard which meant the router was going all the way back and forth. Yup. It’s a game ender. The nice thing is that you can easily rewire them sometimes.
Wrapping it up!
I hope you genuinely got something out of my top 17 mistakes for CNC, let me know in the comments if I forgot something.
Have a great one!
Hill Country CNC & Woodwork
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