Hi!
I have used my cnc for about 4 month now and I saw that it didn’t cut precise anymore. I have tightened the belts and some of the bolts in the middle assembly. It has improved, but not enough. Do you know what else I can do, or if I have done something wrong?
Thanks!
I wouldn’t judge the precision of the machine based on anything with the “recommended” pen attachment. The pen attachment is way to flexible. That causes the tip of the pen to move and often twist to one side. I would be willing to bet you could get very precise cuts it you used the router. If your end goal is to use the machine as a plotter then you will just need to swap out the pen holder for one with less flex. Granted that means you need to be very careful with the z height as you use it.
With that said your crown is one of the cleanest I have ever seen using that pen holder. Well done. you must have had the z height just about perfect.
If you want to test what I am saying you could run that same crown test again but this time you should intentionally smash the Z down more. You will see the pen holder flex all over the place and that will cause the start and end of the lines to not match up anymore.
Agreed, that mount is meant to smooth out table deviations of less than 0.5mm. Extremely light pressure is what is was made for as I typically use a ultra fine 0.3mm gel pen. To do the test as I do, home that pen mount on a sheet of standard copy paper (so as not to leave a dot and get the right starting height), then run my crown Cgode. Improper use and pressure will result in bad lines as the dual torsion arms can only be accurate with minimal loading.
Rigid mounted pens require a perfect surface to work from.
I had a similar problem where my machine got less accurate over time.
I’m not sure when it happened, but at some point, some of the plastic 3d printed parts on the machine had developed a crack. I reprinted the parts and most of the issue is gone. I still have a small flex in the x direction that I’m still trying to figure out what’s causing it.
Do you remember ever crashing the head or doing anything extraneous while the machine was running correctly?
I’m pretty sure my broken parts happened when I burned up a bit and it dug into a bunch of MDF binding up the entire machine.
Yes, that might have happend. I will take a closer look and see if something has a crack. Thanks!
What filament was used to make your MPCNCs? I am learning that PLA is not a good choice. It tends to crack. I am learning from another project I am working on. My MPCNC is mostly made from ABS. Reading some material about the Prusa i3 Originals I have learned that they use PETG for everything structural. So all of their 3D printed parts are made of PETG.
I have an original Prusa i3 MK2 and it is ABS. Up until recently, maybe the MK2s or MK3, I belive Prusa was using a custom blend of ABS; they referenced a custom “EasyABS” in a MK2 blog post (https://www.prusaprinters.org/original-prusa-i3-mk2-3-months-update/). Now, I see a MK3 part update posts recommend printing in PETG except for the nozzle shroud which is still ABS to handle the heat.
If you’re going to print your parts in either abs or pet, add an extra wall, top, and bottom layer. Both those plastics are more flexible then pla.
We used PLA 
I’ve checked for cracks, but haven’t found anything. I even turned everything apart to see.
Because the pen is so flexible, I tried to just cut into wood to see if the result was better… It wasn’t.
I used soft wood (pine) 3mm end mill, F(xy) 900mm/min.
You can see the result in the photo. [attachment file=“IMG_20190401_110825633~2.jpg”]
That is not even remotely close to decent. Something massive is wrong.
What router and endmill are you using? Video of it cutting?
Ensure that you properly fixed pulleys on steppers shafts.
It would be nice if you can make some video of cutting, upload it to youtube and share link here.
Also it would be nice to marking zero point on your picture and attaching corresponding Gcode
Ok, so my guess now is that the end mills are bad quality (they were really cheap), and when I use estlcam I set the machining order to automatic, and that does not work every time. I made two videos and you can that it wobbles. I thought I heard something so I set the speed up to hear better and that was were I heard the bad end mill and that I have to set down f(xy) because it wobbles (I think). I saw things so much better when I made a video. Sorry for the movavi video. I needed to cut the start out and did not want to pay for it 
When I decided the machining order, the result was so much better.
If you see or hear something I am doing wrong, please say something. It’s learning by doing here, and I have not been good at reading online so that’s going to change now.
End mill: https://www.amazon.co.uk/gp/product/B07F3N39TT/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
[attachment file=95347]
Look to your second video. From 2:05 to 2:12. Z axis has been tilted and became vertical when the movement had been ended. Do you see it?
Wrong endmills. You need 2 flute or single flute.
Yes… Can that be caused by the wrong end mill and that maby the middle assembly isn’t tight enough? The middle assembly doesn’t move if I try to move it by hand.
The router has enough torque to move the machine by itself. I’ve had mine run away with a bad cut. End mill got grabby, and pulled itself around in spirals across the board. If it doesn’t rattle when you wiggle the collet, it’s tight enough. Over tightening won’t help.
Barry is right, 4 flute tool is overkill for our cnc. and it’s difficult to evacuate chips with such tools.
most of my tools are single flute.
for ensure that’s tight also try to apply force to the bit, not to router or gantry
also as you can see on your video when cutter moving from right to left the effect is much less just because less DOC
where do you buy your end mills?
In Ukraine 
In two of our local internet stores who specialized on equipment for cnc.
[attachment file=95465]
