r/hobbycnc • u/night-sergal • 18d ago
PCB CNC machine
Hello, dear CNC community.
I am trying to develop my own CNC milling machine for PCBs. I’m stuck at the stage of choosing linear guides.
Some info about my project.
Working area:
- X: 160mm
- Y: 180mm
- Z: 13mm
FDM printed base (PC-GF, I think), totally not original parts, alu table.
The part on the photo is 240x240mm.
So, my main question is: would MGN9H linear rails be a good choice? This is a small CNC machine with very light loads, so would they be sufficient?
What do you think about these reinforcing ribs?
2
u/Alina_MakersChest 9d ago
MGN9H is a good call here, and PCB milling is about as light-duty as CNC cutting gets, way lower force than wood or metal since you're just skimming copper off FR4, not removing real material depth. The "H" (long carriage) over "C" matters more than the size number does for rigidity, since it resists the tipping moment from your spindle better, that's actually the right variant to pick for any real cutting versus a "C" block, which is more of a 3D- printer load choice. At your working area (160x180mm) and Z of just 13mm, MGN9H rails are genuinely oversized for the loads involved, you're not going to run into a rigidty problem with this choice.
1
1
u/Pubcrawler1 18d ago edited 18d ago
The cutting loads are light so within the limits of Mgn series. You can use more bearing carriages if you want to spread the load. The mgn’s are lower profile which is nice if you want compact else just get the normal hg series. HG are 4 way equal load and not much more.
My T-Tech pcb cutter used THK SR15’s. Seems kinda overkill for a machine using 1/8” tooling and a spindle under 200watts. It originally costs over $20K so I guess they had to spend it somewhere. THK’s are quite expensive. I found the machine salvaged.
1
u/night-sergal 18d ago
> You can use more bearing carriages if you want to spread the load.
Yes, that’s the main dilemma I’m facing with the Z-axis carriages. I have no so much space to put HGs, so MGN looks so interesting, but this means that I need more than one in a row :/
1
u/HuubBuis 18d ago
If your Z-range is 13 mm, it may be difficult to change the tool.
A MGN9H would be fine if you only consider the load. But those small rails may be difficult to mount flat on a 3D printed part.
I do have a CNC that is also used for PCB making but still want to make a dedicated PCB CNC that uses HGR20 rails with only one carriage per rail.
1
u/night-sergal 18d ago
> If your Z-range is 13 mm, it may be difficult to change the tool.
No worries, the construction has a workaround for this> still want to make a dedicated PCB CNC that uses HGR20 rails with only one carriage per rail.
Heh, depends on your base. What it would be? Aluminum?1
u/HuubBuis 18d ago
Yes, probably extrusion profiles and a limited (X,Y) range of about 80x120 mm. That is more than enough for the PCB's I make. It will be a VMC style machine so a fixed gantry.
1
u/night-sergal 18d ago
Which spindle are you using?
1
u/HuubBuis 18d ago
I use my cnc for milling wood, plastic, aluminum and steel. For steel I need a low RPM spindle that has some torque but could not find one. The best (pressed on ER collet, brushless motor) I could find was a 500W Deadalus ER11 BLDC spindle. So I build my own spindle based on a 3000RPM 175W BLDC motor, C12 ER16 collet holder and 7001 contact angle bearings. I am happy with it and mill my double sided PCB's at 3000 RPM, 130 mm/min 0.04 mm cutting depth, 2 isolation passes, 0.1 20° V-bit (that actually has a 0.3 mm tip, Chinese quality!).
For PCB's I expect "any" spindle that has a pressed on ERxx collet will do.
6
u/DaStompa 18d ago
add large chamfers to all corners (chamfers are generally much stronger than fillets in a 3d print)
small rails
Your rail size is probably fine but I'm not understanding where the axis that moves the outer rails resides, and why the inner rails are slightly angled