Creating my first CNC

Mostly Printed CNC - MPCNC Advice
1

Hey all,

I’ve been doing research on DIY CNC machines for a while and I’ve settled on the MPCNC as my first learning experience. If all goes well I’ll fork over some money for a more serious setup once I narrow down exactly what I want to do. Right now I’m interested in cutting wood, acrylic and hopefully trying for thin aluminum (1/16 to 1/8) for signs as a small side gig.

I have a friend with a 3D printer willing to print all the parts for me at cost. I’ve been trying to figure out the other details in the meantime:

-I plan to keep my Z axis relatively low (2-4") and I’m going to start bigger with my Y and X (24"x"48 usable respectively). If this isn’t accurate enough going smaller is easier than going bigger later. Has anyone considered using a different material for the outer X and Y guide rods, I figure aluminum is too soft but what about DOM 1020 steel treated to not rust? This would prevent ANY sagging from happening with the longer X or Y axes. Thicker stainless tubes get ridiculously expensive real fast

-I know I want 304 stainless guide tubes but I was curious what most people are purchasing - seamless or welded seam? There is a difference, here is a good read http://www.hysteelpipe.com/steel-knowledge/api-5l-astm-a53-seamless-vs-welded-steel-pipe/

“The dimensional flaw of welded tubing may be its ovality, or roundness. Seamless tubing has a very round and very consistent diameter as a result of being extruded through a die, with typical measured variations in diameter of +/- 0.025mm for a 25 mm OD size. Roll formed welded tubing on the other hand, typically varies about +/- 0.050 mm to +/- 0.075 mm for the same nominal OD. However, for most applications, good concentricity is more valuable than good ovality.”

I think seamless is the best for this application due to it’s more consistent OD. Am I overthinking this though? I can easily get welded seam locally very cheap to the online stores, I can get 30’ of 1" 16 gauge A554 304 for about $50 http://www.tachen.com/catalog/pdf/pipe/A554-inch.pdf

-I’m considering running the DW660 with a rheostat control but I heard the router is very loud. Can anyone comment on this? An alternative is the Quiet Spindle but I’m concerned about its build quality. The cost difference does not matter to me. I’m thinking about buying the DW660 at a local Home Depot and returning it if it is too loud.

-What is the durability of PLA in summer heat? I plan on keeping this in my garage and live in Phoenix, AZ where the temps in my garage could easily reach 120+

I’m very excited to start building this, I’ll be posting my progress along with recording the accuracy of the machine. There seems to be very little information about this on the forums but I did read I can expect about 0.030" or ~0.7mm.

2

Not 100% sure on issues with the seamless vs welded, but a max variance of .075mm doesn’t sound like a show stopper the design could not handle. I can vouch for the DW660 being pretty loud, though its performance with the rheostat has been excellent. As for the PLA question, I also live in Phoenix and my shop is not cooled unless I am in it. I hear you with the summer temps. In the late afternoon I can get readings of over 120F at the west window. That said, I have three printers plus my MPCNC in there and they are all virtually 100% PLA (vast majority is Hatchbox) with only some PETG mixed in on the printers. I have been through three summers in this shop and have only had one failure I attribute to the heat and that was on an extruder tensioning arm on my D-Bot that seemed to warp under the constant pressure from the spring. All other mounts and everything else have stood up admirably. The glass transition (Tg) for pure PLA is around 140-150F, higher for a lot of the blends we actually end up with sold as PLA.

3

Thanks for the confirmation that PLA won’t be catastrophic, my buddy has already started printing me out some parts!

Doing some more research I’m abandoning the thought of using a router as a spindle entirely, I have yet to pick the spindle but I’m leaning towards a brushless 400-600W chinese spindle with RPM control via MACH3. From my research, routers will produce noise anywhere from 85-100dBa and a spindle will be around 50-60dBa, that’s a huge difference and I don’t want my neighbors hating me

Leaning towards just going with the seamed tube for now, any other comments?

4

You can rpm control from most any CAM software. Mach 3 is expensive.

The sound of the vacuum and the sound of the material being cut is all about the same as the router at least for me. I would love a more quiet setup but making a mess is loud.

Seamed should be okay. Can you confirm when you get it, this gets asked a lot.

5

My friend is about halfway through printing the parts for me. I’m starting to select and order the electronics. I was wondering if the DRV8825 drivers on your store have the fast decay pin wired out? I’ve read different things about this online and wouldn’t mind testing it at some point

I’ll be going with seamed stainless due to price. I do have a 1" peice of steel DOM lying around in which I’ll give some comparisons to outer accuracy

6

Bought all my electronics last night, it seems most DRV8825 boards don’t pull out pin 19 to set the decay mode manually. I can mod this later if needed.

Question on the Z-axis threaded rod, the parts list just says the threaded rod and 1 0.75" coupler nut, however this diagram shows several nuts and a spring?

The parts bundle in the Vicious store also shows the same

Any info on the spring size and rate?

7

That is an old picture from the v1 parts, it no longer needs the spring (at least as of 2 months ago).

Z

8

Sorry updating those pics are on the very top of my list of things to do after shipping orders.