Desktop CNC - Corona Design

[Jacek]

This is how I have been spending my "lockdown afternoons" of early 2021 - advancing my CNC project! It's a milling machine / router with working area of 320x220x120mm in 540x500x540mm enclosure - purposed for precision parts making & prototyping. Project is ongoing.

- HIWIN linear guides
- ISEL ballscrews
- GMT 0,8kW 24000rpm spindle
- 1,8Nm NEMA24 motors (3A)

I would appreciate your honest opinions.

[mjeuring]

Prrallel mounting of the 4 slides for the x-stage will be a challenge. In the z-stage you made it possible to tighten the screws of the slides with the stage attached to it. How do you plan to assemble the x-stage on the y?

[Goudgele]

Can you make full use of the bed? Looks like the X motor/bearing block is in the way, so part of the left side of the bed can't be reached by the spindle. If that is the case and you don't want to make the enclosure any larger to move the X motor to the left, you could try to offset the bed a little more to the right.

I'm not sure about the 800W spindle. I have no personal experience with it, but it sounds a bit underpowered if you plan to mill metals. (could be wrong though)

Other than that, looks like a pretty solid design!

[javanree]

I'm not sure about the 800W spindle. I have no personal experience with it, but it sounds a bit underpowered if you plan to mill metals. (could be wrong though)

From experience with an 800W aircooled spindle it works fine even in C45 or 303 stainless with endmills of up to 6mm. Of course you need to adapt your feed rates and depth of cut. But I would , if it's possible , advise for a 1500W model to get some more power in the low RPM range. An 800W spindle is almost useless below 9000rpm

[FreesKever]

I would make both the base and the X-axis bridge thicker for more stiffness.
It seems you have not mentioned out of which material this machine is to be made. Aluminimum?

A big plate for the bottom is relatively expensive to make thick, and has not much use.
Just using a thicker part for the part upto the rails widht is enough. A sandwith construction of for example 2 10mm thick plates with 40mm profiles in between is a good and simple way to get more thickness and stiffness.

I would not easily decide for an 800W spindle. Price difference for an 1.5kW spindle is not so big.

There is a lot of quality, and other differences in the Chinese spindles though.
I made the mistake to buy a cheap 1.5kW spindle. Power is plenty, but it's only ER11. My next motor will be ER20.

For milling metal (Especially steel) you want more torque at lower RPM. Having a bigger motor certainly helps here. Some of the spindles such as advertised on Aliexpress are for "metal". These are more expensive, but often have more or better bearings, and have 4-pole motors, which gives them more torque at lower RPM.

On top of that. You can add an (option for) an extra transmission. The attached picture shows a (Green) ER20 "toolhead" (Common on Aliexpress, in different qualities) with an HTD3M timing belt. The small pulley is just clamped in the ER11 collet, so it's easy to switch between using the 24000rpm spindle directly, or with the transmission.

[Kjelt]

Not an expert but the sides should be as thick as you can afford.
The X plate since it is static mounted can better be a box instead of a plate, even better a torsion box construction.

[Jacek]

Prrallel mounting of the 4 slides for the x-stage will be a challenge. In the z-stage you made it possible to tighten the screws of the slides with the stage attached to it. How do you plan to assemble the x-stage on the y?

Regarding x-stage carts: as per HIWIN guidance: first assemble 4 carts and fix them to "base" edges, fix 1st linear guide to base edge and finalise fixing the second "flaoting" guide with use of dial gauge.

Reagrding X on Y: There are two "pockets" on both side walls, so that the X-axis can be fixated in Z and Y directions to base edges. Than screws will come from through side walls into X-stage. This is still under dev. - I want to fit all electronics behind the X-stage.

Not an expert but the sides should be as thick as you can afford.
The X plate since it is static mounted can better be a box instead of a plate, even better a torsion box construction.

Side walls are 20mm alu. X-stage is 30mm + andditional "shelf" behind it perpendicular, so in the end it is "L" shape.

I would not easily decide for an 800W spindle. Price difference for an 1.5kW spindle is not so big.

The intention was to have a "desktop machine", running from 1-phase 230V in clean office/home spaces + small form factor. 800W means much smaller inverter that can fit within the enclosure. There is lots of small CNCs right now on the market that have even 200-500W spindles. "Kickstarter-famous" 5-axis pocket NC had a 100W BLDC in first version.

For the rest of your comments: I agree. These were all conscious choices and trade-offs.

Can you make full use of the bed? Looks like the X motor/bearing block is in the way, so part of the left side of the bed can't be reached by the spindle. If that is the case and you don't want to make the enclosure any larger to move the X motor to the left, you could try to offset the bed a little more to the right.

Working volume is actually broader than the table itself. In the table and in the X-cart there are pockets undeneath and on the backside, so the X can go from wall to wall (- limit switch safety distance of 20mm on each side). PS. I love symmetry. I was also considering the X motor to be attached to the X cart and a non-rotating screw (non-captive motor with a rotating ballnut).

Thanks all for your insights. Bedankt!