[Portas]

I am a complete beginner hobby machinist and would like to work with a CNC milling machine. Because of my budget limitations, I want to convert a Chinese mini-mill Sieg SX2P to CNC. I wish to cut mild steel with it, but mostly brass and aluminium. I read all of the available articles and sourced all of the 3D models, but I am still unsure of my conversion design.

The plan is to stiffen the machine as much as possible with the rear column stiffener and additional ground plate. I intend to fill all of the cavities with epoxy granite to minimize the vibrations. I also want to upgrade the spindle with a 1.5 kW (2hp) induction motor with variable frequency drive. The head will weigh about 30kg, therefore the Z-axis ballscrew is positioned directly through the centre of mass to minimise wear and side forces.

For the positioning, I intend to use closed-loop stepper motors and 10mm diameter and 2 mm lead ballscrews (from my amateur calculations, this should be enough, because the ballscrews are only tensily stressed with 5x safety factor).

The budget for the whole conversion is around 3000€ (3400$), maybe a bit more. Is there anyone who has already undergone a similar conversion and could help me with some feedback on my 3D model. Additional pictures are available in the Imgur album https://imgur.com/a/x2foxl6 I can also post the STEP file if anyone would like to take a closer look.

Thank you

[cncuser1]

The spindle motor is a big weight that is off center, do you really need 1.5KW. Can you use a smaller motor and be on the center of the column?
The column stiffener will help, but depending on the size of cutters you are using, may not be necessary.
You put alot of effort into the design, try and protect the Z ballcrew and motors and couplings from chips.
It looks like you have linear rails on the Y axis but keep the dovetails on the X axis, if this is true then I would say use one type only on the while machine.

[dazp1976]

That's a lot of effort & money to throw at a Sieg and has a lot of off centre head weight. A servo motor might be better and fit on the head itself.

Myself I'd also compare the cost of buying a new PM30 / AMAT30 or similar and converting that (240kg in total weight). Making the parts using the Sieg then selling it. Shouldn't need to upgrade the spindle motor just maybe change pulley to bump up the rpm.

[cyclestart]

10mm diameter and 2 mm lead ballscrews (from my amateur calculations, this should be enough, because the ballscrews are only tensily stressed with 5x safety factor).

16 mm ball screws are plentiful and can be found cheap. If they fit I use them being a bit cheap myself.

The tray and lip around the table may help a bit with chips. If coolant is planned they won't help much.

[dazp1976]

I am a complete beginner hobby machinist and would like to work with a CNC milling machine. Because of my budget limitations, I want to convert a Chinese mini-mill Sieg SX2P to CNC. I wish to cut mild steel with it, but mostly brass and aluminium. I read all of the available articles and sourced all of the 3D models, but I am still unsure of my conversion design.

The plan is to stiffen the machine as much as possible with the rear column stiffener and additional ground plate. I intend to fill all of the cavities with epoxy granite to minimize the vibrations. I also want to upgrade the spindle with a 1.5 kW (2hp) induction motor with variable frequency drive. The head will weigh about 30kg, therefore the Z-axis ballscrew is positioned directly through the centre of mass to minimise wear and side forces.

For the positioning, I intend to use closed-loop stepper motors and 10mm diameter and 2 mm lead ballscrews (from my amateur calculations, this should be enough, because the ballscrews are only tensily stressed with 5x safety factor).

The budget for the whole conversion is around 3000€ (3400$), maybe a bit more. Is there anyone who has already undergone a similar conversion and could help me with some feedback on my 3D model. Additional pictures are available in the Imgur album https://imgur.com/a/x2foxl6 I can also post the STEP file if anyone would like to take a closer look.

Thank you

I reckon 1204 size screws are ideal for these.
Using 2mm pitch you'll need 500rpm for a rapid of 1000mm/min, you'll be pushing it if trying to go above 1500mm/min rapids.
4mm pitch will only need 250rpm for 1000mm/min.

A mill imo only really needs a resolution of 0.005mm.
I also suggest at least 425oz/in steppers on the table and 1000oz/in min for z.