DIY CNC Milling Machine From Scratch

[totts]

What is the mass of the Z-axis (head, spindle etc) and what are the dimensions of the Z-axis ballscrew? I've made a script to calculate it more accurately, so if you post that information we can make sure the motor you've chosen is the best option. I suspect you may be OK with one of the 3-4Nm Nema 24 motors. The gas strut makes surprisingly little difference if you try to get a reasonable acceleration...

Okay after managing to get on the computer i have made sure my plates are made of steel, and from what i can find the 2.2kw spindle is around 5.15kgs then the z axis is around 45kgs.

[dazza]

its an impressive build so far totts,wheres the adjustable gas strut from and whats it rated at?thanks

[Jonathan]

Okay after managing to get on the computer i have made sure my plates are made of steel, and from what i can find the 2.2kw spindle is around 5.15kgs then the z axis is around 45kgs.

Just realised I forgot to reply to you about this. Using the script I posted here, the difference in torque required with and without the gas strut is around 20-30% and the absolute value is low enough for a 3Nm stepper motor to work well. I'm guessing a bit with some of the parameters, but suppose you put a 20T pulley on the motor and 30T on the ballscrew, the required torque (taking into account inertia of ballscrew, pulleys, carraige and motor, plus friction of bearings, ballnut etc) for 3m/s^2 acceleration is 0.87Nm without the gas strut which is well within the rating of a 3Nm motor below the corner speed. That means you'd easily get about 3.3m/min feedrate. The torque requirement for the same acceleration with 30:30T gearing is almost twice as much (1.67Nm), but if you use 20:20T it's 1.1Nm. The belt stiffness goes down with smaller pulleys, but it's still higher than the ballscrew torsional stiffness so not too big a concern ...

I'd recommend 20:30T pulleys on Z, as around 3m/min should be plenty for this size machine and you get higher resolution compared to 1:1.

[totts]

http://www.strutsdirect.co.uk/produc...-sd03-400-p-76

Their postage is a little high but not to badly priced.

They come in many lengths n sizes, mines adjustable set at 1200N but will release the pressure when everything is assembled.

[dazza]

not bad at all,thanks a lot,
keen to see this mill in action.,i did toy with making my own for a while then bottled it and bought an sx3.

[totts]

Yeah i came very close to getting an sx3, axminster had a 10% off all machines, and when i went on the website they had been reduced due to discontinuing them, and could have picked a new one up for £800!

Only thing that stopped me is the need for a slightly bigger travel and higher spindle speeds.

Have you a video of your sx3 in action?

[dazza]

Have you a video of your sx3 in action?

no not yet I bought it new from arc a while back and immediately ripped it aprt and fitted ball screws and steppers.(wishing I put profile rail on it after seeing what you and jonathan are upto..upgrade for the future maybe)at the minute im on the wiring so a week or two away yet.

[totts]

Will be very interested to see it running! Yeah profile rail is bloody exspensive tho :(

[totts]

Got some steel strips made up now ready to be bolted onto the bed, just waiting for some stainless steel countersunk screws to turn up!

[totts]

Blimey i knew it could get warm but not that hot! I think ill start with the sand!