Router/Plasma CNC Build From Down Under

[Boyan Silyavski]

The Z travel I have is 220mm, which is a standard length by THK Actuators, so presume you are saying this okay. The THK actuators at this length are very accurate, so I need to concentrate on the gantry to ensure it is robust enough/will not flex. I'm not sure what it will cost me, but I still feel it will be more accurate than what I will construct, with less effort!

Its very difficult to find the correct sized actuator for that job. I have been that way. And actually constructing it yourself you will reap all the benefits over ready actuator. You will waste more time and money searching for it. And most of the commercial designs have the rails mounted on the fixed plate, the fixed plate is too thing, all weights too much, travel is too short, the ball screw is not the correct pitch and so on. I spend months looking for a correct one. from the THK ones only the biggest ones are good.

I wander if this is over engineering it? My gantry (pictured above) is RHS 250 (height) x 150mm (wide) x 5mm (thick), reinforced partially by two welded 10mm steel plates over carriages for X axis. I have utilised RouterCNC's extremely useful stiffness calculator posted, and using my dimensions and cutting aluminum, came up with deflection of Z = 6.3um and Z - 1.6um, which I find more than acceptable. Using the new Stand-alone Z axis calculator, at the extreme Z Axis extension of 220mm (which I would only use for wood turns), I get a deflection of 4.185um. Unless I am using this tool incorrectly, I would think this accuracy is more than enough for most builds?

Perhaps there is good reason to make it more robust. You mention vibration. Is this a similar consideration to deflection, or something else that needs to be factored?

I've attached the spreadsheet below.

Yeah but you have 250mm side that can vibrate and i suggest you 100mm side that can vibrate. Which drum will make louder sound 100mm one or 250mm one? Think of it like aditional internal bracing.
Also i like working with one and only profile. And buy by the 6m. So as i see it i would do a machine from 80x80x3 to 100x100x4 and construct all i need from these ones. As they also cut perfectly with small saws at home.

Nice drawings.
I can't compete with silyavski on the frame design ...

Thanks Eddy but if you remember we all came together with that design on my build, i just calculated it the cheapest and lightest possible for acceptable rigidity for ali jobs. Its very funny though, instead of making steel instruments sound, i started to learn how to make steel structures not make sound. Its no much different than Romans did it- Divide and Conquer