Here we go again . . . MK4

[routercnc]

OK so yesterday I managed to take some measurements for the X and Y stiffness of the new Atlas Mk4 machine.

The machine was positioned so the gantry was half way along the X axis, and the Y axis was positioned at the mid point of the gantry. So the X and Y positions represented worst case. The Z axis was lowered 50 mm from home in a typical machining position.

I used a digital luggage scale with a hook on the end to pull on the spindle just slightly above the collet nut (6mm end mill was inserted), while a DTI was pointed to the round section on the collet nut just above the flats.

5kg load was applied (~50 N) and the reading in for both X and Y was somewhere around 0.01 - 0.015 mm. I'm wondering how reliable this reading was given the needle barely moved and 0.01 to 0.015 makes quite a difference on the stiffness values. I guess I really need to buy a 0.001 mm DTI !

Anyway, for Atlas mk4 this works out at:
X between 3333 and 5000 N/mm (0.015 and 0.01 mm respectively)
Y between 3333 and 5000 N/mm (0.015 and 0.01 mm respectively)

My previous mk3 machine was:
X 1000 N/mm
Y 1250 N/mm

So up to 5 times stiffer. It certainly sounds different when machining and as you might have seen in the videos you can certainly take a good cut so long as there is some lubrication. I didn't measure Z this time as it was a bit awkward Vs the previous machine.

I did not have long to explore further but just before I finished I quickly pulled on the ballscrews when the DTI was still on the spindle and could make the needle move a bit. So maybe the limit is the stiffness of the small AC bearings in the ballscrew housings, or come to think of it they might be the deep groove ball bearings? Anyway I think as it is all working well I should stop there otherwise I will never use it to make something !