[Goemon]

Hi Everyone,

Thanks for the helpful input. I should have provided more details.

We are currently spec'ing this as a new machine to be built. The company is Acctek. I've researched quite a bit about them on here and was pleased with what I found. They have also been good to work with so far, very responsive.

What we are spec'ing (in more detail):
-1100x1800 table, t-slot top
-Full table structure with heavier steel (8mm)
-Taiwan Hiwin rails (25mm)
-Taiwan ball screws on XYZ (25mm on XY, 16mm on Z)
-Taiwan servo motors, 750w on each axis
-Rapids are only 4000mm/min
-3.5kw air cooled spindle
-dust collector
-coolant mist sprayer
-control is mach3 on a separate computer

It will looks something like this machine:

http://www.acctekcnc.com/uploadfile/...0095439723.jpg

After communicating with them more, they have clarified that the gantry on these is cast aluminum. Unfortunately I don't have any better pictures of the internal structure. They have though said that a steel frame gantry using 3mm material (about 1/8") can be done for a small up-charge.

I wonder which would be stronger? My guess would be the steel, but as you point out NIC, it depends on the details of the cast aluminum one.

I don't know what gear reduction there is on the servos. Also there is currently only one ball screw driving the long axis Z. Given the span across is over 1m, does having a ball screw down each side make more sense to reduce twisting forces when cutting near the edges?

Thanks,

-Gord

[Edit] Updated the ball screw size for Z, had originally written it was 25mm.

Just specifying "aluminum" or "steel" doesn't tell you enough to gain the required level of comfort. There is an enormous difference in the properties of the various grades and alloys of both aluminum and steel.

Aluminum 7075 T6 has strength that is very comparable to some steels and has superior rust resistance. It is unlikely that you would be getting the best and strongest grades of hardened stainless steel unless you specifically ask for it (and pay the extra costs).

It is also worth noting that, while steel is stronger and stiffer inch for inch, the difference can be 100% compensated for by adjusting the part thickness like people do with epoxy granite. If the steel alloy was twice as strong as the aluminum specified, make it 2" thick instead of 1".

The only area you can't compensate for the difference in properties is on the rails and ball screws where the steels higher surface hardness makes them more abrasion resistant.