Suggestions for machine?

[matth]

Hi all,

I currently have most of the parts required to build a all aluminium router with approx 750mm x 250mm table area. I have some 12mm THK rails for the x & y penty of NEMA34 steppers and 3 ball screws (see pics).
I plan on building the machine out of 44mmx44mm aluminium box section.

I have however come in to the possesion of 3 very big powerfull industrial AC servo motors and drivers (these can take standard step direction input). The servos are approx 1.5KW each!!
I would love to build an 8' x 4' capable router utilizing these but I don't have the space.
Any suggestions on the usage of these units and the router in general??

[santiniuk]

Hi Matth,

It looks like your off to a cracking start with the bits you have there. Those servo's would be worth a fortune but I know what you mean about space being a restriction. (One of the things us UK folks have to put up with....)

From the pics it looks like your sorted for a decent PSU too so your on a roll.

Sorry cannot offer much more than encouragement so good luck with the build

Cheers

[damae]

I've got a similar situation - trying to build a router that meets my needs, and I have motors that are far more powerful than my initial design could ever use.

And like you, I don't want to 'waste' the motors on a machine that would bend (or break) if the motor's full force was applied. Besides, it just seemed wrong.

BIG servos! (is there such a thing as too much power? =)

So I am building a much more rigid machine than I orginally intended. My frame design changed from aluminum extrusions (simple to put together) to steel, and now I'm looking at welders and hoists (to help me lift the heavy beams). By now, I have several sets of motors, due to my not being entirely sure that I wanted to waste the big motors on too small a machine.

Here's the link to my project: Amae Design - 'AKITA' CNC Mill

So you have two basic options:

1. Use the smaller motors with your current design, and save the larger motors for a future project, (Mark II)
2. Design a much more rigid (and/or larger) machine and use the servos.

There's a third option, but it's not very good: Use the servos with your current design.

The problem is that those servos don't lose steps. If your cutter bogs down, or something crashes, the servos will apply more and more power until they achieve the commanded position. By then, however, you may have folded your aluminum frame, or done some other serious damage. So if you plan to use the large servos, I would build the frame much stronger.

Just be aware that it starts with "oh, I'll just build the frame out of steel" and next thing you know, you can't park your car in the garage because of all the tools and equipment you've bought to build your CNC! =)

[WayneHill]

I have a solution to the limited space problem. Build the table vertical and mount it on the wall. The motors are strong enough to move the weight of the gantry up and down. Add a counter weight if needed. This way the chips fall to the floor

[matth]

Thanks for the reply guys, some very interesting reading in those posts. I know the servos are just to massize to be practical in the design I was considering (they'd probably fold my gantry in halve) but their just sat on my bench begging to be used.

Forgetting the servos for the moment let me lay out my current parts list and plan of action.
X axis:
6 x 300mm 12mm THK rails with 6 x carridges
2 x 400 Oz/in Nema 34 steppers
1 x 800mm 25mm balscrew with two nuts

Y axis:
2 x 520mm 12mm THK rails with 4 x carridges
1 x 380 Oz/in Nema 34 stepper
1 x 350mm 25mm ballscrew with 2 x nuts

Z axis:
2 x 200mm 9mm THK rails with 4 x carridges
1 x 250 Oz/in Nema stepper
1 x 150mm 16mm Ballscrew with 1 x nut

I plan on building this machine out of 44mm x 44mm aluminium box section (4mm wall) and I'd like to cut wood and aluminium. I have a mill/drill and plan on milling a shallow channel in the box section to take the 3 x 300mm thk rails that will make up each side of the X axis.
My concern is that the ballscrews are very large and heavy in comparison to the THK rails.

I've worked out that I can acheive a 750mm X 250mm x 100mm cutting area.

[matth]

Any body got some nice long rails and ballscrews that they like to trade for some 2HP servos????

[matth]

Here is the beginnings of my Y axis, the rails have been attached to the box section. I set a fence up on my mill and used a DTI to get it with 0.001" over its length (about 20") I then used the DRO on my mill to drill a series of 25mm spaced holes. The rails are now as parallel to each other as I can get them (Thats not saying much though!).
I intend on building a box/carridge around the box section out of 6mm plate apart from the Z mount which will be another peice of the rectangular box section. The back of the carridge will sit between the ballscrew and the box section. Ignore the cheapo plastic bearing on the ballscrew it will be replaced by a pillow block bearing.
Any suggestions on supporting the free end of the ballscrew??