Moving gantry or bed?

[Helstrom]

I am in the beginning stages of designing my first CNC router setup and I am debating as to whether to have a moving gantry layout or having a fixed gantry and moving bed.

The materials I plan on cutting with my router would be mostly plastic and aluminum. My initial feeling is that a fixed gantry with sliding x table would provide a more rigid support for the Y, Z axis when cutting harder materials, but the moving gantry style seems to be the predominant style on these boards.

What is the advantage/disadvantage of each? I know that the fixed gantry design would inherently have a larger table footprint, but that is not necesarily important. Size wise the working area (cut zone) would be about 24" x 24".

The great vault of knowledge and experience on this board would be greatly appreciated.


Thanks

[ger21]

On a smaller machine, I don't think it matters which way you go. But if you're planning on cutting aluminum thicker than just thin sheets, You'll want a pretty serious machine.

[Helstrom]

I would plan on cutting / carving 2"-3" thick aluminum or plastics. I know that cutting metals can be a pain on a cnc router , but from what I understand it is possible if you use lighter cuts and a single or dual flute carbide bit.

[NickC]

Hi Helstrom,

I am also in the intial stages of planning for a cnc router with similar working envelope ( 24" x 36 " )...I am located in brampton, Ontario.....Have you started buying up some parts as of yet ?

I really dont know where to start - which CNC plans would be suitable for a set up like this ?

Cheers,

Nick

[Helstrom]

Hi Nick,

I have been looking for parts online for a little while and have found that the cost of the rails and guides are going to be the greatest cost... close to $1000.00 for the size of table were both looking at. The accuracy of the slides will impact the repeatability of your cuts so it also depends on what your cutting and how much accuracy you really need.

I have toyed with the idea of using heavy duty drawer slides as a cheap alternative, but still want the stability and accuracy of guide rails .

As for the Framework, Im torn between 80/20 aluminum extrusion which
Will allow for on the fly adjustments as well as design changes but it is $$$
or Steel tubing that requires accurate cuts and drilling and is a one shot deal with little room for error but is much cheaper. Since I will be cutting Plastic and aluminum, i don't believe that MDF supports will give me the level of rigidity that I'm seeking, without it being grossly overbuilt (I like clean lines).

For the stepper motors and drive controller I'll probably get something prebuilt
and plug n play online.


http://www.ipecautomation.com/Produc...mextrusion.htm
Aluminum 80/20 supplier,They also carry slides & ballscrews

http://www.bdi-canada.com/locations_on.html
They have an office in Brampton Slides & screws

http://www.gbs.ca/en/mainen.html
Slides & screws & motors


As for the design, there are a ton of different ones out there, but 95% seem to be of the moving Gantry style which is proven, I just can't decide as to which I want either... I need to pick so I can begin drawing up plans asap and get this project going.

I hope some of those links help


Frank

[rlrhett]

I am a complete noob and am still waiting to build my first one, so take what I say with a grain of salt. However, your original question was as to the pros/cons of a moving gantry.

The one that convinced me was the footprint of the machine. For a fixed type gantry machine, the footprint of the overall machine must be twice per dimension or four times the area of the table, PLUS extra for the carriages and motors, etc. A fixed gantry machine that has a 2' x 3' cutting area would have to be AT LEAST 4' x 6'. A moving gantry adds about 8" to 10" per axis, x-y, regardless of your cutting area.

I'm sure there are other considerations as well.

[Helstrom]

Your right about the footprint issue rlrhett and it is definately one of the only real downsides I can see to a fixed gantry layout. I hoping that someone might have some firsthand knowledge about what the impact the two styles would have on cutting ability on harder materials.

I will probably be going with the moving gantry in the end, but I may still be swayed if it will improve my heavier cuts.

[XYZADave]

Without going into a FEA analysis of some hypethetical design..... What would you rather move, a 200lb gantry or a 20lb block of aluminum?
Jest my 2 sense worth!
Dave

[Helstrom]

Originally Posted by XYZADave Without going into a FEA analysis of some hypethetical design..... What would you rather move, a 200lb gantry or a 20lb block of aluminum? Jest my 2 sense worth! Dave

LOL your absolutely right Dave just the Router alone weighs about 7 lbs
Then add the cross bars Z & Y travels undercarriage etc and I'm sure I would be up to the 60 lb range. I don't think I would be working on anything heavier than 10 lbs.

Oh decisions decisions