Moving Table, or Moving Gantry? (For Router)

[Cryptonic26]

So I'm trying to figure out which design to go with, I'm not extremely familiar with CNC equipment. I'm wanting to change that by building my first CNC router!

So.. as of right now, I can't tell you the difference between them, except which parts move. Everything else is pretty much fuzzy for me...

Is one design easier to manage (long term) than the other? Does it matter?

What about hybrids, with the table in one axis, and the gantry in the other?

[Gizmot]

on a non gantry, the base must twice as large as the smallest part (the table as to move).
thus, a gantry being "twice as small" is often the reason DIY often go with a grantry.

Hybrid seems a good compromise that I may use. Advantage is that you dont need some crazy big motor to move your whole gantry system.

[andy_ck87028]

Please explain hybrid???

Andy

[Russell Allen]

I've played with both moving table and hybrid in school, and looked at a couple moving gantry types, and I really like the moving gantry types.

There are five reasons why:
1. If you are machining pieces that are longer than the table, just cut reference features and move the piece, and run the next section.
2. The motor/controller/power supply only need to be sized (and priced!) big enough to move the gantry, not a table-sized block of oak!
3. The linear bearings and machine frame can be much lighter and stiffer when you're only moving your spindle or router instead of the entire table & work piece.
4. It's much easier to change out your table and hold down method. Need a table with T-slots? Bolt it on. Need a vacuum hold down chuck? bolt it on. Sacrificial table or one-off fixture? Bolt it on.
5. One last trick. Need to machine some feature on a full piece of plywood? Take the table off and use a vacuum hold-down to clamp your machine onto the ply, and machine THROUGH where your table normally is. People will wonder where you keep your giant CNC 8).

I think this horse is dead. I'll quit beating now.

[Cryptonic26]

Awesome response Russell, that's exactly the kind of info I was looking for.

I'm also wondering if one keeps better accuracy over time or if they are simply even on general wear.

...

It just occurred to me that this topic has probably been covered a thousand times here, I didn't realize how large this forum was until last night.. I'll be making better use of the search tool from now on. heh.

[High Seas]

AND,
REASON #6:
With a moving Gantry, you can add a lathe-like device to the fixed table and have a near-instant 4th axis!

Yes. It could be done on a moving table - but imagine the consequences of all the additional weight and wire.
Jim

[bradodarb]

Ideally, I prefer a moving gantry for no other reason than you get the largest envelope for your footprint.

I would however only consider it for an aluminum or steel built machine. You gain a tremendous amount of rigidity with a heavy fixed gantry.

As for the weight(table vs moving gantry)- I'd reckon your gantry + Y&Z axis components + the spindle and tool plates will outweigh most torsion box tables + a part.

Aside from weight, the moving gantry is going to experience much higher inertial loads if you consider the leverage at the tool whereas the table will have a very low center of gravity.

Just my 2cents....