Moveable Gantry or Table?

[barkster]

I've always designed my tables to move on my routers but it seems most people make the gantry moveable and use fixed table. It seems to me that with the loading their could be more torque on the gantry when it is moved and even increased with the taller gantry. What are the pro's and con's of each?

[JavaDog]

See, I read the opposite: That moving the work was the 'not so good' way of doing it...

[barkster]

Just seems it would want to torqe to the side to me, especially if your rails have any play or they aren't perfectly aligned. Boy I wish I would have paid attention in my machine design classes in college.

[JavaDog]

Originally Posted by barkster Just seems it would want to torqe to the side to me, especially if your rails have any play or they aren't perfectly aligned. Boy I wish I would have paid attention in my machine design classes in college.

Well, there is the requirement that you do align your rails correctly. Just one of those things that "must be done". Plus, with rails or slides mounted on both sides, and the ballscrew under the table in the center - not too much of a reason why it should be binding from side to side - there should be no play from side to side.

[ger21]

Originally Posted by JavaDog Well, there is the requirement that you do align your rails correctly. Just one of those things that "must be done". Plus, with rails or slides mounted on both sides, and the ballscrew under the table in the center - not too much of a reason why it should be binding from side to side - there should be no play from side to side.

The best way to drive a gantry is from both sides. You can use 1 motor and drive 2 screws with belts, use 1 motor on each side, or rack and pinion driven on each side... many ways to do it. If driven from both sides, you shouldn't have any problems. As far as gantry height is concerned, just like for any part of your machine, the bigger you make it, the easier it is for it to flex. Small and short is the easiest to make ridgid.

A lot of large commercial machines use moving tables. The only real downside to moving tables is that you need twice (almost) as much room as you do for a moving gantry. A fixed gantry can be built very strong, because you don't have to worry about moving it. But for a hobby machine, space is usually at a premium and the moving gantry design usually wins. I've seen a lot of smaller moving table machines here, but when you start to get over 2ft of travel, you need a lot of room.