What is more accurate

[CNCadmin]

a sliding table CNC machine or a movable gantry?

[E-Stop]

I think the accuracy will be controlled by the axis drive system, regardless if the table moves or the head moves. I think the gantry style is more rigid, though.

[cncman2]

How about for a small hobby machine with a table of 18" x 24" or 24" x 48" ?

[Hawk]

Originally posted by CNCadmin a sliding table CNC machine or a fixed gantry?

isn't that the same thing. If the table slides then the gantry would be fixed , yes ?

I have found both to be good. I find the moving gantry a little easier to nock out of square in the event of a collision. I believe the moving gantry is also cheaper but I am not sure really why it would be but most of the less expensive system use the moving gantry.

JMO

[E-Stop]

Also consider your space requirements. A machine with a stationary table and moving head will take up less floor space than one with a moving table.

[HomeCNC]

Also think about the size of the part. On a fixed table I can hang a long part out with supports and not need to worry about it moving around.

[cncman2]

Great info. I like the sliding table aproch, it seams it would be easyer to build, but would take up more space.

[balsaman]

Mine has a sliding table. Easier to build and it's easier to move the table than an entire gantry assembly.

Eric

[CNCadmin]

Did you build that machine?

[balsaman]

Yes.

I got all the expensive parts from the scrap bin where I work (linear rails/bearings). I work in an autoparts factory and they were scrapping some equipment. I used a FET 3 board from stepperworld. I get 48" per minute rapids on a 27 volt powersupply.

Eric

[Barry Young]

I just started welding up a machine of the same layout this morning. I spent a very long time figuring out how I wanted to build this machine. I need a machine which is very precise. I make wood and brass camera parts which need to be machined to +/-.0015. I felt it would be easier to make a rigid fixed gantry/column and moving table than it would be to make a moving gantry. I realize that a moving table takes up more floor space than a gantry, but floor space was a secondary consideration to rigidity. I machine boards less than 12 inches wide and can saw the brass sheets I use to 12 inch widths. The longest parts I will machine are less than 24 inches and less than 3 inches wide. To be able to get multiple parts from one board, I decided to make the machine have 6 feet of X and 1 foot of Y. Part thickness will always be less than 2 inches. To add some flexibility to the machine, I decided pretty much arbitrarily to build in 5 inches of Z travel plus 6 inches to allow for long cutting tools for a total of 11 inches in Z.

The machine is consructed of 2X2 steel hot rolled tubing with a rather heavy 1/4 inch wall. This is heavy and stiff material. Hopefully it will make a rigid machine.

Barry Young
Young Camera Company

[RICHARD ZASTROW]

Old farts perspective; All the jig borers and jig mills are travelling table. This avoids "racking" and other geometry problems. There are many legitimate reasons for a traveling bridge, but I personally do not believe accuracy is one of them. Extraordinary effort is required to make them so and are easilly "knocked kattywumpus" compared to a properly designed and built rigid bridge type machine. You youngster ever hear of SIP? Keep your humor now.