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cncadmin
03-27-2003, 01:38 PM
a sliding table CNC machine or a movable gantry?

E-Stop
03-27-2003, 02:33 PM
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
03-27-2003, 02:35 PM
How about for a small hobby machine with a table of 18" x 24" or 24" x 48" ?

Hawk
03-27-2003, 07:10 PM
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 ? :D

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
03-28-2003, 06:59 AM
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
03-28-2003, 11:15 AM
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
03-29-2003, 10:58 PM
Great info. I like the sliding table aproch, it seams it would be easyer to build, but would take up more space.

balsaman
03-30-2003, 03:51 PM
Mine has a sliding table. Easier to build and it's easier to move the table than an entire gantry assembly.

Eric

cncadmin
03-30-2003, 05:32 PM
Did you build that machine?

balsaman
03-30-2003, 05:39 PM
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
06-07-2007, 04:02 AM
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
06-07-2007, 06:40 PM
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.

Barry Young
06-07-2007, 06:49 PM
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.

I ran SIP and DeVleig jig borers and grinders for Boeing. SIP makes the best machines I have ever run. Sorry to bust your bubble pops. Lots of younger people run precise machines. They are fine machines. Moore also makes an excellent machine you don't see very often any more. Fellows gear shapers are also very nice machines.

Barry Young
Young Camera Company