Gantry Weight Question?

[dbc1218]

I have been in the planning stages of a cnc router for 6 months and this is my 5th design. I want to get started and order parts but have a question. Here are some of my decided specs so far:

X Travel: 24in
Y Travel: 12in
X Travel: 6in
Fully Supported round rail all axis
1x2 welded steel tube construction
ACME 1/2in lead screws
dumpstercnc anti-backlash nuts
Bosch colt router
Gecko G540

My gantry weights 45lb with this design, will this be to much for this size machine? what stepper could anyone suggest for the X axis?

My goal is to able to hog through wood easily and do some very light aluminum work.

[johnmac]

I have a DIY steel framed 36"x42" router. My gantry weighs at least 100 pounds. I have no problems with the weight. I have ball screws and 425 in. oz. steppers.

Use at least 2 start Acme screws. Try to design the screw mounting so it can be replaced with ball screws later, should you wish to do so.

John

[Phife]

45lbs is pretty light for a gantry, you should have no issues pushing that around with leadscrews.


I have a question about your Z axis, I see you have a wide plate on there with some wide spacing for the Z axis rods. Is there a reason why its so wide? it looks like you are loosing alot of Y travel because of it.

[dkirtley]

My opinion is that the gantry is heavier than it could be. If it were me, I would go larger in cross section and go with thinner walled tubing. The lighter and more rigid the gantry is, the less power it takes to move it around and the less inertia it has to overcome. You can engineer in more strength without adding so much weight.

In comparison, a steel framed tandem bike designed to carry around several hundred pounds comes in at 56 pounds. That is with a span of around 5 feet.

Again, just my opinion, you should easily be able to get the structure of a 2' long steel gantry down in the 10-12 pound range without breaking a sweat and still have enough stiffness to carry your mechanicals, spindle, and cutting loads.

[dbc1218]

I did some more work today on the design. I moved the y axis bearings closer together and used smaller plates to mount the z rails. I also made the router mount plate smaller. This cut a few pounds because those plates are 3/8" thick aluminum. I also gained an inch of travel on the y axis.

I tried to base some of the design on the ideas on CNCroutersource.com there is some good tips on how to make things rigid based on the forces that the gantry sees. Thats why the y axis rails are far apart and the other bearings are father apart then I've seen with other designs. Its helps resist the moments.

[dkirtley]

Originally Posted by dbc1218 I did some more work today on the design. I moved the y axis bearings closer together and used smaller plates to mount the z rails. I also made the router mount plate smaller. This cut a few pounds because those plates are 3/8" thick aluminum. I also gained an inch of travel on the y axis. I tried to base some of the design on the ideas on CNCroutersource.com there is some good tips on how to make things rigid based on the forces that the gantry sees. Thats why the y axis rails are far apart and the other bearings are father apart then I've seen with other designs. Its helps resist the moments.

Looks better. I think you would do well to widen the spacing on the x axis bearings as well. You do lose a little on the cutting envelope but the gain in stability would probably be worth it.