View Full Version : What keeps the gantry from flying up?

Mon 04 August 2008, 17:27
Hi, I have a question:

What keeps the gantry (or the y-car for that matter) from flying up? (Other then gravity)
I see it rides on 4 v-groove bearings, but what keeps it down?
Just gravity and the motors on the racks? But they are spring loaded, so you would be able to lift the gantry right off the x-rails, right?

Please clearify this for me :) thanks

Mon 04 August 2008, 21:00

On one side of the car, you have the pinion gear that rides on the gear rack. The motor is spring loaded so the car is forced on the rails on that side. On the opposite side, there is no gear rack. So instead of a pinion gear and motor, you have a spring loaded bracket with a free spinning bearing that rides on the bottom of the rail.

The gantry has a motor at each end. Pinion gears mounted on the motor shafts ride on long gear racks. Springs on the motor brackets hold the gantry down on the rails. In reality, the assembly is pretty heavy so gravity does the work.

Tue 05 August 2008, 01:02
But they are spring loaded, so you would be able to lift the gantry right off the x-rails, right?

Its also a safety feature, should something go wrong such as the spindle not start or hitting a solid object clamped to the table, the springs give the assembly some "give" allowing the Y-car or gantry to lift off the rails or the motors to climb out of the rack limiting any damage to the expensive spindle or excess load on the steppers. If one were using proximity sensors as limit switches, as soon as the car or gantry lifts, it would cause an e-stop situation stopping all movement. Under normal working conditions the springs and Newtons law have more than enough force to keep things together.

Gerald D
Tue 05 August 2008, 01:11
The common spiral cutter also pulls down.

However, we have often used lefthand spiral cutters that push up, drills (push and pull), and big shape cutters that drastically push up, all of them with no lifting.

If a car lifts, something is wrong with the cutting process. This could be obstructions, or trying to plunge a cutter that should not be plunged (no cutting edges in the bottom core area), or a big blunt shape cutter (ogee, bullnose, etc.)

Tue 05 August 2008, 16:03
Ok thanks for clearing that up!

Thu 07 August 2008, 09:43
Another thought:

When your doing a cutt that requires the bit to plung into the wood, you should probably set the plunge feed rate slower than your regular feed rate and also ramp the plung cutt with vcarve (probably with most other cam programs also). That is supposed to make for less stress on the router and equipment, and less upward pressure as the bit plunges.

You would want to set feed rates and plunge rates according to the density and hardness of your material that your cutting so you don't put ecessive pressure on your router. :):)