After getting discouraged on a recent mill build (due to several factors), I've set my sights on making a second router to distract myself from the mill.
The first router was a R&P machine driven by AC servos and a smooth stepper. In the process of building it, I learned an incredible amount - this new build will build upon that knowledge.
(early) pics of said machine:
My main complains with that machine was the lack of stability with the Servos (due to several reasons), flimsy legs, R&P transmission and the awful problems I experienced with mach3/smoothstepper.
The new machine (the topic of this thread) will be much different:
- 600x900*150 work area (or there about...)
- Hybrid servo driven (4.5N.m closed loop steppers on X and Y, 2.0N.m on Z)
- 2510 double-nut ballscrews on X and Y (Y axis is dual-driven)
- 1605 double-nut ballscrew on Z
- 100x100x6 hollow-section steel used for entire frame
- Welded construction
- Gantry will be 150x100x6 hollow section
- Linear profile rails on all axes (20mm on X and Y, 25mm on Z)
- Laser-cut brackets
- Aluminium profile table top
- Possible sand/epoxy sand fill
- Controller will NOT be mach3. I will probably get a Chinese stand-alone controller (the ones with the screens and controls on one unit)
- Spindle has yet to be decided on - I'd like to get an ATC spindle with a ISO20/ISO25/BT30 nose. Having a fixed collet chuck is truly a productivity killer.
Current weight (pre-sand/epoxy fill) is estimated by Solidworks to be 330kg. This is without a spindle.
There are some details in the photos that have not been detailed yet, notably:
- How the Z axis ballscrew is coupled to the motor (will be belt-driven, probably with an HTD3M pulley)
- The ballscrew mounts on the Y axis, and how they attach to the frame
- Lack of fasteners all-round
I would like to hear everyone's thoughts on the proposed machine. The build will be documented here soon, given that the design doesn't change dramatically as a result of this thread.
some will advise you to add diagonal bracing to the frame and swap around the profile rail and blocks on your z axis so the rails on the back of your front plate.
I also used a lump of box section for my Y axis but none of the sides were flat/even enough to mount profile rail straight to so I plated it then had it ground flat...that was for a fixed gantry though so weight wasn't an issue..
Last edited by deisel; 05-10-2014 at 02:13 PM.
Some others will advise you (among other things) not to use 25mm ballscrews, since for this size machine the critical speed of 16mm ballscrews would be high enough to get decent feedrates. Your Z-axis looks a bit flimsy compared to the rest of the machine.
Thanks for the suggestions.
For the gantry, i'm going to have it stress relieved and then milled back. For the frame, i'm going to use an epoxy bed - i think that getting the frame milled flat would be very, very expensive.
I'll add some diagonal bracing to the frame too.
As for the ballscrews, I think you're right Jonathan - the critical speed for this design in a 16mm ballscrew would be around 1600rpm. That's probably near the limit of what the steppers can provide.
I will thicken the plate used for the Z axis - I would rather not reverse the rails and blocks.
I've added braces to the legs in all directions.
I've also increased the thickness of the Z axis plate that will have the spindle connected to it. Previously it was 16mm, now it's 25.
I have a question regarding the motor selection:
I have 600W AC servos in my possession that I'd like to use for this build instead of the NEMA 34 motors.
They have a continuous torque rating of 1.91N.m. - and with the 10mm lead ballscrews, I will get 1200N of linear force.
The gantry and all components attached to it weighs in at 100kg. From dual-driving the gantry, the combined linear force of both motors amounts to 2400N.
Is this enough to move the gantry with a reasonable factor of safety?
What is your servo encoder count per revolution?
10,000 per revolution.
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