David A's Benchtop CNC Version 2

[the4thseal]

Using the linear rails in this manner is "rigid enough? I would think there would be a serious resonance issue.

[davida1234]

4thseal, thank you for the question.

Functionally, I would say the arrangement of these linear shafts is in line with their intended purpose.
They slide in two ball bushings in a linear direction with axial and radial loads applied along the linear shaft.

In this case, instead of being typically on the Y or X axis, they are used in the Z direction and instead of the
bushings moving, the shaft moves.

Keep in mind that these are two 1.18" diameter hardened steel shafts over a span of about 8" and
the unsupported portion of the shaft never exceeds the ball bushing spacing at any time.

I am pretty sure Peter (peteeng) can show some quick calcs how the two 30mm shafts would compare
to a conventional aluminum extension plate most designs use.

To get back to your original question, I have not observed any resonance issues whatsoever on the
prototype machine over the two years I have been testing it on various materials.

[mactec54]

Hello all,

Some of you might remember, I had posted a thread called "David A's New 2x3 Benchtop CNC" about two years ago.

https://www.cnczone.com/forums/diy-c...h-top-cnc.html

The machine has been running good and received quite a bit of changes in those two years so I thought I start a new thread showing the improvements I made since then.

Good to see you back with more good ideas with your machine build

[peteeng]

Hi David - The proof is in the pudding (prefer lots of chocolate sauce) no need for calcs, if you know it does the job. Keep Making Peter

[davida1234]

Hey, good to hear again from you guys.

On this build, I really concentrated on making all forces
as much planar or inline as possible.

I strongly believe that by minimizing any offsets and
cantilevers you also minimize stress and deflection.

[davida1234]

The sand ballast is finally dry enough for the top to be placed.
There is a 1/4" HDPE sheet covering on top of the plywood:

[davida1234]

The machine frame is on the base:



Now the assembly of the machine can start.

[davida1234]

Machine Assembly:

Installation of machine feet:

The four feet consist of 1" diameter SS bolts and nuts
pressed into plastic bases with 1/4" screw-down holes:



Lift one side of the frame. I use a car jack for that:



Screw in the 1" bolt directly into the bottom of the upright profile:



Do the same on the other uprights.

[davida1234]

INSTALLATION OF Y/A-AXIS REAR CAPS:

Parts of rear caps:



Puts a bit of glue to the backs of rubber bumpers and push into recesses.
No screw necessary as they only work on compression.
I used liquid tape for that but any glue will do:



Rear caps ready for assembly:

[davida1234]

Using the 5/16 cap screws, install rear caps to the back of Y/A beams:



Rear caps installed:

[davida1234]

INSTALLATION OF Y-A RAILS:

All rail mounting surfaces have been machined for flatness:



Y/A axis uses the shorter 20mm linear rails with flanged trucks.
All trucks have been re-lubricated with Mobilux EP1 grease:



Install the self-centering T-nuts with 5mm screws onto the linear rails:



Make sure the grease nippels are facing outwards.
Slide the linear rails with the T-nuts into the top groove of the profile:



Push the rail until it lines up with the front of the rubber bumpers:

[davida1234]

Y rail and A rail on the frame:



Before tightening, wiggle the rails side to side to fully seat the T-nuts:



Slightly tighten the rails by starting from one end.
Then go back to start again and fully tighten:



Once everything is fully tightened, use a piece of plastic and a
hammer to seat the green covers over the screw heads.

[davida1234]

INSTALLATION OF Y/A CARRIAGES:

Y/A carriages:



Remove the four dust covers and brushes on the carriages:





Place them on the linear rail trucks, making sure the 5/16 threaded holes
are towards the front of the machine and the notch faces outward:



Tighten the carriages to the trucks with M6 screws in an
alternating pattern like you do with car wheel nuts:



Y/A Carriages on the machine:

[davida1234]

The gantry uses the 20mm narrow trucks:



Place the gantry beam on the carriages.
Make sure the machined slot is towards the front:

[davida1234]

Install the shorter linear rail like the previous rails:



Flip over the gantry beam. Linear rail fits between the carriages.

Install the longer linear rail to the top like the previous rails.

Upper and lower linear rails installed on the gantry beam:

[peteeng]

Hi David - How are you squaring the gantry rails to the table rails? Peter

[davida1234]

Hey Peter - Final squaring of the gantry will be done after all the mechanicals are installed.

For rough installation, the top of frame in the back is pretty square to the table.

[davida1234]

Take the two front caps and install two 1/4" screws and T-nuts:



Temporarily install the end caps to the back bottom slots of
the gantry beam at both sides as shown:



Slowly push the carriages and the gantry beam to the back
until the caps hit the back beam of the frame:

[davida1234]

Gantry beam will be attached to the carriages using the 4 holes on both sides:



Align the holes on the carriages with the slots of the gantry beam.

Make sure the gantry beam is still up against the rear frame
and slightly clears the carriages on both sides:



DOING THE INSIDE SCREWS FIRST, use a magnet stick to push the
T-nuts into the slot and install the 5/16 screws from the bottom:





Once everything is tightened down, remove the end caps
from the back of the gantry beam.

[davida1234]

Install a bracket finger-tight on both sides of the gantry beam:



Install two braces on both sides.
Make sure the holes are facing down and the short part is up:





Check for squareness:



Tighten down everything.
Gantry beam braces are installed: