Router/Plasma CNC Build From Down Under

[Tinkerer]

Hi Silyavski. Pictures on #16 appear on my computer but not my iPad. I wander if size limitations causing a problem. Have attempted to post again in different formats. I wold really appreciate input from you/others on these designs before I commit to anything.

-i see some I beams on your last table picture, under the top. I beam is way weaker than square or rectangular profile, though looking at it seems stronger. I don't see where and how in a CNC structure we can benefit from using I beam. It twists like crazy, its relatively heavy for what it offers and so on... I would revise that part. use the calculator and see for your self.

I agree with your comments and was also surprised by the superiority of RHS. The workbench does not have to take any twisting or other loads and all I simply want is a strong base which can take significant vertical weight, hammering, etc. Its not a CNC design, just a workbench. I also like the idea of being able to clamp along the side (under the benchtop, facilitated by the I beam shape). Besides I've bught the steel, so will run with this. I agree not suitable for CNC compared to square beams.

Here is another attempt at the pictures. In uploading these, I advise that I have undertaken considerable re-design of a few items (after many days thought) and looking up physical sizes of required components. A summary of changes is given.

1. Gantry

I now have two designs:

A. A design similar to yours (Silyavski) which utilises welded RHS and SHS (per pictures previously posted but not seen),





this utlises 125 x 100 x 4mm RHS (top and bottom) and SHS 100 x 4mm (8mm at ends where I intended to bolt bearing supports but now moving towards bolting supports to Red Plates).

Note Y Axis will now be moved to back of Gantry (see below).

and

B. A single bespoke RHS shape, made out of 5mm plate (using 8mm for sides) which utilises key slots and tabs (some refer to this as 'toy slots' resembling construction of early steel toys. Beam is reinforced by two internal welded plates in the structure.

This later design appeals to me as the components fit together for greater accuracy and welds are more focussed. A draftsman friend of mine told me about the significant inaccuracies (twists, etc) inherent in extruded beams (apparently manufacture starts from a round shape which is then forced into a rectangular or square shape?). He works for a large American firm and they apparently fabricate most heavy industrial components (for heavy waste removal trucks etc) out of plate using this method.

I would have to get components for this design laser cut (he says this is relatively inexpensive - he works for a corporate who pays the bills - will see whats this means to a private budget!). Meanwhile I perfected my technique of drawing Toy Slots.

About to investigate the cost, but waiting feedback from my friend and others before doing so.



1.1 Gantry Drive (Y Axis)

Well the added weight has forced me to consider NEMA 34 motors. After looking at the increased footprint, I decided that I should mount the motor on the back of the Gantry like some other designs. This would marginally improve COG as well, but not a big issue.

2. X Axis

Larger motors and a more careful look caused me to make some minor modifications to brackets. Silyavski, I compared what you built on your first build, and I have headed towards a similar design.

I also moved the motors to the back of the machine, away from the operator and closer to the control box.


3. Z Axis

More or less the same, but I have also included 'toy slots' to facilitate easier fabrication/more accurate assembly.



This design is all steel and requires laser cutting/ machining. The front plate carrying the Rails has 2 of 20mm x 20mm support beams to provide rigidity with the balance of the face plate 10mm. The side plates are constructed of 20mm plate. All 'Toy slotted' and welded. Top plate 10mm thick.

Using the Siffness calculator I believe this will give me a reasonable stiff structure with deflection below 20um in various directions cutting aluminum. I think! It certainly has added to the weight of a purchased actuator which is now a scrapped notion due to their weak structures.

Happy to listen to any views how to do this differently.

Perspective View of Machine



Hopefully these pics are now viewable (I know I got close to the limit last time I posted them and perhaps why they did not appear?). Please let me know if problem persists!

If anyone can consider these with questions posed in my post of #16, I would be very grateful.

One additional question is to do with attachment of support bearings. As mentioned above, I am leaning towards bolting the supports to the plates at the end of the shafts, rather than to the side of the frame/gantry. My rationale is I can control spacing easier (or perhaps not), and that plates offer a flatter, 8mm surface to bolt to. What is the preference/others' experience?

Pictures look good I'm told. Proof of competency will be the building of it!

Richard