Mick H's CNC Router Build
Mr. Mick H. He has been following the build and making great progress. He, just like the other fellow builders have added their own enhancements, which really makes them leaders in building these CNC machines. He noticed that the table, at the sixe of 24" x 48" will deflect a little as the gantry reaches the mid point of the table. He took his reinforcement to another level, shall we say he "spiced it up a bit". He also went the gluing route, as opposed to a mechanical fastened build. With his clean and precise workmanship, as noted in the images, it is a very smart way to go. Remember, if gluing is a consideration, your measurements will need to be somewhat precise to insure a tight fit around the rails.
From Mick (mostly verbatim): I decided to follow your plans initially and use your original dimensions, then once the machine is up and running, cut new parts for machine No. 2. I am now at the stage of a 90% complete build as far as the mechanical components go, leaving the addition of the X-Axis lead screw & all 3 motor mounts as the final items on the mechanical checklist.
Upon assembling the cutting bed and end supports, along with the addition of a bottom sheet of 4' X 2' MDF, then adding the gantry, I have observed a significant amount of sag within the cutting bed when the gantry is moved toward the centre of the X-Axis. I haven't measured exactly how much sag is present, but it is visually apparent...a few mm approximately.
This in itself is not a problem, these situations arise to test us mentally and I think I may have a solution...or two.
a) Re-design the cutting bed to utilize a torsion-box and extend the gantry sides downwards to compensate for the extra depth. (An increase in build time/cost, due to cutting/gluing-up the torsion box pieces and waiting for the glue to dry and re-shooting video footage for this process. Also, motor mounts would have to be moved, which would necessitate re-shooting footage for the X-Axis end plates etc.
b) Use the design as-is, plus an extra 16 skate bearings, nuts & bolts, and some more angle aluminum.
I'll elaborate on b)...
What I propose, is to utilize the machine as per the original design, but add extra linear bearings and angle aluminum on each side of the length of the cutting bed. The lower span members of the gantry, beneath the cutting bed, could benefit from linear bearings above & below riding on aluminum angle attached to the bottom sheet and the underside of the cutting bed. This way would eliminate any sag in the bed, provided that the machine was placed on a level surface in the first place.
The more I think about it, the more I'm inclined to make up a torsion box bed...I'm currently sizing up how many 2" squares and 48" X 2" longitudinal rails I will need. I calculate 9 rails and 136 squares should give me a pretty solid bed that I can utilize on a second machine. Additionally, I will have to redo both end plates to allow for the extra height - around 7", and the original dimensions of the gantry sides will suffice using new material and the originals as templates shifted into alignment for the mod...there is plenty of height above the Y-Axis rail that I'm glad I hadn't trimmed yet!! Another 3 boards should get me where I want to be.
I like the idea of the hardware stored beneath the machine, it makes for a neater setup, but I'm not sure about the keyboard & monitor accessibility (he's talking about this setup under "Pimp My CNC"). Are you making any allowances for dust protection/extraction once you start making chips...e.g. a vacuum attachment? There was a neat idea posted on CNCzone, utilizing brushes nabbed from the guy's wife's ice scraper...something to think about, but before I jump ahead I need to sort out a motor/driver kit. (From Patrick: I do plan on video-ing a vacuum attachment).