my new CNC router design

[animus_divinus]

hey everyone.. just finished (for the most part) in designing my CNC router... it rides along precision ground rods on linear bearings.. 20mm for the base, 12mm bearings for the rest, total of about 28x18x4 inches of travel.. heres a photo of it.. tell me what you guys thing?..

also, since the X axis has to hold the weight of the gantry, motor, and everything on it.. im thinking of having some roller bearings ride along the edges of the 36x25" box...

[ger21]

With those 12mm rails, you'll be able to move the router bit about 1/2" with 1 finger. Seriously. If you must use unsupported rails, they need to be at least 20mm. And even those will still flex quite a bit.

[animus_divinus]

only the Y and Z are 12mm... the main ones are 20mm and im thinking of putting roller bearings on the side to bear the weight of the gantry on the edge of the main box, which would make it fully supported

[Walky]

12m rods at 18 inches for the Y axis will flex a lot. I have some 14" fully supported 12mm rods, out of curiosity removed the supports and supported them at their ends, with the rails in parallel, and I could bend them closer together with my fingers. 20mm can fix that, but it you use really rigid end supports then you could probably get away with 16mm if you don't plan on cutting stuff like aluminum.

The issue is not only about the weight the rods must carry, it's also about the cutting forces and the "lever" effect (that's why fully supported rails are actually screwed to their supports).

[animus_divinus]

hmm.. so, seems the general idea of unsupported rails on the axis' is not a good idea.. i understand, i will revise this... i would like the axis' to travel on rails completely unrelated to the table, giving me the option to easily remove tables and replace them later, to be used for different purposes, or as money allows me to get a better table... so that 25x36 inch box frame of MDF is what i would need to hold my rails.. i have one idea for this

first idea is to cut two 1x36 inch strips of MDF, and fix it to the top inside of the box... cut the top and bottom edges of this strip at 45 degrees and on the cut surfaces, fix strips of steel or aluminum, these will be the surfaces my roller bearings will ride on

cut similar shaped strips to mount on the outside of my gantry to hold the roller bearings, and thatll give me a fully supported rail for the gantry

for the Y axis (side-side), that support piece in the back i could probably sharpen the edges of, and glue aluminum angle onto those edges for the bearings to ride on

for the vertical axis.. where the lip overhangs the router holder, i could place a maybe 3 inch wide piece of mdf vertically.. sharpen those edges (simply by angling my table saw at 45 degrees and running it through both sides) i could then mount blocks to the back side of the router holder to hold the bearings to ride on the rail

question is.. will angle aluminum glued to a sharpen MDF edge have sufficient strength to support the three axis'? and are there any forseeable problems to me using steel L sharped brackets to fix the MDF pieces together to construct the router?... many ive seen have used screws and glue, and i just dont see this as being a strong enough joint to last very long

[animus_divinus]

well, ive finished designing my new gantry and the base platform in which it rides on.. im going to be using roller bearings on aluminum rails, fully supported for all 3 axis'... all i basically have to do is cut the edges of the pieces i was going to use to strengthen the design to a 45/45 degree angle to fit a .5/.5 inch aluminum angle onto.. simple enough.. right?

and well, instead of the bearing blocks im going to mount a block i have designed to hold the bearings... really its a pretty simple adaptation of the origional design...

when i am finished however, i can simply edit the basic sketches i used for the extrusions to fine tune my axis' of travel to whatever i want.. and really, i have about 12 feet of the threaded rod.. its not actual threaded rod.. its the acme rod stuff i believe... got about 12' of that so i could go a 48x24x8 inch travel should i choose to...

also, i have a 10.2" netbook with a mini express card slot with a serial card... this laptop cannot do my 3D designs, but can run the CAM program i need to tell my controller what to do

[awerby]

I've never had any luck gluing anything to aluminum; maybe there's a trick to it, but screws would make it more secure. I also doubt that your half-inch aluminum angle really will have enough stiffness to hold itself flat, unless there's more supporting it than seems evident. And aluminum's pretty soft, so I'd expect some significant wear pretty soon if you're rolling hardened steel against it. Are you sure you wouldn't rather use 1" square-section solid steel bars, ground flat? Or a commercial slide system?

The other problem I see with your drawing is the Z-axis, which doesn't have any travel at all. Usually these things are supposed to go up and down...

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[animus_divinus]

where the aluminum angle is going, the aluminum is fully supported the entire length and width of it... and i COULD epoxy glue the aluminum to the MDF... but screws would probably be better if i can countersink them to fit flush... which would be a better idea because as the rails wear i can simply replace them

the structure that holds the aluminum rail wont be permanently attached to the axis platforms either.. so by adjusting the depth of the screws i should be able to get a very, very snug fit with the bearings against the rails and be able to adjust the tightness of that fit to maintain the machine

so basically, the rails and bearing mounts.. though all fully supported are quite simple to reproduce, fine tune, and replace... and as stated before, none of these components will ever mount to, or touch the table... the table will be removable and replacable with just the release of some screws so that later on down the road i can get a higher quality table on there, especially if i ever decide to mount a plasma cutter on it.. but i dont see a need for this in the near future...

on another note.. i will be buying a small manual mill which i will also be converting to CNC by replacing the cranks with motors and some position switches.. but thats a different project entirely

i like having computers do all the manual labor for me.. leaves me more free time to put into the thinking process of my future projects

[acondit]

I epoxied an aluminum stop block to an aluminum bearing block (for a limit switch). It worked fine but when I tapped it with a hammer it came right off.

Alan

[animus_divinus]

heres what the blocks holding my bearings will look like.. these will comfortable ride that .5x.5 inch angle aluminum

[animus_divinus]

the stop switches i have i think i could possibly route a cavity into the MDF to place them into... so just the lever portion of the switch is exposed... could make it a snug fit and thats all id need to hold them in.. no blocks neccessary

[acondit]

The block was for the switch to touch to activate.