Thread: Mounting motor under table?
Hi guys, It's always a toss up as to how to go about building one of these new fangled things. Whether to fix the gantry or fix the table. I would prefer to fix the gantry myself but then you need twice the room for the table to move underneath it, but it is the strongest method. My gantry's have been moving due to space limitations but your design looks to be relatively small so fixed gantry would probably be the way to go.
On large gantry's it is a good idea to have a greater pitch for the long axis screw due to whipping if turning too fast so to move the gantry/head a certain distance the quickest way possible this method is good. You do sacrifice resolution though but you may not need 0.000001 tolerances. (arbitrary amount)
I have 10mm pitch ballscrews on my Y axis because that was the largest pitch available at the time for the price and my X axis has a 12 start 50mm pitch acme screw with matching anti backlash nut. I have geared this acme screw down to 3:1 which gives me 120 steps per mm which I think is fine for my wood working. Remember that the steppers might be out by a few arc minutes per step but they all come back to the same point after 1 full rotation. There might be small inaccuracies in that 1 revolution but geared down 3:1 it makes them smaller inaccuracies again. It all boils down to how accurate you need it to be.
Temperature comes into play if you have a very big machine as well and if your milling wood then also humidity plays a part.
What would you expect the tolerances to be for PCB routing. I've never done this but I would expect you wouldn't need anything better than 0.002" (But I may be wrong)
You could probably mill Steel, Aluminium, etc but you would only be able to use a very small chip load as your strength and vibration absorbing qualities of the gantry just wouldn't be there. You could do it but it would take ages to achieve something easily done on a bigger machine. Potentially you could mount a diamond wheel to your spindle and grind your jobs but the time taken would be an issue. (you would probably want that 1 year of your life back :-) )
Fixing the gantry will give you the greatest stability and if braced properly then you will have a fine little machine to work with and with the quality of all the parts available today you can't go wrong.
If you need to put bigger things under the gantry then make the table adjustable by being able to drop or raise it. Shouldn't add too much to the design for a small router.
The Chinese spindles are very good value for money if you are after one, and compared to the wood routers, they will give your ears a much needed rest and make your neighbors happy at the same time.
I have a plan in mind for bracing that involves a wrap-around... err.. thingy? Shell? I'll let you know how it works out. I'm moving back to a fixed gantry so the need for keeping everything under the table is less urgent. I still intend to do it, though for other reasons.
At my wife's request I've put everything non-essential on hold after a (or more specifically, another) job fell through at the start of the year. Until I'm earning again, I need to step back for the sake of my wallet and my sanity
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