Looking around here got me infected with the sand table bug and I have now officially started my build.
It will be a regular x/y table (no H-type kinematics) with 2 NEMA17 steppers and direct belt drive for X, indirect 2:1 belt drive for Y.
I got a set of four 8mm dia 500mm long linear bearing sets for $40 and hope they will be rigid enough for this purpose.
TBA6600 drives and a Planet-CNC motion controller that I happen to have from another project.
The somewhat strange foot is intended to match the design of my Norwegian chairs.
Right now I am printing some of the smaller components and will start machining some of the frame and foot parts soon.
One thing I am not sure about yet is the plate that will carry the sand surface. Would a 1/8" aluminum or glass plate do the job? Right now I am planning to use a 1/2"dia x 1/2" long Neodymium magnet and a 1/2" steel ball. What distance is optimal?
Love the chairs… You should have no trouble with either aluminum or glass for that span, you could even go with thin plywood or melamine. I used a recycled back panel from a bookcase that was maybe 4mm thick with mine and although I’m smaller than you it isn’t by much. The shorter the distance between magnet and ball the better. I’ve got 10-12mm.
Ryan, it looks like you could see the linked new pics in my last post. But now I can not see them anymore myself. Weird, but maybe has to do with the Google+ Photo link.
I really miss the old picasa photo sharing, so much easier. For G+, you have to right click the picture in a new window/tab. Then copy and paste that link to share. Doesn’t work everywhere because the link doesn’t end in .jpg, but works here.
Yup lots of private windows. Any change I make I check both ways, the one I have only done probably 3 times is sign in as a fake user to see exactly what you guys see.
Ah, that explains it. I had similar trouble on another forum with pics.
And I am missing the good old times with Picasa. I still use the desktop app, though.
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Yes, I am trying to keep the wiring clean but I had to mill recesses into the base board anyway for space reasons so the wiring channels did not really take any more effort. I closed them with super sticky aluminum duct tape. Holds on tight but can still be removed when needed.
I decided to laminate a sandwich board for the sand surface from 2 thin (0.8mm) aluminum sheets with an 1/8" fiberboard core and use my table glass (1/2" thick) to keep it flat while vacuum pressing. Should be rather stiff and avoid sagging under weight or magnet force but I am not sure yet if I can pull that lamination process off.
I read about a thin foam surface to help the ball rolling. Would a non-slip drawer liner do the job? I still have a roll of that.
I would not put anything in between. the strength of the magnet drops off by the cube of the distance. Every .1mm counts. I use baking soda, so there really is nothing to impede the motion.
G+ is shutting down, but I don’t think they’re killing off photos. At least I hope not. I have almost 13 gigs of photos! That would take minutes to download!!! ???
I hope not as well. while I have only edited pics on Google and the original on the PC, but there are many forum posts with links and they all would be broken
Oh well. Nothing permanent in the brave new cloud world.
As for the foam mat under the sand, I am not sure where I read about that. Maybe not such a good idea, after all.
I will try the baking soda. Given that I am in dry SoCal I guess the likelihood of clumping is small. I have also a bag of fine grit brass powder and some black dyed sand that I may try. But I am getting ahead of myself. Maybe I should first finish the table…
Just noticed, I lied in the thread title…while the free length of my 500mm guide rods is 480mm (10mm on each side to hold them), the linear bearings are about 40mm long and that leaves only 440 x 440mm as useable motion range. Oh well, not so bad.
So, it is running (without cover, feet and housing). I ended up getting an 1/8" acid etched (frosted) glass sheet for the sand surface and the distance between the magnet and the ball is only 4.5 mm.
Here my first test runs. The experiment with the Blues Brothers image was a bit overly ambitious (2mm mace trace distance with a 1/2" ball). But even that looks interesting.
Oh yes. It makes a big difference in appearance, even if I don’t have the cover frame finished yet that will mask the direct view of the LEDs.
And I found the LED dimmer necessary. At full intensity, the LED strip (I used “warm white”) is way too bright. I removed the little dimmer PCB and pot from the plastic housing and installed directly on the baseplate so that I can adjust brightness with a knob reaching under the table. Similarly, the Start/Stop/Pause buttons, power switch, USB bulkhead connector and SD card slot are accessible from underneath the baseplate. I do not have a display or other user interface.
BTW, below is the maze trace pattern for the picture. Clearly too detailed for a 1/2" ball but works in principle. I tried it with an 1/4" steel ball but the magnetic attraction is too weak and the ball gets left behind.
