Perhaps I shouldn't post this here because it's a link to an auction, but I have no connection to him nor am I trying to help him in any way.
But here is a good looking table. Granted, it's probably too flimsy to be very accurate because it uses TSlots and doesn't even have angled braces, and the motors are very tiny, and the Tslots alone probably cost $2000. But still, it has a nice look to it!
I have no idea why more people arn't using the raised sides for the gantry support. It simplifies everything and the only thing you loose is the ability to load from the side.
Also, the rack-and-pinion drive on both the X and Y seems much better when the size of the machine reaches 4x8.
To me it seems that the above table would be almost perfect if the frame members had angled braces and the metal were something a little more stout. I know people here like to use aluminum because it's easy to machine. But still, if you had a metal that was very hard and didn't flex, could be machined precisely, and had good temperature characteristics I think the above design would work well. The design is a sort of "Minimalist design" using only what is needed with as few parts as possible. So even if it were very hard to machine (or have machined) the parts at least there would be few of them. Light steel?
Wow oh wowoooo that's the scheme I was looking at and trying to build!
OPEN Frame/Minimalist - what is this style called? The Gantry has a low profile as the entire "UPPER FRAME" supports it and is integrally linked to the main (manufacturing) board. To me, it seems it will elminate alot of cantelivered weight (aloft) in a "typical configuration". Like I won't be trying to move the Space Shuttle down the launch track - eh?
My thoughts RE: 80/20 or equivelant T-slots - seem to good enuf for me to spend money on ok BUT:
The problem(s) I envision is using the 80/20:
1. As the stand as shown on the page - - Isfoils spent a lot of time it seems putting concrete in his rig to make it more stable - thats STILL a problem associated with the BIG BOY erection set (my wife's name for it) [T-slot by any other name is still a big boy toy].
2. Balsaman added struts (BIG X's) on his Gantry. The scheme you've hit on uses a lower profile gantry by raising the enite axis, and may generate less flex in that portion of the system - But you may need to stabilize it too. The ENTIRE Upper Frame could be stabilized with BIG X's ( placed between upper and lower horizontal frames) or as I plan - mdf etc to contain all the chips/noise .
Mind you, it seems like I've bought a boat load of T-Slot Extrusions from rcrabb so I'm headed down that path and UP THAT HILL>>>> I have assembeled the verticals and lower frame and it is JIGGLY - but I am confident it will stabilize with a bit of tweaking - upper frame and "siding", and gantry.
BUT - I can move it around = play with it until I get it the way it fits my need and then tie it all in. I don't know a real good welder that would have that much patience with me.
But OH The price of variability! If you go with off the shelf parts $$$$$$. I'm having custom "T-Nuts" cut, drilled, and tapped", locally at 25% of the list $$$$ price and no shipping. Maybe lucky - we'll see next week. When I take delivery of the bits.
We'll even know more -- when I get this put together.
oh plans - what are those????
Sorry for the long wind -