CNC Base...rendering included (updated 6/17/10)

[xclr82xtc]

ok guys, heres what im thinking about building 8'x3.5'

the giant holes are for the chip auger, the 6 sets of holes on top are for the rails

the bosses on the sides are for leveling.

there is a large cut out under the bottom...im predicting this is the area the coolant tank will go (heaven forbid it ever leaks!...ill use something that wont rust lol)

also what is not show is the gantry, which im not sure how im gonna mount yet. z/y axis will be in the spindle, x/a/b will be inthe base...

if your wondering why so long, im also going to make this modular so that if i want to put bar in, i can use it as a lathe, while using the spindle as live tooling.

now i just need to figure out how to get this cut out in foam and packed in sand for casting. and how im gonna level/grind the surfaces after casting.

if you have any suggestions please offer them!

OH..and the bose on the center rail, is for the ball screw..i just forgot to put the opening on the side. i was gonna do that when i made the servo mount

[spoiledbrat]

X,

Can you show a rendering of the rest of the machine?

Initial concerns are the 6 sets of holes for the rail. Linear rail manufacturers recommend milling a slot, or at least a shoulder, to align and straighten out the rails when mounting. If you are going to cast this thing, it seems that you want to make everything integral, when possible.

Also not clear about the center cross-member. It seems that it will limit your travel. That said, I am sure that renderings of the rest of the machine will clear that up.

That is a huge casting!

Rob

[xclr82xtc]

im working on it! thats all i i had time to do last night....

[xclr82xtc]

posted new pic in first post. Does that clarify things a bit more guy??

I will be working on the gantry next. im not sure i like the servo there, thats why there is no support built in yet.


by the way..i need to be realistic here...im prepared to spend 20/30k TOTAL to get this thing goin over the next couple of years...think it can happen??? I do..i think the casting/maching of the base will be the most expensive part...Up until the point i get some real deal cnc controls

[spoiledbrat]

I am surprised to see solid cast iron... with unsupported rail bolted to it. Unsupported shafting will lend itself to vibration and flex when cutting or making rapid moves. I think you may be doing that cast iron a dis-service. A nice machined slot will align the rail straight, and rather than 6 screws, we will be talking about 50+ screws holding that thing down.

Check on pricing for discount linear (profile) rails and bearings, or hunt ebay, and spend next to nothing. But be patient.

You saw my last casting project. Not quite as big as yours, but we did get that done for less than 2K. We provided the pattern. Machining the top flat, and drilling/boring multiple holes ran us around 700. I think if you found the right machine shop, that thing could be made to be very precise within your costs.

With a budget like that, you will be able to produce a very capable machine.

Good luck!

Rob

[xclr82xtc]

each one of those rail supports is sitting in a sot that is machined down into the base .250" But, if you dont thing that is good enough, i can come up with something else. I found some 80inch rails 2 for $400, seems about the going rate as 2 47inch rails is $209.


also, those rails will only be supporting the trunion and will only be moving on the X/A/B axis. I also spec'd 1 inch rails, but can go 1.250 if thats wha I need to do. to goal was to make the rails a replaceable part, instead of machining ways. then no need to send out the 4000 pound casting when you need new ways lol.

anyways....let me know what you think about the slots! i can always make them deeper/bigger. Or redsign the rails comlpetely! thats the glory of CAD haha!

later

[RotarySMP]

As spoiledbrat already pointed out, it's kind of pointless going to the trouble of making a rigid cast iron frame, and then mounting skinny flexible bars at three points.

You rendering looks cool though.

[xclr82xtc]

yeah im redesigning it to use linear slides. i had assumed that since the only travel on those rails, they would suffice. i though 1.250 rails were pretty strong..i guess not lol.

[rowbare]

What is this machine meant to do? What kinds of materials are you planning on cutting? You have a work envelope that more or less makes sense for a router but you are talking chip auger.... How are the chips supposed to get to the auger? Won't the table be in the way?

Have you figured out the volume of material in your base and how much it is going to weigh? What does the bottom of the base look like? Your design looks good but does it make sense? Can you deal with a 6-10,000 lb base?

Everything comes down to balance. As others have pointed out, an unsupported rail doesn't balance with a massive cast base.

BTW, that center brace with the balls crew support doesn't make sense. You show rails running the full length of the frame but your ball screw travel is only half that.

I like that you are thinking about this and putting designs out there for critique. You will not only learn a lot from that but you will certainly help others learn. You might want to give this a read: Principles of Rapid Machine Design

bob

[xclr82xtc]

Originally Posted by rowbare What is this machine meant to do? anything a 100,000 dollar haas can do What kinds of materials are you planning on cutting? Mainly MMC's and alumimun, but some steel dies You have a work envelope that more or less makes sense for a router but you are talking chip auger.... How are the chips supposed to get to the auger? Won't the table be in the way? im assuming they would run down the sides of the table and the enclosure like everyother machine Have you figured out the volume of material in your base and how much it is going to weigh? What does the bottom of the base look like? Your design looks good but does it make sense? Can you deal with a 6-10,000 lb base? by volume it should weigh 4k. the bottom is cut out and one end as well to make way for a coolant tank that will roll under Everything comes down to balance. As others have pointed out, an unsupported rail doesn't balance with a massive cast base. hence it has been redesigned BTW, that center brace with the balls crew support doesn't make sense. You show rails running the full length of the frame but your ball screw travel is only half that. i dont plan on getting full length in both directions, on the table. one end will also have a lathe motor mounted. and the lathe head will be able to slide down to where i need it. I like that you are thinking about this and putting designs out there for critique. You will not only learn a lot from that but you will certainly help others learn. You might want to give this a read: Principles of Rapid Machine Design bob

Thanks for the post