My first machine steel or aluminum 4'x4'-4'x8'

[Dougie085]

Well a friend and I decided to build a machine but we want it to be quite versatile. We are looking to machine MDF and Aluminum mostly. We decided we wanted an 8'x4' cutting area. The entire thing will be made of 8020 aluminum extrusions. Majority of the mill table it self will be made of 3030 extrusions. I'm still working out drawings and a little plan as to what will happen. So far this is what I've figured I would need from 8020.

2 10ft sections of 3030 sides of x axis
6 8ft sections of 3030 x axis bracing as well as legs and part of gantry long section.
7 8ft section of 1545 sides of table support between legs. Upright of gantry.
1 8ft sections of 1515 z axis stuff?
2 8ft sections of 2040 bottom of gantry that goes under the table.

This is what I've planned out so far does this sound like its way to much extrusion? Not enough? I'll draw up a picture of some sort later today either in autocad or sketchup. I have not completely figured out autocad though.

As for cutting tools at the start we will use my Hitachi KM12V router. Eventually we will upgrade to a 3-6Hp spindle that can be controlled by Mach 3. We will use Gecko drives and probably 700 oz/in or higher stepper motors. I would like to use this type of bearings http://www.web-tronics.com/liratrkit1.html at least for the x axis I have to figure out where to get some that are around 10ft long though. Any help? We will build a regulated PSU probably or just buy one. Also going to build a custom computer for it something like dual/quad core 2 with 4 gigs of ram. Any suggestions or idea's would be helpful thanks. And some sources for the bearings would be awesome as well!

[ger21]

For your rails, look at www.automation4less.com

[joecnc2006]

you may want to look into 30/60 for the long 10' span.

Joe

[Dougie085]

So you think the 3"x3" is probably not thick enough? Would bow some? 3060 would probably be a good idea.

[harryn]

Just curious - have you set a target for machining accuracy ?

The reason I ask, is that I originally started out with similar goals, machining Al and wood and mdf, etc. After a while, the machines size (concept) grew, and it has become clearer that good enough for wood is not always good enough for Al machining. At least for me, the concept of potentially cutting a sheet or mdf of plywood to +/- 0.050 inches is amazing, but for small parts from Al, it is sort of ok.

I am still struggilng with this area, but starting to come to grips with it by adding thicker sections in and more steel. Frankly, I still don't know where I will end up.

[Dougie085]

Well other people have done the aluminum extrusion builds and have gotten some very good accuracy. I'm planning on figuring a way to brace the gantry well if needed but we'll see. I'd like it to be as accurate as possible without expecting to much from it. The aluminum stuff I would be cutting are probably machining panels for an amp chassis and what not.

Would these bearings work good?
http://www.automation4less.com/lm76osg.htm the 25mm ones I was thinking? 2 per side of the gantry. Still rather expensive but not as expensive as the other ones. They seem very good though.

I was thinking of doing it like this one http://www.cnczone.com/forums/showpo...92&postcount=1
so maybe the 3"x3" would be fine? Basically the side rails would be supported by the table underneath it.

[Dougie085]

I think I may just go with the Hardened rod type bearing system with the linear bearings like these
http://www.vxb.com/page/bearings/PRO...Systems/kit989
Would be cheaper then those other ones and should still work very well. I could use these for all 3 axis.

[ahren]

Definitely use 3060 for the gantry -- deflection and torsion can be a real problem for a span that wide. Also, I would stick with 15 series (rather than going to 2040) to keep joining easier. You might also consider a less expensive material, such as steel tube or C-channel, for non-critical portions of your frame like the cross bracing and legs.

Best regards,

Ahren
www.cncrouterparts.com

[Dougie085]

Yeah after my quote from 8020....I'm thinking up some new idea's. I probably asked for way too much in the quote but was something like...2500 bucks.

[ahren]

For sure. One idea I've looked into before is using pallet rack as a starting frame for a router. It's cheap and available almost everywhere -- you just need to be able to cut the stanchions down to size. You can get different rails that are fairly heavy duty (some of them are made of structural C-Channel) in lengths varying from 8 to 12 feet.

8020 is still great stuff for the gantry and Z-axis, however. The versatility of the T-slots, light weight, and the relative straightness of the material make it a good choice for this part of your machine (that's why I based my component system on it). To save more money on your machine, I would avoid most of 8020's fasteners. As many on the zone will tell you, Home Depot 5/16" carriage bolts work great as a means of connecting the stuff together -- the square shoulder works as an anti-rotation feature in the T-slots.

Best of luck on this ambitious new machine!

Ahren
www.cncrouterparts.com

[Dougie085]

Yeah...Well originally I was planning on doing the entire thing out of 8020. Now I'm thinking of doing the X,Y,Z all out of 8020 but the table part out of some sort of steel channel like Joe did on his 4x4. I really like the look of the 8020 though Heck might even just build a nice heafty table for it out of wood or something. Not sure really. I'm sort of rethinking a lot of my idea's. We have a couple months until we are going to start on it.

[joecnc2006]

Yea, cost was my concern for most people, that why i designed my 4x4 the way i did, to hold the cost down quit a bit. you can see it in my CNC 4x4 Hybrid.

Joe