80/20 EXTRUDED ALUMINUM

[CNCCajun]

I'm in the planning stage of my project, a 4X4 table . . . . As much as I "think" want a heavy duty table, all welded steel, I have had several people suggest go the 80/20 route. It will be plasma only . . .

Any feedback as to Pro's & Con's of this construction method are needed . . . I can not really move forward until I have determined this . . .

I realize a steel table is a lot of cutting, welding & squaring . . . . I am also considering the overall strength . . .

Although my plan is to build a separate table to hold the water tray & grate . . . Probably from steel . . . This will eliminate most of the potential damage to a 80/20 tray caused when loading material to be cut . . .

Any comments welcome,
Thanks,
Steve

[millman52]

Originally Posted by CNCCajun I'm in the planning stage of my project, a 4X4 table . . . . As much as I "think" want a heavy duty table, all welded steel, I have had several people suggest go the 80/20 route. It will be plasma only . . . Any feedback as to Pro's & Con's of this construction method are needed . . . I can not really move forward until I have determined this . . . I realize a steel table is a lot of cutting, welding & squaring . . . . I am also considering the overall strength . . . Although my plan is to build a separate table to hold the water tray & grate . . . Probably from steel . . . This will eliminate most of the potential damage to a 80/20 tray caused when loading material to be cut . . . Any comments welcome, Thanks, Steve

I don't know how well the alum extrusions will hold up on the long haul. I am quite sure the Alum is strong enough. The one bit that I really can't get around is the bolted/clamped joints. You are going to have a gantry mounted to the top running 200+ IPM stopping & heading the other direction. I can't help but believe the joints will have to be watched closely to keep them tight.

I have never used the stuff. So I am not really qualified to answer your question. The above is just a concern I would have. Therefore I'd build from steel.

[freak_brain]

The 80/20 extrusions will cost you more than using a steel construction. However, if you don't have the equipment to fab it out of steel the extra cost is worth it.

Allen

[slkret]

Steve:
I built my machine out of 8020 extrusions and their "barrel bolt" fastening system. I used the 8020 because a got a bunch of it for free along with a large number of fasteners and other misc. 8020 stuff. Wnen I was in the "thinking stage" I considered doing a steel weldment. While the welded steel design would probably been stiffer, I was really worried about weld distortion forcing me into a whole lot of alignment issues or machining the assemblies after the welding. One of the things about the 8020 approach is the ease of cutting the members and putting things together. for cutting, I hav a carbide tipped blade that has a bit too much runout for woodworking but it was fine for cutting the aluminum since i really didn't care about the tiny saw tooth marks on the cut surface. I used a dial indicator and digital protractor to verify the setup on my table saw blade and miter slide. I then made a cut and bolted 2 pieces together and checked for squareness. I had to make a tiny adjustment and I was good to go. with that setup I made all of my cuts and upon assembly, egerything ended up square without any need to shim. The machine went together so easy I could hardly believe it. The 8020 materials are going to be more expensive than common steel structural shapes and tubes. From a stiffness standpoint you can make an aluminum structure just as stiff as a steel one. You just need to pay attention to the section properties and select sizes accordingly. You may loose a bit of stiffness in the 8020 design due to a loss in joint efficiency in the bolted joints compared to welded joints. proper gusseting can probably eliminate that as an issue. The other nice thing about aluminum is its inherent corrosion resistance compared to steel.

Hope this helps.

Steve

[millman52]

There is another huge time savings to using the Alum I guess. NO NEED TO CLEAN & CLEAN & CLEAN & PAINT

[Hirudin]

I also am not qualified to be recommending design materials, but I also will anyway...

One thing I've always heard about plasma tables is that they do not need to be nearly as rigid as router tables. The reason is, the plasma cutter doesn't make contact with the material being cut, so it therefor doesn't have anything trying to stop it from moving. Sure, you want it to be strong enough so it isn't flopping around, but that doesn't take a whole lot of metal.

Regarding the joints: I've made a few things with extruded aluminum (not 80/20 but a competing company). I was very surprised just how strong the joints are one day when I had to pound a joint that hadn't even been tightened apart. I wont get into the details, but I was sliding a piece into another piece to make a "T" intersection. While sliding the pieces together the bolts sticking out from the vertical line of the "T" made contact with the sides of the slots causing them to get screwed in. It started off by just getting tight, but then it reached the threshold where it absolutely would not come off.

I attached a picture of the vertical piece (a 1" by 2" extrusion) after I got it off. Remember, this wasn't even tightened down.

I was using T-Slots made by Futura Industries. They have a unique design where the tabs of the slots are bent inward slightly. When you tighten bolts against the tabs they get bent. It's kind of like having lock-washers along the whole slot.

[ahren]

For a plasma cutter, I think you'll find 8020 to be fantastic to work with. There are dozens of examples of DIY routers built from the stuff on this site (there are also links from my site), and these have to contend with cutting forces, not just their own moving mass. Since you don't have those cutting forces with a plasma, you should be in really good shape. The adjustability is really key, and the t-slots are great, especially when you decide you want to add a limit switch, cable clamp, etc. I highly recommend it.

Hirudin, the 8020 extrusion also has the 2 degree locking feature -- I think a lot of companies have adopted this. The T-slots stuff is great though, and is typically less expensive than 8020.

Best regards,

Ahren
www.cncrouterparts.com

[Hirudin]

Originally Posted by ahren ... Hirudin, the 8020 extrusion also has the 2 degree locking feature -- I think a lot of companies have adopted this. The T-slots stuff is great though, and is typically less expensive than 8020. ...

Oh. I had only bought one type of extrusion from 80/20 and it looked very flat. But now I've put a straight edge next to both and I can see that they are in fact the same. Thanks for pointing that out!

[Dustin407]

I have a tremendous amount of alum. fabrication experience. The extruded alum. is very nice stuff and has many advantages. But it also has some disadvantages. 1) price very expensive compared to steel. 2) Flexibility, alum. is very flexible and this creates problems in the machine world. 3) to get rid of the flex you have to overbuild and this means more material/cost.

I am not saying you shouldn't go with alum. because it is very build friendly. Half of my machine is built out of alum. and the other half is steel. I think what I am trying to say is I dont have enough info. on your design, budget, and tools in the garage to give a proper suggestion.... If this decision was on my shoulders, I would prob. go with steel table, and alum. gantry...

[analogman]

FWIW 80/20 has a downloadable program for calculating flex (displacement) depending upon load. This might help when determining to use 80/20 extrusions or another material.

Quite easy to use.

[LazyMan]

There seems to be a lot of speculation about 8020 type extrusions. I see many comments about how its not as strong as steel beams and how aluminum is not an ideal material for a CNC router. This is in a sense is true, but it is important to put things into perspective. For starters, the shopbot cnc routers use aluminum extrusions for their cnc routers (Bosch Rexroth brand I believe). They use it for their gantry and there frame sides. Perhaps in the large industrial CNC router world, a shopbot is considered a light duty machine. However, it is solid enough to satisfy the majority of the DIYers on this form.

If you still feel that it is not solid enough for your homebuilt machine, then you can do some very basic calculations to get a better idea of what you are dealing with. Just as an example, take a Bosch Rexroth 80x160mm (about 3x6inches) aluminum extrusion that is 62 inches long with both ends supported. Stick 300lbs in the middle and the beam will deflect .002 inches.

Aluminum profile Extrusions are certainly more dimensionally accurate than steel beams. Although they are not suitable for precision metal work, they are are good enough for wood machines.

Although 8020 seems to be the popular choice for extrusions (probably because you get it on Ebay,) its not really the ideal choice for mounting linear rails to because of the reason described in the drawing below.

Most other extrusion companies such as bosch don't do this and are flat, which is preferable.

The main problem is cost in the end. If you can get a good deal on the stuff i would use "8020" type extrusions.

[LazyMan]

Oops forgot the image.