Why use 8020?

[DPF]

Before I go any further, please note: I am just trying to learn and am not attacking anybody's machine design. Obviously this stuff works or it wouldn't be so popular. I'm just trying to figure out if this stuff is right for me and my machine.

It seems like everybody and their dog has at least a few pieces of 8020 or other T-slot aluminum on their machine these days. Some people are building entire machines out of it! It seems kind of pricey for what it is though, why is this stuff so popular?

I would love to learn what advantages 8020 has vs. other methods like Unistrut, wood, structural steel, non-fancy aluminum tubes & angle, etc. I'm working on my first machine and want to learn from others who have gone before me, and all my reading of old threads hasn't really covered this topic specifically.

Thanks,
DPF

[stevespo]

I can't comment on the advantages/disadvantages of the other materials because I haven't used them.

I ruled out Wood/Ply/MDF because it seemed risky for my needs (strength wise) and required sealing to tolerate the climate swings in New England. I don't have the tools to cut/weld steel. Aluminum plate and standard tubes and profiles required too much work, with no easy way to attach pieces quickly and positively.

I really like 8020 for many reasons, not in any particular order.

Reasonable (IMO) cost, availability, many sizes/profiles to choose from.
Cuts, drills, taps easily. A chop saw with a non-ferrous blade works well.
Assembles very quickly.
Easy to mount hardware, rails, screws, switches, etc.
Dimensional stability with temp/humidity changes.
Alignment and adjustments easy with slot mechanism and connecting plates, brackets.
Vibration resistant with sprung edges on the t-slots. Parts stay together.
Good stiffness and mass. Carries loads with little/no deflection.
Rust/corrosion resistant (anodized finish).
It's an intelligent/cohesive system with MANY available parts (8020.net)

Disadvantages?

Can get costly. Depends on budget.
A bit messy to work with with. You wear a lot of AL when cutting it.
Not the prettiest look (think erector set), but it can be beautified with panels, etc.

Also:

There are now bolt on parts (and entire kits) for standard screws, rack and pinion, etc - from cncrouterparts.com. Wish they existed 3+ years ago. It's never been easier to get a design up and running with great performance and minimal frustration.

Steve

[mlabruyere]

I built a complete machine from 8020 because:

1. I could take the design to reality in 2 weekends.
2. The machine is very rigid
3. I can move parts around after it is built
4. There are off the shelf components like www.CNCROUTERPARTS.com
5. I do not have the expansion issues you get with wood
6. I can't weld worth a crud
7. I am not the best carpenter in the world either
8. If I move I can take it apart and put it back together with out a problem

[rschieck]

Because it is reasonably straight .

Rob

[Drools]

- It just works with out a lot of white glue!
- I can take it apart and move it if I have to...
- Scalable, I can change something (upgrade) without remaking the whole machine.
- 80/20 supplies an app to create all the parts in AutoCAD, this is a nice feature.
- CNCROUTERPARTS.COM sells linear carriages for a lot less than the Japanese or German Linear rails (THK, NSK, and Rexroth).
I have good wood working tools and it just did not seem right to use MDF when you can find 80/20 on EBay for a reasonable price.
I found 6 4ft pieces that have the end holes slightly out of tolerance. They worked fine for me since I used a cutoff piece as a template.

[mlabruyere]

To get the rest of the "Body of Knowledge" here on the Zone relating to other materials and techniques will, I'm afraid, take a great deal of work on your part. I know I spent the best part of a year just reading here before I started to buy/build anything. Even then I switched from the JGRO MDF/Pipe based system to my own design using 8020 and parts from Ahren.

I selected MDF as many do because the price seemed right....when I started to build with it I realized MDF was not for me.

[DPF]

Thank you for the thoughtful responses!

Here's another question, why doesn't anyone build CNC machines out of Unistrut? Unistrut is the same idea (modular, bolt together, slotted members) but it seems a lot cheaper at first glance.

Here's a good picture of a basic bolted joint: http://unistrut.com/literature/index...ND800&zm=&pg=5

That whole document shows quite a few different things made from Unistrut if you flip through some pages. Was Unistrut CNC tried before and failed?

[Jack000]

I'm doing a unistrut build right now, but it's getting a bit delayed due to school..
http://www.cnczone.com/forums/showthread.php?t=93234

unistrut isn't a "precision" material like 8020, it will have imperfections and inconsistency between pieces. (the unistrut guys I bought from told me as much, they only cut to 1/8") The stuff is usually used to hold up ductwork and piping in buildings.

8020 on the other hand is designed specifically for precision machinery and motion systems, you can count on it being perfect to high tolerances.

The major difference is price - 8020 is dollars per inch, whereas unistrut is dollars per foot, which is why I'm using it for my machine.

[eigstein]

the original shopbot was made of unistrut ,window rollers,and wire . but it worked.

sincerely,

rjs

[ilya]

As other mentioned above, 80/20 extrusion is intended to be used as a machinery construction profile. It has clearly defined tolerances, and its aluminum alloy is quite stronger than a regular 6061.
That means, if you build something out of 80/20 extrusion, you can count on it to be precise (within tolerances) and rigid.
I doubt that Unistrat can offer that same precision.

Keep in mind that 80/20 profile has a special shape that prevents fasteners from loosing during vibration. This is also important.

Another advantage of 80/20 is this: you can make a completely bolt-together kit for a cnc machine. You don't need to weld anything, and with cncrouterparts.com parts you don't have to machine anything.

Is steel better? Probably. If you can precisely machine it, weld it and then thermally treat it to "relief" the joints. Otherwise, buy 80/20, bolt it and forget it.

_________________________________________________

My DIY CNC machine plans at www.8020CNC.com

[Aryantes]

Originally Posted by rschieck Because it is reasonably straight . Rob

^^^ This is key for me hehe.

I've just started my project as well. (lurking for some time)

I managed to pick up some overstock used 8020 (Lite) on ebay a few days ago.

Being on a budget, I couldn't afford to spend the hundreds of dollars I would need for a complete 8020 2'x4' machine.

However, having done some a decent number of wood projects in the past, I really dislike the idea of having to build right angles and properly planed surfaces from wood.

Everything I pick up from Home Depot is somehow warped/twisted at one point or another. Although most of it is workable, I didn't want to subject myself to this for a CNC machine.

I've decided to build a wooden torsion box (mdf + 2x4) for the base and make my gantry out of 8020. The torsion box should protect me from warping to a good degree.

I wish I had more 8020 at this point. Being able to join things so easily with just a few end connectors, bolts, and a tap or two is extremely convenient.

Being able to count on it is priceless.

[YZF]

My 2 cents:
8020 or other similar aluminum extrusions (bosch, mitsumi) are generally not designed for precision machinery (precision being lets say less than 1 mil/25um tolerances) but are very easy to build with quickly. They are convenient. The limitation on their precision comes from the nature of the extrusion process, they're more likely to be slightly banana shaped.

You'll find most people who use extrusions to build real precision machines end up milling to extrusions to create the accurate surface or edge they need.

Those extrusions generally have very high load ratings but not necessarily high stiffness, so again you'll find most people who are doing larger/precision work with this material reinforcing it to achieve higher stiffness.

I've seen it used in industrial settings for frames, tables, cabinets and various jigs that do not require high accuracy and stiffness. Again, the advantage is they are standard items and easy to interconnect (lots of different options off the shelf there). The motion products offered with them are generally targeted at these sorts of applications as well (so you won't get lifetime, load, stiffness and accuracy anywhere near something like a recirculating ball, ground hardened steel linear rail would give you).

Most people working with wood do not require micron level precision or accuracy so for a wood router application they are an easy solution for assembling a very solid machine. If you compare the properties of aluminum extrusions to something like MDF which some people work with you'll probably find the aluminum an order of magnitude better...

I built a small-ish machine with aluminum extrusions with some aluminum plate reinforcements and the frame feels really solid. It was easy to design and assemble. It worked for me...