[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]

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...

[MikeyC38]

Adding my 2p's worth...

In the UK, using aluminium profile works out MUCH cheaper than quality wood. Was looking to build a Solsylva 37" x 25" machine and the wood alone (American red oak for stiffness and stability) would have cost me £400 ($600!!) alone. 8020 aluminium works out to about £200 ($300) with the following advantages - Stiffness and better temperature stability and ease of construction, as said previously in this thread. I will be using a combination of 6082 T6 tool plate for the ends and 8020 for the rails and gantry. There are also programs available to enable the calculation of the deflection of long rails and on the sizes I have chosen, it is very low (.002"). I expect this frame to enable me to machine light aluminium alloys successfully. This has been done by others in the UK using this approach.

Hope this helps

Mike

[mlabruyere]

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....

I think when we use the term "precise" (when talking DIY wood CNC) a few thousands of an inch will do. I get precise cuts using my 8020 extrusion under this paradigm.

Forgive my ignorance but is 1 mil/25um equal to 0.0025mm? If so that's a really small number....

[YZF]

I think when we use the term "precise" (when talking DIY wood CNC) a few thousands of an inch will do. I get precise cuts using my 8020 extrusion under this paradigm.

Forgive my ignorance but is 1 mil/25um equal to 0.0025mm? If so that's a really small number....

You've one too many zeros in there.. It's 0.025mm. Last time I looked at the spec for extrusion straightness I think it was in the 0.1's of mm's (0.1mm ~= 4 thouhsands of an inch). :-) I guess for wood working this is fine as the wood itself isn't really stable to better than this but to use the term "precision machines" is a bit misleading... The straightness of a THK linear rail (installed correctly) is in the microns, something like two orders of magnitude better than the extrusion...

[mlabruyere]

You've one too many zeros in there.. It's 0.025mm. Last time I looked at the spec for extrusion straightness I think it was in the 0.1's of mm's (0.1mm ~= 4 thouhsands of an inch). :-) I guess for wood working this is fine as the wood itself isn't really stable to better than this but to use the term "precision machines" is a bit misleading... The straightness of a THK linear rail (installed correctly) is in the microns, something like two orders of magnitude better than the extrusion...

Cool....sorry I thought 25um = .0000025 meters which = .0025mm....my bad.

Cool for the THK rail....that's why they are so much $....Even if I got the THK rail I doubt I could get them aligned to within their referenced tolerance. Guess this is why the "real" "precision machines" are tens of thousands of dollars...many tens in some cases.

[diosces]

I choose 8020 for my current build because it's 'able

• Durable
• Adjustable
• Dismantable

Fairly rigid
Extremely fastener friendly, recently found out 1515, 1530 works well with 5/16"-18 carriage bolts,

just received my first batch from the the 8020 ebay store, nicely packaged.
Can't wait for the weekend to start my frame and X-Axis construction

[LazyMan]

The straightness tolerances of ITEM and Bosch Rexroth extrusions according to there catalogs are .3mm/300mm (.012in/12in) and a max deviation of 1.5mm (.06in) over a lenth of 2000mm (79in). I could not find the straightness tolerance for 8020 in their catalog but I highly doubt it is better.

[ilya]

The straightness tolerances of ITEM and Bosch Rexroth extrusions according to there catalogs are .3mm/300mm (.012in/12in) and a max deviation of 1.5mm (.06in) over a lenth of 2000mm (79in). I could not find the straightness tolerance for 8020 in their catalog but I highly doubt it is better.

I've opened up a catalog and here're the numbers:

• Flatness 0.004" per inch of width
• Straightness 0.0125" per foot of length, not to exceed 0.120" over 20 feet of length

Looks good to me. See page 81.

__________________________________________________ ____

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

[stevespo]

I've mentioned this before, but the 8020 I've received has been VERY straight.

With my 2' Starrett straightedge, I couldn't even measure .0015" worth of deviation over that distance. This was consistent across many pieces of 1515, 1530, 3030.

So, the specs they publish are typically much broader than the tolerances they actually produce - which are quite good, IME.

Steve