[pchester]

I've been slowly collecting parts to build a Pro CNC 4x8 inspired machine. The current phase I'm on is trying to source a supplier for the aluminum extrusion.
I'm in Canada and the purchasing options are quite expensive (if you know of any affordable ones, please share), so I've turned my efforts towards Chinese suppliers.
I've found one that can deliver all of the aluminum parts in the attached picture plus 6 legs and 3 leg sections for $1200 Canadian.
The question I have is whether or not these extrusion profiles attached are suitable for a CNC build. I noticed the t-slot is U shaped, which seems less rigid than a profile where the t-nut sits flush. The aluminum grade is 6063-T5.
I'd like to hear any suggestions before I make a fairly significant purchase.
Thank you,
Chester

[wizard]

Well it depends upon what you mean by rigidity!

First; that little bump that the tee nut bears against when tightened is a design element and I s put there on purpose. Doesn’t it do any good with respect to regidity I kids doubt it. I did once read about a theory for its being there but frankly have forgotten what it was.

Second; if you notice the wall thickness on these extrusions is only 2mm which isn’t much for aluminum. That means the outside nuts (the nuts near the corner areas) is only well supportted on one side thus anything bolted to it is not as well supportted as could be. I wouldn’t be real excited about using these extrusions on the gantry. You could try facing the extrusion with plate Aluminum but that would just add cost.

Third; for a gantry beam I’m not sure why people don’t consider steel! Square beams can be had from steel supplies fairly cheap, can be found as scrap at scrap dealers, and often in the drops section at steel suppliers. Yes a steel beam can be heavier but not outwardly so one you mitigate the shortcomings of an Aluminum solution. The rest of the machine can remain aluminum if you want.

Fourth; there are always other options. For example you may be able to have a sheet metal shop fold up a beam for you. This could be of any material the shop normally handles. Another possibility is finding a source for structural aluminum forgings and extrusions where you may gut find square tubular beams. These beams would be used just like their steel counter parts in a gantry.

[ger21]

I'd like to see how they compare to the 8020?

Those look to be on the lightweight side.

[pchester]

Definitely some great points to consider!
I liked the idea of using extrusion if I wanted to extend the bed or make simple upgrades, but maybe I'll revisit the idea of using steel.
That's true about the wall thickness only being 2mm too.
Thanks a lot for the feedback!

[wizard]

Definitely some great points to consider!
I liked the idea of using extrusion if I wanted to extend the bed or make simple upgrades, but maybe I'll revisit the idea of using steel.

It really isn’t a case of one or another, you can use both materials equally well. In the case of the gantry beam you leverage the strength of steel. Much of the rest of the machine can easily be made of anything. The light nature of those extrusions would be far easier to mitigate on the X-Axis in my opinion.

That's true about the wall thickness only being 2mm too.

Actually the machine be had thicknesses up to 2.2 mm but the point remains they are not heavy weight extrusions. Note how they are put together can have an impact on suitability. You could easily do a light machine frame with these extrusions as they can be assembled in a way that is far stronger than a gantry which is only supported at each end.

Thanks a lot for the feedback!

It is worth noting that Mass in the machines base is a good thing in most cases. This due to all movements of or on the gantry causing reaction forces in the machine frame. In otherwords light machines can walk around. Of course mass works against you if you need to move the machine around a lot.