These extrusions seem popular and cheap.
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Can anyone tell me if they ordered this stuff from aliexpress, does it arrive in usable shape? What other hardware should I look for to make a nice big order? I know there's t-nuts, solidifier plates (triangle things), what else?
Screws?
T2020 Al profile are usually available locally. They are very common especially in the last 10 years or so, since the 3D printers took flight. Those profiles are usually available in any shop for makers or 3D printers. Some have black/green/blue/red finish, but beware the finish can easily scratched by other sharp metals or tools, I prefer the natural Al (oxide) finish, the natural color of Al, but matte.
Many times the Al profile seller offers to cut the profiles at specify length, sometimes for free, other times for an extra fee.
There are T-slot nuts, corners and other helping elements to build something out of Al profiles. In pieces quantity they can be quite expensive for a complex build, but if you buy in 500/1000 pcs bags they are cheap. I bought two bags of M3 and M4 T-slot nuts for 20x20 profiles from Aliexpress. Not sure if they are made for imperial units, too, here we use mostly Metric screws (M4 means the hole+thread in the nut is made to match with a 4mm in diameter screw).
For screws, you need to match them with the T-slot nuts. The most common can be M3, M4, maybe M5, not sure. I bought screws in various lengths and head types from a local shop.
Last time I bought T2020 profiles a few years ago. Bought them locally because they were cheaper than the ones from Aliexpress, so search your local shop first. Mine arrived well, no bends no scratches, shipped from another city and they were 2.5meters long, so easy to bend during transportation. Even if locally they might be slightly more expensive, it might worth because Aliexpress deliveries were in average 3 months, sometimes half a year.
In my experience 3-6 moths of waiting for delivery is a very de-motivational factor for any project. Most of the things bought from Aliexpress ended unused, in a box, because 3 to 6 months later you'll move away from that project to something else.
So yeah, good shopping experience Aliexpress, never been scammed, packages arrived without damage (not Al T slots, but other long packages did well, for example 70 cm long linear rails, or 50 cm long and only 5 mm thick fiber carbon tubes). Aliexpress is OK, but the shipping is too long so I give up using it. For T slot profile 20x20 Al, back then it was more expensive than a local buy.