Forgot to say: please observe that regardless if you splice the base  aluminium structure or not, the aluminium should _not_ be holding the weight of he machine. If you wish to do that  you have to reinforce it on the inside with steel tubes. That is not a bad idea under any circumstance since a heater, sturdier and more rigid machine adds to the overall precision and reduces wear.

Since you are building such a long machine, I assume you are building a rack & pinion version like me.

I ordered my aluminium parts from the prepared list you get after purchase from the European company Motedis. It worked perfectly. (I live in Sweden).

They have no longer parts than 2000mm as standard. They do offer longer parts  but be aware that freight costs skyrocket if you do just as you describe yourself. Shipping costs will be substantially higher than the material itself.

I will offer you my thoughts here. I am an engineer and fairly experienced in mechanical machining prerequisite  although I am originally trained and educated on electrical and electronics engineering. Just so you understand from which place I originate my thoughts.

I was originally planning to build the machine longer but ended up with the 2000mm version due to the above reason and workshop space considerations.

I think it will be no problem extending the machine to 3000mm. The rigidity will be enough since the linear rails and the racks add mechanical strength, and so will the spoil board. Here's my suggestions:

* Buy linear rails as it fits. You will need 4 of them 1500mm length or any combination of lengths that give you the correct total length. Remember that you need four glide blocks also for the z-axis (8 in total).

* When you order aluminium  make sure you do not splice those in the same place where you have the ends of the linear rails meet. For rigidity you need the linear rail to cross the aluminium splice point in one piece. Have the two rails meet at another point. The same goes for the racks.

* There are specific t-nuts made for splicing  they have several screw holes and are several centimeters long. They come in many variants, you find them on Temu for example or on Amazon, ebay etc.

* Consider additional structural strength added by steel reinforces across splice points of the base aluminium frame.

* Longer machines mean longer cables. Consider going for a good shielded cable right from the start.

* Connect the spoil board a bit extra with a few more screws.

With those suggestions, I think there is no need to buy full length. Splicing is fine.

Good luck!

Steve

PS. I used to do rockery when I was younger, you must show us what you've built! :)

There are vfd:s for 3-phase power input as well as vfd's for single phase power input. Both feed 3-phase spiindles equally well.

But for single phase power input, the phase to neutral voltage is 110V and 3-phase phase-phase voltage is 240V. Feeding power of X Watts over 110V means higher currents.

Here in Europe we have 240/380Volts. I use single phase for this, it's more than sufficient.  Whether 120V is a good choice for you depends on other loads in the same circuit. Discuss with an electrician. Good luck!

FYI in the United States, 240V goes to every house and at the electrical panel you can create a circuit with 240V or 120V.  Our big appliances will demand a 240V circuit (such as heat pumps, oven, electric water heaters, electric car charging stations, etc) and the rest of the house will be 120V circuits.  True that most outlets will be 120v.

In my woodworking shop I have 3 240V circuits for the big 5 HP machines and 4 120V circuits for everything else. If I needed higher voltage for the CNC then I would add one to my shop.  Therefore voltage requirement is not a driver unless you are talking about needing 3 phase power with higher voltages.

At this point I haven't made a decision on router or spindle but I am leaning towards 1.5 kW spindle and likely air cooled.

I would recommend updating the comments in the download page to remove the comment that only belt drawings are available inside the R&P web pages.

I live in the USA, and shipping maybe different than for you.  For another hobby of mine, I launch high power rockets (think of a rocket that is 3 meters tall and weights 23 kg) and I use Extruded Aluminum as a launch rail system.  For the launch rail, I had to buy a 5.5 m of aluminum from here in the USA and ship it to me.  Shipping cost over 2 times the cost of the rail because I had to ship the single piece of extruded aluminum on a truck as less than a load.  

Bottom line: if you have money for shipping, then it should be no problem.  Otherwise plan on picking it up at the factory and driving it home with the appropriate vehicle.  

  I am looking around the USA for who can cut the steel plates (3mm and 6mm) for the build.  I have heard good words about SendCutSend.com from friends who use them for personal jobs and their employers uses them extensively. My friends say they deliver the product fast and very high quality cuttings with good prices. 

I downloaded the drawing from the Rack & Pinion as a test.  I had to move each part into its own dxf file.  16 parts from the R&P download produced a minimum cost of $508.16 (USD) including delivery. Powder coating would add to the cost which I didn't ask for on the initial quote.  I will also get 15% off my first order by using a link on a youtube.

Are there other sites that I should look at for cutting my plates?