Quote Originally Posted by iGyros View Post
Hi folks,
I am Marcus from Germany (Hamburg). I decided about 3 months ago that I need a milling machine. I am still quite new to the whole subject.
Since then I have been reading and collecting ideas, but I still lack a lot of knowledge and experience. I have built a small CNC laser for "practice" to get familiar with the topic. But of course this is not comparable to a milling machine.
After that worked out quite well, I would like to tackle my actual goal.


My goals:
-I would like to build a milling machine to mill aluminum/steel parts for other projects (steel is secondary and probably not possible at first).
-I would like to build a portal milling machine to mill large pieces of wood and to mill enclosure panels.
-I haven't thought much about the accuracy yet. It should already give useful results, because I want to "improve" myself sometime and want to build a new milling machine with this one.
-I would like a machining area of about 700 mm x 1000 mm +/- 100 mm.
-My main goal is to learn about CNC machining and not to get more than 1500€ and still do something useful with the milling machine.


These are my options:
1. i first build a MPCNC because i have most of the parts lying around anyway. The design and the performance of the milling machine keeps me from doing so. I don't think I would learn as much as I hope with the milling machine. I think I will not be happy with it. Because of the price the MPCNC is still not completely out of the game (for practice).


2. i found the PrintNC project online. This is also an Open Source portal milling machine. It looks much more robust (steel frame, linear guides and ball screws). This is of course reflected in the price, but also extremely in the performance. But the videos here look really promising. Nevertheless, there are many points that bother me about the construction, e.g. due to the construction, a maximum of square tubes with 4 mm wall thickness can be used, the linear guides are screwed directly onto the steel beams (are they not too crooked?) and only one linear carriage is used on each of the guides. Some of these can be safely fixed. But then maybe I can design directly myself.

Maybe someone who knows more about the construction can answer a few questions.
- Do you notice any major errors in the design?
- What do you think about the milling machine?
- I have often read that it is better to screw the linear guide to the side of the portal, because the forces are better absorbed. Is that correct?
- Will it be a big problem that the guides are screwed directly onto the unmachined square tube?
- Is it worthwhile to mill over the steel profiles or to cast them flat with epoxy resin (I can't think of the name "liquid metal"?) or should I then simply place them directly onto another material?

Link to the PrintNC website: https://threedesign.store/gallery/
GitHub: https://github.com/threedesigns/printNC


3. I construct my own milling machine. But I still have many questions. Maybe the professionals can help me a little.

- I would like to build the milling machine similar to the PrintNC (frame made of steel square tubes). I would then go to 6.3 or 8 mm wall thickness and fill it with sand.
- Does it make sense to use steel profiles or are they unsuitable?
- Does it make sense to weld the frame or can I get a sufficiently strong connection screwed?
- When welding I have doubts, because I read about distortion and tension again and again. Is there any way I can avoid this (I have never welded before, but have a good friend who has already promised me his help). I also see a disadvantage in welding, because the subsequent alignment is very difficult.
- Do I "gain" anything from the steel profiles? I hope that the milling machine will be cheaper and at the same time much more stable or is it smarter to use the typical aluminium profiles?
- I would also have a design in mind with a fixed portal. I hope that this will provide stability. Is it worthwhile to build such a structure? I know without a drawing this question is hard to answer, but a "rule of thumb" would be enough for me. Is a milling machine with a fixed portal usually more stable or not?
- I am simply not quite sure how I can face mill the components. I think I have an understanding problem here. If I face-mill the parts on one side first, they will all lie on an uneven side, which is different for all parts. If I now turn the parts over and face-mill them from the other side, both sides are flat, but not all parts are the same, because all parts were previously on a differently inclined side. Or do I have to proceed in such a way that I do not place the components on the crooked side, but clamp them perfectly aligned?

I hope my questions don't seem too amateurish, but unfortunately I can't find much information about building with steel square tubes and if they are often old or not exactly what I want to know. Please keep in mind that I do not know that much about this topic yet. If I have written something wrong, please correct me.

Thanks for the answers.
Your best chance of success as others have said is to buy an existing machine with ball screws already fitted and fit new electronics. There are plenty of examples on the net. The more space you have the bigger and heavier the machine you can buy; bigger machines are generally cheaper because most diy people use single phase and no bigger than a Bridgeport (about 875kg).