Am I being silly?

[brman]

I won't criticise anybody for doing their best to make something work.I started with an MDF machine and drawer runners,which gradually got changed to SBR12 rails.I also use a much derided breakout board off a parallel port running LinuxCNC and it has never let me down.The crux of the matter is that we have the freedom to build with materials we are comfortable with and running software of our choice.If it doesn't meet our hopes,then clearly we made at least one wrong choice-at which point we get to decide what we do about it.

Thanks, yes, I have read enough to know what are the "best" ways of do things but "best" is not necessary most suitable for me at the moment. In my mind it is a compromise between making enough wrong decisions to learn and not making so many I give up

That one statement right there is why you should give up right now.!

If you don't have the budget to buy one and you don't the time or inclination to build one then just call it a day and save your money for when you do. If you proceed then it's highly likely you'll just blow money or as often the case when taken on half-hearted you'll fail and give it up.

I can see why you said that but I think we have different priorities. I see nothing wrong with experimenting for experimentations sake, even if it is not the "best" or conventional way of doing it.
Plus, there is no such thing as failure in my view. If I did nothing that would be a failure as I would have learnt nothing. If I do something and it does not perform as I hoped then fine, there is no failure there as the success is in the learning.

Then you need to be looking at purchasing a solution. Although even those will require you to put some effort in to diagnosing and troubleshooting problems along the way.

As above, I guess I should have made it clearer why I am doing this. It is not just to get a machine that makes parts I want. If that was the case I would just take my cad models to a cnc prototyping place and pay them. It would probably work out cheaper in the end! Lastly, time wise, I am not saying I don't have the time to tinker and fix things, just that I have to take that into account overall. ie. there is no point me spending all my available time making the best steel frame in the world but not having the time to sort the drives/control etc.

This might all sound like I am trying to justify to myself ignoring the good advice here. I am not, honest! I am still concerned about the effort of making a square and flat steel frame though, so I think I might need to consider ally extrusion again. Something for me to think about anyway. If I go that route then the choice between supported rod and profile rail is mainly one of cost vs performance.

Which I think leaves the other question. Fixed gantry, is that the right way to go for a small machine like this?