Hi all.

I'm really in need of some advise and reading through the threads here it appears I might have found the right place!

I previously had a useless MDF(!) CNC router that was a complete waste of money and I have regretted buying it ever since!

That was a few years ago and I am now after something new that actually works.

I already have a set of 4 Nema23 steppers (KL23H2100-30-4B @3.5N.m. They don't seem too bad and drove a 4ft MDF gantry OK. I would like to reuse them to keep initial cost down and upgrade them if necessary later. Same goes for the 36v supply and driver (not sure of the drive make/model as I type).

As for the rest its a clean sheet design.

Requirements
Cutting area: 800x600x100mm minimum.
To cut: Mostly sheet plastics (5~8mm Acrylic) - This is the primary use.
Aluminium parts (hence the 100mm Z requirement)
PCB boards
Some engraving (but I know a guy with a laser engraver so hopefully not)

Budget
I am looking to spend between £800 - £1000.

Construction Ability
I only have a drill press, Mitre/Table saw and no access to a machine shop so anything I can construct needs to either be done by someone else or using these tools. I know a guy who makes gates and things professionally (but haven't approached him yet) so it might be possible to get things welded but I don't know.

Questions
So before I start planning I have a few questions.
1. I have seen routers on here that use aluminium extrusion and I think I can cut that accurately enough on the table saw but they use aluminium plate for the gantry sides and end plates which I can't construct. If I was to go down that path how much (as a ballpark) should I expect to pay to get them made for me? I need this to come in at least on budget.

2. I have also seen routers on here that are made from steel profile which (assuming I can get it welded) works out cheaper? Is there an advantage to using it over aluminium profile or is the profile better for my needs?

3. Screws. I was thinking of dual x-axis screws and singles on the rest. As for diameter and pitch I'm not sure what should be best over these distances. Some of you seem to favour 1610s, others 2005s. I don't mind using pulleys to drive them so I can adjust the ratio between stepper and screw as long as it doesn't add too much to the cost.

4. Rails. Profiled or supported? Cost is really the decider here I guess, and perhaps how I'm mounting the gantry. Perhaps when I have a design in mind I should ask this again! A bigger question is how do I mount either? I don't know how accurate either the profile or extrusion would be and have never used epoxy and don't have access to any milling or grinding machines.

I hope someone on here will be able to answer these for me or impart some advise on these issues. It will help me make some design decisions before I make a start.

Thanks all.
Tom.