Peteeng and Nic77 thank you for the replies!

NIC77 - Thanks for the links, these are certainly some heavy-duty machines made for some series stuff, but without a doubt a good note to take some lessons from! At this stage I'd be happy with the omio CNC performance, so may try and make something similar.

Would you be cutting sheet mostly? For example 10mm thick and less? Have you considered the height of a vise for your Z axis?
Most likely 20mm thick plate and less. I have around 100mm of play which I am hoping which is enough for a vice and a small bit. Good point I will check!

If you reverse how the bearing blocks and rails are mounted on the Z axis, you can get the bearing blocks further apart vertically and possibly squeeze out a bit more Z travel.

Do you mean Y-Axis here? Good point, I am thinking I will do this change. This will bring the Z-axis inwards, reducing the moment arm there, at the same time increasing the bearing block distace. That is what I see more commonly on some of these larger machines also.

If you can pick up some surplus bearings from a good manufacturer, Like Bosh Rexroth, NSK, Genuine Hiwin, anything made in Germany, Japan, and perhaps Taiwan, you will be happy with them. I think the Chinese linear bearings can be hit and miss.

Learning I'm planning to try and start cheap. I can get them from China direct, from known suppliers with reputation inside China - so going to try my luck. You could be right and I'll waste my money, but as long as they get me going to start with.

The acceleration you want is also a factor. Do you have any idea what kind of top speed and linear acceleration you want to achieve out of this machine?

I am not sure sorry - as this is a hobby machine, I am not doing fast production on it. What is a reasonable target do you think?

On thing to consider is if you really want to do this. It may be a better use of your time to buy something and just get to using it. Sometimes these projects can drag on for a very long time.

Thanks for the advice - I think I'll enjoy the design and building process. It's the best way to learn (I hope!). Also, I can get parts fairly cheap so I am hoping overall it will be a lot cheaper! I could be very wrong though!

Changes

Based on some review on the other designs, I am planning to change:

1. Move the Y-Axis Linear Bearing blocks to the top and bottom of the 80x80 frames. This will allow me to increase distance between the bearings, and move the whole Z-Axis assembly inwards by about 25mm reducing the moment arm there.

2. Change to two dual X-Axis steppers, removing the complete undercarriage of the machine, hopefully making it a bit more robust and stable. It will also reduce my side gantry plates by around 200mm so hopefully make that slightly cheaper (or balance out the cost of the extra ball screw/servo/stepper etc). I will buy two 2010 ballscrews with the slightly wider face bearing blocks.

What do you think?