Quote Originally Posted by BikerAfloat View Post
however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)
Excellent

Quote Originally Posted by BikerAfloat View Post
I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz
Your options are limited to having two leadscrews on the X-axis - there is no way you'll get away without two when cutting metals unless the gantry is exceptionally strong which is almost never the case.

I use two motors on my X-axis and have not had any problems due to using two motors. When testing I have had one motor stall, but the gantry is sufficiently strong for this not to cause noticeable damage, especially since once one motor has stalled the other will invariably stall a fraction of a second later.
You can save a little money by only having one motor and using pulleys, but since you want the motor and driver later for a 4th axis you could always start with two motors and if you're not happy with it link the screws with a timing belt and use the now spare motor and driver on the 4th axis.

I urge you to reconsider not using ballscrews. I would add up the cost of the 4 leadscrews you are intending to get along with all the parts they require, then send Chai on eBay a request for the price to get the 4 ballscrews (and rails) you would need with the standard end machining and bearing blocks. I'm sure you will be pleasantly surprised.

You mentioned using the 3Nm motors from CNC4You. These are a good choice since they will be more than adequate for this machine and offer the best price per Nm in Nema23/24 frame size. Currently you've got all the leadscrews direct drive which gains simplicity, however using timing belts gains a lot more than that. You can change the drive ratio (important to get a good feedrate if the leadscrew is quite a low pitch), motor alignment is no longer so critical, plenty of people seem to have problems with couplings breaking and belt drive provides damping which helps reduce resonance issues to name but a few...This is a good place to get the timing belts and pulleys.

Putting a sheet of aluminium on the back of the gantry will greatly increase it's stiffness since it will essentially eliminate bending of the gantry sides parallel to the Y-axis, thus reducing the tool deflection in the same axis.