Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.
chaps, im going to stick my neck out here, and before I even say anything Ive only made one machine... but what I do have in common with CraftyGeek is I am also DIY, so this was my gantry approach, slate it if you will, its not perfect but it was all done by hand with pillar drill hand punch and ruler.

Click image for larger version. 

Name:	1.jpg 
Views:	2065 
Size:	6.2 KB 
ID:	9497Click image for larger version. 

Name:	20130728_210952.jpg 
Views:	2130 
Size:	457.7 KB 
ID:	9498Click image for larger version. 

Name:	20130728_212202.jpg 
Views:	2094 
Size:	447.5 KB 
ID:	9499Click image for larger version. 

Name:	20130728_212638.jpg 
Views:	1973 
Size:	175.7 KB 
ID:	9500Click image for larger version. 

Name:	20130728_213511.jpg 
Views:	21917 
Size:	579.0 KB 
ID:	9501Click image for larger version. 

Name:	20130728_213519.jpg 
Views:	10743 
Size:	477.9 KB 
ID:	9502