Hello Steve;
>
>If I send a 60k line program to a cnc machine from my pc, it takes 2 hours at 38400,n,8,1. If I take that same file and send it to one cnc machine from another it takes 7 minutes. Something in my program is really slowing this communication down.
>
Serial communication are pretty slow.. The slower comm. by network, works under 10mbit or 10 times more than a faster serial communication..

Anyway, Have you tried to change 38400,n,8,1 to 115200,n,8,1.. At the both sides (host, client) ?

If possible, it will increase almost 4 times the speed..

..There is some modifications that can be done to increase (a little) as to turn off the control of errors by software, etc..

..Windows has also a buffer to receive/send data by serial ports, you will find it at your modem's properties..


Can you post here your code ? Maybe we will see something else out there..


HTH

Claudio