Not a lot! Strictly speaking you should use the correct size contact tip for the diameter of wire, but for general home use you won't really notice much difference. The contact tip transfers power to the wire so for critical applications it's essential that it's correct.
weldequip
I have been getting some unwanted splatter with my Miller 350P set on PULSE welding 0.250 mild steel square tubing. I changed wire and still the same. I noticed when I went to change the tip that the gun had an .045 contact tip.
To your point, I had really noticed anything except for the splatter? Do you think this could cause unwanted splatter? When I'm making a standard WEAVE the splatter always occurs as I sweep back across the centerline of the puddle.
Any ideas would be of great help!
Mike Gibbons
Sugar Land, Texas
PS: I ordered some .035 contact tips that should be here in a couple days.
Oh right, I didn't realise you were using a Pulse machine... yes it's critical you use the correct size contact tip to wire diameter in that case.
The whole idea of Pulse machines is to give a superior arc quality & if you are using an over-sized contact tip you won't get proper current transfer to the wire.
weldequip
You're welcome Mike. There are also different qualities of contact tips so beware! If you've ordered genuine Miller no probs. but watch out for inferior copies!
weldequip
I'm running a Bernard Q-Gun which came factory provided with the Miller 350P. I made sure to order genuine Bernard replacement parts. I use Cyberweld since they take PayPal it makes the transaction super fast.
I use Finn Tips from http://usaweld.com and they are the best i have used in 30 years. I switched my alum spoolgun over to them and all the feeding problems i had with the genuine Miller tips stopped....Bob http://www.finn-tips.com/default.htm