I had a student ask me today "Why does cutting half the length off a contact tip make it weld better?"
I said maybe if the tip was messed up on the end causing the wire to drag, cutting it off would be and extreme way of cleaning the end.
He said, "No, I mean cutting a new tip in half before using it. An old guy at my last job taught me that trick and it works."
That's when I gave him a blank stare for a minute, because I'd never heard of such, and told him I've no idea.
I then explained the purpose if the tip, which as I understand it is to transfer electricity to the wire and to preheat the wire ahead of the arc through resistance heating.
I said the only way I could think of that affecting the arc characteristics would be a slight reduction of electrode wire preheating but I don't see how that would make it weld better. I also explained how that should make it weld worse if it allows the wire wander away from center due to the cast in the wire.
Personally, I think cutting the tip in half doesn't actually make the equipment weld better, it's just one of those often destructive habits that some welders develop over the years and I would never advocate the practice.
However, I've also learned through the years that strange things do happen from illogical practices. Immediately rejecting an idea or statement just because I don't agree with it has caused me to put my foot in my mouth more than once.
So, I thought I would ask here if anyone else has ever heard of this, or does it.
BTW - particulars = GMAW, carbon steel, spray transfer, .035 dia wire both Lincoln and Miller equip.
Just curious,
Tim
I think it's a great question.
It might depend on the exact type of end consumable.
The actual "contact" made in the contact tube is "supposed" to happen very near the end of the tube itself. That's just how they are designed.
Having said that.. Reducing the size of a contact tip would change CTWD (Contact Tip to Work Distance) if all other consumables and operating variables remained the same.
A system like Bernard Centerfire would be a good example. There is NO adjustment allowed with that type of end consumable.
A Tweco #4 type setup (with a sliding nozzle) would be harder to prove your student's point.
But we need to know what exact type of consumables are being used.... Light duty tips, heavy duty tips? Tips designed to be recessed into the nozzle? Tip designed to extend past the nozzle? Stuff like that.
Wire feed rates? If you are running in excess of 600 ipm the conversation might change.
Or maybe they are using crappy forigen tips that simply don't perform well under normal conditions and need to be "tweaked" in order to do the job...
Great conversation.
Force the welder to use a longer contact tip to work distance; which is needed with spray transfer (as opposed to the typical short distance used for short-circuiting)????
Just a thought. That does sound odd.
This is an interesting thread. Will some of the more informed wade in with their thoughts? Thanks.
I'm thinking TAC got it right.
After further questioning for more particulars, the student told me that he and the other guy both like to use close stickouts, as you would use for short circuiting, or as he put it, "Shove the nozzle into the plate."
I can see where shortening the contact tip, in this case, would lengthen stickout and thus increase arc voltage.
That would surely make it "weld better", as long as he didn't drag the nozzle in the puddle.
Thanks for all of the replies.
Tim
By Lawrence 
Date 03-23-2012 21:21
Edited 03-23-2012 21:43
Shortening the contact tip does zero practically speaking, to voltage.. (GMAW is a constant voltage process)
The arc length (distance from unmelted end of wire to the work) will remain the same, regardless of the distance from the contact tip to the work. You can demonstrate this by running your GMAW spray with slightly higher than usual voltage so the spray is easy to see comming off the wire; then as you weld, move your gun up and down about 1/2", You will note that the arc length remains "constant" because it is a function of the voltage which is delivered constantly through the power supply.
The current (amperage) will increase as the distance from the the end of the contact tube gets closer to the work (short stickout) and the current will decrease as the distance from the contact tube from the work increases (long stickout) This applies to short circuit as well as spray transfer.
"Shoving the nozzle into the plate" will reduce CTWD thus increasing current.. (less resistence in wire, more energy delivered to work).
Changing CTWD can be pretty dramatic... Try running a spray transfer bead with the gas and wire your discussing... Let's say 500 ipm and 27 volts'ish... run about a 3/8" CTWD distance and look at the amp meter on your power supply.... Then make the same wild with about a 3/4 or 1" CTWD and look at the amperage... I bet you see about a 50 amp reduction maybe more. This phenomena is the same with short circuiting transfer and is why a good welder doesn't need STT to make open roots and a less practiced welder needs it :)
Edit:
What all this has to do with a cut-off contact tip is still a little fuzzy in my mind without knowing a bit more about what's happening in the hands of the operator, and how far the tip is recessed inside the nozzel.
Edit Edit: If the contact tip is shortened and *everything else* is kept the same, there would be a reduction in current at the weld. (thats a fact) :) <typical spray transfer CTWD is 1/2 to 3/4 inch> <typical short circuit CTWD is 1/4 to 3/8">
Edit, Edit, Edit, .035 solid wire requires no preheat............... And if you really wan't to get into the head of your student.. Ask him why with GTAW and SMAW, when you increase the arc length the current remains the same but the voltage increases.??? Heh.
Hello;
I have done this in the past. It wasn't to make it work better though. The tool crib guy ordered the long barrel tips for .045 FCAW and we had short nozzles. We had to get by until the new ones came in. Tried to cut them as square as we could and bevel the edges. Worked OK. Had to take a tip cleaner and clean it out first. Tweco guns and Miller machines.
Have a good day;
Matt
