CTWD stands for Contact Tip to Work Distance.
Another term thrown around is "stickout."
Both terms refer to GMAW as well as FCAW welding processes.
GMAW is more commonly known as MIG and FCAW is commonly called Flux Core.
no matter the process, CTWD its the distance between the contact tip and the weld puddle.
Lincoln Electric has some really good information on recommended CTWD for practically every wire and process in their book Procedure Handbook of Arc Welding.
You can find it at JFLF.org which is the James F Lincoln Foundation...a non profit arm of Lincoln electric.
Another good resource that is free is the Lincoln consumable catalog PDF.
You can download it for free and by using the search function and search term "CTWD" you will find numerous pages listing CTWD for different diameter wires, and processes...along with tons of other information.
Recommended CTWD ( stickout) can vary quite a bit depending on the process.
For example for while the recommended CTWD for Short circuit mig using .035" er70s6 might be around 1/2" or less...
CTWD for Dual Shield Flux Core using .045" might be 3/4"
Some self shielded flux core wires recommend CTWD of over 1 inch.
Spray transfer MIG also uses longer stickout CTWD than short circuit mig welding.
CTWD matters more than you might think but its worth getting right because once you find the Sweet Spot, it can make a ton of difference in the arc.
If you use too long a CTWD on short circuit mig, you risk lack of fusion.
If you dont use long enough CTWD on dual shield flux core, you might get worm tracks.
Too short a CTWD on spray transfer and its difficult to maintain that smooth spatter free arc.
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