[jakeru]

I found some quite detailed info on gas cup and argon flow rate selection in CK Worldwide's TIG welding specification document (a sort of "how to" TIG weld guide): http://www.ckworldwide.com/technical_specs.pdf

There is a chart (bottom of page 4) showing recommended Argon Flow and Cup Size for various tungsten diameters, metal type (Ferrous and Aluminum) and body type (Gas lens and Standard).

Example:
for welding aluminum with a gas lens and a 3/32" tungsten, use a 6-8 cup, and 10-15 CFH Argon.

[nelson]

Hi!
I found this topic searching for cup size guidelines. Is seen lots Jody''s vids and read a lot here but is there some guide for choosing cup size other than a small one for tight spots?
Thank for all the help!
Nelson

[Oscar]

It might be useful to think about what is a good speed of shielding gas flowing out of the cup. If we knew that a gas speed out of a cup were a good speed setting, then it would likely hold true for any cup size. We could then easily determine what cfm is needed to develop a given shielding gas speed out of the cup, for any cup size.

For example, a couple people here said that 10-15 cfm worked well through a #6 cup. The middle of that range 12.5 cfm, which through a #6 cup (.110 square inches) give about 3 mph, or about the speed of someone walking.

Then if we knew that 3 mph were then a good shielding gas speed, we could easily calculate how to get it with any cup size:
#7 cup: 17 cfh (.150" sq) = 3 mph
#6 cup 12.5 cfh (.110" sq) = 3 mph
#5 cup: 10.5 cfh (.077" sq) = 3 mph
#4 cup: 5.5 cfh (.049" sq) = 3 mph

That is essentially what you are already doing when you adjust the mass flow rate anyways. In essence you are ajusting the speed of the gas flow as time goes by. The advantage of using the cubic-foot-per-hour units is that it provides a gauge of sorts to know how much welding time you can get from a cylinder of gas. Not only that, speed readings also need to be adjusted, as you just simply cannot take the "middle ground" to work for everything (the very reason that CFH numbers have a range in the first place). Also the numbers arbitrarily work out nicer (see below)

The speed values you eventually come up with will inevitable be a range in order to take into account variables. For a #6 cup, as an example, you will find the optimum gas speed to be from 1.98-3.72 MPH, roughly, depending on factors like collet body type, tungsten stick out, and joint geometry, just to name a few. As you can see the numbers are "clumsier" to work with, compared with the integer units of CFH.

If you know enough math, you can still easily develop the non-linear function that can spit out the CFH number for a given cup size to match your data table. It will be quadratic in nature, as you can see from the fact that a #4 cup needs about 5.5 CFH, but a #7 which is not even twice the diameter, but already needs 3x the mass flow rate.

[nelson]

Ok, I've read the posts in this topic. From this and the info links it seems like for a given size tungsten, there is one size cup I should use. The gas flow shold be set to produce about 3 mph flow through it.

I had a welder who teaches it at my shop today. He saw my welder from across the room and said the cup is too big. He couldn't know what size tungsten from where he was. I had a 10 with gas lens I was doing tests with previously. What gives?

BTW he never heard of Jody. I guess experts don't watch instructional videos? Nice enough guy. I'm just trying to get the straight dope on this.

[Poland308]

Gas flow rate is relative to cup size. Cup size is relative to gas coverage area needed. Tungsten size is relative to amps. Tungsten size has nothing to do with cup size.