Question on CFM

imported_OWDouglas · Aug 23, 2005

I'm looking to buy air metal shears at harbor frieght and have a question about CFM they have a pistol grip model and an inline model. all the specs are the same except the pistol grip is rated at 4CFM@90PSI and the inline is 16CFM@90PSI. Is the lower CFM better than the higher? because it's a little more expensive.

hhw · Aug 24, 2005

I am no expert in this area, but I do know that 16 CFM@90psi is a goodly amount of air to move. By saying that the unit is rated at this, I'm guessing that means it requires that much to operate effectively. My personal choice would be the unit requiring less CFM to operate, unless you specifically need the inline model.

Bird · Aug 24, 2005

Ron, something just ain't right. I've repaired/rebuilt a number of those metal shears, although not any of the Central Pneumatic brand, and I think I can safely say that Harbor Freight has a misprint on that item. I never heard of any requiring anywhere close to that air volume, and you'll notice that both of those shears call for 1/4" inlet; no way are you going to get that kind of air volume through a 3/8" hose and 1/4" inlet. The air consumption of both of those shears is probably pretty close to the same.

hhw · Aug 24, 2005

I looked into some other tool cats. and the closest I could find for an inline unit was an inline scissors at Northern. It requires 3 CFM. I'm guessing the shear would not be much more. As I said I'm no expert in this area, but 16 sounded awfully high! /forums/images/graemlins/shocked.gif

When I looked at the HF cat., sure enough there it was "16CFM." /forums/images/graemlins/confused.gif It says both units are close in "strokes per minute," so they have to be close in CFM use, does that make sense? /forums/images/graemlins/crazy.gif

Bird · Aug 24, 2005

Yep, Kim, that makes sense. You can see from the pictures and description of size or weight that the air motors in both of those tools are close to the same size (about the same, in fact, as most 3/8" drive ratchets).

Incidentally, the Chicago Pneumatic CP785S, which is about as good a shear as I know of, with about the same number of strokes per minute, uses an average of 4 CFM. Harbor Freight simply has a misprint; can happen to anyone. /forums/images/graemlins/wink.gif

imported_OWDouglas · Aug 24, 2005

Thanks for the info guys, now for the next question, with me being very novice with metal work, which one do you think is more user friendly for manuverability the in-line or the pistol grip. I won't be using it a lot, but I'd like it in the toolbox when I need it.

Bird · Aug 24, 2005

Ron, I never "used" one. I just repaired/rebuilt some, and of course anytime I repaired one, I "road tested" it by cutting up some scrap metal before sending it back to the customer with a 90 day warranty. So . . ., in my opinion, performance is about the same, but the straight model will fit into tight places that don't have enough room for the pistol grip, and it'll take up less space in your toolbox, but if you're doing a lot of work with it, the pistol grip won't be as tiring. So the best one is the one you like best. /forums/images/graemlins/wink.gif

LarryRB · Aug 24, 2005

I've had a pistol grip CP air sheer for probably 15 or more years now. I find it very easy to operate, straight or curves. I feel that I have more control with this model. Might take a few minutes to get use to, they are no problem to operate.