Numatx squeezer set up

[brucehatch]

I'm just starting on my empenage kit and opted to purchase the Numatx system over the standard pneumatic squeeze. Tool performance was very anemic following my first attempt at infusing and bleeding the Dexron III fluid into the simple hydraulic circuit. A second repeated infusion did the trick.
I get acceptable shop heads at 72 psi for -4 (1/8") rivets and 43 psi for -3 (3/32") rivets. I'm sure the readings on my pneumatic gauge will very a bit from any other.
Is there an optimum pressure to use for dimpling? My operating manual is blank on this. Should maximum pressure be used for all dimpling regardless of stock thickness?

[brucehatch]

Originally Posted by brucehatch

I'm just starting on my empenage kit and opted to purchase the Numatx system over the standard pneumatic squeeze. Tool performance was very anemic following my first attempt at infusing and bleeding the Dexron III fluid into the simple hydraulic circuit. A second repeated infusion did the trick.
I get acceptable shop heads at 72 psi for -4 (1/8") rivets and 43 psi for -3 (3/32") rivets. I'm sure the readings on my pneumatic gauge will very a bit from any other.
Is there an optimum pressure to use for dimpling? My operating manual is blank on this. Should maximum pressure be used for all dimpling regardless of stock thickness?

Never got a response to my questions regarding recommended pneumatic pressure during dimpling so I inquired with the Numatx tool developer via a PM. Here is his reply:

Hi Bruce,

I guess the short answer is run the pressure up to as high as you would for riveting. This assumes you are dimpling with the squeezer and a yoke mounted in it (I think this is what you are meaning), as opposed to the squeezer mounted on the end of a C-frame (DRDT-2), which could caused too much stress in the c-frame.

The simple fact is you can not over squeeze the sheet stock, the hydraulic pressure would have to be astronomical to do so. If you doubt this, but a set of flat dies in the squeezer, and squeeze a pc of sheet stock. It wont do anything to the sheet after you release the pressure.

I personally think people get to fussy about the dimple quality, but to each their own. I taught sheet metal to A&P students, and didn't fuss over dimpling to the degree some do. Don't take my comments as a knock on you asking the question, I don't mean it that way.

I hope this helps.

Mark
__________________
Mark Swinford
Aeronautical Engineer
RV-7 N65NX

[jwellman]

For dimpling I've just always ran around 90psi...or if I'm still setup for 1/8" rivets I just leave it at 86. As his reply suggests it makes little difference.
I'm not sure what the minimum pressure would be, although I'll have to test that out now.

Jared

[Jumpbat74]

Can I ask which length squeezer set people are using? I?m finding for 3-3.5 rivets I need 60psi with a long (or tall) set and then some additional washers as shims to get enough pressure on the rivet. This is with the long piston installed. I tried squeezing some AN470AD4-5 rivets for the first time today and it took over 100psi and a couple small washers stacked and I still didn?t have the shop head squeezed enough. It sounds like I?m clearly not developing the hydraulic pressure I should. I bled the system several times on initial setup. I used Pennzoil automatic transmission fluid. Could that be the issue?

[Jumpbat74]

Can I ask which length squeezer set people are using? I’m finding for 3-3.5 rivets I need 60psi with a long (or tall) set and then some additional washers as shims to get enough pressure on the rivet. This is with the long piston installed. I tried squeezing some AN470AD4-5 rivets for the first time today and it took over 100psi and a couple small washers stacked and I still didn’t have the shop head squeezed enough. It sounds like I’m clearly not developing the hydraulic pressure I should. I bled the system several times on initial setup. I used Pennzoil automatic transmission fluid. Could that be the issue?
https://team14le.wordpress.com/2020/...matx-squeezer/

[brucehatch]

Originally Posted by Jumpbat74

Can I ask which length squeezer set people are using? I’m finding for 3-3.5 rivets I need 60psi with a long (or tall) set and then some additional washers as shims to get enough pressure on the rivet. This is with the long piston installed. I tried squeezing some AN470AD4-5 rivets for the first time today and it took over 100psi and a couple small washers stacked and I still didn’t have the shop head squeezed enough. It sounds like I’m clearly not developing the hydraulic pressure I should. I bled the system several times on initial setup. I used Pennzoil automatic transmission fluid. Could that be the issue?
https://team14le.wordpress.com/2020/...matx-squeezer/

I experienced similar results when I first set up my tool some six months ago. I had to repeat the bleed process several times to completely remove any air voids in the system. Once I had all the voids removed the tool works as advertised.
For my setup and regulator 43 psi is all that is needed for -3 rivets, and 75 psi works well for the -4 rivet. It has been pretty consistent.
The brand of transmission oil shouldn't make any difference. There just can't be any air in the line at all.