CherryMax Rivet Puller Question

[NordicDave]

As a preface: This is an academic exercise rather than a “fix-it” question for an actual aircraft.

Referencing the picture below are 4 NAS1398M-4-x rivets set in through holes made with #30 colbalt bit.

Group 1 underlined in Red were set with a common hardware store hand riveter
Group 2 underlined in Green were set with a Huck Hydraulic hand riveter HK150A

Question: Why did the red group 1 rivet stems pull through while group 2 self-plug as expected?



Appreciate thoughts.

 

[Bell206]

Why did the red group 1 rivet stems pull through while group 2 self-plug as expected?

If the material thickness, hole size, rivet grip, etc. are all the same between the 4 holes it is usually caused by a non-standard nose piece and/or the variance in the pulling action of the hand puller. Rivets 3 & 4 are actually pulled a bit short.

 

[Daleandee]

Bell206 hit on the point I would make. It's about the rate and amount of pull. I mostly use a pneumatic puller when building. Variation in line pressure at the gun makes a huge difference. Pulled several rivets in test pieces to find the correct pressure. With hand riveting it can be a bit tricky to get really consistent results.

 

[Craig]

If I remember correctly, NAS1398's require a two stage set. First stage pulls and forms the bulb, the second stage drives the stem lock ring into the head.

Notice the first two show no signs of the lock ring being set, while the second pair has the rings set and visible.

 

[JAWS]

None are acceptable.

https://www.cherryaerospace.com/docs/catalogs/CA-1013.pdf

 

[NordicDave]

Thanks guys for the help. Educational, the coaching I was looking for. @JAWS thanks for the the doc. Reading it was very helpful and helped understand @Bell206 and others comments. I have a few scraps of aluminum, Cherry depth gauge, couple bags of rivets, and a couple of new riveters coming.

BTW, thanks @Craig for explaining the second step for setting the lock ring. Makes sense why the $286 HUCK riveter set the lock ring and the hardware store riveter pulled through. The Huck riveter is going back to ATS as it was leaking fluid and might have other issues resulting in the slightly short pull.

 

[tyndall]

Also note the difference between a CherryLock and a CherryMax. A CherryMax has a built-in washer to set the lock ring and can easily be set with a common hand riveter or cheap pneumatic.

 

[AKBill]

None are acceptable.

https://www.cherryaerospace.com/docs/catalogs/CA-1013.pdf

Thanks for the file, lots of good info

 

[Dan Thomas]

I'm wondering if the puller used on the first two had the wrong nose piece on it, one with a much bigger hole that it should have had. That would let the stem, washer and lock collar get pulled right through. Look at the markings on the rivet heads around the holes on those two, compared to the last pair.

 

[NordicDave]

I'm wondering if the puller used on the first two had the wrong nose piece on it, one with a much bigger hole that it should have had. That would let the stem, washer and lock collar get pulled right through. Look at the markings on the rivet heads around the holes on those two, compared to the last pair.

Good eye Dan. The hardware store riveter has exactly that problem after looking at it again based on your suggestion. The collar is incorrect size.

Here's a couple of pics of the riveter and the packaging for the corresponding Cherry rivet head (click pic to enlarge). The squeezer proved defective and locked itself in the "pulled" position after 6 rivets. Easy to suspect there is a defect which also lead to the rivets pulled slightly shallow?



I've order a replacement riveter and hope it arrives by end of next week.

 

[Dan Thomas]

Pulling shallow is usually a sign that the rivet is too short for the metal thickness.

 

[Bell206]

Easy to suspect there is a defect which also lead to the rivets pulled slightly shallow?

In addition to rivet issues as mentioned above it can also be caused by tool issues especially if the collar is set. Read through all the applicable Cherry references which give somewhat detailed rivet troubleshooting and inspection practices. Those will give you benchmarks to watch out to determine rivet issues. However, hole prep is the first place to ensure a good rivet install. And just because this is a practice session, drill the prep the holes as though the real deal. The Cherry docs also give a good primer on this subject as well.