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CherryMAX stem breaks high or low: causes

What Cherry's CherryMAX process manual (CA-1015) lists for each symptom. Wording and limits are Cherry's.

HighStem breaks high, or does not break

LowStem breaks low

Cherry: a stem higher than the limit is removed and replaced. It is not shaved to meet flushness. Cherry CA-1015 p.13

Grip gauge (269C3): read to the next higher number. On a line, that grip or the next higher. Cherry CA-1015 p.11

CherryMAX stem flushness limits
Rivet dia.A max. (stem high)B max. (stem low)
-4 (1/8").010".015"
-5 (5/32").010".020"
-6 (3/16").010".020"
-8 (1/4").015".025"
CherryMAX stem flushness limits. Cherry CA-1015 p.15

The aircraft's structural repair manual and the manufacturer's installation instructions govern.

Reference only: the controlling drawing, its process spec and the manufacturer's installation instructions govern. How to use these answers

Cherry's wording for each causeCA-1015

Cherry's fixes are quoted as printed in its process manual. A different hole size, rivet diameter or grip on an aircraft is a repair decision for the structural repair manual or the design approval holder, not for this page.

Stem breaks high, or does not break

“PROBLEM: RIVET STEM BREAKS HIGH (OVER “A” MAX) OR FAILS TO BREAK” Cherry CA-1015 p.15

  • Oversized hole. “Rivet installed in an oversized hole.” Cherry CA-1015 p.15 “Double check the hole sizes and use correct drill size for rivet to be installed.” Cherry CA-1015 p.15
  • Sealant on the blind side. “Stem breaks high or pulls through because sealant applied on the blind side decreased friction.” Cherry CA-1015 p.12

Stem breaks low

“PROBLEM: RIVET STEM BREAKS LOW (OVER “B” MAX)” Cherry CA-1015 p.16

  • Undersize hole. “Undersize hole—enlarge the holes to proper size.” Cherry CA-1015 p.16
  • Slanted, misshapen or misaligned hole. “The hole is slanted, misshapen or misaligned—follow carefully the “hole-preparation” techniques given in this manual.” Cherry CA-1015 p.16
  • Rivet too short (wrong grip). “Wrong grip selection (rivet too short). Use a longer grip rivet.” Cherry CA-1015 p.16
  • Joint too soft: structure not clamped. “The joint is too soft—make sure that the structure is securely clamped, enough temporary fasteners are used and, if using sealant, it is applied correctly.” Cherry CA-1015 p.16
  • Tool not in line with the hole. “Tool not coaxial to the hole during installation. Make sure to align the tool and keep arm flexible to avoid side loading the fastener.” Cherry CA-1015 p.16
  • Sealant inside the hole, or too much between the sheets. “Stem breaks low because sealant was applied inside the hole increasing friction or too much sealant was applied in between the structure sheets improperly clamping it, causing the joint to soften significantly.” Cherry CA-1015 p.12

G800 hand riveter: stem will not break

“Problem: The stems will not break to complete the installation” Cherry CA-1015 p.24

  • Jaws need cleaning or replacing. “Check the jaws- replace or clean them as necessary.” Cherry CA-1015 p.24
  • Wrong pulling head or parts. “Make sure that the proper pulling head and optional components are used.” Cherry CA-1015 p.24
  • Low fluid. “Check the fluid level; replenish if low.” Cherry CA-1015 p.24

What to do with the rivet

  • Where sealant was applied incorrectly and the stem broke high, pulled through or broke low, Cherry writes: "In either case, the rivets must be removed and replaced." Cherry CA-1015 p.12
  • “a fastener having a stem protrusion higher than the acceptable limits must be removed and replaced, and not shaved in order to meet the flushness requirements.” Cherry CA-1015 p.13
How the stem limits are measuredA max., B max.
  • “Flushness measurement is done from the top surface of the rivet to the smooth area of the stem around the break (the break-notch).” Cherry CA-1015 p.15
  • “The Locking Collar must be flush or under-flush with the top surface of the rivet head.” Cherry CA-1015 p.15
  • “Collar flash permissible is .005 max.” Cherry CA-1015 p.15
  • The troubleshooting headings tie the letters to the symptoms: high is over A max., low is over B max. Cherry CA-1015 p.15
Reading the grip gauge4 steps
  1. “Place gage into the prepared hole. Make sure the hook end is on the blind side, outside the hole.” Cherry CA-1015 p.11
  2. “Touch blind end. Bring the hook-end close to the edge of the hole (see picture) and pull the gage towards the blind end of the structure until the hook contacts the structure.” Cherry CA-1015 p.11
  3. “Read the grip of the fastener to use. The reading should be done at the visible surface of the structure; if the structure is dimpled or countersunk, measure to the surface of the structure and not to the dimpled/countersunk.” Cherry CA-1015 p.11
  4. “Select the fastener with a grip equal to the next higher number. If the number reading is directly on a line you may use either that grip or the next higher one.” Cherry CA-1015 p.11
  • “it is recommended to measure the structure thickness at the hole-location with the CherryMAX® (269C3) grip gage” Cherry CA-1015 p.11
  • “the in-between gradations represent even grips (2, 4, 6 etc.)” Cherry CA-1015 p.11
  • “Measurement 2 is typical for a flush head fastener. The correct grip is 04 or 05 because the structure aligns exactly with the 4 grip line.” Cherry CA-1015 p.11
  • The stem and rivet materials and the grip range are marked on the head of the fastener and are visible after installation. Cherry CA-1015 p.13

Planning grips for a whole stack? Grip length planner · How grip length works

Hole sizes and drillsnominal and oversize
  • “Use the drill sizes in the table below to produce holes within the required limits.” Cherry CA-1015 p.7
  • Always inspect with a Cherry GO/NO-GO gage to assure drilling accuracy. Cherry CA-1015 p.7
  • “This should be a clearance fit. Do not force the rivet into the hole!” Cherry CA-1015 p.6
Nominal diameter CherryMAX
Rivet diameterDrill sizeHole min.Hole max.
1/8#30.129.132
5/32#20.160.164
3/16#10.192.196
1/4F.256.261
Nominal diameter CherryMAX. Cherry CA-1015 p.7
Oversize diameter CherryMAX
Rivet diameterDrill sizeHole min.Hole max.
1/8#27.143.146
5/32#16.176.180
3/16#5.205.209
1/4I.271.275
Oversize diameter CherryMAX. Cherry CA-1015 p.7
CherryLOCK: the causes are differentCA-1013

Cherry's CherryLOCK process manual (CA-1013) prints its own list. The CherryMAX list above is not Cherry's list for a CherryLOCK rivet.

Cherry's fixes are quoted as printed in its process manual. A different hole size, rivet diameter or grip on an aircraft is a repair decision for the structural repair manual or the design approval holder, not for this page.

Stem pulls through or breaks high

“RIVET STEM PULLS THROUGH OR BREAKS HIGH” Cherry CA-1013 p.25“Rivet stem break notch pulls to .030” or higher above rivet head. Stem may or may not break.” Cherry CA-1013 p.25

  • Pulling head shifts too late. “Pulling head shifts too late–readjust pulling head to shift sooner.” Cherry CA-1013 p.25
  • Oversize hole. “Rivet installed in oversize hole–drill smaller holes or use larger diameter rivet.” Cherry CA-1013 p.25
  • Stack under the rivet's minimum grip. “Rivet installed in under minimum grip–use shorter grip rivet.” Cherry CA-1013 p.25

Stem breaks low, collar not set

“Rivet stem breaks well below rivet head and collar does not set.” Cherry CA-1013 p.25

  • Undersize hole. “Rivet installed in undersize hole–drill out holes to proper size.” Cherry CA-1013 p.25
  • Stack over the rivet's maximum grip. “Rivet installed in over maximum grip–use longer grip rivet.” Cherry CA-1013 p.25
  • Slanted or misaligned holes. “Holes slanted or misaligned–use more care to obtain holes which are properly aligned and normal to the sheets.” Cherry CA-1013 p.25
  • Pulling head cocked. “Installer “cocks” pulling head–use more care to align tool and keep arm flexible to allow rivet to align itself.” Cherry CA-1013 p.25

Stem breaks low, collar set

“Rivet stem breaks below rivet head but collar is set.” Cherry CA-1013 p.25

  • Pulling head shifts too soon. “Pulling head shifts too soon–use 680A159 to verify stroke setting.” Cherry CA-1013 p.25
  • Wrong type of pulling head. “Wrong type head–only Cherry® tools will install CherryLOCK® rivets. Do not use other manufacturer’s tooling.” Cherry CA-1013 p.25

Stem near flush, collar not set

“Rivet stem breaks near flush but collar does not set.” Cherry CA-1013 p.26

  • Stack over the rivet's maximum grip. “Rivet installed in over maximum grip–use longer grip rivet.” Cherry CA-1013 p.26
  • Chips, burrs or dry sealant on the head anvil. “Chips prevent anvil from setting collar–chips, burrs, and dry sealant will build up on head anvil and restrict forward thrust necessary to set collar. Clean thoroughly and readjust.” Cherry CA-1013 p.26
  • Undersize hole. “Rivet installed in undersize hole–drill out hole to proper size.” Cherry CA-1013 p.26
  • Pulling head shifts too soon. “Pulling head shifts too soon–use 680A159 to verify stroke setting.” Cherry CA-1013 p.26
  • “The following problems and solutions apply to both bulbed and CherryLOCK® rivets.” Cherry CA-1013 p.25
  • “Always read to the next higher number (if reading is directly on a line you may use either that grip or the next higher one).” Cherry CA-1013 p.19
  • FAA AC 43.13-1B, of Bulbed Cherrylock rivets: "It is important to select a rivet with a length related to the grip length of the metal being joined." FAA AC 43.13-1B p.4-22
What FAA AC 43.13-1B saysblind rivets in repairs
  • “CAUTION: For metal repairs to the airframe, the use of blind rivets must be specifically authorized by the airframe manufacturer or approved by a representative of the FAA.” FAA AC 43.13-1B p.4-19

Related: CherryMAX tooling, gauges and removal · CherryMAX family · Low clearance puller finder

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Sources

3
  1. Cherry CA-1015 (CherryMAX process manual)
  2. Cherry CA-1013 (CherryLOCK process manual)
  3. FAA AC 43.13-1B