Does anyone know where I can find some high-strength quick disconnect/quarter turn captive fasteners? I've looked into CAMLOC/RAM fasteners and have not found anything that will work. The standard Camloc series are not strong enough (looking for something with allowables similar to an NAS1993 or other 10/32 screw) for the application, and the heavy duty series tend to be too large of a diameter to function in this application (must be .250 dia or less). The fasteners must be approved for aerospace applications, and something maintenance friendly and easy to find (for replacement parts) is preffered. I've nearly exhausted all of my resources so any information/help is appreciated.
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Quarter turn/Quick Disconnect Fasteners
- Thread starter jbennett
- Start date
- Thread starter
- #4
I've already checked both places for something that will work, and have come up empty handed. Everything they have that has allowables that are high enough has too large of a diameter to be used in my application. I need something that has a tensile allowable of 2.5kips or more, and a shear allowable of 1.1kips or more, but is a diameter no larger than .25, prefferably a .194 dia. But thanks for the info.
btrueblood
Mechanical
jbennett, are you saying the shank dia. can be no more than .25" or the head no larger than .25"? Does it need to be corrosion-resisting or not?
- Thread starter
- #7
btrueblood,
The shank dia can be no more than .250, though .190 is definitely preferable. We've speced out a captive screw which does the job, but is not very maintenance friendly. That's why I need a 1/4 turn instead, as this is the main avionics bay door, so it's open basically any time the plane is on the ground for one thing or another.
The shank dia can be no more than .250, though .190 is definitely preferable. We've speced out a captive screw which does the job, but is not very maintenance friendly. That's why I need a 1/4 turn instead, as this is the main avionics bay door, so it's open basically any time the plane is on the ground for one thing or another.
- Thread starter
- #8
jbennet,
As far as I know, all quarter turn fasteners work the same way. You turn the fastener, and it engages and compresses a spring. The clamping forces are inherently low. The engineering of tiny, high force springs is difficult, especially if the assembly must survive repeated engagements. The stud is engaged by a receptacle, which is usually a subassembly of some sort, that allows a lot of room for the stud to move around.
None of this says "high clamping force" to me. If the stud is will constrained, you may get a high shear force out of it.
Low clamping force is an inherent disadvange of quarter turn fasteners. Would a lot of quarter turn fasteners be less inconvenient than a few captive screws?
JHG
As far as I know, all quarter turn fasteners work the same way. You turn the fastener, and it engages and compresses a spring. The clamping forces are inherently low. The engineering of tiny, high force springs is difficult, especially if the assembly must survive repeated engagements. The stud is engaged by a receptacle, which is usually a subassembly of some sort, that allows a lot of room for the stud to move around.
None of this says "high clamping force" to me. If the stud is will constrained, you may get a high shear force out of it.
Low clamping force is an inherent disadvange of quarter turn fasteners. Would a lot of quarter turn fasteners be less inconvenient than a few captive screws?
JHG
btrueblood
Mechanical
Jbennet,
Well, drawoh pretty much tells it like it is. At .250 diameter, you might be able to "custom make" a fastener in a high-tensile or hardenable steel; 2.5 kips in a .194 fastener is starting to push the limits of the ordinary steels in even a captive configuration, much less the details required for 1/4 turn.
Well, drawoh pretty much tells it like it is. At .250 diameter, you might be able to "custom make" a fastener in a high-tensile or hardenable steel; 2.5 kips in a .194 fastener is starting to push the limits of the ordinary steels in even a captive configuration, much less the details required for 1/4 turn.
- Thread starter
- #11
That's what my mentality was as well, and I've tried to pass that on to the powers that be, but they are still pushing for the quarter turns. I already have captive screws installed, I think the biggest heartburn is coming from the time it takes to take the door down now (removing 17 captive fasteners as opposed to the old system which was two snap latches). Thanks for the information.
You could try one of the Tridair products. They make some small fasteners for structural panels.
- Thread starter
- #13
btrueblood
Mechanical
jbennett,
Just curious, but any idea why the design went away from snap latches to captive fasteners? Latches do seem more maintenance-friendly, but maybe they were an aero drag penalty?
Just curious, but any idea why the design went away from snap latches to captive fasteners? Latches do seem more maintenance-friendly, but maybe they were an aero drag penalty?
- Thread starter
- #16
The design went away from snap latches because after the modification we did, the latches were not anywhere near strong enough to handle the worst case loads that could be applied to the door; ie we went to captive fasteners. No there was no drag penalty as the original latches were indeed flush-mounted. I can't go into detail about the installation, but it was extensive enough that we had to manufacture a new door. The original composite door was not sturdy enough to handle the loading, we had to make an aluminum door.
This outfit just help out an acquaintance with an odd fastener requirement.
jbennet,
Something just occurred to me.
If your boss is absolutely determied to have a quarter turn fastener, you can design a high-strength one.
1. Your stud slides into a long, accurate hole in your recptacle, such that it has high strength in shear.
2. For each position to be secured, use two fasteners, rotated ninety degrees apart. Perhaps you can design the receptacle with both positions.
For this arrangement to fail, at least one of the fasteners must shear. Use high strength materials. Get an aerospace PEng to sign off on the design.
Nothing is impossible if you are willing to pay for it!
JHG
Something just occurred to me.
If your boss is absolutely determied to have a quarter turn fastener, you can design a high-strength one.
1. Your stud slides into a long, accurate hole in your recptacle, such that it has high strength in shear.
2. For each position to be secured, use two fasteners, rotated ninety degrees apart. Perhaps you can design the receptacle with both positions.
For this arrangement to fail, at least one of the fasteners must shear. Use high strength materials. Get an aerospace PEng to sign off on the design.
Nothing is impossible if you are willing to pay for it!
JHG
- Thread starter
- #19
Thanks for the input, but they want something that is pre-manufactured and easily obtainable for replacement. It is an item which is prone to need replacement due to the frequency of access to the area. Total design from scratch is not an option.
James Bennetts
Aerospace Engineer
James Bennetts
Aerospace Engineer
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