NAS1351 screw type with double hex or similar
2

Question

NAS1351 screw type with double hex or similar

conrad1 (Aerospace)

(OP)

20 Sep 18 11:31

Gents,

I´m looking for a screw similar to the NAS1351 screw but with another head drive. Obviously, the internal hex at the NAS1351 does only give accessibility every 60 degree. Is there a screw/ head type which provides a better accesibility?
I found a German LN29949 aerospace screw (socket head cap screw) which seems to have a double hex. But the thread is a metric one. I´m looking for a UNJF thread.

Thanks in advance!

conrad

Sparweb (Aerospace) · Answer 1 · 2018-09-21 01:32:45

If 60 degrees per wrench flat is not enough, would a 12-point external wrenching head do?
NAS624/634/644

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

conrad1 (Aerospace) · Answer 2 · 2018-09-21 04:39:37

Basically yes. The flange diameter of these bolts is negligilby smaller than the head diameter of a NAS1351 screw. But they cost 3 times more and if the socket is attached, they need even more space in diameter.
For me it seems that I did not find the correct search term so far. I was looking for "12 point internal" or "double hex internal", but unsuccessful.

3DDave (Aerospace) · Answer 3 · 2018-09-21 09:58:58

I think the answer most people use is a ratchet driver or one that is electrically or pneumatically continuously driven. I suppose one could take a pair of hex keys and give one a 30 degree twist and alternate.

There must be some other limitation in your application that is not being included in the problem statement.

I do see some metric versions, but not English https://www.fastenerdata.co.uk/fasteners/screws/mo... but they are not double-hex; they are 12 point splines.

edmeister (Aeronautics) · Answer 4 · 2018-09-21 13:24:54

If limitation is the amount of head rotation - is there modification possibility of installing bolt thru the support structure & using a nut on the other side; thus only require to hold the head from rotating while nut is tightened.
- Problem with exotic fasteners is that should replacement ever be required - the entire 'usefulness' of the assembly is now reduced - ie: waiting trying for find the replacement part. "A structure is only as strong as its weakest link." Or as happens daily: Expedited shipping charges of $$hundreds to receive a $5 fastener (or some situations where a minimum order of 100 units is required).

conrad1 (Aerospace) · Answer 5 · 2018-09-27 17:33:47

A nut is not possible. The parts are screwed into an aluminium baseplate. I have a strong limitation in accessibility. That means that I can not simply use a extension to apply a ratched or something else. I need to tighten the screws/ bolts with a torque wrench. The standard ratched head/ ratched adapter is too big so I must use these special adapters with a rectangular cross section as the interface. If you use this combination, you can only tighten the screw if you engage and disengage the head.

rb1957 (Aerospace) · Answer 6 · 2018-09-27 17:47:52

How much space is available ?

How much torque ? If not much torque, then could a flex drive work ?? You've got at least the minimum access to work with ... space to put an arm close to the head, space to hold the head of the screw ?

Can you use an Allen key ? You could make allen keys with the key oriented differently on the shaft. yes, a bugger to work with.

Why did you design get painted into such a corner ??

Are you using heli-coils in the base plate ?

I think we need a picture (or several !)

another day in paradise, or is paradise one day closer ?

WKTaylor (Aeronautics) · Answer 7 · 2018-09-27 18:06:03

NO magic parts to fit You needs, as-far-as-I-can-see...

Problem as I see it is that NAS1351 [type] is a cap-bolt which by definition has very long threads relative to unthreaded shank... hence places this part in a unique usage situation.

1. Following 2-bolts [specs] are somewhat similar to NAS1351

MS20073 BOLT, MACHINE, AIRCRAFT, DRILLED HEAD, FINE THREAD [hex-head]
It might be feasible to machine-down the head to attain a significantly 'lower profile'; and then machine a smaller 12-point wrenching-profile to 'what-remains-of-the-head'

MS21098 BOLT, SELF-LOCKING, STEEL, 160 KSI Ftu, 250 °F, 12 POINT, EXTERNAL WRENCHING (EXTERNALLY WRENCHING CAP SCREWS)
It MIGHT be feasible to machine-down the head to attain a significantly 'lower profile' for a 12-point drive ratchet-wrench

In both cases, machining grinding must be done carefully to avoid temper embrittlement [abusive friction heating]; and attain a high quality profile/surface finish.

Magnetic particle NDI required to detect defects from machining.

Brush cadmium plating [low embrittlement solutions] is necessary to protect bare metal.

Etc...

2. It might also be feasible to have a 12-point shear-tension head bolt altered by machining head-down and warm roll-form threading new threads length required to match NAS1351 threads. In this case would be best to make new part from A286 or Inconel bolt... since these alloys are more 'abuse tolerant'.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

conrad1 (Aerospace) · Answer 8 · 2018-10-08 07:00:16

@rb1957: I sorry but I can not make any pictures of the situation. The torque is low enough to work with a flex drive, but that would mean that i have to bend the flex drive about 90 degree. That would have a significant influence in torque. Yes, I use self locking thread inserts.

@WKTaylor: The MS20073 bolt is with an outer hex head. Therefore the diameter is too large especially if the nut is attached. The MS21098 bolt starts with 0,25" thread diameter. The smallest size I need is 0,138" UNJF.

The NAS1351 is absolutely fine except the head drive. The head drive shall look like that: https://www.fastenerdata.co.uk/fasteners/screws/mo...

3DDave (Aerospace) · Answer 9 · 2018-10-08 09:51:32

I'd be looking at sinking a hex recess in the threaded end and accessing it from the plate side, but I'm sure that the holes are all blind, so that's not a possibility.

Redesign cost to put the fasteners somewhere accessible is going to be quite a bit, or just bite the bullet and have a set of sequential wrenches, which is also going to cost a lot.

WKTaylor (Aeronautics) · Answer 10 · 2018-10-08 17:52:53

What about...??

NAS5311 SCREW, FLAT FILLISTER HEAD, FULL THREAD, SELF-LOCKING OR NON-LOCKING, NAS1800 SIX LOBE RECESS

NAS5313 SCREW, SHEAR, FLAT FILLISTER HEAD, CLOSE TOLERANCE, SHORT THREAD, NAS1800 SIX LOBE RECESS, 95 KSI FSU

NAS5317 SCREW, PAN HEAD, FULL THREAD, SELF-LOCKING AND NON-LOCKING, NAS1800 SIX LOBE RECESS

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

WKTaylor (Aeronautics) · Answer 11 · 2018-10-09 14:35:01

Disregard reference to NAS5313... was a long day... fuzzy brain.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

rb1957 (Aerospace) · Answer 12 · 2018-10-09 14:53:33

It's hard to see the fundamental difference you get with a 12pt drive compared to a 6pt hex-drive.

if that's what you need then I'd suggest making your own bolts (since you've exhausted your options).

another day in paradise, or is paradise one day closer ?

edmeister (Aeronautics) · Answer 13 · 2018-10-09 15:12:51

I also agree with rb1957.
I pity the mechanic that has to R&R this item. Ive been involved in numerous situations where the mechanic has to perform some 'miraculous' feat because the installation was rectified by some 'quick fix'. A picture of this situation would help all of us better identify the situation. Does the component have to be positioned in the exact location? Can we mfr a secondary flange - component screwed to secondary flange & secondary flange screwed to main flange - whereupon bolt pattern relocated WRT accessibility. Thus component can be attached to secondary flange outside of installation area?

conrad1 (Aerospace) · Answer 14 · 2018-10-16 10:02:21

The assembly situation is most likely to compare with a long rectangular steel tube. The tube has a through hole and shall get tightened against any other part. The other part has an internal thread for the screw. The through hole is as close to the open end of the tube that there is a clash between the wrench/ key and the tube walls if there is only a reattachment every 60 degree. The tube height is as flat that it doesn´t allow a ratched head and nut.
That´s only a theoretical model to describe the situation.

Sparweb (Aerospace) · Answer 15 · 2018-10-16 19:05:27

Would a box-end ratcheting wrench like this help?

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

Tmoose (Mechanical) · Answer 16 · 2018-10-17 16:28:32

https://images-na.ssl-images-amazon.com/images/G/0...

https://www.jjcraceandrally.com/oncirrus/system/tr...

I think the Ruskies must have hacked into your CAD server and created this NOT DFA/DFM detail.

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NAS1351 screw type with double hex or similar
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