Inspected Screws 3

[drawoh]

This question has been asked here before, almost certainly by me at point in time. I am asking it somewhat differently this time.

Is there a grade or class of metric fastener that comes with batch numbers and/or inspection reports and/or some other form of traceablilty, suitable for mounting in an aircraft? Another option would be UNC screws of some size. Most aircraft screws are UNF or UNJF.

My actual problem is that I am trying to find anti-vibration mounts that will be delivered in six weeks or less. Someone is searching a warehouse, and I am probably going to have to use whatever screw thread is available.

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JHG

 

[VEBill]

'Certificates of Conformance' are typically what's required to get them in the building and past QA RI. I'm not sure if such fasteners are tracked by batch after that - kept in bags with the PN and batch, or dumped into a bin with the others of the same PN.

 

[israelkk]

Try SPS

 

[Sparweb]

Maybe:

http://www.reidproducts.com/index.php?page=na

STF

 

[tbuelna]

There are "NA" spec bolts/screws that have metric MJ type threads suitable for aircraft applications.

As israelkk noted there are also a few commercial aerospace metric thread bolts/screws listed on the SPS website.

 

[drawoh]

israelkk,

I can see stuff in the SPS catalogue that should work. It turns out that my anti-vibration mounts are available from stock with 1/4-20UNC threads. My other option is to drill and tap out the mounts so that I can use an AN bolt.

--
JHG

 

[tbuelna]

The traceability requirement for aircraft fasteners depends on the particular application. As a minimum, the SPS website states their aircraft fasteners are traceable by lot number. But only a few common aircraft fasteners are maintained in inventory by manufacturers/suppliers. If you cannot find a supplier that has a quantity of the particular fastener you require, there is no way you will get it custom ordered from a manufacturer in six weeks time. In fact you'd be lucky to get a custom order delivered in 18 months.

The other option, as you noted, would be to create an "altered item" part number from an existing fastener that has the proper level of traceability and quality control for the application. This is commonly done in the aircraft industry. But you would need to create engineering documentation that defines requirements for procuring the existing part, modifying the part, QA of the modified part, and controlling usage of the modified part.

 

[drawoh]

tbuelna,

The altered item is starting to look attractive. SPS has a traceable, high strength stainless steel cap screw which would suit my purposes if I were the only one doing the ordering. I have a limited ability to prevent someone from using a regular 18-8 stainless steel screw.

The altered item would be the anti-vibration mount. The supplier warned me that modification would void any warranties, but I did not know these things had warranties. If I use 3/8-24UNF, the easiest bolt to find would be the AN6 bolt I would prefer they used.

--
JHG

 

[PBPouw]

I am very surprised to see that you are very concerned about using a Aerospace grade type bolt but the thing you are
bolting down, the vibration mount is of no concern an can be modified without the manufactures approval.
If the vibration mount has metrical screw threads I would guess that this is a commercial vibration mount without any failsafe feature.

 

[drawoh]

PBPouw,

I am using a cup type mount from Shock Tech. Various tapped holes are available if I am willing to wait for them.

I would not call these fail safe. They are all metal, which the aircraft people prefer over rubber.

--
JHG

 

[tbuelna]

drawoh-

One purpose of an altered item drawing is to control the source of the part being modified, which in this case is the fastener. All you need to do is add a table listing the approved source(s) of supply for the part and the supplier part number. You can also add a drawing note describing any traceability requirements at procurement, manufacturing, inventory, and throughout its service life.

 

[drawoh]

Just in case anyone is curious, I called our local rep and got a quote for high strength stainless hex socket head steel cap screws from SPS. They quoted about $70 Canadian per hundred, and 19-20 weeks delivery.


--
JHG

 

[tbuelna]

drawoh- To be honest, that price and lead time you got from SPS seems pretty good. Normally a major supplier like SPS wouldn't even bother to quote a job unless it came from a big OEM. SPS's production capacity is prioritized for US defense needs. You'd typically expect a lead time of 18 months or more for this type of order.

 

[drawoh]

tbuelna,

I figure that, but we cannot manage 19-20 week deliveries, much less 18[ ]months. The price was extremely reasonable. If they hand stocked that stuff and charged $200, I might have gone for it. The stuff we build does not go on the shelves at Walmart.

--
JHG

 

[tbuelna]

drawoh- If you need a modest quantity of a specific 3/8-24 UNJF SHCS made from high strength CRES that is not available from stock, or as a special order from a large supplier (like SPS) within the time frame you require, you might consider producing them yourself using local vendors. You can purchase heat treated CRES bar stock with the required certs. Have the blanks produced by a vendor using a swiss machine. Have the hex socket added by a vendor with a rotary broach machine. Have the threads formed by a vendor with thread rolling equipment. Then have the part passivated and dye-pen inspected by a qualified vendor before delivery.

You will need to produce your own engineering documentation for the fastener, and you will need to collect and maintain all of the documentation required for traceability of these fasteners. But you should be able to get the exact custom fasteners you require within just a couple weeks. And at a cost that should be reasonable.