Adding threads to an existing bolts grip length

[danielcompton]

Will cutting more threads to an existing grip length of an AN6-54 bolt comprimise it's strength?

 

[Kwan]

I'm guessing that AN6 has rolled threads as opposed to cut treads. If this is the case you will impact the fatigue life.

If the bolt is used in tension and the newly cut treads reduce the minimum area of the bolt (minor thread diameter) then the bolt strength will be compromised.

I would also worry about the finish on the bolt. The best bet in my opinion is to order a bolt with the proper grip. Another alternative would be to install a thicker or additional washer (if you are trying to adjust the bolt due to stackup thickness).

Good Luck!

 

[Fabrico]

Any bolt of any quality has rolled threads. It's time to get the right bolt. If you absolutely must use that bolt (which is very unlikely) there are places that can roll more threads onto it.

 

[Rob130]

I have seen dies that are UNJF thread. The J meaning the rolled thread, UNF is a cut thread.

My advice is never use a UNF die to cut threads in UNJF hardware.

 

[FieldTeam]

Everything I have ever read concerning bolt installation states that you should use the correct size grip length. Washers or shims can be used if the grip is slightly longer than the material thickness.
The key words are use the correct size grip length. Nothing says you can cut threads to make up for excessive grip. I would think this would become a special purpose bolt and would be marked as such. That would be pretty rare.
We use NAS1108-60D bolts where the heads have been trimmed for the 707 spoiler mounts and special cad plating was required after bolt modification and new part numbers assigned to the hardware. This would be an example of a standard bolt being modified for a certain application. Why cut threads when you could get a correctly gripped bolt right off the shelf?

 

[wes616]

a -54 bolt ... Are they like $25/unit and your management wants you to monkey them to work instead of buying the -53 or is purchasing only able to find the -54?

 

[Kwan]

So the solution is to educate management. Or fun fatigue damage tolerance analysis which would require the replacement of the bolt every 200 hours.

Saving $25/bolt is the easy cheap way out and will likely cost much more in the long run.

 

[FieldTeam]

A quick search on ILS shows plenty of -50 thru -53 grip AN6 bolts out in the world.

 

[plasgears]

During a stint as a part-time engineer at a sister company making armored cars, I had the following embarrassment. We delivered a full armor version of a large car (foreign country not mentioned). After armoring the floor, one "resourceful" shop guy welded an extension to the seat belt bolt, a grade 8 HT bolt. The customer tore down the vehicle as part of an instructional process and discovered the faux pas. It was very embarrassing. Word got around the industry. We could have ordered a longer bolt within one day; what was he thinking?