Using V notched tensile grips to recover poorly threaded tensile specimens

[DuncanGibbons]

Hi all,

We recently had some ASTM E8 number 3 specimens machined and threaded, a handful of the specimen's threads wouldn't turn into the threaded grips.
Is it possible to test these with V notch wedge grips and if so can/should some of the threaded material be machined away to reduce the risk of slippage (say 0.5mm off the ends)?

If this isn't advisable are there any ways to recover these specimens and still get valid data from them?

Many thanks,
Duncan

 

Whatever grabs the ends is OK, so long as it doesn't impose significant bending load on the coupon.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

What is wrong with the threads? Not enough engagement?
I don't see why you couldn't just use V grips.
Just remember that many threaded grips are self aligning and V grips are not, and there may be a bit of slippage in V grips.

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P.E. Metallurgy, consulting work welcomed

 

[Tmoose]

I'd try to figure out what is wrong with the no-go threads.

We are dealing with a knotty UNC thread pitch errors on a project at work right now.
We never had problems like this before.
In the 2nd or 3rd language inspection report there is a picture in which the Supplier's agent is brandishing a caliper set to 1.000" laid along side the threads of the bolt under test.
The report text says "There should be about 6 threads per 1", which shows about 6 threads as shown in the attached product photo."

They weren't fibbin' when they said "about 6 threads per 1 inch " . Real pitch measurement indicate there are more like 6.1 TPI.

 

[DuncanGibbons]

Thanks all for the info.

I haven't received the specimens back yet, they are still sitting at the testing facility. I will inspect them when I received them.

Hopefully, they can be rethreaded or I will just pull them with V grips.