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Aluminum threads compressed

CallMeShirley

Plastic
Joined
Apr 29, 2020
Hi everyone,

We machine tensile bars out of precut Aluminum stock on a Mazak QT250. I machine the first thread and profile/gage section first then flip the part. However the problem that has arisen is once I flip the part to cut the threads, the chuck jaws crush /compress the first threads that I have made. i tried turning down the pressure of the jaws but if I get too low, the tool starts moving the part inside ever so slowly. Current jaws are the standard stainless.

Any advice on which jaws to use, another method of clamping the parts or any other ideas?
 
Can you start with a longer blank, and do all the cuts in one chucking, including threading both ends? Then just part off from the blank.

If you're using an Instron or similar, you'll be better off doing it this way as the two threaded ends will be on axis. Even small errors on thread alignment will start to bend the gage section, throwing off your test results. Granted, not much, but it's best to avoid these errors if possible.
 
all great advice, all ready given
my two cents, why not bar feed if hole thru head will allow it.
3-6 foot length bars, turn and thread, and part off, use a bar puller, and a stop for the correct length.
 
I have a ER-16 collet holder with a straight shank. I’ve chucked that and use a collet to hold on the threads. This was on a stubby M6 threaded part.
PITA but it worked.
 
Is there a reason you can relieve the back of the jaws and chuck on the smooth center part of the tensile bar? Or is your part not what I am envisioning?
 

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Unfortunately we receive them precut from the customer so I have to flip the part.
ok can you add an operation at the last. locate between centers and drive with a dog and thread one side and flip
locate between centers and dog and thread. simple.
any aerospace parts I try to thread ad the end even after heat treat to prevent threads from being damaged.
ask the customer for bar next time, simple request.
 
If they're doing a proper job, it's not a good idea to clamp on the gage diameter, you'll inevitably do some damage to the surface, compromising the value of the part. Go with soft jaws that are threaded to accept the first threaded end of the sample part. Do make sure the chuck is in good shape so that the three threaded jaw sections maintain proper registration.
 
I assume that because the parts are "pre cut, by the customer"...that using a bar isn't part of the conversation.

I also assume that because it's pre cut, it isn't bar. It's probably a larger diameter Thread. But shit, assumption is the mother of all fuck ups.

R
 
This is a wild guess but I'm gonna assume the customer is cutting 1 or 2 samples off each bar for testing so making them all from one bar would defeat the purpose.
what I use to do if it was a repeating job, and it was a solid LTA I would throw extras in stock, and pull them and ship them when needed, and here is why
we all know a 10 lot is cheaper than a 2 pc lot.
but sell them at the cost of a 2 pc lot, economics.
better profit, we are here to make money, and the loved it, because they got parts in a timely manner
just saying
 








 
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