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No thread relief callout

Azoth

Aluminum
Joined
May 10, 2019
Location
Houston, TX
I have a drawing that calls for 1 5/16-18 UNEF-2B in an inconel bar with an id of 1.2475±.0025. Thread minor is 1.252-1.265 so a topping insert will run into the bore as there is no thread relief depicted/specified on the drawing.
Since the print also specifies in the title block "Thread entry and exit angles must be 25°-45° from thread axis" I figured I'd simply use a single point threader with G76 for the "Thread Chamfer" (pullout angle, which I've read is set by parameter but still need to look into that).

The shop already has full profile laydown inserts 16IR-18, so the boss said to make a thread relief so we can run them.

My concern is that the bar is somewhat thin-walled as it is, and worse there's a groove on the OD right where the internal threads end. I suggested a compromise, that I make a "minor diameter relief" (1.265) instead of a full thread depth relief (1.3125) just so the tool shoulder clears but that didn't fly.

It's a one-off part so I'd prefer it not be scrapped over a decision like this. It's my first week here so I've got to let the boss be the boss, but I was wondering what standard practice is when a thread relief isn't depicted. Can the manufacturer just take it upon themselves to add one if they choose?
 
Does the drawing show a thread relief? If not, you better pull out of the thread when get to the length needed. Don't ring it! or I'll scrap the part.
 
Since the print also specifies in the title block "Thread entry and exit angles must be 25°-45° from thread axis" I figured I'd simply use a single point threader with G76 for the "Thread Chamfer" (pullout angle, which I've read is set by parameter but still need to look into that).
I've never seen a callout like that, but, if you want to play by those rules, then I'd do a straight pull out with 0 chamfer-out ( Pnn00nn on the first G76 line ).
They've specified the pullout angle between 25 and 45 degrees, then the 60 degree thread angle will give you 30 deg/side, so you're gold.

I have a drawing that calls for 1 5/16-18 UNEF-2B in an inconel bar with an id of 1.2475±.0025. Thread minor is 1.252-1.265 so a topping insert will run into the bore as there is no thread relief depicted/specified on the drawing.

That thread callout is wrong!
It should read 1 5/16-18-UNS with the non standard dimension of the minor shown.
Also, you may want to draw that thread in CAD as the minor being that low ( .011 below mean ) may not produce a pitch diameter to be within 1.2764 - 1.2828

Other than that, your boss's suggestion of using a larger pitch insert is the way to go.
 
Does the drawing show a thread relief? If not, you better pull out of the thread when get to the length needed. Don't ring it! or I'll scrap the part.
It does not. That's my thoughts exactly. If I can get a copy of the parameter/programming books to verify the thread pullout angle (if the shop has them).
I've never seen a callout like that, but, if you want to play by those rules, then I'd do a straight pull out with 0 chamfer-out ( Pnn00nn on the first G76 line ).
They've specified the pullout angle between 25 and 45 degrees, then the 60 degree thread angle will give you 30 deg/side, so you're gold.



That thread callout is wrong!
It should read 1 5/16-18-UNS with the non standard dimension of the minor shown.
Also, you may want to draw that thread in CAD as the minor being that low ( .011 below mean ) may not produce a pitch diameter to be within 1.2764 - 1.2828

Other than that, your boss's suggestion of using a larger pitch insert is the way to go.
Idk it pulls up in gagemaker thread disk just fine whether UNEF or not. The 1.247 ID deeper in the bore AFTER the threaded portion IS low. I'll be boring the threaded section minor dia on size.

"Pnn00nn on the first G76 line"
I don't know about that, I may as well do longhand thread cycle if the thread chamfer is zero. Then if the retract is too slow, it will cut a groove and I'm trying to have the thread taper out instead of turn into a straight groove. I'm still not sure on the details of G76 because there's a lot of conflicting comments on the internet. I need to get on a machine and log the readout as the thread cycle runs.

P [number of Spring Passes 00-99] [Thread Chamfer/Pullout/Runoff Distance in Z specified 00-99 as tenths of a lead] [Infeed angle/ Insert Angle 0, 29, 30, 55, 60 80]
The 3rd one is where I'm confused as to how the machine will move because if 29 is standard practice on a manual (AKA Modified Flank Infeed), then 30 would be Flank Infeed, so what would 60 do? And I'll assume 0 is for Radial Infeed.

And that insert is the same pitch (16IR-18 is 16mm triangle edge length aka 3/8 inscribed circle. Still 18 pitch, only it has that leading shoulder that will hit the smaller bore after the thread whereas a single point threader would not.)
 
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Idk it pulls up in gagemaker thread disk just fine whether UNEF or not. The 1.247 ID deeper in the bore AFTER the threaded portion IS low. I'll be boring the threaded section minor dia on size.
I misunderstood your first post then.
I thought the entire ID was to be 1.247 and then threaded.
In that case you shouldn't have any issues, just program the thread as normal.

"Pnn00nn on the first G76 line"
I don't know about that, I may as well do longhand thread cycle if the thread chamfer is zero. Then if the retract is too slow, it will cut a groove and I'm trying to have the thread taper out instead of turn into a straight groove. I'm still not sure on the details of G76 because there's a lot of conflicting comments on the internet. I need to get on a machine and log the readout as the thread cycle runs.

Yupp, Pnn00nn will RAPID the insert out of the thread. You will not have a groove, you will have a partial, incomplete thread.
The slower the RPM you thread with, the smaller the incomplete thread will be.
If you don't want to violate the bore below the thread, that is how you want to program it, and you can even use the full profile 18 pitch insert.
The leading shoulder on the full profile insert is absolutely negligible. It is the trailing shoulder is what does the actual topping, so no worries there to violate the bore.
 
We always told the shop to pull out in 1 to 2 revolutions of the spindle.

Typically:
1: Thread as close as possible to a shoulder and no thread relief = no chamfer out of thread
2: Thread to a shoulder with a thread relief means thread must be full to allow passage up-to the shoulder = no chamfer out of thread
3: Thread to min depth but allow for extension of min bore/max OD = chamfer out of thread @ 45 deg. sometime after min. thd. depth is achieved.
4: Thread to between min and max depth = thread to whatever depth that meets the min/max callout using either chamfer or no chamfer out of thread.

Sounds like the OP is looking for #1.
Minuscule shoulder as it may be, but shoulder nonetheless.
 
Hi All:
Am I alone in thinking this situation just screams out for threadmilling this thread.
I can make a thread termination that's within a few thou of the shoulder and it's a clean termination that's the same radius as the cutter and doesn't put the point of the tool at risk.
Single point threading something tough like Inconel, I'd be worrying about the point of the tool if I don't have a nice gentle pullout or a thread relief groove

Of course I need a live tooled lathe to do it, so maybe it's a non-starter for the OP...but if I do have a live tooled lathe that's what I would do or at least broach the option to the engineer who designed the part.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 








 
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