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Internal Threading in Chrome Moly presenting challenges. Any suggestions?

SmlG54

Aluminum
Joined
Apr 5, 2018
Hey all,

Cant figure out a chatter issue and trying to get some help or even pointed in right direction for informational reference.


Our Machine: Multus U3000 Mill turn using Capto tooling.

Part: M64x6 internal thread. Oal length of 4.5" or so

Setup: Part held in bored jaws at about 3" deep. 1" steel internal laydown bar with minimum stickout held in Big Kaiser 3 set-screw bar holder.
Threads 3" deep.

Material: Some unusual X12CrMo (i believe) with Brinell hardness around 300. Does not like to break into chips.

Cut parameters: 325 sfm (around 500 rpm). Min DOC at .004 per side with starting D at .02".


Attempts tried to far: have went as low as 280rpm or 190sfm (seems to like higher rpm). Also tried Variable Spindle Speed Threading as a function of
machine. I've stayed away from a smaller min doc but maybe I should try that. Wanted to really "cut" this chip as opposed to rubbing.





Anyone see anything terribly off or have any input?




Thanks,
SML
 
My cheat sheet for just basic steel shows a .030 start depth for 6mm, so you're not "really gett'n after it".
You may want to try stepping up your DOC, but it could be an issue if you have a very sharp insert.

I doubt that any of this will effect chatter tho.
For chatter issues while chucked up tight, there have been many that have had good luck by loosening all but one set screw.
Likely keeping the set screw closest to the work tight, allowing the other end of the bar to counter act the mechanical resonance?

(right click and "open in new tab to see full pic - for whatever reason)

KennaThreadingChartCat1010pg683.jpg





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Mechanical Resonance
Ox
 
4.5"+ stickout for a 1" diameter bar seems like a heck of a lot to be asking of a steel bar, especially when cutting such a coarse thread and having so much engagement of the tool. Do you have a larger diameter bar that you can try? Or a carbide bar?

What is your infeed angle for this thread? Are you cutting with just one side of the insert or both?
 
You're probably going to continue to struggle with that as long as you're using a bar in a holder.

Get a Capto integrated 266 threading bar from Sandvik, or a C6 SL40 bar with a 266 head. I cut heavy threads in difficult materials in our NTX with no issue, as long as I'm using those tools.
 
4.5"+ stickout for a 1" diameter bar seems like a heck of a lot to be asking of a steel bar, especially when cutting such a coarse thread and having so much engagement of the tool. Do you have a larger diameter bar that you can try? Or a carbide bar?

What is your infeed angle for this thread? Are you cutting with just one side of the insert or both?


Yeah, maybe so?

When I first read, I thought that his part was 4.5", but that he was only threading 3" deep.
But yeah - if he is sticking out <5" with a 1" bar running a .25" wide profile, that's not likely going to ever go well.

There is plenty of room for a 1.5" bar in there, and that will be over 2wiced as much meat.
And actually, for whatever reason - 1.75" bars seem to be plentifull, if your machine will go that big?
IDK why, but I seem to have oodles of them here. (came with machines)
1.75 bar is actually 3 times the bar of your 1".


--------------

Think Snow Eh!
Ox
 
You were correct Ox on your initial assumption of threading 3" deep in Z.

I tried to be clear with setup info but I see that I could have done better.

Bar is at 3:1 ratio.
Infeed angle at 58deg with alternating flank infeed pattern


I was able to get good threads, probably out of luck but what I did was:

-Implemented Variable Speed function of machine (allowed RPMs to vary between 450-550
-used 'insert stone' on fresh insert (not sure of name)
-reduced minimum depth of cut value to .003" per side (initial was .004-.006 testing conditions)
-A lathe guy did come over and loosen a set screw
- pressed green and got lucky i think.

Gonna look into those integrated sandvik bar along with other suggestions.

We are just starting to tool this machine up for more lathe work so low on options right now.

Looking into purchasing a 1.25" modular carbide bar and head setup.

Thanks for all feed back and help.

SML
 
You were correct Ox on your initial assumption of threading 3" deep in Z.

I tried to be clear with setup info but I see that I could have done better.

Bar is at 3:1 ratio.
Infeed angle at 58deg with alternating flank infeed pattern


I was able to get good threads, probably out of luck but what I did was:

-Implemented Variable Speed function of machine (allowed RPMs to vary between 450-550
-used 'insert stone' on fresh insert (not sure of name)
-reduced minimum depth of cut value to .003" per side (initial was .004-.006 testing conditions)
-A lathe guy did come over and loosen a set screw
- pressed green and got lucky i think.

Gonna look into those integrated sandvik bar along with other suggestions.

We are just starting to tool this machine up for more lathe work so low on options right now.

Looking into purchasing a 1.25" modular carbide bar and head setup.

Thanks for all feed back and help.

SML

Glad you got it worked out, don't think you got lucky as every single one of those are valid steps when troubleshooting thread chatter.

I will stick with my recommendation for integrated or SL bars from Sandvik though, as you simply don't have to do any messing around to get good results.

I tend to avoid boring bars in holders altogether, not only on the mill turn, but on all our lathes. I do have a few bars in holders of course, but I use capto bars almost exclusively.
 
Very good info. I didn't like the whole concept of bar in holder on multi-task machine. My initial preference was capto bars.
Your input solidifies that thought and I will try to steer the company in that direction. Many thanks.
 








 
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