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304SS Threading Problem in Lathe

Italiano83

Aluminum
Joined
Mar 4, 2013
Location
Miami, FL
I'm trying to produce a thread very close to 5/8-18 by single point threading stainless. I have a 900 piece order, of which 650 pieces ran flawlessly. Now, I've been working all day to get my threads to look proper, but they just keep looking like complete garbage (see picture). Nothing changed in the program. I checked spindle alignment and re-zeroed the tool holders TWICE (no noticeable difference between the two times). I've tried two different style tools (one solid carbide and one with interchangeable inserts) with the same exact result. Great Coolant flow and concentration. It can't be the material since all other operations make the part look like a mirror and I've changed bars and no change. For now, forget about the parameters I'm using since they are the same that ran 650 perfect pieces. Any suggestions on what else may have changed all of a sudden to cause this mess ??? Please Help

IMG_5166.jpg
 
Any chance the threading problems changed when a new stick of material was loading into the machine???
Possibly another brand or a different manufacture's bars lumped into 1 order??
Any material build up on the cutting edge?

Is the tap drill (assuming) still holding size? Is it sharp?
 
Any chance the threading problems changed when a new stick of material was loading into the machine???
Possibly another brand or a different manufacture's bars lumped into 1 order??
Any material build up on the cutting edge?

Is the tap drill (assuming) still holding size? Is it sharp?

I've tried two different pieces from two different lots and same result. One was actually from an old lot from which parts ran fine. I drill to size before threading and drill is new and cutting perfectly. The threader is pushing the material rather than cutting it. Threaded minor diameter is .010" smaller than pre-threading hole diameter. No material build up on cutting edges.
 
Very strange that you don't post speeds and feeds....


Its irrelevant since we've been running these parts for months without issue, as well as the first 2/3's of this order. I want people to focus on what else may have changed, because it surely wasn't the program/feed&speeds.
 
How does the flank of the threading insert look?
Could a shaving be forced in between the threading bar and the thread minor during the last few cuts?
I can see tearing on the threads, and what looks like plastic deformation on the burrs....
Are the curely-cue-chips from threading identical to when the parts were running well?
 
There's not that much woodoo magic to this, you either have bad material, bad/wrong tool or didn't set it in properly and having a clearance/rubbing issue.
 
If your using water based coolant make sure the concentration is not very low. We use 7-9 % on 304. If it's under 5% we always have problems.
 
If your using water based coolant make sure the concentration is not very low. We use 7-9 % on 304. If it's under 5% we always have problems.

^^ This. As you have shown you are not an idiot and it is not material and you realigned tools , to me this is the only viable option left. Someone ran low on coolant and threw some water in or it finally needs a total refresh.


Whatever the problem...please report back your findings!

Ps- or it is because you are in FL and you being so close to sea level......
 
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So when did this start happening? On a new bar, in the middle of a bar, you came in in the morning and it was cutting poorly right off the bat? Are you the only one that runs this job? Have you checked the turret alignment?
 
Could also be helpful to see the lin(es) of code you are using, I realize it shouldn't matter, but sometimes it just does, and you need to fudge your infeed angle or something. I would also try running the tool with no coolant just cutting oil, easy way to check if lube is your culprit.

I can see the thread flanks are galling, are you sure the spindle speed hasn't been changed between parts by someone else? Or anything else for that matter, finish pass, DOC, start point? These could all effect the condition of the product.

R
 
All you are saying is all inputs are same but the output is different.
This is not possible unless there is a "ghost in the machine."

Behavior of canned cycles sometimes depends on certain parameters also. You or somebody else may have changed some parameter because of some reason. The code would need to be analysed first. You may like to post it.

If nothing else works and no apparent reason can be found, try lower DOC and rpm. I believe the offset is correct.
 
yes I have a suggestion but no one likes it or tries it or they complain aboot it....but it works fine....try it as see if it fixes problem.....100RPMs and take off small amounts like maybe .001 per side or .002 per side....takes a tad longer but threads will always be toot sweet....if you need to make money then speed up from there....slowly....until your making crap again....then back it down a notch and that should be the ticket....basically run it same as titanium or slower yet....but I run almost all threads at 100RPMs...I need them to be perfect instead of hundreds and hour...I have only one shot and no extra stock.....sometimes its the only stock that exists....try 100 and see what happens....if you have to go larger diameter like 3 inches and maybe 4 threads per....then I speed it up to aboot 300....never more....good luck.....oh one other thing....set the code to run at 55 degrees infeed on compound...again...only thrying it will you see results and be able to make your own determination then...post up a pic then.....bet there perfect,,,,later

I'm pretty new to machining, been doing it for about 3 years now when I started my own manufacturing company, and to this date, I've never been given a more accurate, mind-blowing piece of advice. I cannot post a pic due to our customer confidentiality agreements, but I can tell you that looking at the thread in that 304ss is akin to the birth of my first child. WOW! Sir...you are my hero.

For future reference in this forum, I ended up at about 200RPM and .002" DOC for the time being. It produces a beautiful thread. I need to get some parts out the door so I'll try to play around and speed it up a bit later, but with only a .040" thread depth, it doesn't completely sandbag my cycle time currently.

Thanks again, I'm still in awe

-Jon

If not already? Go back to this. That doesn't fix it then my vote is shit material?

Brent

http://www.practicalmachinist.com/vb/cnc-machining/thread-turning-304-stainless-help-332150/
 
If not already? Go back to this. That doesn't fix it then my vote is shit material?

Brent

http://www.practicalmachinist.com/vb/cnc-machining/thread-turning-304-stainless-help-332150/

Brent, this is the same project. I've been running at 200 RPM, .001" DOC. This is very slow, but produces a beautiful thread where I couldn't get anything else to work...and believe me, I tried a zillion combinations of speeds and doc. Also for all of the others out here, I'm the only one that touches the machine and the program wasn't touched...it just all of a sudden started chipping inserts and/or producing a horrid thread.
 
If your using water based coolant make sure the concentration is not very low. We use 7-9 % on 304. If it's under 5% we always have problems.


Coolant at 8% without factor. Factor for our coolant is 1.25 so that puts actual concentration at 10%. This does not seem to be the issue. I'm gonna mess around with it for a few and see what I can find and then report back.
 








 
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