Threading 4140 troubles

[FTlatheworks]

.557 is correct, but that is the biggest it can be and still be in spec. Your OD is oversized if you went with .625

It’s 5/8 stock that is .622. So, my little theory about the threads being to deep is wrong. Why would that happen at the exact same depth both times? I ran 200 rpm’s because I have never threaded anything under that. Is it really that sensitive to the speed it’s running? I also can’t imagine that im going to have to take .002 doc once I get .040 deep. That would take forever.

 

[RPMWorks]

It’s 5/8 stock that is .622. So, my little theory about the threads being to deep is wrong. Why would that happen at the exact same depth both times? I ran 200 rpm’s because I have never threaded anything under that. Is it really that sensitive to the speed it’s running? I also can’t imagine that im going to have to take .002 doc once I get .040 deep. That would take forever.

Do you know the condition of the material? annealed soft, pre hard, heat treated?? when you say you take .002 DOC, does your dial say .002 or .004? When i thread i take the first .030 (actual dial reading/. 015 DOC) in .01 increments then .005 until i am within /.01 0f my target then .003 to finish.
If the material is soft i would go as fast as you’re comfortable with up to about 2200 rpm which is way to fast. If it’s pre hard, typically around 33Rc that brings it down to around 1750 rpm. It is a common misunderstanding to think that if you go slower things will work. Every material has surface footage that gives the best results and you should always try to get as close as each situation will allow.
.622 is in spec so that’s not the problem. do you have any means of measuring the inserts tip geometry/radius? If it’s sharp i can tell you that you are going to deep. Are you familiar with checking threads with wires?

 

[FTlatheworks]

Do you know the condition of the material? annealed soft, pre hard, heat treated?? when you say you take .002 DOC, does your dial say .002 or .004? When i thread i take the first .030 (actual dial reading/. 015 DOC) in .01 increments then .005 until i am within /.01 0f my target then .003 to finish.
If the material is soft i would go as fast as you’re comfortable with up to about 2200 rpm which is way to fast. If it’s pre hard, typically around 33Rc that brings it down to around 1750 rpm. It is a common misunderstanding to think that if you go slower things will work. Every material has surface footage that gives the best results and you should always try to get as close as each situation will allow.
.622 is in spec so that’s not the problem. do you have any means of measuring the inserts tip geometry/radius? If it’s sharp i can tell you that you are going to deep. Are you familiar with checking threads with wires?

I do not, but I thought 4140 was not hardened, but 4130 was hardened when extruded. I’m not familiar with checking threads with wire, but I know what you’re talking about. I have a starret fish tail gauge for 60 degree tools.

it’s these inserts, I will just go back to hss. I don’t see how I’m going too deep if my threads can’t go deeper than .050.

 

[RPMWorks]

I do not, but I thought 4140 was not hardened, but 4130 was hardened when extruded. I’m not familiar with checking threads with wire, but I know what you’re talking about. I have a starret fish tail gauge for 60 degree tools.

it’s these inserts, I will just go back to hss. I don’t see how I’m going too deep if my threads can’t go deeper than .050.

To be in spec you will be somewhere around .072ish deep from the major diameter, depending on the tip geometry of the insert.
If you are going with HSS you should be around around 620 rpm. Oil is of course important too.

 

[FTlatheworks]

To be in spec you will be somewhere around .072ish deep from the major diameter, depending on the tip geometry of the insert.
If you are going with HSS you should be around around 620 rpm. Oil is of course important too.

Excuse my lack of knowledge, but the insert specs state they can only do a pitch of 3mm-5mm. Obviously pitch diameter is way over that for what I’m doing. Does that tell you anything important?

 

[Ischgl99]

Do you have a link to the inserts you bought? 3-5mm pitch is very course and they might have a large flat on the vee that needs to be considered when figuring out how deep to cut the threads.

You also mentioned the thread depth several times, but the number you give is the diameter difference between the major and minor diameters, are you dividing that in half to determine how deep to cut the thread?

 

[FTlatheworks]

Yes, the diameter I start with is major diameter, then I cut until I reach minor diameter. That’s how I’ve always done it. No I’m not dividing that in half. Here is the link below.

Help me decide on this product: 1/2" 5/8" Boring Bar SNR0013M16+SER1616H16 Lathe Internal Threading Inserts Turning Tool Holder with 5pcs 16ER AG60+5pcs 16IR AG60 Carbide Turning Inserts https://a.co/d/6hdOtIh

 

[mksj]

Insert pitch is 0.5 to 3.0 mm which should cover something like 8 to 48 TPI for an AG60 thread insert. You might try just using the cross slide and locking the compound. I would try 400 to 500 RPM for that diameter. Threading inserts do not require high SFM. As you go deeper into the cut reduce the DOC.

 

[FTlatheworks]

Insert pitch is 0.5 to 3.0 mm which should cover something like 8 to 48 TPI for an AG60 thread insert. You might try just using the cross slide and locking the compound. I would try 400 to 500 RPM for that diameter. Threading inserts do not require high SFM. As you go deeper into the cut reduce the DOC.

I started out with scratch pass, then .008 for the first cut, then all the rest were .005 until the threads chipped at around .050. I Used wd-40 as a lubricant. The metal is tearing, even when I tried to take .030 off to chuck it up.

It has to be speeds and feeds related if it’s a bad surface finish right? When I turned the other side of the stock down, I was using a carbide insert. I attached photos of the first threading attempt when the tools chipped. The second photo is what it looked like when I tried to turn the stock down in the center of the work to try and true it up in the chuck for the second threading attempt on the other side of the stock. The third photo is the second threading attempt where I fixed all of the things people mentioned in this thread.

Sorry if that was confusing, but maybe someone will see something and know more about why this is happening. I will thread with hss tonight and post the result of that.

 

[RPMWorks]

Excuse my lack of knowledge, but the insert specs state they can only do a pitch of 3mm-5mm. Obviously pitch diameter is way over that for what I’m doing. Does that tell you anything important?

In the absence of a pitch mic, this is how you measure the pitch diameter, if you want to be in spec. If you want some specific numbers let me know and I’ll get them for you.