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4140 QT 45HRC speeds feeds and inserts

Ray.Rocha

Plastic
Joined
May 16, 2021
I have been turing a part for a little while and am dissapointed in my MRR, I see companies like Titan CNC that are doing fantastic MRRs and feel Like I should be doing better.

Specifically my material is drill stem used in deep hole oil drilling, to the best of my knowledge it is 4140 with a hardness of about 40HRC. it cuts like 4140 QT but is a little harder.

I have been doing research on the subject but I am not really connecting the manufacturers specs on inserts to my material. When I use the recommended specs I get bad results. not the fault of the manufacturers just my interpretation of the information. So I would like to tap some of the knowledge around here.

I posted something similar on another forum but am unsure it has been noticed by people expert in the field.

I am using Sandvik Coromant - CCMT32.52 PM Grade 4325, I am running it at 130SFM with at .06 - .1 depth of cut, and .006 per rev. I am getting good chip breakage and a good finish. but the MRR is terrible at 1.43 cu inch per minute. I can do a .012" / rev and have good chips but I can seem to move the speed up without greying out the chips. right now they are just turning blue. I get decent life from the insert but even that seem a little bit low. I burn out the insert every 200 or so cu inches.


I have a few parts I make that use this material but as an example 233RPM 24 inch long 3.5 inch diameter turned down to 2.5" 29 inch OAL with a 1.5" hole in the center. it takes me about 80 min to cut the feature. insert angle to workpiece is about 87 deg.

The lathe is a Colchester Clausing mastiff 1400 that I converted to a CNC Lathe with a 12.5HP spindle. 5% emulsion coolant

I suspect I am using the insert wrong. I read it is normal to reduce the speeds significantly when cutting harder steels. but it seems pretty slow compared to the 1130 FPM that the insert says for low alloy steel. or maybe someone knows a good insert for 35-40HRC?

I use the same insert for 1045 and can get about 10 Cu inch/min MRR at about 945SFM .1 DOC .009 feed/rev , I cant get any faster though as this gets to my max spindle speed.


thanks for any input.

 

Mtndew

Diamond
Joined
Jun 7, 2012
Location
Michigan
According to Sandvik's website calculator, using that insert in 4140 with 311 brinell (softer than your material) they recommend 650 sfpm, F.0078" and d.o.c. of .0625"

Given that your material is a little bit harder I'd back the sfpm off a little and go from there. Maybe start around 450sfpm.

Your current sfpm of 130 is way too low.
 

gregormarwick

Diamond
Joined
Feb 7, 2007
Location
Aberdeen, UK
Assuming you have the original transmission on your retrofit and haven't gone direct drive, the Mastiff will handle a much bigger cut with a stronger insert.

If you're using Sandvik, get a CNMG120412 (I haven't learned the american designation system) in grade 4325, and bump your DOC to .2" at a minimum.

Like Dew said, start about 400-450sfm, but bump the feed up to about .012"/r if you switch to the CNMG.
 

Ray.Rocha

Plastic
Joined
May 16, 2021
According to Sandvik's website calculator, using that insert in 4140 with 311 brinell (softer than your material) they recommend 650 sfpm, F.0078" and d.o.c. of .0625"

Given that your material is a little bit harder I'd back the sfpm off a little and go from there. Maybe start around 450sfpm.

Your current sfpm of 130 is way too low.

I will try that tomorrow I have some actual 4140 QT that is about 30-35 HRC that I need turn an downhole tool part. Maybe there is a point that it will cut cooler chips above 400. I did start with those numbers I think. I have moved them around so much I cant be sure. but I used the website calculator to setup my original cuts and specify the insert. I may have started at 200 and backed it down from there.
 

Ray.Rocha

Plastic
Joined
May 16, 2021
Assuming you have the original transmission on your retrofit and haven't gone direct drive, the Mastiff will handle a much bigger cut with a stronger insert.

If you're using Sandvik, get a CNMG120412 (I haven't learned the american designation system) in grade 4325, and bump your DOC to .2" at a minimum.

Like Dew said, start about 400-450sfm, but bump the feed up to about .012"/r if you switch to the CNMG.

I kept the original transmission. so I will go shopping for that insert. thanks guys
 

Stirling

Hot Rolled
Joined
Dec 11, 2013
Location
Alberta canada
I ran that same lathe (not converted to CNC)
Pop in a cnmg 432 insert (general propose grade) spin to 500sfm with a good coolant flow. 0.012-0.014”/rev 0.15-0.20 doc.

Watch for hot chips down the shirt collar!

Modern inserts are amazing. They can handle much more heat. Don’t be to worried about the colour of the chip.
But do not thermal shock them.
Heck, bump it down to 400sfm and the same cut without coolant would still let you better tool life than now.
 








 
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