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How Hard can I Rough under these parameters

Jltorres91

Plastic
Joined
Mar 4, 2016
Okay i always wondered how hard i can rough these materials mild steel 12L14, 15-5Ph,6061, 7075 and 304SS before they slip. These are my current parameters in inches.

Holding onto a 3.0 inch Dia
Holding Grip .150 and .300 with stick out of .5 and 2.0
PSI of 200.
Facing and turning

What im asking here is how hard i can rough these materials before they slip on soft steel 3 jaws.
Depth of cut? SFM? and Feed? Max RPM?

Im currently running mild steel at
max rpm 2800
doc of 0,055
feed of .012
insert CNMG432
sfm of 1200
1.0 steel boring bar and turning holder Mitsubishi Insert CNMG432 MP MC6025



I know im asking a pretty vague questions but i want to know how hard i can push before causing an accident. Also assuming the machine can handle these parameters.

Please also share some Lathe experiences so i can learn a lot more
 
You are right it is too vague, and there isn't a real definite answer, and you're asking about 10 different questions in one-ish.

You cannot ask about 12L14 and 304 and 15-5 and expect the same answer. 12L14 and Aluminum okay, but the others no way.

But lets get some stuff out of the way, you DOC is way too low for a 432 for the OD not facing. Your chuck pressure is low, crank it up if you are trying to hold onto a part. Feed could go up a few notches. The SFM you posted is going to be the one element that needs to change the most betwixt the Alloys. It'll be tough on you trying to run 304 at 1200 SFM.

But if slippage is you first concern, best push some material out of the way and see whats going to work. I have no idea the condition of the jaw boring work, so can't comment on that, just do it right.

Cant just comment on experiences other than to say they usually differ, so Im not going to get into that.
 
okay im sorry.. lets just start with the 12L14. What are decent parameter for that job. Im holding the 12L14 on soft steels jaws machined to stock diameter and holding onto about .150. Whats the highest PSI I can put it too before it does damage to the part or the jaws? Also now assuming the max psi i can put on the piece how hard can i cut on a 3 inch diameter stock holding .15 grip? What would be some good speed and feeds?
 
Well if you are holding by .150" I'm assuming you are using step jaws so pushback isn't an issue. I would feed until the chips break then adjust DoC for spindle HP but you should be able to double where you're at.

SFM will be your biggest variable and I'd suggest starting with the low end of manufacturers recommendations.
 
Nobody can tell you. We don’t know the radius on the jaws, radius and surface of the part, clamping force. The only thing I can tell is that I’d use toothed jaws for roughing, such that bite.
 
okay im sorry.. lets just start with the 12L14. What are decent parameter for that job. Im holding the 12L14 on soft steels jaws machined to stock diameter and holding onto about .150. Whats the highest PSI I can put it too before it does damage to the part or the jaws? Also now assuming the max psi i can put on the piece how hard can i cut on a 3 inch diameter stock holding .15 grip? What would be some good speed and feeds?

PSI is a meaningless number. Different chucks and actuators generate completely different clamping forces at the same pressure.

The manual for your actuator will have charts for converting pressure to drawbar force, the manual for your chuck will have charts for converting drawbar force to clamping force.
 
hey Jltorres :) soft jaws are consumables ...

... do it the right way : [ craft hard jaws] + [ ca525 or tiger inserts or etc ] + high specs ; kindly!
 
you can machine at high sfpm and easily get sudden tool failure which causes cutting pressure to increase over 10x very fast. also at high sfpm tool even if wearing slower it might not last a reasonable time like 60 minutes. like not being able to finish job with same tool cause its wearing out too fast.
.
my preference is for tooling to last long enough i can hear a problem and stop it before catastrophic failure. i would rather hear a problem for 10 or 20 seconds than only 1 second and bang part just went flying
 
The OP’s got a couple of things going on here… Some experience will be easier than trying to calculate (things need better definition for that).

The work holding (generic). I’ll assume he’s got true pie jaws grabbing nearly the whole circumference of the piece, which amounts to less than 1.5sq/in. That’s not a lot of grip & may act pretty well @ .5” stickout but not so well at 3”. I’ll also assume it’s a hydraulic or air system (elastic) which are usually “start set” to 50-75% capacity (for design, setups or calculating). As things are sorted out, then you have headroom for better gripping.

There’s some info here regarding workholding (forces) from enerpac. → http://www.schoolofworkholding.com/...rsity/Lib/Topics/YellowPages/CuttingTech.html
WARNING, that page is for fixture design and not for machine tool horsepower requirements…

The differences in materials is another question. For machinability rating, I still like the % of AISI1212 or B1112 (resulfurized steel). So when you have some good seat time with one material you may quickly easily estimate a good start point for an unfamiliar one. The method does not require you look for specific recommendations, you use you experience on your machine to change by multiplying your (known good) numbers by a percentage & off you go.

So → I know 12L14 cuts really well @ 1050SFPM @ .012”IPR in my machine, (and 12L14 is 170% of 1212). Now I index my material to a 1212 rating by 100%/170% = .5882, Then .5882x1050=620SFPM. I keep that last number.

Then going back to the OP’s list;
12L14 is 620x1.7(170%)=1050SFPM;
15-5ph is 620x.48(48%)=297SFPM;
304SS is 620x.40(40%)=248SFPM;
Mileage varies with aluminum ratings, some go from 320% to 480% & others rate from 120% to 240% (with 1212 & B1112 @ 180SFPM=100% rating). So I’ll guess...
AL6061T is more than 320%, 620x3.2=1984SFPM (safe start);
AL7075 will be less than 480%, then 620x4.8=2976SFPM (high limit)


Good luck
Matt
 
crash

usually older machinist who has had many crashes where damage was expensive and machine was down for repairs for weeks to months is not so eager to push the limits
 
hy :) targeting a top tier high specs requires statistics on a stable setup, many inserts, constant material and hard jaws

playing with soft jaws wont get you far :)

try this : clamp a large diameter inside soft jaws at high hydra pressure ; than clamp same thing inside hard jaws ... you may feel how quick is the material clamped with hard jaws, while soft jaws will hesitate a little, because jaw compression occurs

same hydra applied on hard jaws will deliver more grip at the contact area, while soft jaws will consume a fraction of that grip, because of jaws compression

targeting same grip on soft jaws as on hard jaws requires much more hydra pressure : jaws must be compressed a lot, and at this point something may fail :) kindly !
 
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hard jaws are much close to a thing called "solid rigid" than soft jaws :)

a "solid rigid" is a "solid" that can not be deformed

a "solid rigid" is the idealization of a solid :)
 
hy :)

same hydra applied on hard jaws will deliver more grip at the contact area, while soft jaws will consume a fraction of that grip, because of jaws compression

Strongly disagree.
Hard jaws are made to work over a range of sizes so the contact patch will vary depending on stock size.
Soft jaws can be bored, offering full contact with the OD of the stock.
I hate hard jaws.
 
Strongly disagree.
Hard jaws are made to work over a range of sizes so the contact patch will vary depending on stock size.
Soft jaws can be bored, offering full contact with the OD of the stock.
I hate hard jaws.

He's on my ignore list, most of what he posts seems to have some knowledge behind it, but no wisdom. I hate hard jaws too, rarely use them. Sometimes on hot roll when using a bar feeder/puller, but not often.
 
i craft hard jaws and so i can push specs :)

... just a few hours ago i finished grinding a set, and now it works on a lathe

and others are running from december last year ... etc

- rough id
- circular grooves + circular chamfers
- longitudinal grooves + longitudinal chamfers
- heat treat
- grinding for cca 0.2 radial depth
... good outputs : tirr + grip :)
 
Hard jaws are made to work over a range of sizes so the contact patch will vary depending on stock size

hard jaws :
... may be for a specific diameter or for a range
... may not input plastic deformation, or may input a bit of plastic deformation, or may bite strong

they are a finished product, but may not fit well for a specific aplication :)

Soft jaws can be bored, offering full contact with the OD of the stock

soft jaws do not exist :)

... but a semifinished product, that you machine how you wish to fit a specific aplication

soft jaws from vendors are not jaws, but serated prismatics :)


it is more comfortable to sell a semifinished product, so the client to finish it

custom ( hard ) jaws available on request



there is a difference between using a cnc and machining :)
 








 
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