need help w basic programming

ohiolatheguy · Aug 19, 2015

Hi all, im new to this, ive been a lathe operator for a long time but never been involved with programming due to no programming on the floor...anyways now im thinking of taking a dif job offer but will need to do some basic programming... my question is what is the most normal user friendly formulas to figure out my speeds and feeds for basic lathe operations like turning, drilling, tapping, etc...I will just be handed a blueprint and have to program it,im ok w the codes and layout etc.. just need the basic formulas...any help would be great, im trying to get a head start before taking the offer..thanks

rlockwood · Aug 19, 2015

3.82 is the magic number.. surface speed*3.82/working diameter = rpm. rpm * advance per revolution = feedrate (in advance/minute)

But speeds & feeds for turning are actually even simpler, particularly if you're using constant surface speed. Feeds will be given in actual advance per revolution, so no calculation is done there, and surface speed is entered directly. You'll still need to know how to calculate surface speed for instances where CSS isn't available (drilling, boring, etc) but it covers a lot of it for you.

Heinz R. Putz · Aug 19, 2015

Take a look at youtube, put in my name, Heinz Putz, and you will see 5 parts of a CNC DVD called "CNC Partmaking".
A good section of this DVD is the simplified calculation, shortcuts and reasoning for lathe speeds and feeds.
Learn all you can, write back with any questions.
Heinz, doccnc.com

ohiolatheguy · Aug 20, 2015

thanks for the response, couple of questions, the formula for rpm, where do you get what the surface speed is suppose to be ? and as far as feed, what does advance per rev mean

Greg White · Aug 20, 2015

it means inchs per rev
like .005 or .011 per rev.
Good luck with your new job!
Gw

yardbird · Aug 20, 2015

Whatever little handy speeds and feeds formula/calculator you choose to use in your programming remember to limit the RPM to what your gripping situation will tolerate.

without a limit (G50) on the RPM you'll be wide open when at X center line. Just saying...

Brent

Mtndew · Aug 20, 2015

ohiolatheguy said:
thanks for the response, couple of questions, the formula for rpm, where do you get what the surface speed is suppose to be ? and as far as feed, what does advance per rev mean

You say you've been a lathe operator for a long time, but you never bothered to learn how fast your machine was cutting and why? ABL = always be learning.

The surface speed (sfpm) is dependant on your insert grade, the type of material you're cutting, etc...
advance per rev is feedrate as in inches per revolution (IPR).

TeachMePlease · Aug 20, 2015

I... I don't mean this to sound as harsh as it's gonna, I swear...

But you don't know speeds and feeds, like, not even the basics, or where to find them.... But you say you know G&M codes? And they're gonna have you programming at the machine? Are they aware that you're gonna need help, or do they think you're ready to come in and start making good parts on day one? Because depending on your answer, it could be a rude awakening for both you and the new employer.

Good luck to you, and don't hesitate to post specific questions here... I've never found a more knowledgeable, helpful group of sarcastic mfers in my life.

ohiolatheguy · Aug 20, 2015

Thanks for all the input, it will for sure help, and to answer a few of the concerns, I figured advance per rev was just another way of saying feed rate i just didn't wanna assume that's what it meant and ive never heard anyone in my shop refer to it as advance....I am familiar with the lathes ive been on the last few years and ive actually written about 10 programs for basic jobs but since im familiar with my machines Ive been able to do them using other job programs as samples and take feeds and speeds from them without knowing formulas, but if I take the other job I will be on other types of lathes and jobs so I will not have the familiarity that I do w the jobs I run now...ive already been working there part time and they are very happy w what ive done and they are fully aware of my lack of programming experience..i wouldn't wanna set me or the company up for failure...the question about the 20tpi thrd... im pretty sure with threads I just take 1.0/20 so it would be .05... I do appreciate everyones help

Mtndew · Aug 20, 2015

ohiolatheguy said:
Thanks for all the input, it will for sure help, and to answer a few of the concerns, I figured advance per rev was just another way of saying feed rate i just didn't wanna assume that's what it meant and ive never heard anyone in my shop refer to it as advance....I am familiar with the lathes ive been on the last few years and ive actually written about 10 programs for basic jobs but since im familiar with my machines Ive been able to do them using other job programs as samples and take feeds and speeds from them without knowing formulas, but if I take the other job I will be on other types of lathes and jobs so I will not have the familiarity that I do w the jobs I run now...ive already been working there part time and they are very happy w what ive done and they are fully aware of my lack of programming experience..i wouldn't wanna set me or the company up for failure...the question about the 20tpi thrd... im pretty sure with threads I just take 1.0/20 so it would be .05... I do appreciate everyones help

Yes 20tpi is 1/pitch so a feedrate of .05ipr
We all gotta start somewhere when it comes to programming, but knowing the basics will get you farther faster. A lot of it comes from experience running various materials in various situations, there is no static d.o.c. and speed/feed for any certain type of material.
Same goes for knowing how much you can get away with concerning jaw depth and max spindle speed.
Experience is the best teacher.
The best starting point is to know which brand and grade of insert you're programming the part for and use their recommended speeds and feeds and depths of cut and adjust from there.

ohiolatheguy · Aug 20, 2015

ok so im pretty clear on that now, thanks to the responses, another question about rpm, my machines are 1"max bar diameter so we only use g97 so im only putting in one rpm per tool, the other shop that im probly going to go to does bigger parts so they use g96 a lot, so....I know with the g96 you put in the 2 dif rpms....does one come from the start diameter and the other from the finish diameter? I know the dif between g96 and g97 one is constant sf and the other isn't but never knew where the two dif numbers come from w the g96

npok · Aug 20, 2015

ohiolatheguy said:
ok so im pretty clear on that now, thanks to the responses, another question about rpm, my machines are 1"max bar diameter so we only use g97 so im only putting in one rpm per tool, the other shop that im probly going to go to does bigger parts so they use g96 a lot, so....I know with the g96 you put in the 2 dif rpms....does one come from the start diameter and the other from the finish diameter? I know the dif between g96 and g97 one is constant sf and the other isn't but never knew where the two dif numbers come from w the g96

;
;
;
G50 S1500;
G96 S450 M3;
;
;
;

G50 S1500 sets max RPM at 1500 rpm.
G96 S450 M3 tells it to maintain 450 SFM & kicks the spindle on.

litlerob1 · Aug 21, 2015

As said in post #2, 3.82 is the magic number. There are 3 basic elements for determining appropriate SFM 1. Diameter of the spinning object (tool or spindle in your case). 2. The material you are cutting. 3. The material you are cutting with (HSS, carbide, diamond try not to use your fingers). G96 controls "Constant Surface Speed" so once you have determined what your surface speed should be ie. You are cutting Aluminum with Carbide should be 800 to 2000 SFM, so you would input that as G96S2000 value, so when the diameter of the part is getting smaller the spindle speeds up to maintain Constant Surface Speed knowwhatimean? You will also need to lock Max spindle speed (G50) because theoretically at X0.0 that is an infinite Surface Speed and the machine don't know the difference so it'll try to do it. For me G50 is the very first line of code that I input, I changed all my post processors so it outputs G50S**** on the line after the program name.

The formula for finding CSS and appropriate RPM are; Diameter x RPM ÷ 3.82 = Surface Feet per Minute. And 3.82 x SFM ÷ Diameter = Revolutions Per Minute. So the key is knowing what SFM you want to run and now you have all the formulas you need to figure out the values you want to use for G50, G96 and G97.

Robert my ±2

Mtndew · Aug 21, 2015

ohiolatheguy said:
ok so im pretty clear on that now, thanks to the responses, another question about rpm, my machines are 1"max bar diameter so we only use g97 so im only putting in one rpm per tool, the other shop that im probly going to go to does bigger parts so they use g96 a lot, so....I know with the g96 you put in the 2 dif rpms....does one come from the start diameter and the other from the finish diameter? I know the dif between g96 and g97 one is constant sf and the other isn't but never knew where the two dif numbers come from w the g96

Uhhh G96 doesn't use 2 different rpms.
I think you might need more training of basic turning knowledge before you start on the programming side of things.

Mtndew · Aug 21, 2015

Doug said:
g96 s250
g76 s500 ;min rpm
g77 s1500 ;max rpm

G96 = constant surface speed
G76 = Threading cycle
G50 = max rpm

Your point is? :confused:

litlerob1 · Aug 21, 2015

Doug said:
It depends on the control, one of mine uses G76 as min rpm, G77 as max rpm.

The only time I ever saw that was on an Omniturn control which is retrofit control for Hardinge lathes and others probably. But they are such tiny machines, I never used it because everything on there was 1" or smaller, barring special circumstances. I see zero benefit for a min. spindle speed, maybe you can enlighten me?

Again I agree with Dew there are not 2 speeds for G96.

G96=CSS
G97=Constant Speed
G50=max RPM
Generally but it's good to know there are different ways to do it, some Fansuc controls use G50 for work shift if I'm not mistaken. But someone tell me please why would you need a Min. RPM?

Robert

Mtndew · Aug 21, 2015

litlerob1 said:
But someone tell me please why would you need a Min. RPM?

It's probably one of those features that's there...just in case someone needs it.
I've never had a situation where I needed it in 30 years of running cnc's. :typing:

npok · Aug 21, 2015

litlerob1 said:
But someone tell me please why would you need a Min. RPM?

Robert

I could see it on a machine with a large/heavy chuck/spindle running parts that spin up & down a lot.

It'd save a lot of time staying in the SFM range 80% of the time rathe than 90% if 80% means avoiding going from 1500 down to 300 over & over (think 20" chuck).

litlerob1 · Aug 21, 2015

npok said:
I could see it on a machine with a large/heavy chuck/spindle running parts that spin up & down a lot.

It'd save a lot of time staying in the SFM range 80% of the time rathe than 90% if 80% means avoiding going from 1500 down to 300 over & over (think 20" chuck).

I run a CNC lathe with an 18" chuck, What I do is apply a G97 for the appropriate SFM per diameter before the tool even approaches, by the time the tool gets there it is already running, then before it starts cutting apply G96. But that is just me. On a second thought maybe it's a torque H.P. thing, 'cause at 200 RPM those little machines that use Omni will stall out in a heartbeat. Maybe?

Robert my ±2

Philabuster · Aug 21, 2015

Mtndew said:
Uhhh G96 doesn't use 2 different rpms.

Even if the control does not have the minimum RPM code, you still need the G50 Sxxxx command to clamp the max RPM when using CSS G96 Sxxxx, hence two 'RPM' numbers for the noob.

As Yardbird said in post #6, forgetting this line can result in disaster if the machine tries to go full speed on a setup that cannot handle the strain. :hitsthefan:

need help w basic programming

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