CNC lathe tool nose compensation (G41/G42) troubles

[MachineAmateur]

Hello,

Now i've been trying to find any guides with varying situations, but nothing so far, everything describes the tool nose 3 with run of the mill profile turning. I also suspect that the crappy lathe i am using does not properly compute certain situations and might be the culprit here, but i want to first make sure i am doing it right. The manual is awfully short on this issue and has incorrect descriptions too.
- Lathe has turret between operator and stock.
- Only one tool datumn is available (cannot use left and right offsets for same tool), this might be the reason why i will fail at this task no matter what
- Radius from right to left works with G42 properly, nose setting 3, no issues there
- I have tried nose 3 and 8 and there seems to be no difference in the behaviour. Is it correct to think that nose profile 8 is used to create left and right corners by switching G41<>G42 or is it only used to compute the Z variation between them (essentially any nose setting would behave as rounded insert)?

What i am attempting to accomplish is to use a grooving insert (1mm radius so basically round nose) which would profile a small stud that has one reverse radius at the chuck end (right before the parting). This makes it impossible to use the typical right-to-left profiling run as i have to switch something in between to get the reverse edge. Another thing is that i am attempting to learn this thing properly and use the flimsy grooving tool as intended, so i would rather push into the stock than sidestep into it as the tool visibly bends from the forces when doing so. So reversals will happen.

Here is a simple example code for testing which makes the routine do some crazy stuff (it might plunge straight in or attempt to create full circle etc.), i've attempted to use both commands. Note that this is not the actual profile, just for testing with the end of stock for less material waste.

T2.2
G0 X18 Z-5
G1 X16 ;Stock at 16mm
G1 G41 X16 Z-2 ;Lead into the tool nose compensation, left to right
G3 U-4 W2 R2 ;Counter clockwise arc ending at Z0, edit: W-2 changed to W2
G0 X18

If i generate the same code, where instead plunging i come from right to left at X14 Z0 with G42 it works properly.

 

[DouglasJRizzo]

Generally, with TNR, you can't "re-enter" a part. You also can't switch directions on the fly.
If the controller only has one offset per tool you're stuck doing the math by hand (or CAM system) and generating the part that way.
What machine/control is this?

 

[MachineAmateur]

Generally, with TNR, you can't "re-enter" a part. You also can't switch directions on the fly.
If the controller only has one offset per tool you're stuck doing the math by hand (or CAM system) and generating the part that way.
What machine/control is this?

Thanks for the info, there is not a lot of material regarding lathe TNR available and probably the reason is its complexities..Lathe is a no name chinese crap, not produced anymore, but was cheap too! I actually just realized that it does the G02 and G03 backwards, 02 produces counterclockwise and 03 clockwise arc.. I can basically use the code reversing using G41+G02, but the next operation afterwards whether G01 or G00 starts creating circles so it is not usable.

I've had no problems with CAM software, just wanted to create something by hand and ran into this..

 

[chad883]

Your code on the G3 line has a W-2. That finishes the rad at Z-4, not Z0

 

[sinha]

It is doing circular interpolation the way front-type lathes do.
G02/G03 apparently reverse. Same with G41/G42.

 

[MachineAmateur]

Your code on the G3 line has a W-2. That finishes the rad at Z-4, not Z0

That seems to be typo only on this example, maybe on some testing too though (it was very confusing). I actually did the program today with I K just to be sure it was not the radius mode messing up. Oh well, it is a bugger for such a simple thing.

I suck at math so is there any calculators for 90 degree fillets and 45 degree chamfers?

 

[Skubeesnak]

There are apps in google play that will calculate rad for you. Little cam systems so to speak

 

[guythatbrews]

Generally, with TNR, you can't "re-enter" a part. You also can't switch directions on the fly.
If the controller only has one offset per tool you're stuck doing the math by hand (or CAM system) and generating the part that way.
What machine/control is this?

You can switch directions on the fly when in TNRC mode, if by on the fly you mean for example grooving in and right back out.

Disregarding tool right or tool left for purposes of explanation, and for the OP's 1mm radius tool, if you plunge in to a diameter and make a dummy move to the other side of the tool, so a Z move of 2mm, you can come right back out and the tool won't move in Z. The control still sees the tool on the same side of the cut. It's handy to do this sometimes, like when grooving.

 

[DouglasJRizzo]

You can switch directions on the fly when in TNRC mode, if by on the fly you mean for example grooving in and right back out.

Disregarding tool right or tool left for purposes of explanation, and for the OP's 1mm radius tool, if you plunge in to a diameter and make a dummy move to the other side of the tool, so a Z move of 2mm, you can come right back out and the tool won't move in Z. The control still sees the tool on the same side of the cut. It's handy to do this sometimes, like when grooving.

I've never tried that. I'll give it a whirl on some scrap aluminum when I get a chance.