We are running some 3/8-16 threads in stainless steel that are eating inserts and giving a poor finish. I'm trying to figure out exactly what effect all the parameters will have on the process.

We're using an 16ERMAG60 TT9030 insert and it is programmed as:

N4(3/8-16 3A THREADS)
G97M13S2000
M98P1
T0404
Z4.825
X.475
G76P040030Q0020R.0010
G76X.299Z.94P0383Q0020F.0625R0.
G0X4.0
M98P1
M01

If I understand it correctly the 04 in the first P line is going to make it do 4 finish passes at the final depth.
(Question 1) Does this mean that it will turn the threads down and leave .010 per side, and then in 4 finish passes take that .010" material off? Or does that mean after it gets down to size it will run 4 additional passes all at the same final size?

The next 00 in that P word is going to cause it to not do any chamfer on the end of the thread where a 10 would make it do a 1/16" chamfer. (1.0 x .0625 pitch) And a 20 would make it do a 1/8" chamfer.

The next one is causing some debate in our shop. I am reading the operator's manual, the programmers manual and the posts above to say that number should be 60 for the insert we are using 16ERMAG60. The old time tribal knowledge in the shop is saying it should be half of the thread angle which is why they have it at 30. ("That's the way it's always been") But the programmer's manual says the 6 possible values for this term are 00, 29, 30, 55, 60, 80 degrees. Well, if it were double, a 160 degree insert would seem silly.
(Question 2) What should it be for this insert?
(Question 3) How exactly will the tool path be different if that number is 30 or 60 (or 0 or 80)?

Still in the first line, the Q word will make it take a min .002" per pass and the R term will make it leave .010" per side for a finish allowance.

On the 2nd g76 line we have the minor thread diameter of .299 for 3/8-16 threads in the X word. The Z is the length of the threads.
The 2nd line P word is the Single Depth of Thread which the Hardinge programmers manual says is calculated as .61343/TPI for a straight thread which in this case is .61343/16=.0383 giving the term P0383

The 2nd line Q word is the depth of the first pass and we have it at Q0020 which means that we are only taking .002" on the first pass. (Question 4) Does this mean that it will take only .002" for each pass? The programmers manual says this should be calculated as the (single depth of thread) / (the square root of the number of passes). If so, I get something like 366 passes would produce the .0020 value? But when it runs it is only doing 23 passes. Using that formula, for 23 passes it should be Q0080 and for 12 passes it should be Q0110. (Question 5) How does this number affect the number of passes and the depth of cut of each pass?

F.0625 is the lead and R0. means no taper on the threads.

Here are links to the pages in the manuals I found that pertain to the g76 on the fanuc controllers.

Hardinge Programmer's Manual g76 pages
http://www.filedropper.com/g76programmersmanual

Fanuc Operator's Manual g76 pages
http://www.filedropper.com/fanucoi-tcg76pages

So, there are 5 questions in bold above and any help with those would be great.

Thanks in advance.

I'm glad I found this because I'm a true dummy here.We are running some 3/8-16 threads in stainless steel that are eating inserts and giving a poor finish. I'm trying to figure out exactly what effect all the parameters will have on the process.We're using an 16ERMAG60 TT9030 insert and it is programmed as:N4(3/8-16 3A THREADS)G97M13S2000M98P1T0404Z4.825X.475G76P040030Q0020R.0010G76X.299Z.94P0383Q0020F.0625R0.G0X4.0M98P1M01If I understand it correctly the 04 in the first P line is going to make it do 4 finish passes at the final depth.The next 00 in that P word is going to cause it to not do any chamfer on the end of the thread where a 10 would make it do a 1/16" chamfer. (1.0 x .0625 pitch) And a 20 would make it do a 1/8" chamfer.The next one is causing some debate in our shop. I am reading the operator's manual, the programmers manual and the posts above to say that number should be 60 for the insert we are using 16ERMAG60. The old time tribal knowledge in the shop is saying it should be half of the thread angle which is why they have it at 30. ("That's the way it's always been") But the programmer's manual says the 6 possible values for this term are 00, 29, 30, 55, 60, 80 degrees. Well, if it were double, a 160 degree insert would seem silly.Still in the first line, the Q word will make it take a min .002" per pass and the R term will make it leave .010" per side for a finish allowance.On the 2nd g76 line we have the minor thread diameter of .299 for 3/8-16 threads in the X word. The Z is the length of the threads.The 2nd line P word is the Single Depth of Thread which the Hardinge programmers manual says is calculated as .61343/TPI for a straight thread which in this case is .61343/16=.0383 giving the term P0383The 2nd line Q word is the depth of the first pass and we have it at Q0020 which means that we are only taking .002" on the first pass.The programmers manual says this should be calculated as the (single depth of thread) / (the square root of the number of passes). If so, I get something like 366 passes would produce the .0020 value? But when it runs it is only doing 23 passes. Using that formula, for 23 passes it should be Q0080 and for 12 passes it should be Q0110.F.0625 is the lead and R0. means no taper on the threads.Here are links to the pages in the manuals I found that pertain to the g76 on the fanuc controllers.Hardinge Programmer's Manual g76 pagesFanuc Operator's Manual g76 pagesSo, there are 5 questions in bold above and any help with those would be great.Thanks in advance.

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G76 Threading Cycle, Multiple Pass (Group 00)

* A - Tool nose angle (value: 0 to 120 degrees) Do not use a decimal point
D - First pass cutting depth
F(E) - Feed rate, the lead of the thread
* I - Thread taper amount, radius measure
K - Thread height, defines thread depth, radius measure
* P - Single Edge Cutting (load constant)
* Q - Thread Start Angle (Do not use a decimal point)
* U - X-axis incremental distance, start to maximum thread Depth Diameter
* W - Z-axis incremental distance, start to maximum thread length
* X - X-axis absolute location, maximum thread Depth Diameter
*Z - Z-axis absolute location, maximum thread length

- Tool nose angle (value: 0 to 120 degrees) Do not use a decimal point- First pass cutting depth- Feed rate, the lead of the thread- Thread taper amount, radius measure- Thread height, defines thread depth, radius measure- Single Edge Cutting (load constant)- Thread Start Angle (Do not use a decimal point)- X-axis incremental distance, start to maximum thread Depth Diameter- Z-axis incremental distance, start to maximum thread length- X-axis absolute location, maximum thread Depth Diameter- Z-axis absolute location, maximum thread length

* indicates optional

NOTE

The P values are modal. This means if you are in the middle of a canned cycle and a G04 Pnn or an M97 Pnn is used the P value will be used for the dwell / subprogram as well as the canned cycle.

G76 Threading Cycle, Multiple Pass: [1] Z depth, [2] Minor diameter, [3] Major diameter.

Threading Cycle, Multiple Pass: [1] Z depth, [2] Minor diameter, [3] Major diameter.

Setting 95/Setting 96 determine chamfer size/angle; M23/M24 turn chamfering ON/ OFF.

G76 Threading Cycle, Multiple Pass Tapered: [1] Rapid, [2] Feed, [3] Programmed path, [4] Cut allowance, [5] Start position, [6] Finished diameter, [7] Target, [A] Angle.

Threading Cycle, Multiple Pass Tapered: [1] Rapid, [2] Feed, [3] Programmed path, [4] Cut allowance, [5] Start position, [6] Finished diameter, [7] Target, [A] Angle.

The G76 canned cycle can be used for threading both straight or tapered (pipe) threads.

The height of the thread is defined as the distance from the crest of the thread to the root of the thread. The calculated depth of thread (K) is the value of K less the finish allowance (Setting 86, Thread Finish Allowance).

The thread taper amount is specified in I. Thread taper is measured from the target position X, Z at point [7] to position [6]. The I value is the difference in radial distance from the start to the end of the thread, not an angle.

NOTE

A conventional O.D. taper thread will have a negative I value.

The depth of the first cut through the thread is specified in D. The depth of the last cut through the thread can be controlled with Setting 86.

The tool nose angle for the thread is specified in A. The value can range from 0 to 120 degrees. If A is not used, 0 degrees is assumed. To reduce chatter while threading use A59 when cutting a 60 degree included thread.

The F code specifies the feed rate for threading. It is always good programming practice to specify G99 (feed per revolution) prior to a threading canned cycle. The F code also indicates the thread pitch or lead.

If you are looking for more details, kindly visit CNC Threading Machine Supplier.

At the end of the thread an optional chamfer is performed. The size and angle of the chamfer is controlled with Setting 95 (Thread Chamfer Size) and Setting 96 (Thread Chamfer Angle). The chamfer size is designated in number of threads, so that if 1.000 is recorded in Setting 95 and the feed rate is .05, then the chamfer will be .05. A chamfer can improve the appearance and functionality of threads that must be machined up to a shoulder. If relief is provided for at the end of the thread then the chamfer can be eliminated by specifying 0.000 for the chamfer size in Setting 95, or using M24. The default value for Setting 95 is 1.000 and the default angle for the thread (Setting 96) is 45 degrees.

G76 Using an A Value: [1] Setting 95 and 96 (see Note), [2] Setting 99 (Thread Minimum Cut), [3] Cutting Tip, [4] Setting 86 - Finish Allowance.

Using anValue: [1] Setting 95 and 96 (see Note), [2] Setting 99 (Thread Minimum Cut), [3] Cutting Tip, [4] Setting 86 - Finish Allowance.

NOTE

Setting 95 and 96 will affect the final chamfer size and angle.

Four options for G76 Multiple Thread Cutting are available:

1. P1:Single edge cutting, cutting amount constant




2. P2:Double edge cutting, cutting amount constant




3. P3: Single edge cutting, cutting depth constant




4. P4: Double edge cutting, cutting depth constant

P1 and P3 both allow for single edge threading, but the difference is that with P3 a constant depth cut is done with every pass. Similarly, P2 and P4 options allow for double edge cutting with P4 giving constant depth cut with every pass. Based on industry experience, double edge cutting option P2 may give superior threading results.

D specifies the depth of the first cut. Each successive cut is determined by the equation D*sqrt(N) where N is the Nth pass along the thread. The leading edge of the cutter does all of the cutting. To calculate the X position of each pass you have to take the sum of all the previous passes, measured from the start point the X value of each pass

G76 Thread Cutting Cycle, Multiple Pass

%
o60761 (G76 THREAD CUTTING MULTIPLE PASSES) ;
(G54 X0 is at the center of rotation) ;
(Z0 is on the face of the part) ;
(T1 is an OD thread tool) ;
(BEGIN PREPARATION BLOCKS) ;
T101 (Select tool and offset 1) ;
G00 G18 G20 G40 G80 G99 (Safe startup) ;
G50 S1000 (Limit spindle to 1000 RPM) ;
G97 S500 M03 (CSS off, Spindle on CW) ;
G00 G54 X1.2 Z0.3 (Rapid to 1st position) ;
M08 (Coolant on) ;
(BEGIN CUTTING BLOCKS) ;
G76 X0.913 Z-0.85 K0.042 D0.0115 F0.0714 (Begin G76) ;
(BEGIN COMPLETION BLOCKS) ;
G00 G53 X0 M09 (X home, coolant off) ;
G53 Z0 M05 (Z home, spindle off) ;
M30 (End program) ;
%

Thread Cutting Cycle, Multiple Pass

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