Formula of the reduced infeed thread cutting.

[Laurens-3DTechDraw]

Hi guys,

We use G76 for thread cutting on the machine, because it runs smoother but the problem is you don't know the first pass depth. So is there I way I can get the formula for this or can we find a way to get this info in the post?

[asrimohdyusof]

hi, i try using G76 for thread cutting in FANUC but it fail..Now i using G33 and programing bit long..G33 working very well in Fanuc 21i

[parobillard]

@Laurens-3DTechDraw

Can you send a "dump" of an exemple?

[Lonnie.Cady]

@Laurens-3DTechDraw all software I have used has allowed you to specify the depth of the first pass.  With out this I don't see how you could accomplish G76 threading.

The typical constant volume equation is 

D = depth of first pass specified in G76 (this should be input by user)

D2(total depth) = D*SQRT(2)

D3(total depth) = D*SQRT(3)

Dn(total depth) = D*SQRT(n)

Not sure how they planned to thread with out having the ability to control the depth of cut on first pass.

could you use the thread depth and the number of stepdowns to calculate your Q value for the initial cut?

[Laurens-3DTechDraw]

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@Lonnie.Cady wrote:

@Laurens-3DTechDraw all software I have used has allowed you to specify the depth of the first pass.  With out this I don't see how you could accomplish G76 threading.

The typical constant volume equation is 

D = depth of first pass specified in G76 (this should be input by user)

D2(total depth) = D*SQRT(2)

D3(total depth) = D*SQRT(3)

Dn(total depth) = D*SQRT(n)

Not sure how they planned to thread with out having the ability to control the depth of cut on first pass.

could you use the thread depth and the number of stepdowns to calculate your Q value for the initial cut?

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I understand how they planned it.

You can't command the number of passes and the first infeed depth.

Because they would effectively be different numbers to drive the same calculation(For the volume of the cut).

So they chose to only give you the ability for the number of passes and nothing else.

Which I think is wrong, though they should allow for both, and make you pick the one that suits you best.

[Lonnie.Cady]

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@Laurens-3DTechDraw wrote:

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Because they would effectively be different numbers to drive the same calculation(For the volume of the cut).

So they chose to only give you the ability for the number of passes and nothing else.

Which I think is wrong, though they should allow for both, and make you pick the one that suits you best.

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I also understand it, but you cant do a constant volume with out specifying the first pass depth. 

They are not the same calculation, they are different calculations and there for require different inputs. 

So how did they "plan" for you to use constant volume?

[Laurens-3DTechDraw]

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@Lonnie.Cady wrote:

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@Laurens-3DTechDraw wrote:

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Because they would effectively be different numbers to drive the same calculation(For the volume of the cut).

So they chose to only give you the ability for the number of passes and nothing else.

Which I think is wrong, though they should allow for both, and make you pick the one that suits you best.

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I also understand it, but you cant do a constant volume with out specifying the first pass depth. 

They are not the same calculation, they are different calculations and there for require different inputs. 

So how did they "plan" for you to use constant volume?

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Since the shape and size of the triangle you are cutting away are known(Thread depth and Angle), you can calculate the total area of that triangle.

If you have the area you divide that by the number of passes(given by the user) and you know how much of that area each pass needs to take.

From there you can calculate how deep the first cut needs to be to get to that area(The shape of the insert is also known of course).

It's not the most basic goniometry but isn't rocket science either.

So that's why I said you can give in or the first depth(since that gives the same info as what I described above) or give in the amount of passes you want.

[Lonnie.Cady]

I agree not rocket science. 

So how does it handle threads that are not triangular?

I guess it is pretty weak implementation if if relies on the threads being a specific geometry.  I cut many threads that are not triangular.

Butress

Modified flank Butress

proprietary threads with a negative flank

Acme

and custom ground for windback seals.

[Lonnie.Cady]

If you are try to get the first DOC could you set your clearance to .1" over the major diameter then just do the math from the first cycle point?

In the example I used, I set clearacne to .1" over the major diameter.

Or you could set your top height to the major diameter and do the math and use   the operation:topHeight_value, 0.352 and subtract it from the first cycle point.

.904 clearance

.704 major diameter

From the post dump 

I can do the following math.

305: onCycle()
  cycleType='thread-turning'
  cycle.clearance=0.4520000043733852
  cycle.pitch=0.04999999924907534
  cycle.incrementalX=0
  cycle.incrementalZ=-1.69977052943913
  cycle.retract=0.4520000043733852
  cycle.stock=0.4520000043733852
  cycle.depth=0
  cycle.bottom=0.4520000043733852
  cycle.feedrate=0
  cycle.retractFeedrate=0
  cycle.plungeFeedrate=0
  cycle.dwell=0
  cycle.incrementalDepth=0
  cycle.incrementalDepthReduction=0
  cycle.minimumIncrementalDepth=0
  cycle.plungesPerRetract=1
  cycle.shift=0
  cycle.shiftOrientation=0
  cycle.compensatedShiftOrientation=0
  cycle.shiftDirection=3.141592653589793
  cycle.backBoreDistance=0
305: onCyclePoint(0.33411142394298643, 0, -1.5024999182993972)
306: onCyclePoint(0.32670174996683915, 0, -1.5024999182993972)
307: onCyclePoint(0.32101612391434314, 0, -1.5024999182993972)
308: onCyclePoint(0.31622289672611265, 0, -1.5024999182993972)
309: onCyclePoint(0.31200001558919593, 0, -1.5024999182993972)

(cycle.clearance .452) - (.1 clearance) - (cycle point .334) = .018"

or

(operation:topHeight_value, 0.352) - (cycle point .334) = .018"

second pass .008" or .026" total

third pass .005" or .031" total

fourth pass .004" or .035 total

it seems to check out close .018 * sqrt(2) = .0255

.018 * sqrt(3) = .0311

.018 * sqrt(4) = .036"

[Laurens-3DTechDraw]

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@Lonnie.Cady wrote:

If you are try to get the first DOC could you set your clearance to .1" over the major diameter then just do the math from the first cycle point?

In the example I used, I set clearacne to .1" over the major diameter.

Or you could set your top height to the major diameter and do the math and use   the operation:topHeight_value, 0.352 and subtract it from the first cycle point.

.904 clearance

.704 major diameter

From the post dump 

I can do the following math.

305: onCycle()
  cycleType='thread-turning'
  cycle.clearance=0.4520000043733852
  cycle.pitch=0.04999999924907534
  cycle.incrementalX=0
  cycle.incrementalZ=-1.69977052943913
  cycle.retract=0.4520000043733852
  cycle.stock=0.4520000043733852
  cycle.depth=0
  cycle.bottom=0.4520000043733852
  cycle.feedrate=0
  cycle.retractFeedrate=0
  cycle.plungeFeedrate=0
  cycle.dwell=0
  cycle.incrementalDepth=0
  cycle.incrementalDepthReduction=0
  cycle.minimumIncrementalDepth=0
  cycle.plungesPerRetract=1
  cycle.shift=0
  cycle.shiftOrientation=0
  cycle.compensatedShiftOrientation=0
  cycle.shiftDirection=3.141592653589793
  cycle.backBoreDistance=0
305: onCyclePoint(0.33411142394298643, 0, -1.5024999182993972)
306: onCyclePoint(0.32670174996683915, 0, -1.5024999182993972)
307: onCyclePoint(0.32101612391434314, 0, -1.5024999182993972)
308: onCyclePoint(0.31622289672611265, 0, -1.5024999182993972)
309: onCyclePoint(0.31200001558919593, 0, -1.5024999182993972)

(cycle.clearance .452) - (.1 clearance) - (cycle point .334) = .018"

or

(operation:topHeight_value, 0.352) - (cycle point .334) = .018"

second pass .008" or .026" total

third pass .005" or .031" total

fourth pass .004" or .035 total

it seems to check out close .018 * sqrt(2) = .0255

.018 * sqrt(3) = .0311

.018 * sqrt(4) = .036"

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Yeah you can calculate it from the given info.

(This was a really old thread bumped by someone else, I've moved on from G76, find that other cycles work just as well and are much easier to program)

I suppose the system relies on the shape of the tool now that I think about it, and the system only allows for threads that are the same shape as the tool.

So it is a limitation of the system but I'm pretty sure you could do it like designed now and does constant volume for all supported thread tools.

[Lonnie.Cady]

I did not even look at the dates, I just assume all post are new. 

The real problem is there are no other supported geometries for threading at this time.  Unless I am missing something.  What cycle did you end up going with?  I was under the impression from the first post that the G76 ran smoother on your machines.

I also think that the old constant volume thing is maybe not as relevant as it once was.  I have the sandvik 266 threading inserts and their recommendations don't really seem to follow it all that much.  Probably another area where it is going to be difficult for software to follow vendor recommendations.

[Laurens-3DTechDraw]

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@Lonnie.Cady wrote:

I did not even look at the dates, I just assume all post are new. 

The real problem is there are no other supported geometries for threading at this time.  Unless I am missing something.  What cycle did you end up going with?  I was under the impression from the first post that the G76 ran smoother on your machines.

I also think that the old constant volume thing is maybe not as relevant as it once was.  I have the sandvik 266 threading inserts and their recommendations don't really seem to follow it all that much.  Probably another area where it is going to be difficult for software to follow vendor recommendations.

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I usually assume the same. But since I was the topic starter I knew that it wasn't.

On the Siemens, I run G32/33 and on the Fanuc, I run G92. I found the retraction feed was different for G76 and G92 on the fanuc.

And now they are the same it runs great.

Well, we use the 266 Threading and just fill in the number of passes and actually run constant volume. Works great. But doing what the tooling guy says is really hard with threading indeed.