Let’s talk about the purpose of the IHS backlash .02 added by the post processor.
Can anyone from Langmuir state the reason that is in the post processor?
I see some referring to it being necessary only on thinner material but this doesn’t make sense to me as your material flex has the potential to vary throughout a whole sheet.
It seems to me that is to account for “play” within the z axis lead nut or IHS mechanism itself.
My programmed cut height comes out perfect without changing the post processor so it seems as though it’s there for a reason.
Springback in Fusion is what compensates for material flex. Backlash is supposed to compensate for play between the lead nut and screw.
I’m not familiar with the older version of the IHS cycle, so maybe it was necessary when using that version.
The current version sets the Z zero when the switch closes, with the Z axis on the way up. The act of lifting the Z carriage removes any backlash, because the weight of the torch and Z carriage keeps the nut in constant contact with the threads of the screw.
So are you saying there are two different styles of z axis or two different post processors? I don’t quite understand this. I thought there was only one post processor and it had the .02 built in.
I didn’t fully understand the spring back term (I don’t use fusion) until recently, and fusion adds that “backlash” .02 on top of whatever you put in “spring back” right? So 0 springback in fusion results in .02 still in the post, but .02 in springback results .04 in post.
If under stand correctly, yes, Fusion adds .020" springback and .020" backlash for a total of .040" from Z zero. If we enter a negative springback value, Fusion still computes with the .020’ backlash adjustment. (i.e - -0.020 = 0.0000" - Springback less 0.020" equals X. If Sringback was set to .0.000", backlash would still be 0.020".) A negative springback value will correct the Post. (i.e. - Springback of -0.040" will nullify the springback / backlash adjustments.)
Some of the new post’s have the ability to adjust this, but the base 1.6 post does not. If you’re using 1.6, please adjust your pierce height / cut height based on the above. (You may have to change pierce height / cut height based on real world environments.) Please verify actual cut height / pierce height before making substantial changes.
The Z axis is the same on all versions. There was a different IHS sequence in a much older version of the Firecontrol post processor. That version had the torch probe down twice before setting the Z zero.
I don’t have any examples of that code, so I don’t know if that version used the opening of the switch, on the way down, to set the zero. That sequence would require a backlash compensation, since it would take the reading in an unloaded state and then rise to a loaded state.
I know this is throwing out more confusion but the “backlash” is really an interesting concept/solution for the variations of the movement of the plate under the weight of the torch.
These are the variables that confuse me:
If the slat is directly under the torch position, it would not matter it the metal was thin or thick…it isn’t going to “give.”
Thin metal backlash will vary based on the distance from the nearest slat.
Some metal, even 12 and 10 gauge may not be totally flat. That is why I am glad I have THC and Nominal Voltage available.
I am sure that the engineers did lots of testing but, at best, this 0.02 inches is a compromise: Not an exacting science approach.
What you are referring to is spring back. The metal deflects under the weight of the torch and then springs back when the torch is lifted.
Backlash is the play between the threads of the nut and the screw. When the lead screw reverses direction, the backlash is the amount that the screw must turn before the nut starts to move.
I’m trying to nail down the advice that’s being given on modifying the post the remove the backlash compensation. Earlier it seemed like you said the backlash compensation is not necessary because of the weight of the z axis. In this post you say it’s the amount the screw must turn to start moving before the nut starts to move?
Another point is that if your using nominal voltage your pierce height maybe too high with the .04" added. The cut height will be determined by the nominal voltage entered not the programmed cut height so it should be correct. It only when using smart voltage that the additional programmed height will cause the torch to cut too high.
I was defining what backlash is for ChelanJim. When the lead screw changes direction, there is a small amount of rotation of the screw that takes up the play in the threads, but does not result in directional movement of the nut. The software records those steps in the stepper rotation as directional movement, when no movement has actually occurred. This isn’t an issue for X/Y movement, since they have anti-backlash nuts.
To be clear, I don’t feel that backlash compensation is necessary using the current version of the IHS cycle. Since the Z zero is set when the switch closes and the lead nut is loaded in the correct direction.
I don’t have code to examine for the much older version of the IHS cycle, that probed the torch down twice before setting the Z zero, so I’m just speculating that it used the opening of the switch to set the Z zero. In that scenario, which is opposite of the current IHS sequence, the backlash compensation would have been necessary. The reading would have been taken with the screw driving downwards and the screw must reverse direction to lift the torch to pierce height.
I suspect that the compensation in the post processor was a holdover from the older version of the post processor.
That was a good explanation. I think it’s taking better shape for me now. But if the .02 wasn’t necessary, wouldn’t all of our programmed cut heights be off by .02?
Apologies for the delay, not sure why I didn’t get a notification that I was tagged in this thread.
The purpose of the IHS Backlash is twofold:
To account for flex in the material as a result of the torch contacting the sheet during the IHS sequence, and…
To compensate for any potential delay between the brass contacts separating (breaking the continuity of the IHS switch system) and the Z-axis actually stopping.
Both of these factors are highly variable - you can set the cut height lower if neither appears to be affecting you regularly!