IHS cut height accurate?

Doing some testing with the torch off. Notice the cut height entered in Sheetcam does not match the cut height on the table. It is slightly less. I am not able to slide the .06" guide under the torch when the cut height is set at .06". Is the working correctly?

There are two factors that will affect your actual torch heigh when using IHS. The first is how stiff the material that your cutting is. The IHS has a switch mechanism in it that must overcome the weight of your torch as well as the 0.5 lb pre-load force in the IHS switch. What this means is that if you are cutting sheet metal, the material can act as a spring itself when pushing against the IHS switching during height sensing. This will decrease the actual height sensed by the switch. As a result, you will notice in our documentation we refer to an ‘IHS Spring Back’ constant. This is basically just an amount that you should add to our cutting height in CAM software when cutting sheet metal to account for the ‘springiness’ in your material. If you are cutting anything like 16 gauge and thicker you will likely not need this.

The second factor that affects IHS height is the backlash in the IHS system. When your torch moves down and touches the material, the lead nut trips a switch letting the electronics know that this is the plate height. Unfortunately, this data transmission can take a split second and in this time the lead nut might still be moving downward. As a result, you would need to account for this additional travel that the lead nut needs to move back up until the switch is closed. You will see us refer to this additional travel amount as the ‘IHS Backlash’. After testing a few dozen Z-axis systems in our shop, we determined the average switch lash to be about 0.020.

To sum this up, if you want your cut height to be 0.060" and you are cutting sheet metal, we would recommend that your actual programmed cut height is something like 0.100" in the program (0.060" cut height + 0.020 for IHS Spring Back + 0.020" for IHS Backlash). If you are cutting plate, you can omit the Spring Back and your cut height would be something like 0.080".

Hope this helps!

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Ok! Thank you! That helps!

Kristi

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The SheetCAM post I looked at seemed to already take the 0.02 backlash into consideration, resulting in GCode:
G0 Z0.02 (IHS Backlash)
G92 Z0.0

So would it not be more accurate to only do:
cutHeight = 0.060" cut height ideal + 0.020 for IHS Spring Back

?

Yes you are correct. We baked in the 0.020" switch backlash into the post processors for Fusion and SheetCAM but I thought it would be worth explaining.

We’ve found that on thinner material, it really is necessary to use an IHS Spring Back value to get the best results.

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I don’t think ours had the backlash tolerance built in. When I set the cut height to .080", the shim fit exactly. The material we are testing it on does not have any give to it at all.

Kristi

.02 Backlash is in the g-code. Not sure why we still need to add it. The material we are testing it on is 16 gauge aluminum. It doesn’t look like it is giving any.

Mike,

Can you direct me to the IHS documentation you are referring to. I am not able to find it.

Thank you,
Kristi

Has anyone seen the opposite of this scenario? I have made a few cuts and I’m trying to dial everything in, but I set my cut height to .060" and measure around .090" when the program is paused with the torch off. I was able to compensate for this in sheetcam by using .040" as cut height and measuring .060" but seems like something is a little off here. Is it possible that my Z-axis speed is to high and it’s not stopping quick enough on it’s way back up from the touch-off? I need to check my pierce height also. I’m guessing that it will be off as well.

Since the new update to thc ours is higher than it is supposed to be as well. We just edit in Sheetcam to make it correct.

Played around with this a little more tonight. Seems like if I run the .040 cut height it puts right at the recommended .060 if I measure. I checked the pierce height and that was pretty close to .150 when set at .150. A little odd, but manageable. Also found I am nowhere near the hypertherm cut charts. Their recommended speeds cut all the way through, just some decent bevels on the cuts. Still working to dial that in.

Did you ever find a actual fix for this or are you still lowering your cut height to compensate? Im having the same issue