Compensating for Bit Shape when Touching Off

When you "touch off" brad point or V-shaped drill bits, but you want the bit to drill all the way through the material, how do you adjust your settings or programs? June 8, 2008

I recently purchased a Selex Mate and am using Cabnetware. I was wondering what the best way to adjust for the drill bits to drill all the way through our material would be, since using the touch off device measures from the point on the bit. The Cabnetware tech tells me that we shouldn't adjust the depth in the NC program and that I should adjust the offset in the machine software. The problem with that is when you use the touch off device, you would have to go in and change the drill bits manually every time. Kind of defeats the purpose of a touch off device. Any input would be appreciated.

Forum Responses
(CNC Forum)
From contributor I:
I have a 2006 Omnitech Selex Mate. My controller is an OI Fanuc. The touch off device is used for the 8 position tools only. They have a setup in the controller that you use the spoil board for the touch off. This allows you to get the shoulders of the brad point and not just the point. Talk with Omnitech. These guys are top notch and more than willing to help.

From contributor V:
I used to run Komo 4X8 made by Omnitech. The tech from Omnitech told me that the correct way to set it is by changing the offset manually after every spoil. The procedure he taught me was to add the spoil depth and .005, which in my case was .015. To access it in the machine, you go to parameters, then zero offset only change the ones on the far right. They should be - whatever, add the number you got to it and keep the negative. There should be a group of five at first, then another group. The touch off wand only works to touch off the motor; there is no program for the drill box. Note when you replace the spoilboard you subtract from this same offset. Measure the width of the old spoil with a pair of calipers. Spoil the new one to however you want it, then measure the width of the new one. Subtract the old from the new. Then with that number subtract it from your offset. Even doing it exactly by the book doesn't keep it right, so don't be afraid to make it go deeper or pull back on it.

From contributor B:
Another option: In your NC center tool catalog, there is a value for each drill called add to through cut. Increase this number to add extra depth whenever the drill bit is set to go through the material.

From contributor E:
That sounds like a nightmare. I just read that and already forgot how to do it.

From contributor J:
It doesn't matter whether you calibrate "touch off" the drills manually or automatically, most CNCs work the same way. When you calibrate, you're basically setting the zero point on the material and the software controls the depth from there on. If you want to go deeper, then you'd have to manually adjust the height offset... normal with most CNCs. If you use the brad point drill bits and calibrate it from the flat end, then you wouldn't have to manually adjust the depth at the machine or in your software. The problem isn't with the touch off device with Omnitech or any other brand. Manually or automatically, the solution would be to calibrate the area of the drill tip to where you want the cutting tip to stop. Just like if you were to calibrate a V-bit instead of a flat bottom bit and trying to make the V-bit go deep enough to the diameter of the V-bit tool. Some software systems may allow you to indicate the different drill bits and would automatically compensate for the distance. Check for this option within your software setting as well.

From contributor E:
Does that method work for G81 and G83 drilling cycles in the controller also?

From contributor J:
I don't see why not, since canned cycles are nothing more than repeat format codes to shorten the lengths of the programs. But since you asked, I would assume that you may have suggestions for everybody on how to overcome this inconvenience with canned cycles?

From contributor E:
I was asking in reference to how the touch off device can work to establish the G98 or G99 plane the G81/83 drilling canned cycle uses as the Z reference since the spoilboard is probably not the best thing to use as a retract position or a reference plane. If you don't see it as a problem, why do you request my advice to overcome the inconvenience?

From contributor J:
I didn't clearly understand your original question, but now I do - good point though. Thanks for your input.