AVHC sense pressure?

[MoparJon]

As I understand it, the AVHC senses the surface of the metal by coming down to make physical contact, and somehow the resistance in the servo motor is able to be read such that the AVHC knows when the torch hits the metal.

How well does this work with thin metal? If I were cutting some 26 gauge which had warped up, it might be relatively easy to push down on it without meeting with much resistance at first. On the initial sense, if the torch were to push the metal down for say, 1/4" before it recognized that it was meeting with some resistance, this would result in an a pierce where the torch is sitting right on the metal.

Is the above scenario a potential problem, or is the AVHC sensitive enough on the initial touch to prevent this?

Thanks!

[Like Butter]

An excellent question, I wish I had an answer but we're in the same boat.

[MoparJon]

An excellent question, I wish I had an answer but we're in the same boat.

Thanks. I thought it was a decent question, but I guess I could be wrong.

At any rate, I do have the answer now, having purchased an AVHC and am in the process of setting it up. The question was actually addressed in the installation manual, so I'm not sure why we didn't get an answer here. (I wish Torchmate would post this stuff on their web site instead of having to spend $2500+ before getting the documentation...)

To paraphrase the manual, the torch will put 5-10lbs of pressure on the metal when sensing it. I notice that this can be adjusted in the height controller, not in lbs but as a percentage (a percentage of the servo motor's torque, I assume.) The factory setting is somewhere around 14-15%. I played with this a bit and this appears to be about as low as you can go. I tried 10% and various other settings, but the friction within the height control itself was enough to cause a false sense. About 14% seemed to be the lowest I could go and have it reliably contact the metal. If you are interested, I could try to measure the actual contact pressure, perhaps by placing a scale under the tip. I do have a postage scale which would be quite accurate, but the tip contact is such a short duration that I don't know if the reading would be able to stabilize in time for me to read it. I can certainly give it a try though if it is something you'd be interested in. If nothing else though, the manual does say 5-10lbs, so we've got that to go on.

According to the manual, I was correct in my assumption that if the material flexes, the initial torch height will not be correct. The manual lists two ways of compensating for this. The first way is if the flexing is consistent, you can adjust the pierce height. For example, if you wanted a pierce height of 1/4" and upon sensing, the material always flexed 1/4", you would set your pierce height to 1/2" such that you get your 1/4" gap after the material has flexed back. The second way is to use a hand torch style drag tip such that a standoff is always maintained, even if the material is touching the torch.

IMHO, neither method seems perfect; if by some chance the flexing was consistent, I'd definitely go with the first method, but I don't see this happening in the real world since a torch sense between slats as opposed to right on a slat with flexible material is going to be different. The second method would give you a safe pierce to be sure, but I think you'd have to compensate for the drag tip by increasing your cut height, otherwise it might drag and catch on the material during the cut, and that increased cut height will likely result in a cut with a wider kerf and/or more slag. (I think PlasmaCam uses a drag tip, so this method might be OK, as long as the material is anchored well enough so that it won't allow the torch to shift it? PlasmaCam might just be allowing the torch to float on top of the metal though as opposed to the AVHC being held by a servo.) Another thing I wonder about with the drag tip is what if the torch pushes down between slats far enough that the cut height is actually below the top level of the slats? If this were the case, I wonder if the tip of the torch would actually crash into the side of a slat? If so, that can't be good.

I built my table with slat supports every 3", but I don't put a slat in each one, I generally cut with a 6-9" gap, depending on the material I am cutting, mostly just to save wear on the slats. I think that if I need to cut thin material though, I might need to go with that 3" slat spacing. I had also thought about basically tack welding thin material to the slats in order to help prevent this deflection, but I'd rather not weld on the table with all of that expensive electronics around.

I haven't gotten everything set up as of yet so obviously I haven't had a chance to try it on any thin materials, so I might be overthinking things. I'll just have to see how it goes. As soon as I am set up, I do plan to cut a bunch of 18 gauge, but that's probably the thinnest I will be doing at the moment.

Sorry for the length of my reply, it certainly doesn't have the authority of a factory response, just user to user, but I hope it helps you out somewhat! (Probably just raises more questions!)

[gshst]

we cut 24 ga sheet and the lowest torque we can set it at is 14 we also make sure to clean the hieght and keep it lubed to help in the sensing