Bad lens - but not at first glance... Epilog Helix

[Rodne Gold]

Depends what you actually mean by "banding" , if its longer alternating patches of lighter/darker engraving , it's usually not lens related In general , the banding that is like proper "bands" of differing engraving at random or even distribution is caused by mechanical , software, tube or fluctuating electrical supply issues. You really have to define the type of banding you getting and under what conditions it occurs to effect the correct solution.
It is certainly possible that what you say could occur , the banding that occurs in this scenario would always happen at the same points relative to the table and not relative to the graphic.

[Dan Hintz]

I see your point, but in that case the pattern would likely be non-repeating as it would slowly change from left to right over the entire table, not every few inches. Anything is possible, though...

[Doug Fennell]

I tell you, I'm goin' nuts at this point with the banding issue. I'm at the mercy of Epilog to a degree with their troubleshooting on this - I've had 2 Epilog techs tell me 2 completely different things. One says tube, one says optics. I wasn't trying to play them against each other or anything like that either... I just called back the next day after I tried the troubleshooting the first tech suggested and got another tech. The current tech's name is Ian Vanderjag. Truthfully, I don't care if it's the optics, tube or both - I just need the problem fixed. Optics should be here tomorrow - put them in, do an alignment and see what happens I guess. The tube in my helix is 5 years old, so that very well may be the issue.

[Zsolt Paul]

I'm not sure I agree with your assessment that it was the lens, Z... here's a quote from that thread:

The beam covers a large portion of that lens, so rotating it would have little to no effect on the beam hitting the spots or not (not to mention you're rotating a round lens, which just changes where on the incoming beam the spots hit, not if they hit). The more likely explanation to the disappearance of your problem would be to you fiddling with the lens holder, applying pressure to the rails, the connecting band and cogs, etc.

Not sure if it was clear from that quote (from my old post) that I rotated NOT the original lens, but the new one I just got a day or two prior. This one only had one small spot on it (unlike the original lens) and it was off center enough that by rotating it, it went out of the way. I believe the beam width is too narrow to reach that spot. There were 2 times when my banding issue went away:
1: when I put in the new lens (then the new lens strated doing after having observed a drip on it which had stained it permenantly so #2)
2: when I rotated the new lens so that the beam would hit a virgin part of the lens

Both times ONLY changing the lens made the problem go away.

[Dan Hintz]

Not sure if it was clear from that quote (from my old post) that I rotated NOT the original lens, but the new one I just got a day or two prior. This one only had one small spot on it (unlike the original lens) and it was off center enough that by rotating it, it went out of the way. I believe the beam width is too narrow to reach that spot. There were 2 times when my banding issue went away:
1: when I put in the new lens (then the new lens strated doing after having observed a drip on it which had stained it permenantly so #2)
2: when I rotated the new lens so that the beam would hit a virgin part of the lens

Both times ONLY changing the lens made the problem go away.

That just doesn't make sense in a properly set up machine. Let's say the spot was 5mm off of center... rotating the lens still leaves the spot 5mm off of center, but now it's simply in a different location. If the beam was properly centered on the lens, it will still be partially occluded by the spot. The only way the beam could no longer be affected is if the beam was not hitting the lens dead center... which means you have a set up issue.

If you were observing condensed water on your lens (drips), you have a serious water contamination problem that needs to be dealt with... another set up issue.

[Zsolt Paul]

That just doesn't make sense in a properly set up machine. Let's say the spot was 5mm off of center... rotating the lens still leaves the spot 5mm off of center, but now it's simply in a different location. If the beam was properly centered on the lens, it will still be partially occluded by the spot. The only way the beam could no longer be affected is if the beam was not hitting the lens dead center... which means you have a set up issue.

If you were observing condensed water on your lens (drips), you have a serious water contamination problem that needs to be dealt with... another set up issue.

Speaking strickly for my machine, assuming that the beam stays 100% center at all times at all places of the bed is a huge assumption, even when it IS set up correctly. My bed is pretty large (51x51 inches). Indeed, as it travels from extreme left to extreme right (or from one corner to diagonal opposite), there might be a slight deviation from dead center. Lets say for example the beam goes from center to slightly right as it travels. If I have a bad spot on the lens on the right edge of where the beam hits the lens, and I rotate it 180 degrees, the bad spot will be on the left and the beam will never be hitting it (since it only moves from center to right). This actually would explain the banding pretty well.

Even if the rotating wouldn't have worked (lets say for example the beam moved from equally slightly left of center to slightly right of center) replacing the lense would have cured it (as it did for me the first time). I now have a new lens in and don't have the problem.

Regarding the moisture issue.... we have been having EXTREMELY humid weather for weeks. I have a long hose AFTER the compressor and a water separator just as it enters the machine. Not sure how much more I can do about that. I now check the lense after every job and so far there has been no spots on the lense, exept yesterday after a job that ran over 3 hours straight cutting wood. I cleaned it right up. I'd say that's not bad.

[Doug Fennell]

Oh man, I am so glad it's fixed...
652.jpg

Installed new optics and ran the file - no more banding!! I NEVER would have thought this would have been the cause, but the proof is what it is. I'll report back to say if it stays fixed or not.

[Dan Hintz]

Is that banding I see in the fence about halfway down the visible portion of it, or is that merely a stain on the fence and in the original photograph?

[Frank Corker]

I saw that too and wondered if it were banding.

[Doug Fennell]

I don't think it's banding - there is a darker area on the photograph in that area, but not that pronounced. Photograve accentuated it? What would be the next thing to test I wonder? It is without a doubt vastly improved if this is banding.