Laser Engraving Wine Barrel Staves

[Roger Lueck]

Has anyone had any success using a long focal length lens (3") for engraving barrel staves in the longitudinal orientation of the stave?
OR
Has anyone devised a method to keep the lens in focus for laser engraving a wine barrel stave over a distance of more than a few inches?

[Joseph Shawa]

They do make a 5" focal length lens.

[Roger Lueck]

Than you for the response. I was hoping someone had devised a way to compensate for the curvature of the staves as the 5" lens does not engrave fine details very well.

[Kev Williams]

Depending on how bad you want to engrave barrel staves, some Western machines, like my LS900 Gravograph, you can program the table to automatically adjust for focus on curved or stepped items...

[Glen Monaghan]

Somebody posted a "punkin roller" and someone else posted a "poor man's rotary", both of which had attachments to the gantry that rolled the engraved object from back of the bed to the front as the gantry advanced. You could adapt that idea to rock the stave such that the part directly beneath the gantry was always the part touching the bed and, consequently, at the proper focal length. Unfortunately, common laser beds are only 12-18 inches deep (back to front), which might not be enough space to allow for engraving across the middle area of your barrel stave in a single pass. Although you probably have enough space across the bed (left-to-right), and the scheme wouldn't work very well in that configuration due to the speed of the head, plus the rising end of the stave might hit the gantry if you engrave too far to the left or right side, plus the mechanical connections for the roller device to the head would be more problematic than connecting to the gantry (and you'd have much greater risk of skipping steps if your head uses stepper motors without an encoder).

[Kev Williams]

I sometimes wonder why someone hasn't adapted a Z-stepper motor to vertically move the lens tube just for this purpose. It would be very easy to program the lens to move same as my table does in my LS900, based on user input. A bit tougher but still doable would be for the lens to move based on 3D rendering, the lens could reliably move on the fly while rastering at full speed. A major benefit of having the lens move rather than the table, is that there would be no interference between the part you're engraving and the lens; moving the table upwards to engrave the low spots of an item mean the high spots can smack the lens if you're not careful. Almost impossible for that to happen with the item static and only the lens moving... almost ;)

[Brian Lamb]

No connection and it looks really rough, but this would illustrate the idea that Kev is talking about. This has a Z axis that could be programmed to follow the curve of the barrel stave as it travels the length of it.

https://phoenix.craigslist.org/evl/hvo/d/diy-cnc-router-with-35w-laser/6246716829.html

[Glen Monaghan]

A major benefit of having the lens move rather than the table, is that there would be no interference between the part you're engraving and the lens; moving the table upwards to engrave the low spots of an item mean the high spots can smack the lens if you're not careful. Almost impossible for that to happen with the item static and only the lens moving... almost ;)
The lens, being smaller and less massive, could more easily and quickly be moved than the table, so that's a good reason for fixing table height and adjusting lens on the fly, but "Almost impossible for [a collision] to happen with the item static and only the lens moving"??? How is it any safer (with respect to possible collision between lens and a high spot) to move the lens rather than the table? If raising the table a distance X to get a spot in focus gets a high spot up to the level of the (fixed height) lens where they potentially could collide, then leaving the table height fixed and instead lowering the lens by -X to get into focus would also get the high spot and lens on the same level and so the potential for collision remains.

[Kev Williams]

My point is that the lens would continually move to stay exactly 2" from the work it's engraving. There would be limitations of course, such as a 2" step in a piece of anodized aluminum, you could only get so close to the high step before the lens will make contact. This is true no matter what. If I program my table to engrave 4 steps, starting at the highest and working down, I'm the one who has to make sure the lens or focus plunger doesn't smack the high spot. But working in 3D with the lens able to move in the Z axis as fast as the X axis moves, the software, assuming it's programmed correctly, won't let a collision happen, and trying to engrave in a place on a lower step that's impossible because of interference, you'll get an error message saying so rather than a collision. Engraving stepped objects would best be done one step at a time, and the computer will adjust the lens. But a curved barrel stave, the X can raster the length of the stave, and as long as the gantry will clear the highest point of the arc, no problem.

I drew this up to explain myself :) --
actual size of the arc (stave) is 19-3/4" long and the arc is 4" tall. A moving-lens system could raster from end to end while the lens continually raises and lowers, staying perfectly in focus, AND not have any clearance issues. Note the guideline I placed at the lowest lens points, it passes thru the top of arc, interference- If careful you can manually keep a collision from happening, at least until the machine goes home. With this setup, never a clearance issue, within limits of course...
365283

[Scott Shepherd]

There's no way possible you'd do that Z movement at full speed of most western lasers. 140 ips and you'd want to be moving the z-axis up and down to follow the curve? Not going to happen on a physics level.

[Brian Lamb]

There's no way possible you'd do that Z movement at full speed of most western lasers. 140 ips and you'd want to be moving the z-axis up and down to follow the curve? Not going to happen on a physics level.

Then raster in the Y direction and you'd only need to move the Z axis up and down very slowly as the engraving proceeds down the length of the stave. It could be done in the software or just turn the barrel depending upon machine travel limits and the size of the barrel.