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Roy Sanders
09-27-2015, 11:23 AM
Hello Group

I finally think my learning curve is getting shorter. Now it is the fine tuning between graphic design, software, and setup. I wonder if there is a formula or a 'typical' trick to getting this kind of engraving right over and over, as in multiple pen job. The picture is my first pen success. I do not have a jig, or know how to make one, and I have what is called a 'simple' rotary device.

I appreciate any feedback on how to set up to get a successful multiple pen job.

322255322257 The picture is not mine, the basic design is the same.:confused:

So now, if you were going to make 4 pens how would you set this project up to get a consistent and successful run?

As always, Thank You for your generous help

Roy :rolleyes:

Glen Monaghan
09-27-2015, 11:50 AM
There are at least two possible problems here. First, small variations in diameter result in larger variations in circumference (a change D in diameter results in a change pi*D in circumference) so, for example, if one pen is 0.1" narrower than the next, it will be about 0.314" shorter in circumference. A design that fits perfectly around the slightly thicker pen will overlap on the thinner one. If size changes from pen to pen, you have to adjust the artwork to suit each pen.

The second issue is with the rotary itself. Simple roller-type rotary devices rely on friction to turn the object that you place onto the rollers. Light-weight and/or smooth objects are problematic due to slippage. So you risk lots of problems trying to engrave a continuous wrap-around design without leaving a gap or overlap. Even a repeating pattern such as your celtic knot can be problematic, as shown by the varying spacing in your picture. Some roller type rotaries have a spring loaded idler pushing the object against the rollers to help reduce slippage. The other thing to do is size and space the design elements such that the "error" (what would be a gap or overlap) isn't obvious. In your example, you might place fewer of the knots around the circumference of the barrel so that there is a larger gap between each one. With a large enough gap, you can't easily see that the space between the last and first ones (which might vary due to pen size and/or slippage) is different than the constant space between the others. I'm guessing you have 5 knots engraved around the pen and the 1st and 5th nearly overlap while there is a visible gap between the others, so you easily see the spacing problem. If you reduce the number of knots to 4, you likely won't be able to easily see the discrepancy.

Roy Sanders
09-27-2015, 12:37 PM
Excellent reply, thank you. I will do the reduction. So what if I cut a .25" piece of acrylic into a wheel, say 1" diameter with a center hole the same size as the Pen tube? then I would insert a 'dowel' through the pen barrel and into the wheels. I would wrap the acrylic with one layer of tape to give grip, or maybe adhesive fine grit sand paper. Then the diameter would stay constant, and the graphic adjustment you suggested would play out as you think?

Your reply sparked the above 'jig' idea. I was already pondering the notion because none of my pen barrels are straight, therefore causing the barrel to ride only on the center.

Thanks, I'd like to see your thoughts on this jig idea.

Roy

David Somers
09-27-2015, 3:56 PM
Good morning Roy!

The thing you need to be concerned with is the actual diameter of the pen or other surface you are actually engraving on. Your software needs to know the diameter of that surface in order to function correctly. Your acrylic "wheels" may be the same diameter for every job but the actual surface of each pen is going to vary unless you are using a replicator or are extremely good at replicating the diameter by hand on the lathe. As Glen said, a slight variation in the diameter of a pen will result in a greater change in the surface area of your pen and you need to account for that in your graphic if you want things to remain lined up the way you want.

Think of this from a different perspective. If you have a 1 inch dowel on the lathe and you put a dot on the surface that dot will rotate a given distance in 1 revolution of the lathe. If you then put a 10 in dowel on the lathe and put a dot on its surface that dot will rotate a much greater distance in the same 1 revolution of the lathe. Even slight differences in the diameter of the dowel results in pretty noticeable differences in how far that dot will travel in one rotation of the piece. And that affects the size of the graphic you need to evenly cover the pen when you engrave.

it is the same principle that allows you to spin your pens at 3,000 RPM on the lathe, but would make you run for the hills if you attempted to run a 30in diameter bowl at the same RPM.

Some of the laser software packages will account for this when you tell them the diameter of the piece. They will scale the graphic to fit. But some don't and then it is up to you to change the graphic to match the new diameter.

Does that make sense?

Dave

Gary Hair
09-27-2015, 4:14 PM
The thing you need to be concerned with is the actual diameter of the pen or other surface you are actually engraving on. Your software needs to know the diameter of that surface in order to function correctly. Your acrylic "wheels" may be the same diameter for every job but the actual surface of each pen is going to vary unless you are using a replicator or are extremely good at replicating the diameter by hand on the lathe. As Glen said, a slight variation in the diameter of a pen will result in a greater change in the surface area of your pen and you need to account for that in your graphic if you want things to remain lined up the way you want.

That is true but won't matter if done properly, and I'll explain why.

Regardless of the diameter of the pen and the diameter of the wheels, if you turn the wheels exactly 360 degrees then the pen will turn the same 360 degrees. Yes, the surface area of the pen may be less than the wheels, but it still turns 360 degrees. So, the image will absolutely fit the circumference of the pen as long as the wheel doesn't slip and the pen and wheel are fastened together so that they turn together.

The wheel can't be too much larger than the pen so I would size the wheel to be just slightly larger diameter than the largest pen, and make sure the smallest pen isn't any more than a couple hundredths of an inch smaller. Size the drawing to fit a cylinder the diameter of the wheel. No matter the size of the pen, if it's within the focal range of the laser, the graphic will always fit perfectly around it, seamlessly.

This way you would never have to change the graphic as long as the pen is within the dimensions that work with that particular wheel. You could even make up several wheels and several drawings to accommodate a variety of pen sizes.

Roy Sanders
09-27-2015, 5:08 PM
Hi Dave

Yes, I do. A 1" acrylic drive wheel will turn the same whether a 3/4" barrel is between them or a 23/32, or 24/32. However all three of the barrels will turn at different speeds. (I actually remembered that principle once i read your reply.) I do not do much math in my current career.

Trouble is I am early out in a month and my niche business will require more math than it does during this learning/building phase.

thank you

Roy

Rich Harman
09-27-2015, 5:24 PM
I made a similar jig when engraving beer mugs. It consisted of two ~5" diameter circles joined by bungee cords. Each circle had a smaller hole cut in it to center the mug. It worked very well as long as no repositioning was required. In other words, making a second pass was not possible because it would not be in the exact same position after rotating around one way and then back.

For the purposes of making the graphics fully wrap around the pen the idea of acrylic disks should work just fine. I would only caution to be sure that the assembly does not "walk" down the rollers as it turns, messing up the alignment.

Glen Monaghan
09-27-2015, 11:16 PM
Agree, Gary, using the wheel jig that Roy described will nullify the problem with variations in pen diameter, and you don't want the wheels to be hugely different in diameter than the pens. You still have the slippage concern, with the jig because of the basic roller design. I don't think a layer of tape would help much, but something like 200 grit sandpaper or an emory cloth might do nicely. Even still, I'd expect misalignment on occasion if attempting an edge-to-edge wrap-around design, and still recommend the idea of using fewer repeated elements with enough space between to hide any offset errors from start to end.

Dan Hintz
09-28-2015, 7:29 AM
322257

A quick read of the replies says you've been aimed down the right road in terms of pen diameter being an issue with roller-style rotaries. So, I'll offer a possible solution... maybe. How mechanically inclined are you?

If you don't intend to use the rotary for anything else, remove one of the rollers completely. Replace the other with some form of spring-loaded tension clip and make it direct drive. Build up an acrylic fixture that allows you to slip pens in/out of it quickly using the new spring-loaded feature. Direct drive will guarantee you are sized appropriately every time.

It will take some jiggering, but you'll be much happier with the results.

Roy Sanders
09-28-2015, 9:01 AM
Hi Dan,

I am mechanically inclined enough to do the alteration you described. I am using it for other applications though. My wish is to learn how to engrave glass, wine bottles and wine glasses. I keep reading about the difficulty of laser engraving glass, so i am taking it easy.

thanks

Roy

Glen Monaghan
09-28-2015, 12:40 PM
You don't really need to remove one of the rollers. I mentioned adding a spring loaded idler to the existing setup. The spring tension presses the object more firmly against the rollers, increasing friction and reducing slippage, and can be made to remove or move out of the way if not needed for larger objects.

Dan Hintz
09-28-2015, 1:34 PM
You don't really need to remove one of the rollers. I mentioned adding a spring loaded idler to the existing setup. The spring tension presses the object more firmly against the rollers, increasing friction and reducing slippage, and can be made to remove or move out of the way if not needed for larger objects.

This won't work, Glen, due to the difference in diameters between pens... it's not about preventing slippage.

Think of it in the extreme. Put a 24" diameter glass vase on the rollers. Now spin the vase a full circle. I'll assume those rollers are 1" in diameter... it will take 24 turns of the rollers to fully turn that vase. Now put in a 1" pen... you only need to spin the roller once.

If you move to direct drive (the roller is the pen), one full rotation of the "roller" is one full rotation of the pen, every time, despite any variances in the pen.

Glen Monaghan
09-28-2015, 4:55 PM
Ah, I misunderstood what you were describing. You're essentially converting from a roller to a sort of chuck arrangement, which obviates the need for the jig wheels he proposed. However, he doesn't want to reconfigure the rotary so the jig wheels are a reasonable alternative which, when the rotary/jig wheels/artwork are all configured correctly, will take care of pen variances (within limits), and a spring loaded idler would then be a good idea to minimize slippage issues.