I'm want to try engraving on curved glass plaques - I need some advice and guidance.

[Roy Nicholson]

I'm going to try to engrave plaques similar to the attached.

I normally do not have any problems engraving on glass but these will not fit in my rotary device.

I see people talking about working out the midway point but please. What does this mean.

I take it I may have a problem working out the focusing point? Samples are arriving within the week so I'll play with them then.

I don't know what the difference in height in the curve is overall. I think it may be close to 2 cm or .75 of an inch.

I'm pretty sure it's engrave din reverse on the rear of the glass.

Regards

Roy N.


curved-surface-1-qpr.jpgcurved-surface-2-qpr.jpg

[Rodne Gold]

Various focal point lenses have differing depths of field where they have enough power density to engrave. You will be limited as to how much of the curve you will get decent engraving on due to this. Your stock 2" lens will probably have a depth of fiield of 4-7mm where it can engrave. If you moved up to a 4" lens ,you might be able to engrave more of the curve , however the spot size gets a lot bigger and you wont achieve as good engraving. I would suggest that you wont be able to effectively engrave these curved glass plaques unless you limit your engraving to the centre .

[Dan Hintz]

Rodney described the problem, but not all is lost if you're willing to do a little work. You'll need to split your engraving up into multiple pieces (or depths, if you will). For example, the "center" strip might cover letters that are within 1/8" of the focal point when the bed is raised to height 'X'. The two strips surrounding the center may be within 1/8" of the focal point when the bed is raised to height X+1/4". This continues until you are either done, or the strips become so small as to be impractical (the the carriage starts hitting the object).

[Rodne Gold]

Heh - that's a lot of work....what he will also find is that due to curvature the beam will not hit the glass square on but at an angle , that will also give him hassles.
I wonder how hard it would be to design a "part rocker" or a variable focussing system for the head , perhaps something that just changes the lens distance based on some sort of doppler system? Cmon Dan , there's a worthwhile project for you

[Dan Hintz]

Cmon Dan , there's a worthwhile project for you

It's nothing I haven't considered, that's for sure... but until ULS gives me access to their driver code (fat chance), I'm not going to waste my time trying to work around their own series of bandaids. I wasn't thinking real-time (doppler), more of a scan-before-start type of setup, but still...

[Michael Hunter]

You are thinking too technical Dan!

How about this -
Place the glass so it rocks in the Y direction (up and down the bed).
Hang rollers from the x-beam, lightly pressing on the glass so that the part of the glass under the carriage is flat.
The glass would probably need to be on top of "stick mat" or something similar so it didn't skid about.

[Gary Hair]

Sandcarving - no worries about focal point. Besides the fact that sandcarving is the ONLY way to mark glass (my opinion) you don't have to worry about focusing the laser. I would make a photoresist and blast away. By the time you guys come up with a clever method of moving the glass, I'd be done and drinking a cold one...

Gary

[Hilton Lister]

Not really a job for the laser in my opinion. Much less hassle to mask and sand blast.

[Dan Hintz]

You are thinking too technical Dan!

I was trying to come up with a solution that could be used for any non-flat object (what about a hubcap?), not just a partial cylinder that can be rolled.

[Michael Hunter]

Wow - serious project then Dan!

This train of thought led me to think about a cheapy "rotary" for cylindrical objects.
I can't justify the £1,000+ that Epilog ask for their rotary here, as I only get around one request per year that could use one.
A set of rollers and a pusher glued under the x-beam might work and should only cost a few £. Time to break out the CAD.

[Rodne Gold]

You can get a rotary from China real cheap , the one with the chuck is $180 and one similar to the other 2 pics , cept it has knurled cylinders rather than the rubberised disc rollers shown is $123 - I'm sure you can adapt em for your laser.

[Dan Hintz]

Go for the chuck type... when deciding between Epilog and ULS, Epilog ranked lower on my list because I saw slippage as a problem with their rotary.

[Roy Nicholson]

Thanks everyone... good job I've got a sandblasting set up available.


Regards

Roy N.

[Michael Hunter]

Yipee! - Just got this year's rotary enquiry.

Nylon cylinders 9.5" diameter and weighting 35lbs.
Too big a diameter to fit into the machine at all, let alone with a rotary underneath.

Just so pleased that I did not waste money on a rotary!

[Roy Nicholson]

Here's my attempt at those curved plaques.

I'm quite pleased with the result so far.

I kept the engraving to the central area of the plaque.

I'll try shortly to see what the extreme engraveable surface area is.

It'll be worth wasting a plaque as a test.

My phoography skills aren't the best.

Regards

Roy N.