Deep engaving on granite?

[John Stephens]

I am quoting a job for engraving a quantity of granite
markers. They will be outdoors.

My client wants the engraved letters to be deep enough for people
to do a pencil tracing over. It does not have to be as deep as
routed or very deep rotary engraved letters.

I have several lasers so time is not a great issue.

Does anyone have any tips on how to get some extra
depth in the letters with or without repeating the burn
many times?


Thanks for your help.

John

[Gary Hair]

"You can't get there from here..."

A laser only fractures the shiny surface of granite, it doesn't get any depth. You can run as many passes as you like, it's not going to get any deeper. The ONLY way to get depth is by mechanical means - sandcarving, chisel, etc.

Gary

[Dee Gallo]

What Gary said.

[George M. Perzel]

What Gary said and Dee concurred with

[Richard Rumancik]

John, probably your best choice is to use the laser to cut a stencil with PSA on the back (from heavy mylar or light rubber). Then you can get someone to sandblast the granite to the depth you need. (I'm assuming you don't have sandcarving equipment.) If it works for you then you might consider some equipment in the future but maybe linking up with an experienced sandcarver would be the easiest approach in the short term. You might want to get some scrap granite pieces to do some experiments on.

[John Stephens]

Richard, Thank you for the reply and advise. We actually
do some sandblasting but only on glass so far. On glass we
use vinyl bumper sticker stock to cut stencils on the lasers.
Do you have any suggestions for the material we should use
for the granite stencils. As we will be blasting deeper than on
glass we may need something a little thicker with stronger adhesive.


Thanks again,

John

[Richard Rumancik]

John, I'm sorry I don't have any specific products to recommend - I tested lasering a 3M rubber stencil material many years ago but I am not really into sandcarving. Some people have had success with mylar type sign materials - you could also double it up if need be. But it depends on how you are going to cut the stencil. The traditional way is with a cutter-plotter but it sounds like you have just been using the laser. Are you laser-cutting the stencil and then using transfer tape to apply it to the granite? I suppose that if the granite is not too thick and not to heavy you might have luck applying the mask directly to the granite, lasering, weeding, and then sandcarving. In which case you could layer vinyl or mylar to give it more "blast" resistance. Maybe some active sandcarvers can offer some specific product advice.

You might ask the people at Rayzist if their Lazermask product would do what you need. I think it is normally used on glass but it might stand up long enough.

http://www.rayzist.com/Film/Lazermask.php

[Gary Hair]

John,
To blast granite tiles you'll want to use 70 grit, any finer and it takes way too long, 1/16" nozzle, 65 psi, and 10 or 20 mil resist. I use Anchor T227, it's 22 mils thick and it's polyester based so it is perfectly safe to laser. You could use 116 or T226, but they are both high tack where the 227 is medium tack, high tack on polished granite is too sticky and will be difficult to remove. Clean the tile with denatured alcohol, apply the resist, laser, weed and then roll with a rolling pin to ensure the stencil is stuck after weeding, then blast away!

Gary

[Richard Rumancik]

Gary, if I ever try this I'll follow your suggestion on the Anchor products.

John, if there are large sections, the high-tack might be difficult to remove, but it depends on what level of detail is required and the font sizes used. The last thing you want is to have the center of a character blow off, and with a small font you need to watch for that. Also if there are thin sections high-tack might be needed to avoid lifting.

Can't say for sure, but if the high-tack is used, a heat gun would probably help release the adhesive. (It is sometimes surprising how a little heat can make a stubborn adhesive release easily.) Gary, have you tried heat on the Anchor product?

[Gary Hair]

Richard,
Since I stopped using high tack on polished surfaces I haven't had any problems with removal. The medium tack is plenty sticky enough even for the smallest details. I have one recurring job that I use medium tack on slate tiles, not very smooth ones, and there is a line around the border that is 1/16" wide and text that is 24 point - no problems with either. As long as you make sure the nozzle is 90 degrees to the stencil and you don't stay in one place too long, medium tack will stick to almost anything. I have gone as high as 80 psi but that's pushing it.

Gary

[John Stephens]

Thank you all.

John

[Brian Backner]

One thing I have used as a resist is "ProtectoWrap" - a self-adhesive and thick rubberized material for flashing and waterproofing windows - you can get large rolls of it at Home Depot or Lowes for less than $20.

The particular job I ran did not need the material to be lasered - we just cut it with an Xacto knife. It held up very well to 60 grit AlOx as long as you kept the gun moving.

I don't have a roll of it handy right now, but I don't think it's PVC based - I'd certainly want to check that before trying to cut up a piece in my laser,though!

Brian