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Author Topic: Hint about signage engraving  (Read 447 times)
Mark81
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« on: January 26, 2019, 16:46:11 pm »

I'm not sure if it's correct to post here this question or in the General usage section. My first questions on this topic are more related to a general cnc use than to the CamBam usage.

Let's talk about signage engraving. I'm going to try to engrave quite large stocks (for my standards...) say about 500 x 300 mm. The material is three-color ABS. The first color is obtained engraving at 0.1 mm depth, the second one at 0.3 mm depth. Overall thickness is 1.6 mm.

The first questions that come to mind is about how to handle such a "large" stock and guarantee the planarity.
Some people use a double-side adhesive tape, so my question is: is it enough to pocket the dummy plane (i.e. MDF) and then place the tape? I'm afraid about the 0.1 mm precision along the whole area. I mean, does not the tape squeeze under the bit?
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Bubba
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« Reply #1 on: January 26, 2019, 20:49:29 pm »

That's tight.. First question comes to my mind. How flat is the table and the relation of the spindle to the table is? If you got quality double sided tape, it may work.. Used this tape in the past (in my working for loving days) to hold an aircraft parts for very critical machining, and it held fine as long as I was paying an attention. Clean surface a must. And it also can be problem to remove the table from the part itself. Practice first.

Here is the tape I was referring to..

3M™ Double Coated Film Tape 9589   
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My 2¢
dave benson
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« Reply #2 on: January 27, 2019, 00:34:37 am »

Hi Mark
 
This software may be of use to you, I use this software (for engraving text on the battery compartment of my turrets) and it works very well.
The guy in the youtube link does a good job of explaining how to use the software.

http://www.scorchworks.com
http://www.scorchworks.com/Gcoderipper/g_code_ripper_doc.html#probe
https://www.youtube.com/watch?v=Yq_j3nZeFsM&t=349s

Dave
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Mark81
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« Reply #3 on: January 27, 2019, 05:17:13 am »

How flat is the table and the relation of the spindle to the table is?

I cannot wait for the new CNC to find out! Cheesy
It should arrive in few days.

Quote
If you got quality double sided tape, it may work...

Thanks, I'll give it a chance!

By the way, I found these products:

https://www.gravograph.com/products-and-consumables/consumables-and-engraving-materials/engraving-accessories/gravogrip

https://www.gravograph.com/products-and-consumables/products/engraving-machines-and-mechanical-engraving/mechanical-engraving-accessories-and-auxiliary-equipment/regulating-noses

but I don't know their price nor if they (especially the second one) are suitable for hobbbysts CNCs.
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Mark81
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« Reply #4 on: January 27, 2019, 05:18:57 am »

This software may be of use to you, I use this software (for engraving text on the battery compartment of my turrets) and it works very well.

Very interesting, thanks! I really need to add a probe like that!
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kvom
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« Reply #5 on: January 27, 2019, 12:48:28 pm »

For similar work I bought a vacuum chuck from Pierson workholding. 

https://piersonworkholding.com/vacuum-chuck/

Using this system I was able to hold 1/8" acrylic sheet and cut down to with 3 thou of the backing paper.  Not cheap, but if you do a lot of signs it may be worth exploring.
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lloydsp
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« Reply #6 on: January 27, 2019, 14:14:01 pm »

I have a larger router with a vacuum table.  The ritual there is to thoroughly clean the vacuum table, apply a NEW sheet of porous backer to it (medium-density fiberboard), then mill the entire surface 'flat' according to the router head's reference. 

The sheet might not be of the same thickness over its entire surface, but the top surface is perfectly-registered to the gantry's perception of what is flat.

We can routinely get 1-2 thousandths of an inch across the whole 4' x 8' table.  Needless to say, this could be adversely affected by looseness in any axis or 'torquing' of the spindle relative to the y-axis mount, if one were cutting too-aggressively.  But the depths of cut you're stating wouldn't challenge it a bit.

Something you might do is to apply a 'false top' to your table, fastening it with screws (recessed a bit from the top), and ensuring that there are sufficiently screws across the entire surface to prevent any buckling or bowing.

Then, mill off the top surface of the false top in order to assure flatness.  Since you don't use vacuum hold-downs, the material could be of a non-porous plastic capable of being attached-to by double-stick tape.

Lloyd
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Bob La Londe
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« Reply #7 on: January 27, 2019, 15:07:09 pm »

A method I use often for flat stock is to glue it to a sacrificial backer.  Sometimes that is not desirable as the stock may be damaged from breaking the glue bond either mechanically or with heat.  For those cases I'll use a sacrificial backer like MDF (or if coolant is used I'll use aluminum) I'll mill the backer flat, lay down a layer of painters tape on the backer, lay down a layer of painters tape on the stock, and then super glue them together.  I just use generic painters tape and generic super glue.  A very light misty of water on one side of painter's tape will activate the glue very quickly on the other side, but you better lay it down accurately the first time.  After machining I use a putty knife to wedge under the tape and work the piece up carefully to no over flex it.  Then I just peal the tape off the stock and/or off the backer.  Quite often when I cut out wood plaques I don't even cut the backer.  Just into the tape.  I can often do the next batch without even resurfacing the backer.  

You can't do "heavy" milling this was, but you can do modest milling and engraving with no problems.  Sometimes if it will be to time consuming not to do heavy milling, I'll the do the prep as above, then I'll drill clamping holes through waste areas and tap the hole below the stock for clamping screws.  If the stock will have holes I may mill or drill some of those with light force milling and drill and tap the stock below for clamps and clamping screws so I can finish with heavier milling.  

There are painters tapes that have a little stronger bond, and super glues with special activators, but its not enough improvement in my opinion to be worth it.  I just get a good brand of blue painters tape.  I do buy the 3 inch rolls so I can cover a backer plate or a piece of stock more quickly.  A slight gap between the rows of tape is not usually an issue, but an overlap can cause problems.  I do roll or burnish the tape in place to make sure is sticky side is engaged all over the surfaces. 
« Last Edit: January 27, 2019, 15:09:09 pm by Bob La Londe » Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
dh42
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« Reply #8 on: January 28, 2019, 02:49:51 am »

Hello

Also there is floating heads that exists and can solve problem with uneven surface on large engraving. (solve both problem of table not flat or material not flat)

https://www.sorotec.de/shop/Engraving-unit---Depth-control-GT43-6197.html

Attached is the PDF of the previous version of the head if it can be useful to do a DIY version.

++
David

* Tete_a_graver_GT-43.zip (1534.1 KB - downloaded 9 times.)
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Mark81
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« Reply #9 on: January 28, 2019, 17:32:15 pm »

As far as I understand the spindle should be inserted into the 43 mm collar.
If I'm right, there are two main downsides with this method. Firstly, it requires a quite heavy change in the machine setup. You cannot (easily) jump from a standard milling and a compensated one. Secondly, it's not suitable for machines (like mine...) with an industrial spindle with its own fixing.

Instead, in a previous post in this thread I linked a product from Gravotech ("Regulating depth noses") that should do the trick. But here the downside is you cannot use any tool, but you have to buy the exact one you want.
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Bob La Londe
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« Reply #10 on: January 29, 2019, 17:04:17 pm »

If cutting through layered plastic to create multi color signage I think that a machined flat spoil board and a glued down solution such as the one I suggested (easiest cleanup) or others would work well enough.  The layers should be sufficiently thin thick such that any minor variation should be easily overcome.  
« Last Edit: January 29, 2019, 19:14:11 pm by Bob La Londe » Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
Mark81
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« Reply #11 on: January 29, 2019, 19:04:01 pm »

Got it.
It may take other 2-3 weeks, but when I'll do the first tests I'll report here the results.
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