Messages

4181

Show"N"Tell ( Your Machines) / Re: The Laser Project.

« on: April 02, 2015, 06:47:49 AM »

Hi Ian,
 
Pre-heating or pre-cooling the glass is something I will have to try.
Perhaps tangential lines may make it easier to remove the parts - I don't know but I suspect that the fracture produced in radial lines may continue in a straight line rather than following the shape - something else for me to try.
Thanks for the suggestions.

Tweakie.


(There are more details of the tensile stress cracking technique in this document  http://www.jklasers.com/images/ZeroWidthGlassCutting.pdf )

4182

Mach SDK plugin questions and answers. / Re: 5 axis kinematics coming soon !!!

« on: April 02, 2015, 05:31:35 AM »

Very impressive 

Tweakie.

4183

Show"N"Tell ( Your Machines) / Re: The Laser Project.

« on: April 02, 2015, 03:17:00 AM »

Hi Terry,

Many thanks for the suggestions, they are gratefully received.

You are, of course, absolutely right about behaviour with a scribed line ( I have seen your excellent demonstrations with bottle cutting) but, unfortunately, CO2 lasers don’t produce the right kind of line. Because of the wavelength the CO2 beam is absorbed into the material causing some surface micro fracturing and some melting with the bottom of the kerf being randomly rounded and this prevents the glass from breaking along the line (many before me have tried this method without success).

The patented idea of ‘tensile stress cracking’ turns the tables, so to speak and relies on the laser beam being out of focus to heat the glass rather than mark it and it is usual to cool the glass some 10 or so mm behind the passage of the beam. For me, this is OK for straight lines but the toolpath starts to get extremely complicated for shaped working (where tangential control may be necessary for the air/water mist cooling nozzle).

With my experiment I attempted to create as much thermal shock within the glass as I could manage and it sort of worked (at least I got the discs I needed) but I found that it was necessary to create a fracture at an edge for it to follow the toolpath line and there is a technique to doing this. Perhaps, when I get more time to spare, I will investigate this further and hopefully be able to produce better quality results.

It is certainly a subject for thought. 

Tweakie.

4184

Show"N"Tell ( What you have made with your CNC machine.) / Re: Guitar Strings.

« on: April 02, 2015, 02:32:02 AM »

Thanks for the kind words guys.

The machine is currently awaiting new stepper drivers which will operate at a higher voltage and tests have shown that this will hopefully (32 x sq. rt. of inductance and all that) double the winding speed.

The significant difference (visually) between these 'custom strings' and 'store bought strings' is that they are finished both ends to a defined length. This initially caused problems as the actual number of turns of wrap can differ considerably from the theoretical (calculated) number but, on the plus side, it can use a round, cross section, music wire core instead of the hex / oct sections usually used.

Development of the machine and the controlling software will no doubt continue way into the future (a bit like a CNC machine never being totally finished) and when the time is right I will try to get some video's made of it in action.

Tweakie.

4185

Mach4 General Discussion / Re: New people welcome !! Come in here and introduce your self!

« on: April 01, 2015, 12:27:56 PM »

Hi Mark,

Welcome to the forum.
As a luther, this should make you smile http://www.machsupport.com/forum/index.php/topic,28721.0.html

Tweakie.

4186

Show"N"Tell ( Your Machines) / Re: The Laser Project.

« on: April 01, 2015, 11:46:47 AM »

Thanks for the encouragement guys, it is much appreciated.

If only I knew the secrets of shaped glass cutting it would all have been a lot easier insofar as selecting the correct toolpath for the job. In my ignorance I just used a standard toolpath (as shown in the top of the picture) and although the glass cracked, with that layout it is not going to come apart any time soon. Brute force (more power) worked but it is not really the right way to go about it.

To cool the glass I used cold air (passed through half a dozen turns of tubing submersed in an ice bucket) with the glass resting on a milling machine parallel which had previously been placed in the deep freeze for a few hours.

There has to be a better way – it’s just a matter of dreaming it up.

Tweakie.

4187

Show"N"Tell ( Your Machines) / Re: The Laser Project.

« on: April 01, 2015, 08:35:28 AM »

A bit of experimentation here…

It is not possible to cut soda-lime glass with a CO2 laser but, some while back, I read a couple of patents which cover a ‘fracture technique’ where the laser is used to heat the glass (causing compressive stress) and then the glass is cooled (causing tensile stress) which in turn creates a fracture along the defined toolpath.
Obviously I have much to learn here but needing 2 x 20mm diameter, opaque glass, discs I thought this process may be worth a try.
I found that straight line fractures are relatively easy to achieve but circular fractures needed a bit more thought.
On my first attempt I found it impossible to remove the discs so using slightly more power on the second run I created radial fractures in all directions and I now have the two required discs which fit the intended application perfectly. The edge quality is not that good (but that is unimportant for my application) although I think refining the technique will lead to better quality results.

Just thought I would share the info for any others that may be interested in experimenting with laser glass cutting.

Tweakie.

4188

General Mach Discussion / Re: Homing problem - Slave Axis stopped responding

« on: March 31, 2015, 01:47:44 AM »

Hi Plan_B,

Thanks for reporting back on the solution to the problem - this will no doubt help others who find themselves with a similar issue.

Tweakie.

4189

Show"N"Tell ( What you have made with your CNC machine.) / Re: 1/5th Scale V8 Blown

« on: March 30, 2015, 07:17:28 AM »

Words just cannot describe the wonderful work you produce Steve. As Scott has said:- WOW !!

Tweakie.

4190

General Mach Discussion / Re: program skipping commands (not steps)

« on: March 28, 2015, 11:55:57 AM »

Just out of curiosity, is your Gcode program longer than 500 lines of code ??

Tweakie.