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Monday, September 13, 2021

MoBeam: Vertical Adjustment Slide

 Adjustment Slide

Not yet knowing what's the best way to adjust focus for my L7X I decided to build a slide that would enable simple adjustment of the diode modules vertical position. 

UPDATE: this design has been deprecated and replaced by: https://donsthings.blogspot.com/2021/12/mobeam-laser-head-mounting.html

Available Designs:

Some lasers come with a slide... that would have been nice! Laser module w slide
I also found a few on: 
This is a simple design and concept. Replace the stock carriage interface plate with one that has a sliding channel for the diode module. The up/down motion is achieved by loosening a binding screw, sliding the laser module, and then retightening the screw. 
This may be too simple for long-term use but I needed to make a fast prototype that would allow a large yet simple range of adjustment. Using this proto I will identify how much range & precision the vertical adjustment needs to have.

Once the adjustment needs are identified I may change the approach to a screw slide.

Stock Interface Plate

This plate is removed from the unit, the slide replaces its function. I used the stock interface plate as a template to get the holes of the new plate in the right place.
Tape this plate to the blank you are using for the new slide and drill through it to get the fastening holes in the right place.

Slide Design

The slide consists of 3 parts. backplate, side guide, front cover. This is a simple design to help me understand what the final design will need in regard to adjustability. If the head does not need much vertical adjustment and accuracy is not a factor, this may be a good approach. Otherwise, a screw-driven approach may be better. 

Backplate:

This plate mounts directly to the carriage using the stock top thumbscrews. For this plate to mount flush on the carriage it must have features drilled to accommodate the belt and tire mounting bolts.
Note: you will notice many holes in the photos of the slide. I reused some old plastic that was previously drilled. Therefore ignore the holes in the picture and reference the drawings.
Note the heads of the tire mounting bolts and belt retainer

Side Guides:

These two parts create the walls that the laser head slides within. There are two 8-32 nylon adjustment thumbscrews that hold the head in position in the slide. 
These parts also have two #4-40 inserts pressed (with heat) into their edge. These inserts are used to mount the front cover. I used SAE fastners but any type small fastener that will fit edgewise into the guide will work. I got my inserts from McMaster
The thumbscrews came from my fastener collection but most any 8-32 fastener can work. I think I got them at Lowes, Ace is another place to check. I used nylon to prevent galling the side of the laser module.

Right side view

Left side view
Front Cover:

The front cover is made from .080 acrylic but thickness is not critical. This cover exists mainly to keep the side guides from deflecting when the adjustment screws are tightened against the laser module. In a future design, this cover may be replaced as part of a safety cover once I verify what the focal point dimensions are. 

Update: modifications

I had to cut the assy off just below the screws. At the proper focal distance, the slide was in the way of the microscope and blocked me from adjusting the lens. The focal point was set at 30mm below the lens's surface.
*USB microscope used to set the focus.

Modified Slide

Picture

Slide Fab

Attached are 1:1 traced drawings (not CAD) in case you want to fab a slide. These drawings are traced from the actual part and some nominal dimensions taken from the actual parts are added.
 
I made this from 1/4"  & .08" clear plastic (Lowes), cut it on the table saw and drilled with metric twist drills. The larger holes were drilled with Forstner and step bits.
 
I clamped the stock adapter plate to the new slides backplate as a template to get the mounting features in exactly the stock positions. I drilled through the stock plate and into the new backplate.

The laser head was mounted in holes B (see drawing). Make sure the head is at 90 degrees to the back plate. Then acrylic glue was applied to the side of the guides which were then clamped to the laser. This insured an accurate fit to the laser module.  

Drawings

A simpler Slide?

Trace Method of Prototyping

When I am modifying an existing machine I like to build proto's by what I call the trace method. I remove the original parts that I want to modify or replace and use them as a template for drilling & cutting the features that I want to keep. I also sketch a 1:1 drawing for reference and sharing. I attach the template using double-back tape or simply copying the 1:1 drawing and gluing it to the surface with stick glue
If I plan to make a more precise or easily replicated part I create a CAD/CAM version, otherwise, I am done. If you need a CAD/CAM version let me know in the comments.

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Enjoy,

Comments are always welcome.

Please, consider using the donate button on the sidebar if you found this post valuable!

Don

Saturday, September 11, 2021

SANWU BG20W Optics & Module Interface

 SANWU BG20W Optics

There are 4 common types of diode laser lenses:

  • 3 element
  • G2 (short focal) (cutting)
  • G7 (similar to 3 element lens)
  • G8 (Used in VG-L7x)

The G8 has these specs:

  • Optimal focal range: 30-100 mm
  • EFL: 8mm
  • NA: .2
  • Best focal range 70-75 mm
  • Smallest laser beam spot: 77 x 130 microns (0.0030315 x 0.00511811")


Laser Resolution

G8 Effective Resolution = 
  • x = 1/.0030315 =329.9 
  • y= 1/.00511811 = 195.38
This suggests that the beam is not round. The focus tests show the beam to be round?

Laser Module Interface

I need the interface specs for the 4 pin connector on the laser module.
Emailed SANWU with no response!! 
Bring out the scope!

Pin Assignments

  • 12V [red]
  • Gnd [black]
  • TTL [wht]
  • TEMP [blue]

Connector Part #

Don't know what is on what pin yet.
Is this the connector part #?: XH2.54 4 pin
From NEJE spec: 4pin PH2.0 (red: 12V, black: GND, yellow: PWM, green: temperature signal)

Module Interface Specs

Not sure if these specs apply?

1. The third yellow interface line is the TTL control line, the voltage range is 3.3-12V, the frequency is 0-20KHz, and it needs to be grounded.

2. The input voltage of the red and black wires is 12V3A - 12V5A, do not connect them in reverse, otherwise, the module will be damaged.

Laser Module Temperature

Temperature profiles from NEJE information

The laser diodes temperature is displayed at the top of the VigoWorks interface so when using it calculating the temp is not necessary. I assume that the stock firmware shuts down the 12V power on over temperature?

When using Lightburn + MinGRbl this info is not available so it may be necessary to calculate temperature and interlock the laser module 12V power external to Lightburn and/or the controller.

When using a non-stock controller and software how does a laser module over-temperature condition interlock the laser power so as to prevent damage? 

Connection of NEJE module to Various Controllers

References:

https://endurancelasers.com/an-endurance-laser-lens-pack/

https://en.wikipedia.org/wiki/Laser_diode

Enjoy and Please Comment,

Don

What's The MoBeam Plan & Progress??

The Strategy for Mobile Laser Diode System (MoBeam)

I have had a K40 for some time and have been watching the evolution of the Laser Diode engravers. I recently bought a cheap VG-L7X unit with the intention of making a unit that is much more portable and simpler than a K40. (No cooling and simple optics). That said I have low expectations for cutting with a laser diode. Turns out that I use my CNC router for cutting most times. Most of my work is in wood and plastic.

I just started my learning phase and you can monitor progress here. 

I will try to keep this status page updated as the build progresses!

What Controller?

The choice of a controller is a many factored one dependent on your key wants. Mine are:

* What are you going to do with it... engraving and some thin material cutting. 

* What toolchain do you want to use? .i.e. How will you design the parts you are going to engrave?

* What computer OS you are running [this is often just a religious discussion :)]

* How will you connect to the engraver; usb, wifi, SD card?

* What protocol will the controller support. The most universal IMO is Gcode.

* Controlling from a computer, the local SD card or both.

* Size: fits into the enclosure schema

* Availability of firmware source code for troubleshooting and modification**

* The availability of schematics and wiring diagrams **

* The availability of free technical support**

** these are critical IMO for a scratch builder.

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Mini Ggbl

I have decided to use the AwesomeTech controller MiniGrbl as it meets my needs, I know @Paul_de_Groot at AwesomeTech. Note: Paul is a member of this forum 

A key need for me is the use of Lightburn to design and drive the unit. It will handle all the formats I need including Gcode that I may create from another tool like Fusion 360.

https://awesome.tech/product/mini-gerbil-2-axis-controller-for-k40-laser-cutter/

What Mechs

I plan to use the frame that came with the VG-L7X with stability and enclosure modifications.

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My Planned Work Flow

Completed:

  • Review all documentation
  • Improved the X-axis stability by adding eccentric bushings.
  • Initial Power up, successfully burned
  • Learned about Laser Diode optics/lenses; the focal point, length, and spot size

In process:

  • Checking out the stock software and controller
  • Document stock controller wiring
  • Aquire docs on the laser unit
  • Design Z adjustment mechanism

Planned:

  • Design/Fab Small safety cover over laser
  • Interlocks & alarms
  • Integrated design and documentation of the AwesomeTech Controller
  • Wiring diagram and schematic for the entire unit
  • Mount for an upgraded  controller (AwesomeTech)
  • A full enclosure that allows placing the unit on top of targets materials
  • Full system check
  • Design mobile air assist
  • Design mobile air extraction and filter

Maybe:

  • Firmware changes for interlocks, laser, and air control

Name

Since the main theme of this project is mobility I think I will call this unit MoBeam

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Enjoy,

Comments are always welcome.

Please, consider using the donate button on the sidebar if you found this post valuable!

Don

Thursday, September 2, 2021

VG-7x Carriage Modifications

 The Not So Stable Carriage

After the assembly of my VG-7x I noticed significant play in the carriage in both the X & Y-axis.

Laser diodes are sensitive to operation at the correct focal point. IMO movement of this nature would affect the engraving quality. So I set out to remove that error. The video below shows the large "slop" in the stock carriage.

Adding Eccentric Spacers

Inspection of the carriage revealed that there was no mechanism for adjustment of the wheels with the V-slot. The design apparently expected the tire mounting hole placement to be accurate enough to make a tight fit. 

There is a small amount of play in the axle bolt holes due to the hole tolerances. There is also some slight movement possible since the upper plates holes (5.9mm) are slightly larger than the lower plate holes (5.5mm). I don't know if these hole sizes are intentional or just an artifact of fabrication. In any case, they do not allow enough adjustment. 

So I set out to learn how CNC machines are designed to allow adjustment of the carriage tires to the V-slot interface. I already had a hint since I built a CNC router using V-slot extrusions. 
It's pretty conventional for these carriages to use eccentric spacers in one set of tire axles as a means of adjusting the play out of a V-slot carriage. The eccentric spacers allow the tire axle to be adjusted toward and away from the V-slot by rotating the spacer. 

My plan was to make a cloned set of carriage plates and redrill one set of holes to accept two eccentric spacers. The cloned plates would allow me to try out the concept without damaging the stock parts.
I found the eccentric spacers on amazon

Cloned Plates

I removed and traced the plates onto the graph paper. While I had the plates out I started dimensioning the part in anticipation of later doing a CAD version. Full-scale PDFs of those are attached. I may or may not create F360 designs depending on community interest. In the meantime, I find it quicker to make 1 proto part set by hand and I did so. 

The two stock plates were used as templates and their outline was scribed on 1/4 plastic (Home Depot). 

I simplified the outline into a rectangle before drilling the hole features using the stock parts as a template. To accurately drill the holes I double back-taped the stock plates to the proto material (plastic) and drilled through both. 

I reassembled the carriage using the cloned parts to check that everything fit and it did. While doing this I realized that I only need the bottom plate as the top plate is not part of the adjustment schema. I just need to ensure that the top plate did not interfere with the bottom plate's axle adjustment. 

I disassembled the carriage again and redrilled two holes (7mm) to accept the eccentric bushings. The bushing was a tight fit and I needed to tap them in with a hammer.
Note: there is a feature on the bushings that indicates the smallest adjustment location.
Cloned Plates

Modified Carriage

The photos below make the assembly self-explanatory so I will only give the highlights. 

Everything fit properly. I actually did not need to adjust the spacers at the smallest spacing the eccentric spacers did their job and now the carriage rolls smoothly with no play and minimal friction. The acid test is to ensure that the carriage is not too tight for the steppers to drive. 

I worried that the top plate would interfere with and perhaps bind the axles. They did not because I  assembled, adjusted, and tightened the carriage without the top plate and then installed the top plate with the thumbscrews. 

I also was aware that the cloned plates were a bit thicker than the stock plates and expected the axles to be too short. In the end, I used the cloned bottom plate and the stock top plate. That combination left just enough room for the top thumb screws to be installed.

I also wondered why the stock plates had such fancy features (curves). I still don't know why as the simple rectangles have worked fine ... so far. That is with the exception of the lower right of the bottom plate. A corner needed to be cut away to allow the wiring harness to reach at the carriages X extreme.
 
Top And Bottom Cloned Plates

Top Cloned Plate (not used)

Cloned Bottom Plate

Assembled Carriage. Note the cutaway corner

Eccentric Spacer 

Fully Assembled Modified Carriage

Assembling the Tires and Axles

It's important to assemble the axles, spacers, and tires in the correct order which from bottom to top is:
  • Axle 
  • Lower plate
  • Eccentric Spacer
  • Tire
  • A small stock plastic spacer
  • Top Plate
  • Thumbscrew
Note: The Al spacer that comes with the eccentric kit and the large stock nylon spacer are not used.

Documents

This Document Contains 1:1 sketches of the bottom and top plate so that you can fabricate your own prototype bottom plate. So far it seems the top plate can be used as-is and a clone is unnecessary. You could also just drill the featured eccentric spacer holes on the stock bottom plate. That said I would wait until more testing is completed before hacking the stock plate.

Conclusion

The new carriage configuration has reduced the "play" and the carriage is substantially "stiffer". I have yet to test it in operation..... new problems may appear. 

This is not an expensive change ($2.20 for 2 spacers) and I am surprised that Vigotec didn't include this in their design. Then again perhaps there is something I missed... time will tell.

If you are having a problem with your FG-7X image quality and or holding FL, especially at higher speeds (vibration) you should consider this modification.

Enjoy and comment,
Don