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Sunday, November 11, 2018

Improving the K40 Optics: Mirror #1 replacement

K40 Mirror Mount and Adjustment Redesign: Part 1

DRAFT

Its has always been my plan to replace the mirrors in my K40. This past month my K40 has been acting up. It acted as if the HVT was gone and I was getting intermittent operation of the laser. I decided to replace the coolant and then troubleshoot the problem. In the process of clearing the bubbles out of the tube, by lifting and inverting it I managed to knock the #1 mirror out of alignment. Looking at the mounting and means for adjustment I decided it was far time I replaced the mirrors and their cheesy mounts with something better.

There are 4 posts that pertain to improving optical components and alignment:
Improving mirror #1
Improving mirror #2
K40 optical alignment tool theory & design
Using K40 alignment tools

Donate:

Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Parts:

  • Adjustable Lens Mount [ebay]. This part seems to keep changing. If this link goes dead try searching for: "20MM/ 0.79'' REFLECTION MIRROR FIXTURE MOUNT FOR Co2 LASER MACHINE 1 PC Redsail"
  • 1/4" Acrylic [lowes]
  • 6- 4x.7mm flat head screws [Lowes]
  • 1- 4x.7mm pan head screw

Replacement Assemblies

The photo below shows the mirror mount assemblies. On the right is the stock mount and on the left is the mount I bought from ebay.


eBay mount. Note much better adjustment screws and mirror securing ring. 


Design

Since the eBay mirror assy. is  larger than the stock unit a new mounting design was needed.
I decided to make a two axis mount since the entire assy. needed to be moved forward and back as well as positioned at 45 degrees to the exit of the laser. 
Four parts make up the new asy. From left, nut-plate, base-plate, sub-plate and rotary plate.


Base plate

To utilize the existing holes I designed a base plate and a nut plate. The stock designs base was bolted to the laser compartment using two screws and nuts. In this design the nuts were impossible to get to especially the rear nut. Instead I used two screws and fabricated a nut plate that could be held in place from inside the machine.

View from front of machine


Adjustable sub-plate

The sub-plate mounts on top of the base-plate. Slots allow it to slide perpendicular to the lasers output.
Note: I had to mill the surface of this plate slightly to get the beam in the middle of the mirror. The dimensions of this and the other parts will be added after testing is complete.


Mounting the mirror assy.

The mirror mount assy is screwed to the rotating plate from below with flat head tapered screws. The holes in the rotating plates are countersunk.


Rotating sub-plate

The rotating plate is mounted from below to the sub-plate and allowed to rotate. The mirror mount assy. is mounted onto this plate with tapered flat head screws allowing the mirrors to be positioned at 45 degrees to the lasers output. This screw hole is also countersunk. 

 Locking screw

A locking screw is added from the top side of the subplate to allow the rotating plate to be locked into position. 

Completed Mirror Sub-assy



Installation

The completed assy. is mounted on top of the base-plate. The mirror is coarsely adjusted by positioning it front to back and in a rotary fashion until the beam is in the center of the mirror and directed toward the #2 mirror (on the gantry). The sub-plate and rotary plate are locked down and ready for fine adjustments. The three adjustment screws on the mount are fine mirror position adjustments.

Fabrication

This unit was fabricated by hand but was designed to be fabricated using CNC machines.

Fusion 360 was used to create the design. Links to the design will be available if there are enough readers interested in building their own.

Laser Cut: 

All of the features of the parts should be able to be laser cut except the countersunk holes which are easily drilled using an appropriately sized centering drill.

CNC Router: 

The entire set of parts should be able to be milled by a cnc router.

Next

Mirror #2

The stock mirror # 2 will also be exchanged with a similar design as was employed for mirror #1 described by this post!

Laser Alignment Jig

For some time I have imagined a simpler way to align the K40 optics using a jig. Since I will have to realign the optics after I complete the installation of the new mirrors I plan to implement said jig. Stay tuned!

Alignment & Test

The entire optical path will undergo a realignment with the expectation that when finished my K40 optical path will be stable, robust and repeatable.

Enjoy and please comment,
Don

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