Lens getting hot and melting holder

LightBurn Hardware Compatibility
1

Hi all, I bought a plastic lend holder as it’s adjustable. Today I have changed the lens out for a new one, did a test fire to make sure the lens is in the right position. Once it was went ahead and fired the laser. It marked the wood, went about 1/2 way though but 15/20 seconds in the lens fell through the holder as it had gotten hot enough to melt though the holder.

Does anyone know why this has happened? I had the lens the correct way up…

2

If the lens has any dirt on it at all, it will absorb some of the energy from the laser and heat up. Technically it does this anyway, but it’s much worse if the lens is dirty.

3

I took the lens out of the packaging, wiped it clean and put it in the holder and gave it another wipe just to be sure. I thought I had everything all sorted to get on with making some bits. I really have no idea what could have caused it

4

The mirror contained in the lens holder assembly may be misaligned and directing the beam to the wall of the lens holder, or the lens holder assembly itself may not be plumb.

Check the alignment of the final reflection by removing the lens and cone from the lens holder tube and reinstalling it into the assembly. Then apply a strip of masking tape or painters tape to the end of the lens holder tube (where the cone screws in). Pulse the laser and asses the burn on the tape to see if you are reflecting to center of the lens.

5

I did the masking tape to check alignment before doing the job and it was perfectly (as perfect as you can) in the centre of the lens

6

Can you post some pictures of the assembly, lens, and mirror?

7

IMG_2645
IMG_26453024×4032 2.45 MB
IMG_2646
IMG_26463024×4032 2.29 MB
IMG_2647
IMG_26473024×4032 2.31 MB

8

that’s the holder - the heat distribution is symmetrical

9

I do not understand how this fits together or is assembled on your particular machine. Can you illustrate that in a picture?

Also, that appears to be 3D Printed and it may not be the most suitable material for this application. Is it a 3D printed part?

10

IMG_2530
IMG_25303024×4032 2.01 MB
IMG_2531
IMG_25313024×4032 2.17 MB

here is a picture. Yes, it is 3D printed

11

Unfortunately the design of your lens holder assembly (laser head) is not ideal. It is my recommendation that you change out your lens holder assembly with one like this:
image

  • Your lens has very little cover / protection from particulate contamination on the top surface. A tube holder will greatly reduce the chances of this because the open entry for the laser is vertical and to the side of the lens.
  • Your air assist does not pressurize the area of space within the lower section of the lens like a tube and cone assembly does. This is a very effective means of protection from smoke and soot collecting on the under side of the lens.
  • The material used on your holder combined with the design does lend itself to explaining the heat soak on the lens as well as the melting.
  • You will have more stability in the metal lens holder assembly that may improve your overall quality in production.
  • If you’re not already set up for and using a 20mm lens, you can make it happen in the process of swapping out the lens holder assembly
12

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