K40 Not cutting 3mm MDF

[Kinsway (Keith Taylor)]

The jigs for both the fixed and Y Axis mirrors and the laser head work well in that I can place the tape on the jigs then slot over the fixed and Y mirrors lens cap or the laser head. It’s a fair point about protecting the mirrors so I have closed off the holes and indented the position of the holes which are now only 0.5mm from where you would place the tape in any case.

Part of the problem of aligning the mirrors is that I need more adjustment of the head both in the vertical and horizontal, so I have printed a head part which includes the drag chain bracket that makes adjustment easier. I sense that I may need to re-align mirrors periodically so making the process easier will pay dividends. But, as if that was not enough, I realised that in homing, my drag chain was fowling the back of the cabinet. This in turn seemed to push the gantry cradle upwards and so may be part of the problem.

Correct position

Pushed upwards
As you can see in the two photos, the cradle can easily be pushed upwards out of the rollers. I tried adjusting the rollers tighter against the gantry, but this only tightens the movement along the gantry so does not work. Although I appreciate there should be no undue pressure on the cradle, and I have fixed the drag chain bracket problem, nevertheless it seems odd that this should happen at all which led me to think that maybe my cradle was incorrectly assembled or missing a part or something else, but I can’t find any posts on this as an issue. Any comments? I certainly don’t have this problem on my printer where the rollers are firm in their guiderails. Anyway, I hope to be able to pull all this together tomorrow and carry out re-alignment testing again. The one good thing about all this is that I am learning a lot about my k40 !!

[Kinsway (Keith Taylor)]

Hi All,
Eureka, I think I am now moving forward. The results of my checks and tests are as follows but they do beg a few further questions which you may be able to clarify for me:

CHECKS.

1. We have already confirmed the LPS is ok.
2. I have confirmed that 2.25v (45% power?) provides a 15mA maximum input current used for cutting. Should I stick at this as a maximum?
3. I removed the air assist drag chain to ensure it did not impact on the results and is still causing an issue with the cradle popping out of its pullies when homing. Am I right in that the pulley wheels are not fixed in the eccentric inserts?
4. I have not flushed the tube yet or changed the water but will do this week.
5. I note that the stock lens is chipped. Should I replace it and if so whilst doing this the stock mirrors as they tend to come as a set?
   
   

WATER COOLING
It has been particularly hot over here, so the reservoir is normally above 20C even in the morning. I am using 2L ice cream tubs filled with water and frozen to put in the water. I usually put 2 in (4L) and wait about 30 mins but the water only cools maybe 3 to 4C. When cutting I see the temp rise quickly so is there a cutoff point where I should stop for fear of compromising the tube?

MIRROR RE-ALIGNMENT
I carried this out using Tim Fawcett’s instruction downloaded from the site:
The results are as follows:
Before I started, I noted the subframe was not quite square to the box which I have corrected.
I printed a new head bracket to increase the height by 5mm and with more side Y axis movement

All spots are within the mirror windows but not directly on top of each other. Is this good enough to cut or should I finesse?
The position of the fixed mirror is central but low. As I understand it, the only way to centre it is to raise the tube. Is it worth doing this?
Align Y mirror close is where the 2 X direction measurements are closest to the tube
Align Y mirror far is where the 2 X direction measurements are furthest from the tube
Align mirror all are the 4 measurements from the extremities of the bed
Align lens holder is with the head mirror removed.

RAMP TEST
I performed a ramp test and as expected around 50mm with around 2mm tolerance was the sweet spot but it was difficult to measure the distance accurately. See cutting test.

CUTTING TEST
I performed the same cutting test on 2.5mm birch ply at 15mA and 10mm/s with air assist which works well (other than the drag chain). The first cut was one pass using my 50mm tool from the material to the underside of the head and it just about cut through. I had seen a post from Ned, where he sets the height within the material, and when I did this, it cut cleanly through. I am going to test at different heights to fix the ideal height and make a new tool. On a roll I tried 3mm MDF with 2 passes and it cut maybe 2.5mm. My local hardware store has 2mm MDF and it was on the way to cutting through with 2 passes.

Thanks to all for your assistance and in advance for reviewing this update. Any further questions or comments would be welcome.

[donkjr (Don Kleinschnitz Jr.)]

One other test that can tell you about the perpendicularism (word?) of the beam through the objective lens (head).

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Put a target on the bed held down so that it will not move at the correct focal length.
Fire the laser
Lower the bed and fire again without moving the target.
If the beam is moving through the head perpendicular to the surface the two spots on the target should be on top of each other. If they are displaced the beam is not perpendicular to the objective lens.

Note if you do not have a moveable bed you may have to rig up spacers that you can remove to change the distance from the head to the target. In this case, make sure that the position of the target relative to the head does not change as you remove spacers. You can do this with a jig that ensures the spacers are always located in the same spot.

[Angel_Rosa]

How I fixed that algae issue on neck of laser tube.
I dropped 2 ounces of Clorox bleach and a spoon of baking soda. In 2 hours all junk was gone. 2 years have passed and laser tube is fine. Hope it helps. ^¡^

[Kinsway (Keith Taylor)]

Apologies for my tardy response but unfortunately your notification had dropped into junk.
Thanks for the advice and I will give it a try as yes I do have a moveable bed.
I did a height calibration of my bed and noted that one full turn of the screw is around 1.5mm so my process is to use my tool to set 50mm from the underside of the head to the target (assumes it is around 0.8mm from the underside of the head to the lens) and then turn it 1 or 2 turns up depending on the thickness of the target to the focus is on the middle of the target. As a rule of thumb this seems to work as a rule of thumb.

[Kinsway (Keith Taylor)]

I understood my mistake from day 1 one using antifreeze but I had seen a YouTube video on using glycol. Flushing the tube, changing the water and introducing algaecide is my next job and I take your point on the possible impact. Although I have read the excellent site article on cooling, using 4L of ice in ice cream tubs only reduces the temp by around 3C and so I am concerned that this might also be impacting on the laser’s performance. I will create a separate post on this subject which is likely to be my biggest challenge going forward particularly in this hot spell.

[Kinsway (Keith Taylor)]

Many thanks. Do you mean that you maintain the bleach and baking soda in the water mix or you used it to flush the tube? I am about to flush the tube in the next few days.

[mcdanlj (Michael K Johnson)]

Don’t fire the laser with bleach or baking soda in the water.

Cooling the K40 laser tube

Algae growth is a problem, as it interferes with water flow directly, deposits on the glass, prevents heat transfer, and on and on. Algae (green gook) growth is bad. There are aquarium additives that kill algae, and some that seem to not make your high-resistance distilled water more conductive. Tetra AlgaeControl has been tested to not make your water more conductive. A few drops of the right stuff in several gallons seems to be enough. Tetra AlgaeControl appears to be unavailable in Europe, but Tetra’s AlguMin has been reported to work well. Bleach is not recommended.

[Kinsway (Keith Taylor)]

I thought I would complete this post with a final update. I fixed the drag chain problem as the beam was partially impacting the chain at the home point and sometimes dragging the pullies out of the eccentric cams. I finally flushed the tube and to my relief it does look like it was debris in the neck as it flushed it out without a problem. I have now refilled the reservoir with clean distilled water and algaecide. I then re-checked the mirror alignment, and it is still very close at all four corners. I also checked the perpendicularism which looks fine. This left me one final problem in that I simply could not get the water temperature much under 20C, so I have posted a new topic on how I have resolved this problem. As it is I can now cut 3mm MDF as per the original problem, 3mm Ply and 4mm acrylic by raising the table from 50mm by half the thickness of the material as one turn on the table is around 1mm. This seems to work well so I am good to go. By carrying out my cutting tests of power, speed, in time these will be an indicator of the tube beginning to fail. In this regard I went through 3 diode laser heads. I presume this is the case where, in the first instance, I would increase the current to get the same cutting performance, but I do hope this is a while off yet.

[donkjr (Don Kleinschnitz Jr.)]

If this problem is solved can you mark it as such, please?