Issues with Pirhana Laser Cutter?

[Malcolm Napier]

As indicated in a recent post, I spent some significant time yesterday using the Pirhana Laser Cutter. The time was much greater than I anticipated because of a couple of issues that I encountered.

I was cutting 2 sheets of 2mm clear acrylic, both of which were close to the full size of the bed. I had a third sheet to enable me to undertake kerf setting, test cuts and other calibration, so that the cuts on the main two sheets were as good as they could be.

Both issues were related to bed levelling The first was when I tried to level the bed, it appeared to be some way out of level. Specifically it was more than 5mm higher at the left hand side of the machine (when looking at it facing the window in the machine room and the roller door entrance to the space). Inspection revealed that there was a strip of MDF underneath the bed, which must have been put there intentionlly to achieve that effect. I chalked this down to the previous user temporarily adjusting the machine and forgetting to reset the adjustment and was going to post accordingly. However, a brief chat with MikeThe Bee as I was leaving and he was arriving leads me to believe that there might be a larger issue with that side of the bed? If there is, then it may be intermittent because that piece of MDF needed to be removed yesterday, in order to enable cutting across the whole area of the bed. I raise this so that other users are aware of the potential issue and also to establish how it might get fixed?  

The second issue concerns the level at the back of the bed. In the centre and slightly to the right of centre for a distance of at least 50mm and a width of around 300mm there was a significant low spot. Significant in this case means that a cutting speed of 15mm/s was required to cut clean through 2mm laser in this part of the bed whilst 25mm/s would achieve the same objective. This is a 60% increase in time and cost to achieve the same effect. Significant also means that the cutting process made much more of a mess in that area of the bed - which was noticeably harder to clean up (due to, I am guessing, incomplete ablation/vapourisation). I have attached pictures. The stuff that is hard to remove is not the white "spray". If you look closely, there is a black shadow behind the white spray, close to the edge of the knife. That requires serious elbow grease to remove.....

I am only an occasional user of the laser cutter (although the ability to use it is a significant part of my reasons for being an rLab member), so there may be some 'A' level technique for bed levelling that I am not aware of. If there is, then I would be grateful to know and will even volunteer to write it up on the Wiki. I suspect that the problem becomes worse the thinner the material to be cut, due to the relative lack of stiffness - so mine might be an unusual use case.

However, it got me thinking. We have had a discussion where we have concluded that we need a "commercial" 3d printer. Something that you can load a file onto and "just print". I fully support that conclusion. Yesterday, I spent 2 hours "calibrating" the laser cutter so that it would cut reasonably across the whole bed (I expected to spend 30 - 45 minutes testing kerf settings in the design), an extra 40 minutes watching the cutting process and then at least another 30 minutes cleaning up additional residue that would not have occurred had the bed been level.

Do we need to have a similar discussion about loading and "just cutting" on the large laser cutter?          

[Norro]

I thought that wedge was under there precisely in order to level the bed. Tony uses the laser cutter all the time so I would be surprised if that was causing it to be out unless someone has moved it while he was on holiday.

[Tony Short]

Basically the bed is warped and lower at a point roughly 2/3 from the right-hand origin.

If you are cutting less than the full area, which is the case for the vast majority of projects, having the wedge under the left-hand side fixes this problem for the 2/3 to the right. However if you are cutting across the whole bed there is no workaround, other than cutting at a slower speed to guarantee cutting all the way through. If people remove the slatted base, and place it back in the wrong way you will find that everything is out of whack.

We spent quite some time getting the actual bed levelled recently, but the slotted rack really needs to be replaced. I will look into getting that sorted ASAP.

Cleaning will always be needed, and depending on what you are cutting there will be more or less. 2mm is often styrene rather than acrylic (which is too brittle) and that melts rather than vapourises, hence a lot more mess. ABS is the same.

It shouldn't take 2 hours to calibrate for cutting, perhaps you would benefit from some refresher laser training? Just ask!

T

On Saturday, 27 May 2017 10:09:17 UTC+1, Malcolm Napier wrote:

[Laurence Rochfort]

I second that the slats shouldn't ve removed for cleaning. In fact, perhaps it should be mentioned in the induction and on the machine?

For large area cutting, I cut slices of the thinest material I have, sand them to wedges, and use them to level my material.

For a project where the material itself was also not flat I made small C clamps with magnetic bottoms to hold the material flat relative to the bed. My kids stole them though :)

That said, for material up to A3, and even A2, it's a plug and play machine.

[Malcolm Napier]

Is the issue of the bed not being level documented anywhere? I was not aware of it.

Although I only use the laser occasionally, I like to think that I am a competent user for what I wish to achieve and I did help restore the laser that was donated by Richmond Makerlabs, repaired by rLab (mainly Richard & Ryan, but they left the mechanicals to me) and now is owned and used by Surrey & Hampshire Hackspace.

What took the time was having to start from scratch, map the bed height and then working out a speed that would cut through on all areas of the bed. A fair comparison would be to know how long it took for the regular users to establish the degree of unevenness that was provided in Tony's email and then maybe add a bit on.

The material was bought as acrylic and branded Acryliglas. I did not read the data sheet but will now try to look it out.

[Alex Gibson]

By the way I did a job recently aimed at improving the slotted rack a little to make it easier to clean, which was effective. 

 

I loosened the screws along the edge and tensioned the thin metal strip along the edge which retains the blades, re-tightening the screws from the middle screws out.  Now it holds the blades better and it’s possible to clean almost all the blades in situ without them falling out. 

 

I did put it back in the same orientation I found it and ran a test afterwards and it still cut fine, so I don’t think that contributed to any issues, just letting people know that happened…

 

Alex

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