AIR EXTRACTION

[H.J.G.]

HI ALL,
I am building a laser with a 900 X 600 stage from L.O. in fact apart from the framework it is very much along the lines of Andy Kunz laser build on rc groups. My question is how do you determine what is the required air extraction rate.
Also is it better to have 1 or 2 exhaust vents and are they best fitted in the bottom of the "firebox" or the side?
The dimensions of my Firebox are 970mm long X 640mm wide X 300 mm deep which works out to 0.186 cu mtrs so if I removed this much air per sec my extraction rate would be 60 X 0.186 cu mts /min = 11.16 cu mtrs per min how does this pan out with your laser cutters?.

[AndyKunz]

I have a single 4" on mine. I hook it up to my dust collector blower (looks like this: http://www.toolwise.com/tool/21335-craf ... or-842.php

I block off the unused honeycomb with rectangles of wood or paper to leave about 1" around the wood I'm cutting, which is way more area than the 4" duct. It draws the wood down nicely and gets rid of the smoke well too.

It's not especially quiet, though, in large part because the air it draws is high velocity through the 4" duct. If you had more area on the duct face and fan, you could move the air much more quietly.

If I could put a 20" house fan to draw off the smoke I'd do it. I used the dust collector because I had it. I'll be improving this on the machine at some point. The wood draw-down is important too, though.

Something to experiment with!

Oh, and the foil-covered plastic box is working out fine!

Andy

[H.J.G.]

Hi Andy,
Thanks for taking the trouble to reply, nice laser you have built by the way. It seems to me that a higher diameter (5" /6") inline fan may be the way to go with a speed regulator so that I can step back from overkill.
Perhaps I am trying to over analyse this, and just go with the flow
Since you have got a very similar machine to mine (still building) could I be cheeky and ask you any relevant questions that may arise should I get stuck / unsure?

Henry

[AndyKunz]

Since you have got a very similar machine to mine (still building) could I be cheeky and ask you any relevant questions that may arise should I get stuck / unsure?

Absolutely! Either here or there.

I am waiting for a part number from Marco for the air nozzle extension, and then I will publish the complete bill of materials on that thread.

I've cut a few kits on it now, and still have some things I need to learn, but the learning is fun too!

Andy

For those who are wondering what he's talking about, it's this thread: http://www.rcgroups.com/forums/showthread.php?t=2243133

[H.J.G.]

Hi Andy,
Just re watched post 206 on RC groups which shows your laser cutting Balsa initially rather badly. It seems that you have left of the nozzle and had no air asst hence your previous comment about waiting for a nozzle extension. Are you using a long focal length lens?. The 2nd cut went a lot better, be careful that you protect the lens.

[AndyKunz]

I'm using a 63.5mm lens. The tip is too short, and about 50% of the power it lost with it on due to shining on the metal instead of through the hole. Yes, I'm waiting for the extension to be available from Marco. Since that video I have rigged the air assist to keep the lens out of the smoke, but still without the cone. (Getting impatient!)

The 63.5mm is perfect for this machine for cutting balsa. The table is all the way up, the lens focus adjustment is near the middle of its range.

I have cut 1/16 and 1/8 balsa and 1/32" birch ply with about 0.1 - 0.2mm wide cut at the bottom and not much more at the top. I can't wait to see how nice it does with the air nozzle on there!

I used the ramp method to get the focus correct. Maybe I should do a post showing how I did that. I also had the guys at work 3D print a focus tool that I tweaked to match what the ramp showed. See this thread: http://www.rcgroups.com/forums/showthread.php?t=2292449

Andy

[H.J.G.]

I originally ordered a 50.8 mm lens, and again like yourself wish to cut balsa and lite ply + birch plywood. How well this will work with this focal length lens I will have to wait and see,in the meantime I have requested a 63.5mm adaptor + barrel +nozzle from Marco so that I can cover more bases.
Only having a kerf of 0.1 to 0.2 mm seems very good, how much charring do you get on the edges and how much smoke marking do you get on the balsa or ply?
Have you tried PPI during any of your cutting?.

Henry

[AndyKunz]

One of the things about laser cut kits I've gotten in the past is the amount of smoke damage on the backside. I wanted to minimize that, so I played with different settings of cut speed and power to reduce it. I don't mind if the part is held in by a few stronger fibers here and there.

I posted photos over in RCG thread to show what it looks like, along with the settings I'm using now. They're subject to tweaking.

So far I have no smoke marking on my stuff unless I do something stupid like cut text in vector mode (you can see an example in the photos). Now, that is. The first balsa I cut was pretty charred and left some nice marks on the honeycomb

Andy

RCG post: http://www.rcgroups.com/forums/showthre ... st30175635

Settings:

CUTTING
Current "OK" settings:

1/32" MEDIUM BALSA
160 mm/sec
30% vector
15% corner

1/16" MEDIUM BALSA
130 mm/sec
40% vector
15% corner

1/8" SOFT BALSA
100 mm/sec
35% vector
15% corner

1/32" BIRCH PLY
70 mm/sec
55% vector
30% corner

Monokote Trim Film
250 mm/sec
22% vector
17% corner

[AndyKunz]

Re PPI:

I used these settings to get a dark, deep engraving on balsa. They gave a dark, not-as-deep engraving onto luan ply. It would be OK for labeling medium or hard 1/16 or thicker, but too much for 1/32". Speeding it up or reducing the PPI might help. What I'm doing now is cutting the wood in vector mode, and then putting a half-size image of the wood onto the plans with the parts ID on it.

FWIW, I like the slower speed because it doesn't jerk the machine back and forth so much.

Engrave balsa (dark)
1 pass
200 PPI
100 mm/sec
20% power