My SH-350 has landed !!!

[bratan]

leak is unlikely - with powerful (how poerful BTW? ) smoke extraction there will be lower pressure inside the machine and there be inflow of air through all the pssible openings. for leaks i would check the high pressure side of your fan
with that acrylic will outgass for sometime after being cut and that will smell. i run a DIY smoe extractor built around blower fan from household HVAC, huge amounts of airflow even with the restriction of being drawn through 14x24 box with 6" of activated carbon in it . i usually let the machine vent for at least 10 seconds after the job finished before i open the lid, and the acrylic wil still smell. lasermark material will smell even longer.

I build this "instructables" extractor. It uses 392 CFM centrifugal fan. I discovered it leaks somewhere near top of the filter, but can't figure out why. Added some more sealing, fan is sealed good with caulk. I think smell is passing thru top layer of carbon somehow... And not just acrylic, even smell from burning wood seeps thru like there's no filter there....
I might try different design, i.e. box shape...

[agrasyuk]

i seen this solution and didn't go for it , one reson is the fan itself. maybe i'm over the top conservative about it but 400CFM is IMHO not enough and that rating is before any kind of flow restriction. I don't have math calculations to back my doubt, but i think this solution also does not hold enough carbon for the job

. if there isindeed no leaks i wonder if environment you workin in has to do with this. as i found my scrubber works extremely poor when temps are below freezing (i work in unheated garage). my theory behind is moisture trapped on carbon (its quite humid at my place) freezes and blocks any gas adsobtion. i exhaust outside and it smelled very bad working during this winter. now when above freezing temps are here there is no smell outside at all, just the outgaing when i lift the lid.

[bratan]

i seen this solution and didn't go for it , one reson is the fan itself. maybe i'm over the top conservative about it but 400CFM is IMHO not enough and that rating is before any kind of flow restriction. I don't have math calculations to back my doubt, but i think this solution also does not hold enough carbon for the job

. if there isindeed no leaks i wonder if environment you workin in has to do with this. as i found my scrubber works extremely poor when temps are below freezing (i work in unheated garage). my theory behind is moisture trapped on carbon (its quite humid at my place) freezes and blocks any gas adsobtion. i exhaust outside and it smelled very bad working during this winter. now when above freezing temps are here there is no smell outside at all, just the outgaing when i lift the lid.

I'm going to take reading on air flow with my anemometer tonight and post results.As for carbon, I think it actually took more than needed. I ordered 55 lb and used 3/4 of it (probably at least 30 lb)...
Interesting about temperature, it's actually very cold in my basement (around 50F) but not humid...
If I don't get this working I'll have to vent outside. Fortunately I have window near cutter. Unfortunately it swing out glass type, so I need to figure out how to fix and position 6" duct in it...

[miketola]

Works fine. Different machine but same idea.

https://docs.google.com/file/d/0ByJi...p=docslist_api

Another side two computer fan blowing.

https://docs.google.com/file/d/0ByJi...p=docslist_api

[bratan]

Works fine. Different machine but same idea.

https://docs.google.com/file/d/0ByJi...p=docslist_api

Another side two computer fan blowing.

https://docs.google.com/file/d/0ByJi...p=docslist_api

Nice! You got same fan as I! Not sure I want/can drill thru solid foundation of concrete tho
Good idea with fans btw. Question, are you using epoxy to hold those pins?

[miketola]

Yes it,s epoxy. Used many many hours. No problem.

[bratan]

Took some wind measurements. When filter not attached to laser cutter I get 1074 ft/min or 336 CFM (if my calculations correct). With everything attached to laser cutter I get about 210 CFM inside.
I'm planning to take a duct tape and seal top 2-3 inches of the ring holding activated carbon and also attach extension pipe to the motor so it seats deeper inside pre-filter. Other than that, I'm out of ideas

[agrasyuk]

your construction looks really clean and well done. i see foam sealing strips on the edges, i assume motor to plate is also properly insulated. to me it seems very unlikely that you could have gotten a batch of bad carbon. so the only question that remains is whether the thikness of of carbon that you have is sufficient for the job. i read somewhere it should be 5-6", 4" at the least, but can't find it.
again, i don't have any academic way to prove it , nor i had personal experience with this exact construction, but as i see it the carbon will get compacted under its own weight and more air will pass through upper layers due to less flow restriction, which means not all your carbon load is participating in filtering effort equaly. does it really matter i don't know, but thats why i desided to go for a vertical airflow for my filter.

ADD:
will repost picture of my solution here as well (front panel removed, carbon container empty, changed machines since)

[bratan]

Thanks for posting picture btw!
I added some "Gorilla" duct tape to the top rim of the outer cage filter and it helped a lot! There's a very little smell now coming from the filter, it's virtually gone. I think you right about carbon getting compacted, this is not a good design...

[itmaxx]

glad to hear you resolved the mistery.

I am thinking about the carbon get compacted by weight and so: what about divide the 6" filter in 3 filter of 2"? could this help to keep the flow steady and the filtering effect efficient?

[bratan]

I posted a DIY on my site, how to make pin bed. It was super easy btw, and cost me about $60.
Now I'm trying to figure out settings for different materials. If everyone can share theirs it would be awesome. Plywood is real tricky. I got few different kinds from Lowes and 1/4" white birch plywood almost doesn't cut at all. I managed to do partial cuts at full power and 3 mm/s speed but it caught fire in the process.
5.2mm lauan plywood cuts great, but I just tried some 1/4" solid oak and I was shocked that it get's sliced like butter at 5 mm/s at just 25% power!

[miketola]

Good work. Almost same as mine pin table :-)

I think pin table is best of all tables.
Only if you make alot of small parts and they drop down and laser beam burn it when it cut next one.

I have 40w laser and i cut 4mm birch plywood 23 % power and 10mms. 3mm acryl 26% power and 10mms. 4 mm acryl 48% and 10mms. 3 mm HDF 27% and 10mms.

[agrasyuk]

interesting. it looks like i'm getting nothing close as far as power from my 800mm tube compared to you guys. to cleanly cut 2.5mm acryl i use 12-14mm/sec at 75% power. for 6mm i use 8mm/sec and do 2 passes at 75%. 75% power transalates into 16mA and i don't go over that. what is the actual thikness of your 3 and 4mm sheet in inches?

if you getting such good preformance "5 mm/s at just 25% power" why not increase speed (and power) for better finish ? it seems like you have plenty in reserve.

[bratan]

interesting. it looks like i'm getting nothing close as far as power from my 800mm tube compared to you guys. to cleanly cut 2.5mm acryl i use 12-14mm/sec at 75% power. for 6mm i use 8mm/sec and do 2 passes at 75%. 75% power transalates into 16mA and i don't go over that. what is the actual thikness of your 3 and 4mm sheet in inches?

if you getting such good preformance "5 mm/s at just 25% power" why not increase speed (and power) for better finish ? it seems like you have plenty in reserve.

I'll have to check what settings I used with my 2.4mm arcylic...
I actually tried increasing speed, but power requirements jumps drastically. At 8 mm/s I had to use 60%, and at 15 mm/s it went almost to 95%. I actually don't see much difference in cut quality between 5 mm/s and 15 so I decided to use lower speed with lower power. I'm very new to laser cutters, so I'm still figuring out when it's better to use faster speed with higher power, etc...

[miketola]

There is alot of different plywoods on market. In finland we have good guality birch plywood. It depends what glue they use. If you buy "wrong" plywood you can,t cut it. It just burn black and smoking. Poplar is soften than birch etc. Because of my lens dof is only 7mm, so it,s max what i can cut.

[miketola]

Bratan. Are you aure your focal lenght is correct?

[bratan]

Bratan. Are you aure your focal lenght is correct?

Yes I'm pretty sure. I found it draws thinnest line at 19mm from the end of the nozzle (lens is actually higher). To cut I lower nozzle by 1/2 of material thickness. I made a "jig" tool from acrylic to calibrate height for different materials. My z-table is not 100% level tho, I spend a lot of time adjusting it (after I removed timing belt), but it still a mm or two off in some corners.

[miketola]

Ok. I have different machine but focal lenght and dot size and dof you can calculate them. I cut max 6 mm material. Quality is important to me. I need small dot and good engraving quality. Also its important to cut easily. My table is now good and i cut all 4mm to thin paper with same settings easily. I dont use any acryl measurement stick. I watch quality and cutting power. If you think your focal is now ok. Take plywood and put power like it just almost cut it. Then lift table 1 mm and test and 2 mm and test. Then put table down 1mm and test etc. Last check your plywood and best cutting quality. 1-2 mm wrong and its means. What lens there is ? 2" 2.5" ?

[bratan]

Take plywood and put power like it just almost cut it. Then lift table 1 mm and test and 2 mm and test. Then put table down 1mm and test etc. Last check your plywood and best cutting quality. 1-2 mm wrong and its means. What lens there is ? 2" 2.5" ?

Thanks, I'll try that. I have no idea what kind of lens I have, but I suspect it 1.5". I never measured focal distance directly from the lens...
Different subject, does anyone know how much water is ideal to cool laser tube? I'm currently using 2 gallons (7.6 liters)... I'm planning to get cylindrical aquarium and use it as water container, wondering what capacity should be...

[miketola]

Its important to know your focal lenght. What is the distance from lens to your material about. I think its more than 2" with stock lens. I,m just thinking is there same machine with different focal lenght on market. Its also importan clean lens sometimes and check its not upside down .