My general experience is that orientation of the fan really doesn’t matter.
The big things as others have pointed out is that you don’t want to go from 4 → 8 → 4 again. You can go from 4 → 8 → 6. If you can avoid the reduction at all, that is great. In my case I could get an 8inch exhaust port installed on the side of my house but I could get a 6 inch.
I do notice a difference between the T6 and the T8 in this configuration. The T8 can do the same job the T6 can but at a lower setting. During the cut I noticed the T6 would still ‘leak’ fumes. Basically there was a small odor. With the T8 cranked fully up, I don’t notice any smell at all, except off gassing that happens when you remove the material.
Also, you want the run of piping to be as straight as possible and as short as possible. As someone else pointed out, the extra curves in the pipe run will caused decreased air flow.
Pretty much any other hose. If you search for plastic dryer hose, you’ll get lots of options. I can’t even remember where I got mine.
So they do matter. Mostly messing with you, but that’s why I mentioned it. To me, it doesn’t help to have great suction out of the machine if it still ends up in my room.
Just curious, have you tried expanding foam or a liquid rubber/flex seal? Although you can’t see it in the picture I posted earlier, all of the metal on metal joints have an expanding foam on the inside of the connection to air tight seal it.
The flex seal is great for patching outside holes when they appear.
The cheap hoses have pin-holes in them. They’re just low quality… you’d have to patch the entire hose. I am using a silicone seal for joints in my case, if that’s what you mean.
This cannot be over-emphasized! For maximum effectiveness, the fan must suck the air from the end of the run rather than pushing it from the start. I placed my fan outside my shop and have not had a bit of trouble with smoke/odor since. FWIW, I have not removed the internal fan and have not had any issues at all.
Is 205 CFM and your exhaust hose is long, With both running it would barely be enough. If you took 3’ out of the hose beyond the external fan so there was only enough to make the turn and make it horizontal above the Glowforge you would get much better results,
If you search for plastic dryer hose, you’ll get lots of options. I can’t even remember where I got mine.
I am using a silicone seal for joints in my case, if that’s what you mean.