Thread: Clearing the air

This morning I turned a jig for making 100mm BMHs. They are much easier to make than the 150mm ones.IMG_0542.jpg

... and to complete the morning, I've modified my 18" Jet bandsaw to have a 100mm BMH on the bottom cabinet. The cabinet door has a square cut out of it to allow adequate air intake. IMG_0546.jpgIMG_0551.jpg

Looks good arie.

RE: 100 mm hood being easier to make that 150 mm.
It depends on the PVC used in the ducting. The first lot of 100 mm PVC were easier to make than the 150 mm but the second lot were harder with the PVC splitting very easily from over or under heating.

A search on the webs showed this was identified some 8 years ago as audiophiles were making Bell mouth hoods back then from PVC using a "push over a static former" method. The method I develop using a lathe is a but better and easier that this. Anyway, the Audiophiles found that PVC with a "foam core" was more likely to split. They had more trouble with the 150 mm pipe as well.

The foam itself is made of "lower density" PVC and is sometimes coloured red/pick, green and white and appears to behave differently in terms of temperature responses that the outer more dense layers. I have not found any one is better or worse than the other but they can be a PITA.

The main annoyance with making the 150 mm ones is my tail stock does not quite have enough throw to make the hood in one pass and I have to reposition the tail stocks to get that extra 5mm of throw.
Technically there should be enough throw but my former has a slight taper just prior to the 37.5mm radius of curvature. I kinda like it there so I decided to wear the annoyance.