Thread: Improving machine cabinet dust ports

Originally Posted by BobL

Hot oil is messy, but I reckon boiling water would be a goer as it would be quicker than a hot air gun - I have thought about doing that , I didn't like the idea of dripping water onto the CI lathe bed although once could of course wipe it off before hand.. With boiling water the stub end of PVC would need to be dunked in and out of the water to get the spread of temperature needed (you don't want it uniform or it can ruck) and by the time you get the PVC out of the water and onto the former etc the PVC will probably lose 5ºC, (more if the former is not preheated) and further hot air treatment will still be needed to get it to 105 - 110º. I recently bought myself a 10L SS pot for metal bluing etc - might give it a go next time.

Following on from Doug3030's suggestion and this post I just tried out using boiling water as a preheat of the PVC piece being made into BMHs.

Couple of things I learned.

1) Setting the hot water saucepan up, cleaning up afterwards, and waiting for it to boil takes time so when only making 1 or 2 hoods it's not really worth it. For more than 3 hoods I'd say it is worth it. You still have to preheat the former again after making every hood with the hot air gun because the former cools down while waiting for the hot hood to cool down. Wiping the hot fully formed hood on the former with a wet rag and sucking lots of shed air across it with the DC speeds this process up considerably.

2) Even if you have just a few cm of boiling water in the bottom of the saucepan AND you put the lid on the PVC the steam heats the whole PVC piece so it goes floppy and out of shape makes it very awkward to handle and then you have to reshape the pushed end or it rucks up an ruins the BHS.

3) Dipping one end on the PVC piece into the boiling water for about 1 minute seems to be the go. By the time you put the piece of PVC onto the former and bring the tailstock pusher up to the cold end of the PVC the hot end loses about 10 - 15º, more if the former is not preheated.

So, overall good idea if you are making more than ~3 hoods.

The latest 6m length of 100mm ducting has a daily deep scratch about 2m along its length and this is what happens when I try to make BMHS out of pieces from this section of that pipe. In this case the tear has not appeared on the other side so it would still function fine but better off not risking it
BMHscratch.jpg

I think I have also firmed up on why the bell mouth of some hoods are formed asymmetrically and it appears to be related to a couple of things.
By asymmetrical I mean the variation in OD of the outer edge of the hood - usually it's widest and narrowest IDs are 90º apart and can vary by +/- 5mm.

The most obvious factor is the ends of the PVC pieces not being cut square, but a less obvious one is uneven PVC ducting wall thickness - not much that can be dine about this.
Despite careful attention to squareness one of the hoods today came out with almost a 20 mm difference in OD and sure enough the wall thickness around the duct varies considerably.

Summary - avoid scratches and check the wall thickness of the ducting does not vary too much.

back on page 4 ! Bueller mentioned his jointer, this one pic is the same as minejointer.jpg although mine is better (slightly) condition.
The opening one left is 160mm high and 220 wide (from memory)

Was thinking about raising the jointer itself off the base, adding a bell mouth with 90* elbow coming out same way.
Would still have to sheet metal a little around bell mouth?
where would I get extra air flow from?

Originally Posted by Tonto

back on page 4 ! Bueller mentioned his jointer, this one pic is the same as minejointer.jpg although mine is better (slightly) condition.
The opening one left is 160mm high and 220 wide (from memory)

Was thinking about raising the jointer itself off the base, adding a bell mouth with 90* elbow coming out same way.
Would still have to sheet metal a little around bell mouth?
where would I get extra air flow from?

Look in Bueller's workshop thread where he shows what he did.

hells teeth, Bueller sets up some high standards, dont expect that from me, I want to start making stuff and if I starting restoring I'd be pushing up daisies before we got anywhere. Great idea with the cardboard template though

Hi Bob, as you know I have a thread going about my DC upgrade etc, shown here. I'm looking to upgrade my dust port on the TS and thought I would get your thoughts.

After reading this thread I checked my TS and realised that apart from the outlet port being too small, the air intake is completely inadequate. The only real opening for air intake is the blade tilt slot on the front of the machine. It is about 350mm long by 25mm wide which gives about 8,750mm² .

So the idea is to block off the existing port and cut a whole new port at the rear. The new port will be 150mm with BMH and will have the added benefit of being in line with the blade. I would then cut air intake holes in the front around where the data plate currently sits. As a starting point, a 100mm square intake hole gives me an extra 10,000mm² . Added to the tilt slot that gives me 18,750mm² which is pretty close to the 150mm dust port. So to get to double the surface area of the dust port I would need another 2 x 100mm square intake holes adding another 20,000mm, to the total, so 3 x 100mm square holes in total.

My questions are:

Am I on the right track?
Is three 100mm square holes the best idea?
Considering the inside floor of the cabinet slopes down to the left hand side (where the existing port is,) should I try to get my new dust port on the rear over to that left hand side as much as possible or is it better off in line with the blade?

Thanks, Peter

Originally Posted by 3 toed sloth

The only real opening for air intake is the blade tilt slot on the front of the machine. It is about 350mm long by 25mm wide which gives about 8,750mm²

Strictly speaking long narrower slots should be under rated in terms of area but 25 mm is border line - maybe derate by 1/3rd? so say you have about 6000 mm²

Am I on the right track?

YES

Is three 100mm square holes the best idea?

As long as they are not too small the number of holes doesn't matter

Considering the inside floor of the cabinet slopes down to the left hand side (where the existing port is,) should I try to get my new dust port on the rear over to that left hand side as much as possible or is it better off in line with the blade?

Id go for the LHS placement.

Thanks Bob, just wanted to check before I start chopping.

My latest improvement is to the dust port over the lathe - the 150mm BMH tended to get in the way of the worklight for the lathe and cast a dark shadow over the work I was doing.

So I have made a perspex donut and glued and sewed some LEDs to it to light up the workpiece.

Here are some photos. As you can see, I have broken the LED string half-way around. Sometime I will replace the LEDs.

The donut does not seem to adversely affect the suction - if anything it improves it slightly.

Originally Posted by BobL

At the Mens shed there will be a need for quite a number of BMHs so I thought I'd see if I could find a way of making them cheaper than the previous posts and quicker than the MDF sandwich method... The method uses standard PVC ducting and a wooden former mounted on an MDF base plate on a lathe like this...

Next step, make a former for the 6" BMH.

BobL, I'm making plans to make BMHs for our shop from 6" PVC following your guide here. A few questions: Did you complete your 6" former? If so, did you do anything differently for this larger size? Do you think the entire former could be made from layers of MDF turned to the required shape?

Originally Posted by Rushton

BobL, I'm making plans to make BMHs for our shop from 6" PVC following your guide here. A few questions: Did you complete your 6" former? If so, did you do anything differently for this larger size? Do you think the entire former could be made from layers of MDF turned to the required shape?

Post #68 in that same thread shows what I did
Improving machine cabinet dust ports

And yes you could use MDF.
I've made hundreds of BMHs with my solid redgum formers and they still work fine.
I saturate my formers with machine oil to help expand the PVC over the former.
I don't know how MDF would go long term being slathered in machine oil.
OTOH MDF is cheap so making another should not be a problem.

bringing this thread back into action hopefully, maybe it could be a sticky.

I have my own idea but stuffed if I can draw it so that its understandable.
but making a open base rectangular box that would cover the blade and open both ends, one end would be glued to a 100mm round perspex/polycarbonate/acrylic tube. This would be fixed to 100mmPVC pipe and dust extraction hose.
This PVC pipe would also raise & lower for different thickness timber.
The base of perspex/acrylic/? pipe would have thin brushes bristles to gently rub over the cut timber and help seal .

sounds good in theory.

Originally Posted by Tonyz

The base of perspex/acrylic/? pipe would have thin brushes bristles to gently rub over the cut timber and help seal .

sounds good in theory.

I've tried several versions of this.
Here was the last time I used bristles in 2013 - I use truck mudguard bristles
IMG_3535.jpg
WIP here Bristle Guard edges for dust collector hoods and guards
I gave up on the bristles a few years later - I didn't like the way it blocked the view of the workpiece and blade.

My solution is complex and elaborate - but it could be simplified.
Ducting update.
Don't just look at the first picture - read on.

For TS OH guards, after days and days of testing, the principles I have found that make a difference on fine dust extraction are,

1) Back of the OH guard should be completely open
2) Take of should be as far forward as possible - about above the point where the blade passed through the TS table.
3) Slope teh front of the guard upwards towards the operator as this will deflect the dust up into the take off port.
4) Maximise air flow - 4" duct minimum.
5) incorporate a rise and fall mechanism to keep the hood in contact with the workpiece as much as possible.

Don't worry too much about the chips.

had a brain snap/fade has anyone looked at mounting an overhead dusty from the T S fence? rather than from one side Just the frame to hold it not the hose/pipework?
I was toying with ideas and the thought...
instead of timber or metal frame coming from side/end of table saw, mounting on Fence wouldnt require as much strength

or am I shooting pigeons again.

Originally Posted by Tonyz

had a brain snap/fade has anyone looked at mounting an overhead dusty from the T S fence? rather than from one side Just the frame to hold it not the hose/pipework? .

It might collect the dust on one side but very little from the other.