Thread: Improving machine cabinet dust ports

At the mens shed we have a 24" twin drum sander still under warranty that has 2 x 4" ports on it that seem to manage the fine dust on boards less than about 6" wide but even this still leaves visible sanding dust embedded in the webbed rubber feed belt. When the warranty runs out later this year we plan on replacing the 2 x4" ports with a single 6" but I doubt that will still pick up stuff down on the feeder belt. Because it was mainly coarser dust we just put a cardboard box under the end of the belt and let the coarse dust fall into the box. Invariable someone would move the box and forget to replace it.

To help get around this one of the handier guys at the mens shed has done the following.
The 50 mm tube has a 3mm slot cut into it that is the length of the bely and it just sucks the dust off.
Because its mainly coarse dust the vac doesn't spew as much dust out of itself as it otherwise would.

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I just realised it's pretty similar to one of the collection ports on my BS at home.
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After I reversed the slot around the blade I found it almost unnecessary - now I use it catch small offcuts so that they don't fall onto the floor.

Originally Posted by BobL

I just realised it's pretty similar to one of the collection ports on my BS at home.
Cathctray1.jpg

After I reversed the slot around the blade I found it almost unnecessary - now I use it catch small offcuts so that they don't fall onto the floor.

I guess it doesn't matter too much in the bandsaw application, which appears to be mainly to catch duat being swept / pushed off the table, but if you wanted a more even airflow across the width it would make sense to taper the gap/opening from smaller near the start to larger at the end.

Just a thought/observation.

Cheers, Dom

Seeing these reminds me that I need to build a new collection mechanism on the BS. It's so simple it's clever.

Bob in the past you did tests on vacuum cleaners and found them to be little slice and dice dust pumps in their own right. Isn't the one pulling dust off the conveyer belt going to do the same and actually make the area around the sander air worse to breathe? I would think that a 4" pipe with a 1/2" slot connected to the overhead system would be better and perhaps a little quieter.

Pete

Originally Posted by QC Inspector

Bob in the past you did tests on vacuum cleaners and found them to be little slice and dice dust pumps in their own right. Isn't the one pulling dust off the conveyer belt going to do the same and actually make the area around the sander air worse to breathe? I would think that a 4" pipe with a 1/2" slot connected to the overhead system would be better and perhaps a little quieter. Pete

Yep Agree that your solution would be better.

Originally Posted by BobL

PVC starts to soften at 80ºC and melts anywhere from 100 to 260C depending on what additives are used.
It starts decomposing at ~140C which is usually before it melts releasing HCL gas which is pretty nasty.
The decomposition process is also autocatalytic - i.e. once started if not cooled immediately it self propagates.

PVC pipe has anti softening agents (metals like calcium and tin, they used to use lead so watch out for old grey PVC) added so it doesn't soften as much at lower temperatures or melt at too low a temperature.
So even though it starts to get soft at 80C it needs to be much hotter than this to enable it to be reformed.
For example 100C (boiling water) is not hot enough to work PVC pipe - I've tried it a few times..
So ideally you want to keep it lower than decomposition temperature (140C) but soft enough to work.
You also don't want it really soft or it will bulge, droop and flop all over the place.

I've used hot oil a few times and found it a bit messy.
Thats why I like the lathe and hot air gun.
It works a treat on small areas like BMH and should be OK for flanges once I get a bit of practice.
It will also be a lot quicker than waiting for a pot of oil to heat up, and then cool down so it can be put away..

Hi Bob

I’m about to start trying to make some 150mm BMHs. I wondered whether your heat gun had adjustable temp and if so what temp you use. If not I suppose I’ll use the suck it and see technique.

Originally Posted by jmk89

Hi Bob

I’m about to start trying to make some 150mm BMHs. I wondered whether your heat gun had adjustable temp and if so what temp you use. If not I suppose I’ll use the suck it and see technique.

My heat gun is a Ryobi adjustable temp model and I used ~300ºC on the gun.
However, what matters more is the temp of the PVC so I used an IR gun sensor to do this.
The optimum temperature for stretching the PVC over the former seems to be around 105ºC
Less than this and it may tear/split, much more and the PVC will decompose and char (turn brown).

Once the PVC started to stretch I found it easiest to
- apply heat and pressure with the tailstock until the PVC started to make a creaking noise,
- then stop applying pressure and apply heat until the creaking noise stopped
- Repeat above two steps.

Originally Posted by BobL

My heat gun is a Ryobi adjustable temp model and I used ~300ºC on the gun.
However, what matters more is the temp of the PVC so I used an IR gun sensor to do this.
The optimum temperature for stretching the PVC over the former seems to be around 105ºC
Less than this and it may tear/split, much more and the PVC will decompose and char (turn brown).

Once the PVC started to stretch I found it easiest to
- apply heat and pressure with the tailstock until the PVC started to make a creaking noise,
- then stop applying pressure and apply heat until the creaking noise stopped
- Repeat above two steps.

Thanks for that info, Bob

The mens shed recently acquired a 20"/5HP thicknesser
The dust extraction post is advertised as being suitable for 125 mm ducting but the opening has a lip on it restricting it to 110 mm.

The following is a Q&D way of improving the air flow and dust capture from the hood normally supplied with this machine.
NB if this was my machine I would remove the existing port and completely rebuild the sheetmetal top incorporating a reverse BMH into the outlet.

Nevertheless, for folks with limited metal working skills the follow is easier and would probably nearly achieve the same result.

1) Start by removing the hood from the thicknesser and placing a 150 mm coupler/junction (or in our case a Male/Female large radius 90º junction, make sure you place the female side of the junction) over the top of the hood outlet port.

2) Mark the extent to which the PVC junction, as is, covers the metal port with a marker pen - this is line A

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3) Measure and mark another line 25 mm (line B) below line A. The aim is to soften the female end of the PVC junction using 2 heat guns and push the softened junction onto the outlet until the female end of the PVC reaches line B and it forms a neat fitting oval shaped match. The reason for heating the female end of the junction (or just a piece of ducting) is because it is 160 mm wide ID as opposed to 154mm wide ID.

4) Make sure you heat the end of the junction evenly and watch out you don't heat too far back along the junction or it will fold/ruck as you can see has partially happened in the pictures below. If you overheat the PVC you can start to decompose the PVC (it goes brown) which will make it brittle.

5) Once the female junction end is soft the whole junction will be quite hot so, unlike us, use gloves because you will have to push and hold the hot junction in place while it cools. Presoak some towels with water to wrap around the hot end often junction once it reaches line B. This helps cool and harden the softened PVC and help permanently set the new shape. Keep the deformed PVC junction on the metal port till it has cooled right down and even after that leave it on there because it can shrink further and may not go back on as far as you wanted it to.

4) With the deformed junction in place drill some holes for bolts around the outside of the PVC.

5) Cut off the end of the metal port to line A.

6) Add the bolts. We used flat head 3/16" nuts and bolts.

Sorry I could not photograph the sequence, and only later when it was all done did I have an access to a camera so I disassembled the hood and took these photos

The opening is now an oval of about 7" x 5"
IMG_4459p.jpg

Here you can see me playing amateur gynaecologist and the "ruck the was caused by over heating too much of the junction.
It looks worse than it really is. The cross section available for air flow is still much greater than the original opening.
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Adding the bolts. Normally we would have 3 books doing that job.
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All done.
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This is not the position the thicknesser is normally used in.
This machine is on a HD cast iron base and is rolled out into an alley hence the need for the extra flexy.
Anyway it works great.
You do lose 6" of the width of the pass back rollers on top of the machine so it means the wider boards need to be turned on their edge to use the rollers.
Using the 90º bend also gets the flexy out of the way of the wood coming through the machine.

Just to let you know - I managed to make a BMH using the 150mm electrical conduit. So anyone who wants to use conduit for ducting etc, it is feasible to use heat to make it more malleable.

Originally Posted by jmk89

Just to let you know - I managed to make a BMH using the 150mm electrical conduit. So anyone who wants to use conduit for ducting etc, it is feasible to use heat to make it more malleable.

Grea,t how do they look?

Originally Posted by BobL

Grea,t how do they look?

Not too bad - I'll post a photo over the weekend.

A couple of photos of one of my BMHs made of orange conduit.

The message is clear - if I can do it, anyone can!