Thread: Making a hood for drum sander

Originally Posted by woodPixel

So, what does the bar actually do? I suspect it's to provide some attempt at creating sufficient vacuum at the front for 50mm users. If the bar were removed, there simply wouldn't be enough CFM to clean the front of the drum. I think removing the bar after adding 100mm (or greater) suction would be A Good Thing.

I'm not so sure.

at Tech we had a 6 or 8" belt sander with something like a 3' platen. Fired up and sanding there was a very visible dust stream tracking along the belt and into the dust "hood" a proportion of this stream tracked all the way around the belt.

On the Chinese copies, the bar might be acting to break up the laminar flow around the drum forcing the dust stream to develop turbulence within the hood, in turn allowing the dust "port" to scavenge the turbulent air.
Reducing the turbulence, even with a 4" port might make dust collection less effective.

Originally Posted by BobL

I would look to replacing the entire grey cover with one that has a 150 mm outlet and is about 50 mm wider on each side and sits up about 50 mm so plenty of air can get in and sweep away the dust.

Something like this.
Attachment 387426

Make the port 150 mm - you can always easily add an adapter to a 100 mm port but the other way around is more or a PITA.

Has anyone actually done this modification????
Kryn

Originally Posted by ian

I can only comment on the machine I've used. Connected via the 4" port to a 2Hp dusty, there was no visible cloud of dust in front (the in-feed side) of the machine. If the user stood in front of the drum their clothing didn't collect a noticeable coating of dust. However, the low velocity areas inside of the dust cowl were typically heavily coated in very fine dust.


my maths were: 100 mm = 4", 150 mm = 6", Pi is common so can be ignored.
If 3500 CFM can be got through 2 x 150 mm plus 1 x 100 mm ports, then a single 4" port can achieve 600 CFM connected to the same DC.
(4 squared)/{(6 squared x 2) + 4 squared} = 16/88 x 3500 = about 600 CFM

Nope - classic mistake in Dust control and one I see over and over again on these forums.

While its a fair approximation at the sorts of FPM and the very large X-sectional areas used in high rise building air conditioning, it doesn't scale proportionately with X-sectional areas at the sorts of FPM in dust extraction.

Even I got it wrong, a 4HP DC could achieve 600CFM through a naked 4" port but there's no way it would pull 1300 CFM.

The most a completely unrestricted 4" port (i.e. zero length ducting and hose) will allow through it with a 2HP DC is about 570 CFM and I have actually measured this - it's in the generic 2HP DC thread.
However, by the the time even a short length of 4" ducting and flexy is added, and the very restricted nature of the cover on the sander is taken into consideration my experience says it will drop to under 400 CFM.

The 1300 CFM I referred to is just a scaling based on the length of sanding drum.
If 1100 mm needs 3500 CFM then 400 mm needs ~1300 CFM
The ability of any DC to generate that is a separate question.

Originally Posted by KBs PensNmore

Has anyone actually done this modification????

Originally Posted by KBs PensNmore

Kryn

I haven't seen any.

Originally Posted by ian

at Tech we had a 6 or 8" belt sander with something like a 3' platen. Fired up and sanding there was a very visible dust stream tracking along the belt and into the dust "hood" a proportion of this stream tracked all the way around the belt.

On the Chinese copies, the bar might be acting to break up the laminar flow around the drum forcing the dust stream to develop turbulence within the hood, in turn allowing the dust "port" to scavenge the turbulent air.
Reducing the turbulence, even with a 4" port might make dust collection less effective.

Correct.

I recently added a belt scraper (a strip of thin SS) to the 5 O'clock position of the drive roller on my 6" belt sander and it makes a big difference to the amount of dust dragged by the belt around the drive pullet and dropping off on the underside of the belt.
The scraper doesn't actually touch the belt - its about a thickness of a piece of A4 paper away from the belt and is position adjustable.

This shows the scraper and the path taken by some of the air and dust coming off the belt - red arrows.
Posn1.jpg

This why I repositioned the BMH as shown here -
Sideonview.jpg
Now there's no visible dust dropping off under the belt but there is still some dust appearing under the belt over time indicating that invisible dust is getting past the gap.
This I will check with the particle collector.

Note the very spacious gap so that air can be grabbed around the BMH.

Here is another shot and you can see some dust that has impacted onto the scraper and not been collected by the BMH.
SanderF1.jpg

This belt sander has another issue in the the motor calling fan drags dust off the top of the belt - that's why I have a 5" duct extracting air (and dust) attached to the calling fins of the motor.
Now that this motor extraction is in place I could remove the motor fan but this involves major dismantling of the motor so it won'y be happening for a while.

This is still far from perfect so I also have 1200 CFM of general shed extraction operating directly above the belt sander

thanks Bob

apart from ease of mounting was there a reason you mounted the air flow disrupter at 5 o'clock rather than say 3 o'clock?

Originally Posted by ian

thanks Bob

apart from ease of mounting was there a reason you mounted the air flow disrupter at 5 o'clock rather than say 3 o'clock?

Mounting was made easier and some of the dust would have a chance to spin off by itself as it went around the roller.

Originally Posted by Toymaker Len

Maybe you could cut open a length of plastic 150mm pipe and then shape it to fit using a hot air gun.

I've got this same drum sander and have been thinking about better dust extraction too. Mine came with a hard 90 deg bend glued onto the 50mm port, just in case the flow wasn't bad enough already! That's safely removed, but dust extraction is hopeless.

I was planning something like Len has suggested. 6" pipe, split and opened up a bit to fit the width of the cabinet. Main connection to 6" ducting at one end, with the other end left open to increase airflow.

Trav

Leaving the end open to boost the airflow suggests to me that the majority of the air coming in will be from the side of the machine, where the dust is probably at its least. I would favour the majority of the airflow coming off the bed, somewhere near the middle and down close to the gap between the belt and fixed part of the hood.

I'm wondering whether to bias enhanced airflow in front of the machine (as the drum spins forward), behind the machine ( dust carried through on workpiece and belt) or neither.

we're using the dust extraction from the side method with an 80 year old home made drum sander at the mens shed.
Its just a piece of 6" duct and a couple of brackets.
The hinged flappy thing stops folks putting the wood in the wring way.
We've only tried hooking it up o a 4" port on a DC 3 and for up to about 50 mm wide stock it seems to work OK with visible dust
It start to struggle on >4" wide boards but its better than nothing.
More air flow would be possible by removing the end cap at the other end and using 6" ducting
Sorry about the poor quality of the photos - dirty phone camera lens

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