Thread: Dust Hood For Bosch Glide Saw

That's a very nice extraction setup. Bosch Glide is notorious for its lack of dust extraction. The dust goes everywhere except into the dust bag. I have the same saw.
The only thing that I would do differently is to have the connection to the DE from the bottom and have some sort of hopper adapter. Dust is heavier than air and so it has a tendency to drop and so extraction through the bottom should give a even better result.

I've never done of these but I agree these are "tough sons of beeches" to deal with.

Originally Posted by Chris Parks

IThe air is drawn through a slot at the bottom behind the saw and is a proven way to deal with the dust thrown from a mitre saw. There are quite a few videos on YouTube showing a few different variations but they all seem to work given the dust eaxtractor is big enough to draw enough air through the slot. The slot needs to exceed the duct size size by about 2.5 times due to technical reasons I have no hope of explaining as I do not totally understand it myself but I am sure Bob will or has in the past. Here the slot is shown as it will be installed

Sounds/looks good in principle.

A couple of comments.
Firstly I would try to remove the serrated edge look along the curved gap as any air flow will experience resistance around any points or right angles on edges that it has to pass around.
Something like this.

SCMShood.jpg

Next, the 2.5x area criteria assumes the cross sectional area of the opening is the same profile (i.e. square or round or rectangular) as the ducting.
When there are gaps or elongated slots the area has to be bigger.
Ideally the gap should be no narrower then the smallest dimension of the cross section of the ducting but in this case this would lead to too large a gap at the corners so I would suggest starting about where I have drawn where the gap is and uses a curved panel that you can slide up or down to vary the size of the gap.

A smaller gap will provide faster air speed and remove more chips while a wider gap will allow more air to flow and reduce the fine dust loss into the shed.
A neat system would be to be able to run the saw with a wide gap while cutting, and then be able to drop the gap down to collect up the chips.

Last of all I wonder if given you are using a plenum (box) whether it was even worth using 3 x 100 mm ducts - I would have just plumbed a 6" duct into the plemun. Also I would have flared the plenum from the full width of the hood down to the 6" duct. The plenum as shown with the 3 x 100 mm ducting ending on a flat surface inside the box will offer some resistance (i.e. the 3 ducts will fight each other for air) which is unfortunate given you have gone to considerable effort with the 2 x 150 mm Y's to get the 3 x 100mm outlets further back in the ducting.

If you go with the 1 x 150 mm duct I would use an internal BMH inside the plenum. You could use 3 x 100 mm BMH inside the plenum. This will improve overall flow but this will not prevent each of the 100 mm ducts fighting each other for the same air.

Whatever you do it will be interesting to see how it works. My guess is with a big DC is won't matter all that much.

My present hood works on the same principle and will lift chunks of timber the height of the plenum into the duct with no problems. Everyone thinks it won't and the extraction should be at the bottom but the design does work and a bottom pipe is unnecessary. If a an extractor with less air flow was to be used then I might agree with you but I haven't had the problems you describe. Dave TTC was using my saw and he could not believe the difference having the extraction working made.

Your comments are noted Bob and thanks.

If it works, keep doing it

I really only put this up in answer to those who expressed an interest in what I was doing as the Bosch saw presents some big problems in regard to DE. We can argue the technical issues all day but in the end each installation is unique and requires a suck and see approach in most cases. What generally happens in my experience is that a solution is arrived at without anyone being able to say of it is optimal or not because the alternatives are never tested. I think what I have built will work, how well it works is something else again because in all likelihood it will stay the way it is. Having said that feel free to copy, suggest and modify as much as you want if the design appeals to you.

Originally Posted by Chris Parks

My present hood works on the same principle and will lift chunks of timber the height of the plenum into the duct with no problems.

Just a note that this is is not always a good guide to fine dust capture. The ability to lift chunks is an indication of clearing visible dust and is as much of an indication of pressure differential, which increases under a restricted air flow and is not a guide to total air flow which is what fine dust extraction relies on. An extreme example of this is a vacuum cleaner, these generate lots of pressure hence can pick up lots chips, but have very low flow so cannot capture anywhere near as much dust at source as a regular DC.

Unfortunately the only way to know if any system really works is to count dust particles in the middle of the shed while the cutting is taking place. For most DCs there will always be a trade off between fine dust and chip pick up. With a ClearVue this is less of an issue.

Hi Chris,
I have the same saw .... and the same dust and chip problem ... it is perhaps the worst saw I have had for dust.

It sprays the @#$# around better than my old muck spreader ever did.

I use a shop vac attached to the vacuum outlet on the head of the saw ... but your design with the curved back is just what I'm looking for to catch the fine dust and sprayed chips .... and to get the DC involved.

Thanks for sharing

Regards

Rob

PS Is Helensburg near the Fink?

Loving it so far. Hope to be there or a test run soon.

Dave TTC
Turning Wood Into Art

Feel free to ask questions if needed.

I will add more tomorrow as I have finally got the bench semi built and the dust hood and saw all hooked up to the DE system but I thought I would post this initially. It is a sliding base the saw sits on so it can be moved back and forth to line up with the measuring fences each side of the saw and it made it easy to get the saw as far back as possible into the hood. Anyone who owns one of these saws will testify handling one is not easy due to the weight and it is a two man job for a little bloke like me to move one. The threaded rod moves the front mounts back and all four mounts sit on HDPE which slides easily on the T track. Another thing this allows is to move the saw quickly if sub fences are used or removed as I would not be able to do that on my own. Dave TTC will testify how heavy this thing is.

Yes I was thinking of getting a glider to replace my 12" DeWalt. Phew after lofting Chris's. Man that thing is heavy.

Spoke to Chris last night and sounds like the hood works a treat. I thought the last one was good but this one I am told is even better

Dave TTC
Turning Wood Into Art

This is primarily to show how the dust hood works but I suppose some of it belongs in other sub forums but in the end it was all designed to do one thing, try and tame the dust coming off what is universally agreed a very hard saw to get good dust collection from.

The Saw Installed with dust hood

Glide Saw Installed.JPG

The top plenum with blast gate

Glide Saw Installed.JPG

Showing the back of the saw against the curved face of the plenum

I can't Get it Any Closer.JPG

Saw Sitting on the sliding base. I used this base as a way of installing the saw with minimum clearance to the curved face. It made it very easy to just wind it back into position and align the fences with or without sub fences on the saw. To set up the clearances without it was just about impossible unless I was prepared to accept the saw sitting more forward and I had enough headaches as it was. I just attach a drill with socket and drive it back or forth and it works perfectly.

Saw Sitting on Sliding Base.JPG

Iused a bit of 25mm thick MDF to test with



The MDF Cutting Test.JPG

The saw before the test

Before Cutting MDF.JPG

And after 8 cuts

After 8 Cuts of MDF.JPG

And the whole thing showing the Incra fences. On my previous bench I had a Kreg fence system set up but I have always liked the idea of the repeatability Incra gives so I thought I would give it a go. I am going to set up a pin location system so the fences can be lifted away and the put back with no need to measure anything. I tossed around the idea of using a Wixey but it got to hard and in the end it would do no more.
Showing Incra Fences.JPG


The hood leaves a small amount of debris in the centre right behind the saw but that is no surprise and if I was fanatical I can think of ways to overcome it but this will do me. I am going to wind up the VFD to 70hz and see what happens but my gut instinct tells me it won't do a lot with a 150mm duct. The experience in the US has been that 7" duct is the ideal size for the CV1800 but that is mission impossible in Oz without spending a real lot of money. Overall I must say I am surprised at how well it has worked but I still have an open mind on my original idea of 3 x 100mm ducts coming out of the top of it instead of the single 150mm but I have too much too do and that will have to wait.

Looks good Chris

Dave TTC
Turning Wood Into Art