Dust extraction using a bench grinder ?

[jimbo123]

Hello,
I’m considering building some sort of impeller based dust extraction system for my workspace to replace the shop vac.
Having looked around for 240v motors I’ve not found anything suitable yet. However it occurred to me the possibility of using a bench grinder as the motor source to either drive the impeller via belt or straight bolt on attachment to the axle of the grinder. Has anyone heard of an example of this or am I completely potty ? Jim

 

[Terry - Somerset]

Hello,
I’m considering building some sort of impeller based dust extraction system for my workspace to replace the shop vac.
Having looked around for 240v motors I’ve not found anything suitable yet. However it occurred to me the possibility of using a bench grinder as the motor source to either drive the impeller via belt or straight bolt on attachment to the axle of the grinder. Has anyone heard of an example of this or am I completely potty ? Jim

I would hesitate to suggest you are potty but there are a few things to consider:

• any ducting required for other machines - eg: bandsaw, disc sander etc - will need to be routed via the grinder which may not be in the right/best conveniently location
• you would probably need to fabricate the impeller housing - I am not sure how straightforward this would be
• options - (a) exhaust the extractor directly outside with no dust collection, (b) via a cyclone and exhaust the remaining dust outside, or (c) collect all the debris and put filtered warm air back into the workshop.
• this all has design implications - eg: unfiltered stream of debris probably needs more robust impeller to avoid damage from larger "chunks"

Personally I think the grinder option, whilst an innovative approach to dust extraction, is probably a non-starter as basic extractors start at ~£100 - less s/h on Ebay.

 

[Phil Pascoe]

I suspect many grinders are built for intermittent use.

 

[Ttrees]

Ya need both really, and for an extraction system what keeps the air clean,
and not just machines, you need a large impeller in the range of 15" or thereabouts...
It'll supposedly take a 5hp motor to run that.
Why does it need be so powerful, it's cuz you want a very large surface area of pleated filters,
and a tall enough cyclone to keep the filters very very clean.
Could blow it out through the wall instead if poss, but the same goes for the heat.
Bill Pentz site has loads on that, someone here has recently/had? one built to such a spec,
and a bargain at that. 500 quid(ish) IIRC
3 phase motor, with inverter to run off 240v, though 16" impeller& 5hp motor would need 16a,
or commando sockets, and a hefty rated MCB /wire to the main breaker,
and thats just for running that alone.

If I ever seen a proven design, what's in-between what you can buy, and the above, say a 3hp/4hp/5hp(3 phase) motor w/VFD, (specifically one what's able to de-rate motors, that is)
and 14"ish impeller, then I'd likely be half way there!...

...but seemingly that just doesn't work very well atall, and more often than not, folks end up
having another go, and sticking to Bill's plans.

Being a gullible optimist, I still think there must be some middle ground here,
going with a wider cyclone seems suggested for lesser hp motors,
It's all on Bill's site, but it's really outdated website, and too scientific for me to
question why there's no middle ground...

I don't mind having even the one quick change hose system,
but my adaptable solution seems way too wacky of a proposition for those with the knowledge to comprehend.
I'd be happy enough using it after the machines, to clean up the mess, and the air afterwards.
That would be a good solution for me, futureproofing and all that.

Still on the lookout for an old machine, what might make a good donor,
but something with some oomph seems to keep it's value,
compared to the 1hp (fine and most dangerous dust particle spreader) chip collector bag systems,
what commonly go for about a hundred quid.

A Thien baffle is another thing you could look up.

Tom

 

[jimbo123]

Thanks to you all for your replies. Putting design, fabrication and parts aside you've all pointed out many other considersations which Ive not. Youtube has many guides however they all seem way over the top for my needs. Increased time has meant increased use of my work space and the vac is not up to the level of dust Im producing so Im looking at options. Thanks.

 

[Inspector]

A grinder motor is basically the same as any other motor and should be able to run all day. The biggest problem is unless you find a large industrial one of 10" or more they won't have the horsepower for the job. You don't say how big a shop you have or the machines you have. It will have a bearing on how you approach it. Bill Pentz's site Tom referred to in case you want to spend a week of evenings reading. Dust Collection Research - Home

Tom the reason Bill doesn't have a middle ground is that cyclones have internal resistance (static pressure losses) that along with ducts/hoses and filters reduces what they can draw. Separator lids and baffles have greater losses. Bill advocates 1000CFM at the tool (actual not claimed in the brochure) to capture fine dust and that can't be reached with cyclones less than 3hp.

I have been reading about dust collection for decades out of personal curiosity and while recently poking around found some information on square and hexagonal cyclones. They haven't been used in woodworking dust collection that I know of but I think would be easier to make than a round bodied type. What woodworker can't make a box or cut bevels of 60º? They, especially the hexagonal, perform almost as well as a traditional cyclone, or at least that is what I read in the paper on them. If you can find a motor and impeller it might be worth trying using basic sizing from Bill's calculator.

Here is a paper on them. https://www.researchgate.net/figure/Configuration-of-hexagon-cyclone-I_fig2_288019598 There are others but one needs to be in a university or you have to pay to read them. I'm not wanting to go back to school and am too cheap to pay. You might find more searching Square Cyclone Collectors and Hexagonal Cyclone Collectors or variations.

I'll add that a lot of what is in theses papers is way over my head too but I can follow most of their conclusions.

Pete

 

[jimbo123]

Thanks Pete, Yes Bill's site is quite a masterpiece and will get some dedicated reading time.

This question certainly has attracted some real technical know how from you all. My initial thought was surely there is someone out there who's had make do and perhaps toyed with the idea. Especially where in my case cost (of a motor second hand or otherwise) and availablilty are issues.

To add further light to my individual case; most of my tools were inherited and shoehorned into my available space. It wouldnt matter how many or few tools I have in my space (18' x 8' extending soon to 12') as every tool is/will be ducted and gated, therefore would only need one tool ducted to the dust extraction unit. I think scale is probably my issue, that being dust extraction small enough not to take up room but will extract efficiently from my most dusty tool. Im also trying to think of ways to use what Ive got or can get easily hence the bench grinder idea. (converted one into a disc sander but dust is a major issue at the moment). The dust vac isnt much more than a domestic vacuum and not up to the sort of sized tools Ive inherited or own. Ive a CNC 2' x 2' (wood milling only), table saw and router table combo, another table router (different sized collets), wood lathe and chop saw.

I think however conclusively following all of your great input that Father Christmas may jusy have to intervene and fork out for a second hand extraction unit (health and safety) being the selling point here.
Jim