Extractor ducting

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

TRITON

Established Member
UKW Supporter
Joined
5 Oct 2014
Messages
3,661
Reaction score
2,731
Location
Sunny Glasgow
Looking to sort something out to connect large extractor to tubing around the room, for obvious reasons.

I initially started looking at Axminster, as they do kits, but after a brief look about ,i mean ducting is ducting and it doesnt have to be specifically sold as being for dust extraction in woodworking workshops.

So Screwfix seems to have the right stuff and it is considerably cheaper than Axminster. For example, a length of 100mmx915mm at Axminster they want £28.98. But at screwfix, a 100mmx1m is £8.49. So quite a saving. 90deg, joins etc from screwfix are again much cheaper then Ax.
Im sure there will have to be a little fiddly abouty, but the savings considerable comparing the Ax kit, and the actual amount I'd need

So what do other here use ?.

Also, there is square duct which is even cheaper, and i see from a link on one of the threads someone has installed that and it looks quite good, Certainly neater, though personally I'm not sure- being square not round, but hey ho, i suppose it would work, cant think why not.
 
Two things that may appear to be unnecessary complications but are important:

1 - Flexible ducting is very attractive for lots of reasons....... but it will add internal friction losses that will seriously impede the fan's performance - also it's a krap-trap for dust and small debris. It's best left as short as possible for connecting vibrating parts to the straight stuff.

2 - Static. Please do some serious fact finding on the subject of dust-generated static and earth-bond everything. It can be explosive.

Finally, the shape on short sections is not crucially important. What is important is the flow distribution and losses where ducting changes directions - elbows, bends and the like. Go for long, gentle sweeps if you can, rather than abrupt 90 degrees.

It's of these things that can be done well or can become a future source of regrets, so it is worth getting it right with some serious research, rather than least cost.

Good luck.
 
cant think why not
From my reading it does seem the ideal is circular ducting kept as short as possible with as few bends as possible!

Circular ducting will cause less friction than Rectangular.

When managing bends it suggests using a couple 45deg couplings instead of a 90 to help mitigate the turbulence caused.

I'm learning though so happy to be corrected but @Inspector has linked some good resources in his posts on the topic
 
2 - Static. Please do some serious fact finding on the subject of dust-generated static and earth-bond everything. It can be explosive.
It is pretty much impossible to generate enough dust in a home system to have an explosion. The minimum threshold of dust in the air for an explosion is 60g/m3 which resembles a very heavy fog. Below that and nothing will ignite it and at a certain point above where it won't ignite either. A 100mm duct flows roughly 680m3/hr. So to have a concentration in your duct that will explode from a spark is, if my math is right, (60g/m3 x 680m3/hr) divided by 60 = 680g/minute. What woodworking operation do any of us have that can cut or sand 680 grams of wood every minute? Factories and big cabinet shops with very large wide belt sanders or big CNC router yes. So dust explosions in a home shop from static....nope. The reasons for controlling static are the annoying shocks which could be a dangerous distraction if cutting and the damage to sensitive electronics like the computers in cnc routers. Further to this I remember reading that you must have ducts a minimum of 250mm in diameter to generate a hot enough spark to ignite the dust flowing through it. Again something that no hobby woodworker has.

Now fires in the system from friction burns from dull router bits or saw blades making embers can start a fire or metal sucked up an hitting the impeller making a hot spark that lands in the bin/bag and smoulders into a fire are possible and do happen all to often. They need to be watched for but static explosions in your shed are not going to happen.

Pete
 
Have a look at the underground sewer waste pipe 110mm May work out cheaper for you

I think Axminster or Charnwood do a waste to 100mm adaptor also if needed

You tube “man in shed “has a video re the waste ducting and about static ( he is an electrician) might be worth a look
 
From my reading it does seem the ideal is circular ducting kept as short as possible with as few bends as possible!

Circular ducting will cause less friction than Rectangular.

When managing bends it suggests using a couple 45deg couplings instead of a 90 to help mitigate the turbulence caused.

I'm learning though so happy to be corrected but @Inspector has linked some good resources in his posts on the topic
I have haven't I? 😉

The rectangular duct does cause more friction but it is minimal. Play with this calculator and you will see that a 4" round duct, 400CFM, over 30' has a water column loss of 2.742". Same cross sectional area in a square duct of 3.54" has a loss of 2.9". Correction. That should be 3.26". The difference in bigger ducts is not as bad. As long as the square ducts are strong enough not to collapse under suction you'd be fine.

The bends. Ducts not diving. 🏊‍♂️ The worst is a non radius 90º and the pair of 45º fittings is better by a long shot. A radius elbow is better and when you get to a 1 1/2 radius bend (sheet metal) or 1R in a smooth fitting like PVC then the pair of 45º fittings have more resistance. Have a boo at page 54 to see the differences. On this side they calculate fitting losses as the equivalent of round straight duct. Easy to visualize the differences.

Pete
 
Last edited:
Looking to sort something out to connect large extractor to tubing around the room, for obvious reasons.

I initially started looking at Axminster, as they do kits, but after a brief look about ,i mean ducting is ducting and it doesnt have to be specifically sold as being for dust extraction in woodworking workshops.

So Screwfix seems to have the right stuff and it is considerably cheaper than Axminster. For example, a length of 100mmx915mm at Axminster they want £28.98. But at screwfix, a 100mmx1m is £8.49. So quite a saving. 90deg, joins etc from screwfix are again much cheaper then Ax.
Im sure there will have to be a little fiddly abouty, but the savings considerable comparing the Ax kit, and the actual amount I'd need

So what do other here use ?.

Also, there is square duct which is even cheaper, and i see from a link on one of the threads someone has installed that and it looks quite good, Certainly neater, though personally I'm not sure- being square not round, but hey ho, i suppose it would work, cant think why not.
I use this company and the products are good quality and way cheaper than any others have quoted, and they have a fixed price delivery charge of £12.95.
Huge range and they are also very helpful if you need advice,
Ed
Ductstore
 

Latest posts

Back
Top