Thread: Ducting update.

Bob sorry to be a pest but I've got a couple more questions for you since most of that pdf blows right by me.

Do these loss numbers work equally for both suction and pressure systems? An air delivery system verses a dust collection system?

If I read the elbow examples correctly a round duct 90 with a 1.5 radius and a square duct with a 2 radius have equal losses of 17'. Correct?

Thanks
Pete

Originally Posted by QC Inspector

Bob do these losses hold true for each duct size, 4",6", etc.?

Yep.

Originally Posted by QC Inspector

Bob sorry to be a pest but I've got a couple more questions for you since most of that pdf blows right by me.

No worries - happy to interpret where I can.

Do these loss numbers work equally for both suction and pressure systems? An air delivery system verses a dust collection system?

The numbers differ markedly on the direction of the fluid i.e. between expanding and contracting flow.
Post #75 shows the expanding flow losses.

Here are the contracting flow figure extracted from page 67 of the Engineering Cookbook
Duct-transition.jpg

If I read the elbow examples correctly a round duct 90 with a 1.5 radius and a square duct with a 2 radius have equal losses of 17'. Correct?

Correct.

In their introduction to the Engineering Cookbook ducting design section they only mention speeds up to 3000 fpm so losses may change at higher (more turbulent) speeds
In most case this should not change the order shown on any one table but crossing from one table to another may not always apply.
e.g. The losses shown for rectangular elbows without vanes are shown as much higher that those with vanes . At higher speeds as used by DCs the vanes would seriously impact flow so I would be wary about adding vanes. Could be another one to measure.

The Engineering Cookbook also states the following about the ducting design section.

This section is intended to help estimate duct systempressure loss when preliminary equipment selection is beingmade. It can be useful for cost estimating, preliminary proposalsand other situations where a complete system design is notpractical. It is NOT intended to replace comprehensive systemdesign or analysis by quali ed professionals.

Thanks again Bob.

I'm curious if the losses for square ducts are close enough to consider using square instead of round. With the CV-Max on it's way I'll be needing 8" for the mains but haven't looked at prices for the 8" PVC sewer/drain pipe and would consider making square from melamine coated chipboard if it costs less and the losses would be tolerable. I suppose it would be too much to ask if you could knock up a square duct to test with your calibration setup you are playing with in your other thread?

Pete

Originally Posted by QC Inspector

I'm curious if the losses for square ducts are close enough to consider using square instead of round.

Square is fine in terms of just flow.

With the CV-Max on it's way I'll be needing 8" for the mains but haven't looked at prices for the 8" PVC sewer/drain pipe and would consider making square from melamine coated chipboard if it costs less and the losses would be tolerable.

It's not just the cost its ease of construction and then subsequent mod. It depends on what thickness of material you use. I did a costing a while back and here in OZ it was not that much cheaper than stormwater pipe. The junctions can be made for much less as they are usually built into the ducting but of course much more time is needed to make them.

One problem here in Oz is that 8" PVC ducting is not available and even the 9" PVC is 240mm ID so is closer to 10 than 9" although the CV -max at the mens shed seems to work fine with the 9" PVC ducting.

If you wanted to build an fully optimised system I believe that 7" round ducting is supposed to be the way to go. This equates to a 6.5" square duct which doesn't take up much more room than 6" ducting. For a single operator setup, a larger trunk line to allow more than one machine to be used at the same time is not really needed although it can be handy for general shed ventilation.

The inlet to the CV cyclone body is itself rectangular and a short rectangular to 8" round transition is provided.
If you want to go with square you might be better off doing rebuilding this entire transition, from its rectangular opening to whatever suits you e.g. the 6.5" square ducting.

On the CV inlet at the mens shed use the supplied rectangular to 8" round entry and attached an 8" round to 9" round transition. A complex curved entry into the shed is done using a short length of 9" diameter flexy onto a short length of 9" galv duct and then a 9" round to 240 mm ID PVC pipe adapter was made using some of the 240 mm PVC pipe. It's not ideal but its what we had on hand and decided to use that.

At the mens shed we did not purchase the 1R outlet (available to purchase from ClearVue) that connects the impeller to the muffler.
Instead I made a 2.5R connection see Mens Shed Dust Collection
The small downside is the moves the muffler further away from the cyclone so the cyclone and muffler takes up a bit more floor space.

The other issues to consider with square ducting are
- nearly all machine ports are round so "square to round" transitions have to be made to cope with this. These are a bit of a PITA to make so they operate efficiently. OTOH virtually no standard machine port is the right size anyway so if you have to open them up then why not make them square?
- Square Bell mouth hoods would be tricky to make and not work as efficiently as round versions - for this reason alone I would stick with round ducting. Nowhere else in your system will you get a FREE +12% flow for the very little effort it takes to make them.

I suppose it would be too much to ask if you could knock up a square duct to test with your calibration setup you are playing with in your other thread?

Unfortunately it would.

hello all


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Last October I had a go at a new TS guard extraction and this is what I came up with

Details here
Ducting update.

Although it worked better than my old Hood I was still not happy with the scatter of chips out the front especially compared to what several other members including Lappa and DomAu were getting with their guards.

So back to the drawing board and after a lot of mucking around here is my next effort.
It uses the same black "Dust Picker arm" attached to an overhead steel truss, as the previous hoods but this time the arm supports a rectangular Al frame and a new Polycarbonate (PC) hood is suspended from this frame by 4 Al arms on bearings.

Note also the much shorter length of flexy in use. I really wanted to use the older style TC flexy as it is less restrictive but it was too stiff to use in this situation. The rest of that piece of CT flexy will be attached to that other 100 mm Y junction to use as a "cleaner upper" hose.

TSguard1.jpg

Below is a close up view.
B - bearings - there are 8 small (22 x 6 x 8mm) bearings that allow the hood to freely pivot "back and up" as show by the arrows.

The PC is a mix of 1.5 and 2mm thickness as I wanted the guard to be stiffer than the previous one shown above which is only 1mm thick.
Because this PC was in pieces I could not make the hood out of one folded piece so I had to join the pieces together and did this by folding, drilling and tapping the PC and used 1/8" CS brass screws - this worked really well.

The major difference between the shape of this hood and the previous one is the front of the hood is angled 45º away from the blade which deflect any chips thrown forward by the blade up into the clearing air stream. This is what Lappa and DomAu and others have used successfully and it does indeed work a treat. I did try steeper angles (75 and 60º) but even with the counter weight the hood would not lift smoothly which did not help starting the cut in a smooth manner.
TSguard2.jpg
The weight of the hood and flexy is near neutral as it is supported by a steel wire cable that attached to the old using a small Al bracket and shackle. The cable runs up to the ceiling through pulleys to a counterweight over in nearby wall cavity. I can easily lift the hood with very little forward pressure.

Here is the counterweight in the wall cavity.
Those discs are lead weights of about 1/2 kg each
COunterWeight.jpg

Below shows close to the max height the guard can swing out of the way (~95mm) - the supporting frame itself can also be raised up to any height so it starts the guard above the TS and also can be swung/pivoted to either side so that it can be quickly moved right up out of the way.

This also shows the clearance of the front bottom of the guard to the blade so I can afford to move the whole guard back towards the blade a bit more.
Maxcut.jpg

This shows the starting position of the front of the guard. That folded lip "L" provides stiffness to the front of the guard but I will remove most of it so more sawdust is deflected upwards into the clearing air stream.
TSguard3.jpg

The downside of the front of the hood at a 45º angle away from the blade is the view of the front of the blade is severely restricted.
This is what the operator would see from the normal operating position.
View.jpg

To see the contact point of the blade with the material one either has to bob down to this position
View1.jpg

Or alternatively look over/above the guard like this which is not so bad
View2.jpg

There are a few this still to do and one its to reattach the LED light and lock down all the PVC junctions.

All these hoods have the same problem, the fence cannot be used close to the blade with the hood close to the surface of the saw to contain the dust during cutting. I have no need for that on my slider but it is a real problem on a cabinet saw and if that sort of operation was done on a prolonged basis there would be a lot of dust escaping.

Originally Posted by Chris Parks

All these hoods have the same problem, the fence cannot be used close to the blade with the hood close to the surface of the saw to contain the dust during cutting. I have no need for that on my slider but it is a real problem on a cabinet saw and if that sort of operation was done on a prolonged basis there would be a lot of dust escaping.

Yes this can be a problem.
All of my hoods have been able to swing side to side so that the gap between the fence and the blade can be as narrow as you are prepared to go. I have tried it out with a 12 mm gap and it was OK. I'll take some pics once its all complete
The PC won't shatter if it contacts the blade and the sides of the hood can be easily replaced if they get badly mangled.

Originally Posted by BobL

Yes this can be a problem.

It would appear that this hood can't be moved sideways.

Originally Posted by Chris Parks

It would appear that this hood can't be moved sideways.

The whole guard/support bracket and arm rotates at the ceiling.
It's not a perfect seal with the material, especially away from the line of the saw, but it's way better than not being able to move it at all.
Here is the LHS.
LHS.jpg

The RHS is restricted by a router fence attachment to the TS fence but I use an Al extrusion that acts as a false fence that attaches to the T-SLot on that side of the fence.
In this show I have simulated the false fence with a piece of pine.
RHS.jpg

EDIT: I just realised there's at second pivot point on the support frame that can take the tilt out of the hood to get it flat to the table even when its hard over to the left or right side.

I need pictures of the aluminium extrusion and how it works. It does not sound like it would do the job or specifically the job I was asked to design for.

Originally Posted by Chris Parks

I need pictures of the aluminium extrusion and how it works. It does not sound like it would do the job or specifically the job I was asked to design for.

There was a bit of shed roof leak this morning and had to move stuff to clean up and I found the fence/extrusion and put it onto the main fence and took some photos.
When I say extrusion its not specifically designed for this purpose, it was just a piece of are Al extrusion I found in a skip and I adapted to to suit.

FF3nce.jpg

It is held in place with 3 socket screws onto a 6mm nut that sits inside a T-slot on the main side of the fence.
The false fence can easily be moved by loosening the socket screws and sliding it back and forth.
I usually use it with the end just past the start of the blade.

If the Router fence is not installed the false fence screws straight onto the main fence but as I like to leave the counter fence on I added brass stand offs.
The original extrusion was symmetrical about the Deep V-groove on the side so you can see what I cut off to get the shape I wanted.
It's far from any sort of ideal shape and there will almost certainly be better shapes if it was custom made.
Standoffs.jpg

This shows how close the fence can be to the blade and still allow the guard to drop down between the blade and fence.
This translates to about a 10mm cut.
I'm a bit chicken to operate this close and usually I go no closer than about a 15 mm cut.
If I need to go closer I lift the guard up and it still catches most of the fine dust especially the dust the saw blade pulls up from the cabinet at the back edge of the blade
fence1.jpg

For this photo I have also tweaked the second pivot point to get the hood making non-tilted contact with the table

FFence.jpg

The main pivot point up on the roof truss is the one shown in the photo below.
This pivot runs on a large surface ares HDPE washer which together with that crinkled contact collar has enough friction so the whole arm and hood can be swung sideways up to a point and it still stays put.
Bracket2.jpg
Pivoting at this point of course tilts the hood down near the table but the hood can then be levelled and lowered using the arm adjustments.

The other pivot point is this one, there's a large plastic knob in behind that screw and this allows the hood to be level with the table top.
Guard2.jpg

Here you can also see another problem in that when the guard is hard over to the left it conflicts with the Mitre slide.
I usually only use it like this for ripping when the mitre slide is not used. However, I do have an idea for an "offset mitre slide handle and angle setter" that I might get to one day.

I realize that this design won't suit many people a few folks can suspend their TS guard from their roof, and that it's over engineered for what it is. I posted it because someone might get some ideas from it.

Looks the business Bob, I don't think I could make one that flash. The light is a great addition too!


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I said I was going to make an off-set mitre slide so I could use the over head guard close to the RHS of the blade, but while ferreting around under the TS looking for something else, I came across my 45º mitre slide (which I purchased over 10 years ago and I think I have used it maybe 3 times) and decided to see if I could adapt that.

All I want to be able to use it is in full 90º mode so I took the handle off and drilled a new pivot hole hole in the slide so the slide could be moved about 15 mm further on from the old pivot hole.
I then turned up a steel collar (C) that has a slightly wider rim that slots into a groove cut into the mitre body
A 1/4" socket screw passes through the collar and fits into the old zero adjustment needle hole and tightening this locks the mitre onto the slide and enables some adjustment of the 90º position.

The handle is removed and a nut served onto the handle and then its is reinserted into its usual slot and a washer and nut added to the underside.
There's no positioning capability but OK and I can still restore the 45º mitre to its original state if I need it.
Mslide1.jpg

In the following two shots you can see the clearance and blade position
Mslide2.jpg


Mslide3.jpg

Of corse it doesn't cover all situations, like short size pieces but its better than nothing.