Thread: DC Maintenance time

Thank you for showing us yet again why DCs are best placed outside the shed.

Your flexy link between the impeller the chip catcher is WAAAY too long and being floppy like that will restrict the flow - I'd try and do the whole thing using solid PVC.
It should not be too hard to set up a 90º PVC junction pointing upwards from the impeller, Then make up a 100mm ducting "U" to join the impeller to the Chip collector.

BTW It doesn't look like your chip catcher isn't catching much fine dust?

Bob, what I didn't take a pic of was the cake of dust inside the filter.

As to the rest, I will have to look it closer. Even to raise the impeller out let to the level of the chip catcher, to remove the large bends.

Is series of 45° bends more gentle, thus less resistance, than a straight 90° bend?

This is the eternal WIP
There is always something that can be modified and improved.

Originally Posted by Pat

Bob, what I didn't take a pic of was the cake of dust inside the filter.

Yep - a lot of folks think they can use a chip catcher tso they can forget about cleaning the filter, but all that happens is the chip catcher removes the chips and lets the fine dust through to clog the filters.

As to the rest, I will have to look it closer. Even to raise the impeller out let to the level of the chip catcher, to remove the large bends.
Is series of 45° bends more gentle, thus less resistance, than a straight 90° bend? .

There are two common kinds of 90º bends - 1R and 2R bends.
1R has a radius of curvature of the bend of the radius of he pipe itself.
It's usually used in stormwater applications
ie a tight bend
DSCF4551_150px.jpg

2R has a radius of curvature of the bend of ~2x the radius of he pipe itself.
This is used in DWV (sewage) fittings
DSCF4555_200px.jpg

In 100 mm ducting sizes, 1R loses about 7.5% of the flow while 2R loses about 5% of the air flow.
2 x 45º loses 10% of the flow! so are n fact worse than either

I have not tested bends using flex flex extensively but for the same radius of curvature of the bend, flex bends are approx 2x worse than PVC bends.
Some flex is better than other.
The "stiffer" grey Timbecon flex seems to be less "lossy" than the "floppier" translucent Carbatec flex.

It does not seem to pay to use flex with larger radii of curvature because this increases the length of flex used which maintains and even increases the flow loss

Since you are using a chip separator why wouldn't you cut out the antiaircraft gunsight in front of the impeller? It will help a little with air flow.

Pete

Pete, I sometimes turn wet timber and acrylics and the guard prevents clumps of streamers hitting the fan, especially if some lazy so and so forgets to check the separator often enough. So it is a fail safe for my laziness, as the streamers clog the hose and cause the DC motor to change pitch and then I notice that.

Not the best, but it is reality. I have tried to implement a better system of regular maintenance, but my lathe calls me . . .

When I was using my 2hp with pleated filter and cyclone separator I'd turn the paddles before and after every use. Was changing the bags one day (prob after 6 months of use) and decided to stick my head inside and take a look at the filter. I realised that yes the paddles did something as i can see the dust falling off into the bag, but didn't do enough IMO to clear the embedded dust in the filter.

Y'know, I have the same DC and chip collector setup in my home workshop... and you've reminded me that it must be time for me to bite the bullet and do the same.

Thanks, ya mongrel.


BTw, that aircraft sight? I cut mine out and put some fine galv mesh (y'know... small chicken wire?) over the end of the central pipe in the chip collector lid instead. Serves the same function, but I can remove the strands while I'm emptying the barrel, instead of having to remove the line at the impeller. Also improves the airflow into the impeller... although it's really just moving the inefficiency up the line.

Far from perfect, but it works well enough for the lathe.

For maximum airflow it's best to not have anything in the way.

If you get blockages then you can install something like this - made from a pot plant.
In 7 years I have had to open it up once when a large rag got sucked in.
Impellerwindow.jpg

An alternative is an PVC inspection hatch like this.
130214_061.jpg or this STORMWATER_JUNCTION.jpg


Its a bit trick to get your hand in there if its only 100 mm but much easier if 150 mm ducting is used

Originally Posted by BobL

For maximum airflow it's best to not have anything in the way.

Agreed, but when turning wet timber or acrylics you get long steamers... imagine throwing handfuls of 6-18" lengths of raffia string into your DC line.

They have to be caught somewhere along the line or you end up stalling the impeller, much like a lawn mower picking up and choking on long grass/raffia/nylon rope. Due to their lightness and length they'll often pass straight through the chip collector, especially if it's not emptied as often as it should be.

I personally prefer to accept the catchment and it's incumbent efficiency loss than to risk burning out the motor.

I've turned lots and lots of PVC and green wood and got great long streamers and never had a problem. I also use a catch guard (see below) but I take it off when turning streamers. Maybe my impeller is just better at mincing the streamers? Backwards curved impellers are better than straight vaned impellers at clearing streamers - maybe check which one you have?

If streamers are a problem, and to guard against the loss of a piece of work, to retain max air flow a screen should at the air intake hood where the opening is the widest so the chances of blocking fine dust uptake is reduced. If the guard is inside or over the end of plain ducting much more air flow is lost.

Below shows the two setups I have tested (1" SS mesh) Mesh on the outside of the hood in line with the ducting,
lathenew.jpg
For 6" ducting, placing the mesh on the outside of the hood loses ~1% of the flow, placing the mesh on the inside of the hood, or in line, loses 4% of the flow.
On 4" ducting, outside hood loses 4% inside duct loses 12%.
This is of course before streamers have an impact - when the streamers hit the comparative losses become even greater.

Having the guard on the outside of the ducting means no opening up of any chip collector or ducting to find that small piece of work that gets sucked up or removing streamers from the guard.

Hmmm. Significant figures.

I don't use mesh on the outside of my hoods as I've shaped them to "fit around" the pieces I'm turning, rather than having them offset. I hadn't thought about fitting it inside the hood though.

How are you determining the efficiency losses? Do you have the equipment to do quantitive testing? (Sorry if you've already established this in other threads elsewhere, but I've been intermittent on the forums these last few years for lack of time and have a huge back log I'm wading through.)

I ask as my setup uses what is basically 15mm hexagonal chicken wire; a fairly fine gauge of wire. I made a 150x90mm(ish) cylinder with one capped end (also the mesh) and uses a hose clamp to fix it to the intake end of the duct from chippy to DC.

I'm wondering if this actually gives any improvement over simply stretching the mesh over the end in a planar fashion. My head says yes and it feels like it does... but I have no figures to support one way or t'other.

Have you tested this sort of config before? If not, care to run an experiment?

Originally Posted by Skew ChiDAMN!!

Hmmm. Significant figures.

I don't use mesh on the outside of my hoods as I've shaped them to "fit around" the pieces I'm turning, rather than having them offset. I hadn't thought about fitting it inside the hood though.

I have tested many hoods and the best overall are Bell Mouth hoods (BMH) as they collect more air, are nice and compact so can be placed behind machinery up against walls, or don't poke out too far into the shed. As well as collecting more air and hence dust they collect more air from the front as opposed to most other hoods that collect a lot of air from the sides of hoods.They also produce the highest air speeds further away from the hood than any other hood. They work really well for spindle work and while they are not perfect when turning large objects but they do significantly reduce chip scatter.

The theory for these hoods was worked out about 50 years ago and its why they are used as air intakes for carburetted engines and also as ports on loudspeaker cabinets.

This is not a definitive test but it is an indicative test

The real test is done with my wearable particle counter which shows when this is happening I am breathing air with the same level of dust in it that is in air outside the upwind side of my shed.

How are you determining the efficiency losses? Do you have the equipment to do quantitive testing?

Air flow calibration measurements
I have 3 calibrated air flow meters and 30+ years of experience in using these types of meters.

Better still I have access to a pro level particle counter and I have made 4 particle counters so I can assess what the flow means in terms of particles.

I ask as my setup uses what is basically 15mm hexagonal chicken wire; a fairly fine gauge of wire. I made a 150x90mm(ish) cylinder with one capped end (also the mesh) and uses a hose clamp to fix it to the intake end of the duct from chippy to DC.

I'm wondering if this actually gives any improvement over simply stretching the mesh over the end in a planar fashion. My head says yes and it feels like it does... but I have no figures to support one way or t'other.

Yes it should be better. I have done some Q&D testing of mesh spacing and mesh size. It looks like mesh spacing is more important than mesh size/ so what your setup gains in area could be lost by the smaller mesh spacing.

Have you tested this sort of config before? If not, care to run an experiment?

I will add it to the list of experiments I will run next time I set up my test pipe. If you look in the above link you will see that setting up my test pipe takes over teh entrance space into my shed so I tend to save experiments up and do them in a batch rather than set up for just one experiment.

A significant benefit in having the guard outside the ducting (right next to where you are working) is it can be put on and off as required for that machine and easily cleared without opening up ducting or chip collectors etc. If its inside a chip collector it's there for all machinery whether they need a guard or not