Thread: DC-7 3HP Mods

Getting the dust outside either by putting the DC outside or inside an enclosure and venting outside is the single most important thing you can do with any DC.

Originally Posted by HeadScratcher

. . . before I start please no lectures on 3HP isn't enough to suspend the dust, etc, etc, etc,

The minimum size of a DC depends on the size of the shed, the machines you have, the activities you perform and the length of time you spend in the shed.
A modified 2HP in a 4x3m shed might be adequate to clear fine dust from a 14" BS used a day week. A 10 x 20 m shed with 5 HP DC will not be adequate to clear the dust from a 1200 mm wide drum sander.
A 3HP DC should be OK for most basic DIY machines in a shed up to about 6 x 6m - I assume 6" ducting and dust ports on machines are in use

I am not particularly fussed on the Y piece, and would like to remake this out of wood or metal.

The DC7 design is quite old (1960's?) so the Y piece is not its finest feature.
The newer designs use an integrated impeller /bag housing to create the shortest possible path way for the dust/air.
Because if this I initially though that getting rid of the Y would be the most significant thing you could do but it has to be done carefully because otherwise it could create preferential air pathways.
You absolutely must use two bags because two bags have half the resistance of one bag and this really helps with the flow.
Few people realise that while the bags are moderately clean a two bag DC has less resistance than even the best cyclones.

One way to modify a DC7 would be to make it more like the newer designs - look at carbatech and timbecons latest.
Make up an MDF box - cut the bag holders in half and insert these into the top and bottom of the box and then add the impeller to the side of the box like this.
The inside of the box should have curved rather than square ends (i.e. no corners) so the air would circulate.
Screen Shot 2017-04-22 at 6.03.41 PM.png

When do you expect to be moving into the new house, best and worst case without and with delays? If less than a couple years with delays I would be tempted to use it as is and build the closet around it. On the other hand if you are expecting to be over 2 years at the earliest then mod away.

Pete

Watching this discussion with interest as I too have a DC7.

Bob I have a fairly sizable CNC machine so I could cut out a double bag enclosure without too much hassle, do you have any internal drawings of your design idea?

Pete hard to say but we have bought the block, we just need to go through the steps of building, so the council may alter our time line as much as our doing.

Glenn do you have access to a CNC?

This doesn't look like it would be too difficult to make something like this. In fact it may be easier than trying to modify the existing housing.

I haven't seen the inside on that particular DC but I would assume something like this.

Screen Shot 2017-04-23 at 10.05.29 AM.png
However I would be wary of just plonking a naked impeller inside a home made housing.
Presumably the Carbatech version has the curved profiles and gaps around the impeller optimised for flow.

Unless you have a lot of time to start experimenting with impellers and measuring air flows (have you even got the gear and did you read my recent post on this) I would stick with using the existing impeller and impeller housing and just bolting it on to the end of the filter bag housing like this.
Screen Shot 2017-04-23 at 10.11.13 AM.png

Re the above; The problem I see in using the existing housings is to join them together and add the impellor. At the moment they are two separate dust separaters with an impellor in the centre.
Using a single one and mounting the impellor, reasonably easy, but it will need two for the airflow.

Originally Posted by Lappa

Re the above; The problem I see in using the existing housings is to join them together and add the impellor. At the moment they are two separate dust separaters with an impellor in the centre.
Using a single one and mounting the impellor, reasonably easy, but it will need two for the airflow.

I reckon it would be dead easy.

Make a rectangular box (red line)
Add curved defectors inside the box Orange curved bits. These could be galv plate.
Cut current bag holders in half, and cut holes on top and bottom of box to suit half bag holder - CS screws on inside edge would do.
Use existing impeller and flange and bolt it onto a corner as shown.
This is basically all mine is.
Screen Shot 2017-04-23 at 12.39.28 PM.png

Carbatech no longer sell the model I have but timbecon has a similar one
Screen Shot 2017-04-23 at 12.47.30 PM.png

Although centre would be better remember the existing impeller placement in its current housing is not symmetrical and doesn't have two openings so it would need to be rebuilt to suit two opneingsbe

In between doing other things I knocked up this model in SketchUp. Top and bottom would be easily made on the CNC and probably the inside pieces as well. Would probably want to pull the current housing apart to see how much distance there should be between impeller and the wall to try keep similar pressure.

Your diagram shows an even spacing around the impeller - while this will generate some flow it won't be optimum.
The spacing should be tapered and the tips of the impeller should almost be touching the sides in the middle.

Dust-Collector-New-Design2.jpg

How much - I don't know - it would need to be worked out by fluid dynamics simulation. Get it wrong and you won't have enough pressure or too much pressure and it will sound like a banshee.

You could get an approximation by asking someone to take their cover out of their carbatec DC and copy that,

Bob,
I was talking about your last statement and the following image you supplied.

"Unless you have a lot of time to start experimenting with impellers and measuring air flows (have you even got the gear and did you read my recent post on this) I would stick with using the existing impeller and impeller housing and just bolting it on to the end of the filter bag housing like this."

IMG_0255.PNG

I agree that to build a new housing would be easier than trying to adapt what the OP has (two separate housings) into the image showing a single housing that you supplied in your post. Modification using what available would require building a new housing.

Thanks Bob I spotted that too when I pulled the one in the shed down. So I redrew it. Also included square ends since it will go in a cupboard and be attached to three walls.

Originally Posted by BobL

Your diagram shows an even spacing around the impeller - while this will generate some flow it won't be optimum.
The spacing should be tapered and the tips of the impeller should almost be touching the sides in the middle.

How much - I don't know - it would need to be worked out by fluid dynamics simulation. Get it wrong and you won't have enough pressure or too much pressure and it will sound like a banshee.

You could get an approximation by asking someone to take their cover out of their carbatec DC and copy that,

Since it is feeding out both sides 180 degrees apart I actually think it would nearly be impossible to create too much pressure. He's my thinking... in the original housing there is probably 280 degrees of increasing wall size to create the pressure, and feeding out both sides that area is more like 90 degrees at both exits. So I think I could nearly have the tip touching and providing I open up reasonably quick it shouldn't over pressurise.

In order to reach full output size it has to have a fair amount of increase rate.

Originally Posted by HeadScratcher

Glenn do you have access to a CNC?

Headscratcher .. no CNC here [emoji848] .. yet.