Curved Inlet

[phil (admin)]

Just a reminder, filters need to come off when chalk comes out.  The chalk will blind a filter faster than any other material I've used.

[Mike F]

Flexible ducting arrived today so I managed to get a test installation set up. I am feeling much happier now I have done a little more testing. I have made a short video but don't know if I can embed a YouTube video in this forum so I'll just post this link for now https://www.youtube.com/watch?v=uHVHt42zfjs and hope it works. The test was done by dipping the inlet, flexible duct into a container of dust and chips collected from previous machinings. Not very scientific but useful.

I raised the outlet to approximately 50mm above the bottom of the inlet and it appears most of the finer dust is now able to fall through the drop slot. However, I did notice that quite a bit of the finer dust remains suspended at the top of the separator, circulating indefinitely until the DC is turned off. As they were very fine particles I was unable to see what then happened to them as I neither saw them fall through the slot or get drawn into the outlet. There is a trace of fine dust in the outlet, flexible duct.

[jdon]

What a relief that such a good looking build is working well, but what kind of wood are you working with that leaves light blue sawdust?  ???   

[Mike F]

Jdon; if you look closely you will see blue, yellow and shiny silver bits :)

If you have read through the whole thread, you will realise I machine a lot of moulds and plugs for model aircraft. Most are made from epoxy board which is basically a huge block of epoxy resin that is filled with some kind of filler. I suspect it is talcum but the manufacturer will not tell me as the composition is a trade secret ??? Sometimes I will machine aluminium hence the shiny bits. It is the blue and yellow epoxy board that is giving me problems with the dust clogging the DC filter bag after just a couple of hours machining. I have some loooong, fifteen plus hours machining jobs coming up for a large scale model I am building and I needed a solution. Hopefully the separator will be the answer.

I made my CNC machine some years ago and, if you really want to send yourself to sleep, there is a very long thread on my build on the CNCZone forum http://www.cnczone.com/forums/cnc-wood-router-project-log/6840-sure-im-ready-ive-started-building.html

[Mike F]

Phil; looking at the video, do you think the baffle could be rotated further from the inlet as the dust appears to be hitting the baffle just at the end of landing area rather than at the start? I'm not sure if the landing area is supposed to collect the dust, as it drops out, or whether the dust should be falling directly into the slot. If it is the latter, then maybe I should move the landing area back, toward the inlet.

[phil (admin)]

I think if you rotate it any further you might run the risk of scrubbing once the drum starts to fill.  Right now you see the incoming airstream spread out and push the debris hard against the baffle.  If the slot were where, the airstream would spread right into the drum and possible suspend debris that had already been separated.

I say let it fill and watch it for a while, don't make any changes yet.

[Mike F]

Thanks, Phil - I look forward to getting down to some serious machining and I will report back when I have a few hours completed, hopefully without having to clean the filter bag. Thanks again for the forum and the advice held here.

Mike

[Mike F]

Time for an update with a few photos. I apologise for the quality of imagery but photography is not one of my skills.

I have done quite a bit of machining since the last message and in that time the DC has not been over taxed in terms of filter bag clogging. With the amount of machining I have done I would expect to have to clean the bag by now so, this is a big plus. However, there is a lot of the fine dust still getting through as can be seen by the evidence of dust in the outlet duct and the amount collected in the DC bag.

Also of interest is the track of dust left on the baffle. Does this indicate the drop slot is in the wrong place?

The other photo is of the dust that has collected on the outlet, above the bellmouth and a small trace of dust clinging to the top of the separator.

I am at a bit of a loss as to what to change, if anything, as the initial tests showed that a low set bellmouth allowed a lot of dust into the outlet. The thought then was to raise the outlet to near the top of the separator but the photos would suggest there is a lot of fine dust up there too. Any suggestions would be welcome.

Although it is not perfect, it is a lot better than I had before and is a great addition to my workshop - thanks again Phil and Retired.

Mike

[ducky911]

It seems to me that the bell mouth is encouraging the air in a bigger diameter that may be dusty. I know that retired2 has tested it for CFM efficiency but I like to see a test for fine dust efficiency. And Bill Pentz does not have a bell mouth or an air straightener. Food for thought.

really like your build.

[Mike F]

Ducky911 thanks for your reply - I think you may be right that the bellmouth is collecting the exit flow from a larger diameter than a straight outlet would. This will be pretty easy to test although I have no way of measuring its efficacy. I suppose we are hoping that the turbulent air, around the inlet of the outlet, will be of a smaller diameter than the bellmouth and therefore not encourage so much of the fine dust to enter? It may then make more sense for the outlet to be closer to the top of the chamber.

Thanks for the compliment on the build - despite its defficiencies it is still a very worthwhile addition to the workshop.

Mike

[Schreck]

It seems to me that the bell mouth is encouraging the air in a bigger diameter that may be dusty.

Good point.  We have been using the bell mouth shapes that are available in the marketplace, but they may not be the best shapes for our application.