Curved Inlet

[Mike F]

That last picture is very similar to mine.

Yes, not surprising really, I looked at your thread before drawing this version and took some inspiration from it :)

Bernard; I absolutely agree. The CFD analysis will be invaluable once we have an existing unit modelled precisely and can compare theory to practice. Retired's version would appear to be ideal for analysis.

Incidentally, I see references to 1H and 2H systems but am a little confused. At first I thought the H referred  to the distance between the top and the baffle being the same distance as the diameter of the inlet but then I realised this cannot be the case as you cannot have a 1H version if the inlet ends in a rectangular form, where the H would then have to refer to the depth of the rectangle. So, my question is; what does the H actually refer to?

Cheers,

Mike

[BernardNaish]

Hi Mike, I think retired2 coined the term. A one "D" is a Thien top hat where the top plate and the baffel are spaced by a distance equal to the height of the rectangular inlet just as in retired2's build. A 2D is twice the height of the rectangular inlet.  It has been suggested that this will help separate fine dust by reducing turbulence from circulating air and debris hitting the air coming into the chamber. retired2 has suggested it may not need to be 2D but perhaps 1 1/2 D or less and I think this certainly makes sense with regard to debris because the videos show it hitting the inlet point about two thirds or three quarters down its height. Ain't this great fun. I think it brings out the creativity and the development engineer in us all. I hope one day an easily built TTH will equal or surpasse the best cyclones. Cheers B.

[Mike F]

Hi Bernard,

Thanks for the explanation. Reading through lots of the threads would suggest that a 2H (D - not sure which) should be better than 1H and as I have the room, I may as well go at least 1.5H. It makes sense that the outlet be lower, if possible, than the inlet in order to minimise the bypass.

As promised, though I am very embarrassed, here is a shot of my DC in a sorry state. The problem I have is that the materials I am machining create an awful lot of dust, rather than chips, and this dust clogs the filter very quickly and once blocked, the dust find any nook and cranny it can escape from. With the DC being sited in the garage, the other side of a brick wall from my workshop, I don't always get to see the problem as it occurs.

I am sincerely hoping the separator will help with the bulk of the problem.

Cheers,

Mike

[BernardNaish]

Yes I see what you mean Mike. I had quite a bit of very fine dust escaping from the plastic bag on my DC today. The bag seal is rubbish as many are. I sealed it up with duct tape and as I believe it will take well over a year for it to fill I can live with the need to clean off the tape glue. That is with a crude Thien separator before the fan. I also emptied my bin today and I have a natural airflow between two building that draws away the dust when I empty the bin into a plastic bag. Even then there is a lot of fine dust and this without sanders just a band saw making fine dust. With your ultra fine resin dust how do you handle this emptying?   Regards, B             

[retired2]

Actually, I think it was Phil who first used the 1D and 2D shorthand for top hat chamber heights, and I think it was in a conversation I was having with him so that might be how it got attributed to me.

I don't think the shorthand nomenclature is intended to mean strict dimensions.  I think they are just approximations, but Bernard's explanation is still correct.

Now with regard to which is best, that is what I was hoping superptrucker could help us with.  In fact, height was the first variation of the standard build that I suggested he simulate.  I really don't have an opinion about which is best.  Intuitively, it would seem like a deeper chamber would be better, but without testing with instruments we can't really be sure.  In fact, someone would have to built two separators, identical except for height, and then test both.

[BernardNaish]

I have been thinking the same thing retired2 and have drawn up a design that would allow extra chamber height to be added to a version of your build. Hence no need to make two and they would be identical except for the chamber height.

I keep having to remind myself that I am really a hand tool wood worker and that I want to make furniture but my fascination with innovation keeps pulling me back to this forum.

[Mike F]

Bernard; Emptying the bag and cleaning the filter is a messy job. The bag is relatively easy - once I have shaken as much dust out of the filter as possible (whilst holding my breath) I remove the collection bag and place it upright on the floor. I then get a plastic, bin liner and place it over the collection bag and then invert the whole lot. Raising the collection bag then fills the bin liner while vacating the collection bag. This process creates no extra dust and is dead easy to do.

The biggest problem is cleaning the filter bag. Just the action of removing it from the machine creates quite a lot of fine dust. On removal, I carefully take it outside and shake it into the wheelie bin before reaching inside and turning it inside out. Once inside out it gets put in the washing machine for a quick cycle. I have found that the filter bag has lost some of its effectiveness over the years and could do with replacing but I cannot find a replacement anywhere. It appears that this particular, Rexon model is no longer available :(

With regards the height of the unit, like Bernard, I would like to make my design capable of being easily altered by simply replacing the chamber wall. We will have to wait and see if this will be as easy as it seems.

Mike

[BernardNaish]

Mike,

If you know all this I will shut up. I tend to be an interfering know-all so please do not be offended.

I am deeply concerned that you may be exposing yoursel to a lot of very dangerous dust. If I understand correctly you fabricate with composites using fibres and resin. The fumes from the resins are bad enough but the dust generated by machining the resins is lethal. I suggest you should be wearing a full face respirator when machining and certainly when you empty the bag or even going into the DC room.

I will try to get a sketch and a construction method posted of a design for a top hat that can be grown in height by adding spacer rings. This has the advantage that you can play easily and the basic TH is exactly the same each time. Thus comparisons are easy and hopefully comparative measurements can be made that would be so helpfull to everyone here.

[retired2]

Mike,

If these people don't have the filter bag you need they will make it, and they will make it  larger for better performance.  Don't know about cost.

http://www.americanfabricfilter.com/facts.php

[Mike F]

Hi Bernard, not offended at all, I appreciate your concern. The only time I am exposed to much of this dust is when I clean out the system. One of the beauties of CNC machining is that you can walk away from the machine :) Some of the programs can take up to twelve hours to run! I also have a very good, brushed hood around the spindle that does a really good job of taking all the chips away. The worst machine for dust not being extracted efficiently is my bandsaw. There was a thread here somewhere, may have been one of yours, that documented an alteration to a bandsaw to make extraction better and I may have to do something similar. Incidentally, none of the materials I machine have fibre in them and I make a point of not machining glass or carbon fibre. It's definitely a no no.

I look forward to seeing your sketch for the adjustable height version.

Retired; thanks very much for the link. I did a search for something similar in the UK and came up with a couple of hits. I will be contacting them after the May Day bank holiday,

Now a question - what, if any, difference will I see if the internal diameter of the separator is smaller than the drop box? You can see my intended drop box in the photo but it would make installation easier if the separator were 400mm (15 3/4 inches) to 425mm (16 3/4 inches) The drop box is 460mm (18 inches).

Cheers,

Mike

[retired2]

The fact that the separator is smaller than the drum will make no difference.  However, within reason a larger diameter separator will probably perform a little better than a small one.

[retired2]

This may be the bandsaw modification you were referring to:

http://www.jpthien.com/smf/index.php?topic=537.msg2846#msg2846

However, the final chapter was never added to the post.  After some use and testing, I finally concluded the 2" connection around the blade wasn't doing much for me other than weakening the draw on the large port that was doing most of the work.  I removed the 2" pipe, covered the slot in the door with a piece of painted aluminum and it works even better. 

[Mike F]

Bernard, I must apologise. Re-reading my reply to your concerns about my health made me realise it seemed rather trite. It wasn't meant to be. Having been a teacher of Design Technology for thirty odd years before my retirement, due to my wife's ill health, I am acutely aware of the health risks of dust and airborne debris. When I retired I no longer had access to the school's workshop facilities and decided to extend my existing workshop. Right from the start of this exercise I installed ducting to all my machines and installed a decent sized extractor. It has worked very well indeed but the DC does have its shortcomings hence the desire for better separation to alleviate the need for such often cleaning of the filter bag.

I don't know if anyone on this forum machines acrylic foams but I was wondering how effective the separator is with very lightweight particles? A lot of the model aircraft work I do involves 3D profiling of foam blanks before they are put into moulds. The dust from this foam is particularly good at clogging the filter bag and if the Thien Separator can solve this little problem, my prayers will be answered. The particles are not particularly small but they are very light in weight.

Cheers,

Mike

[BernardNaish]

Mike, Not trite at all. Never know if hobby workers are as aware as you. I had too many years in labs where one of my jobs was Departmental Safety Officer.

Back to the important stuff. Regarding your floating dust. I suspect that most of us here are thinking that the Thien baffle can remove a lot, if not all of the very fine dust as well as the large shavings. If this fine dust is separated then why not your tiny bits of foam? Usualy a narrower drop slot is used to remove the fine dust but I suppose your particles are relatively low density hence larger than most dust particles so the slot may need to be a little wider. How do we know. We just have to try it out.

My build (see link and photos below) uses a cheap dust bin, a cheap bucket, a length of pipe and some MDF. Ignore all the guff about brackets because I threw these out within a few days. Just wedge the baffle into the dustbin with a bit of 3/4 inch dowel so that it sits just below the rectangular inlet. In under an hour you can have an experimental lash up working. Mine worked so well that I have not bothered to change it.........yet. You can now play with slot width, slot edge profile, depth of baffle below inlet etc. My guess is that you will find a set of dims that work well. Please let us know.

http://www.jpthien.com/smf/index.php?topic=857.msg4947#msg4947

[Mike F]

Bernard, yes, I have read your build and although I could do a quick lash-up, I fear that it would remain a 'lash-up' even if it worked only 70% effectively. As I have the wherewithal to produce a reasonably well made unit in probably just as little time as it would take me to do a 'lash-up', I am tempted to go that route. My design background tends to get in the way sometimes :)

Attached are some renderings of my proposed unit for criticism. One question I have is of the baffle. I see most baffles seem to be made from thin material, presumably to aid separation and reduce turbulence at the interface between separator and drop bin. In my design I have made the baffle and base out of 18mm MDF but have chamfered the  bottom edge to minimise turbulence somewhat. I can re-do the design to make the baffle as a separate item but is this necessary?

Cheers,

Mike