I have a query.
Has anyone here designed a stationary dust shoe? I have found a lot of dust shoes that move with the spindle, but I was looking for an adjustable dust shoe design where you can set the depth, and the spindle runs through it. It has it’s advantages in that the brushes do not get crushed, or run the risk of being cut by the bit at deeper depths. If there are no current designs, I may have a go at designing one.
One of my early designs was the dust manifold attached to the U axis on my machine. But the vacuum for dust systems works on airflow, not vacuum pressure. So what happens is the air will be pulled from around the gap at your spindle and not from the table or stock below where the cutting is going on.
If you made some kind of accordion like attachment then you could stop the leakage I suppose. But at that point it would just be better to have it attacked to the spindle.
My PCB mills all have the fixed dust manifolds and you know what the #1 thing I am doing on those things? Digging copper and fiberglass dust out of every nook and cranny.
Perfect, DAlbers! Thanks!
I don’t know how I missed this. I’m subscribed to Alexandre on YouTube.
Subnoize,
With a stationary Z shoe, the brushes are always in contact with the surface. Unless you’re doing a 3D carving, where there is a bunch of z travel difference, it shouldn’t be an issue? OK, I see where you’re going. The gap in the body of the spindle if cutting deep. It’s not convolute over the spindle diameter, so allowing air to escape around that gap. Good information!
Thanks Subnoize!
Yep!
The most common dust manifold you will see around here is a large oblong clamp that has a magnetic holder for the brush, almost like a shoe (which is probably why everyone calls them a “dust shoe”). Those are also very inefficient because the opening is in effect much larger than the diameter of the vacuum tube attached to the vacuum motor (carrier tube or hose).
So again, if you want maximum dust and swarf collection you have to keep the size of the opening the same size as the carrier tube. Which is why you see the people like myself who have problems with the dust getting that opening as close to the tool and as close to the same size at the carrier tube as possible.
What I did eventually was print a nylon sleeve that the spindle fit into when it came down and a rubber ring around the actual spindle that plugged that gap. But it was tedious and then I got the ATC and that mandated a new non-fixed design.
Youtube has many examples of those fixed designs though. I am just telling what I have been figuring out over the past 5 years so you can just ignore me 
Its not inches H2O or inches Hg, it is pure CFM, cubic feet per minute. Never get wider than the carrier tube (vacuum hose) but you can get just a hair smaller right at the opening. That will drop the pressure and increase the velocity of the air (google Bernoulli’s principle) and create a “snatch” effect to pull the dust in BUT you will have a dead spot somewhere in line behind that. The dust will want to fall out of the stream as the air slows back down and the pressure normalizes. The exact place that will happen is in direct correlation to the constriction of the orifice.
Complex science! Best of luck. If you need any help I have tons of research so I can shorten your journey if needed.
Here’s one that’s its own axis:
Hoping to rekindle this discussion. Looking at starting the design phase and avoid the first few obvious pitfalls. I currently have a Powertec dust shoe - typical oblong shape we’ve all seen. Works fine for my shorter tools but useless when I reach for the 1/2" Whiteside chipbreaker and some of the flatteners. Also, the shortest tools really jam up the brushes.
As far as motion, I’m not picky. I don’t require linear rails or automatic positioning, software control or anything fancy. I would probably design with plywood in mind initially, and maybe a final build with HDPE or a combination with 3D printed ABS or PLA where it makes sense. I’m thinking 1/2" increments are more than adequate if not fully adjustable.
Just remember, effective suction requires you to keep the orifice of the “dust shoe” the same size as the hose.
Any size increase will reduce airflow speed substantially. Any reduction will increase the air speed at the constriction but you will then get an equally large increase in pressure and this lower airflow just beyond the constriction. Thus you will see material fall out of the air stream and build in that part of the hose.
As such, all of these “dust shoes” are really just a suction hose positioned next to your spindle. The brushes are the only thing that really makes it effective.
In a stationary design you will have a necessary gap between the spindle and the manifold which will leak suction as well. So they tend to only be good with large airflows up around 1,000 CFM or higher.
A great way to test he efficiency of your design when its finished is to take the brush off and make a few cuts and see how much dust escapes.
Good luck.