Shot Blasting Cabinet Mods

[Roger]

I've just updated my much improved Syphon modification for any Blasting Cabinet which is now available on Thingiverse here.

If you've ever had one of these Blasting Cabinets, you'll know that they just don't work that well. The media refuses to flow smoothly up the feed tube, and there's very little you can do to improve it. I've tried some of the ideas that are shown on the Internet, but none of them work.

The Syphon is 3D printed and fits into a hole that's cut into the bottom of the sump door. The outlet now slopes down so that the Media is much more inclined to flow down it. The fluidisation from the first version has been mostly removed so that air doesn't try to escape up through the Media, back into the cabinet.

The outlet of the Syphon now has an Air Mover style of nozzle printed as a complete annular arrangement, and this changes everything.

I've also designed an Air Mover that fits in the hose so that you can put a couple of those in the bottom section where the Media tends to otherwise pool and block the flow. I found two to be enough, and you can now deliver so much Media that you can't see anything if you go too far. I've fitted a regulator which feeds the Air Movers, but you can probably just use one of those adjustable restrictors. You only need a few PSI for it to work, so even if your compressor isn't huge, it doesn't waste enough air to prevent it from working.

Here's the Cyclone Filter that I designed for it too. This works amazingly well, considering there was a lot of guesswork in the design.

Hopefully someone will find this useful.

[SteveW]

Guys,

As I've reported here years back I cobbled together a simple blasting cabinet using a saved 32" TV cardboard box with a wedge removed from one side/top and fitted a bit of rescued secondary double glazing taped on as a viewing portal. It got the job, refurbishing the club loco's livery, done and I learnt a lot. Mostly not to mess with it again.

The biggest problem was exhaust air. If you're dumping 10cfm of air into the box, 10cfm of heavily dust laden air needs to escape and it does wherever it can. The little filters I've seen on cheap cabinets don't work after a few seconds of dust accumulation. Nothing short of a labyrinth filter that allows free flow of air and the time for the dust to settle out.

A cyclone filter was way beyond my means years back and I don't recall Mr Dyson had got going yet. I am still on the search for an old discarded Dyson to rescue the cyclone filter system to use a pre-filter for my ageing Wickes vacuum cleaner. Seems these old Dyson vacuums are a bitch to fix once the motor goes. The Wickes vacuum paper filters were useless from day one and the optional cartridge filter doesn't work too well now. Currently I'm using a bit of old carpet wrapped around it as the primary filter and this works well.

I did all my grit blasting at the bottom of the garden in the greenhouse to keep all the leaked dust away from my workshop. I also used the full length of all my hozes to distance my compressor. There was a lot of dust. The down side was the sudden pressure loss as the air dragged in the long hose. A secondary local reservoir would have helped.

The other struggle was using the reinforced plastic pressure hose inside the cabinet. It made using the gun very difficult and inflexible. Replacing this with a flexible rubber pressure tube solved this one.

[Roger]

Nov 16, 2024 13:57:34 GMT SteveW said:

Guys,

As I've reported here years back I cobbled together a simple blasting cabinet using a saved 32" TV cardboard box with a wedge removed from one side/top and fitted a bit of rescued secondary double glazing taped on as a viewing portal. It got the job, refurbishing the club loco's livery, done and I learnt a lot. Mostly not to mess with it again.

The biggest problem was exhaust air. If you're dumping 10cfm of air into the box, 10cfm of heavily dust laden air needs to escape and it does wherever it can. The little filters I've seen on cheap cabinets don't work after a few seconds of dust accumulation. Nothing short of a labyrinth filter that allows free flow of air and the time for the dust to settle out.

A cyclone filter was way beyond my means years back and I don't recall Mr Dyson had got going yet. I am still on the search for an old discarded Dyson to rescue the cyclone filter system to use a pre-filter for my ageing Wickes vacuum cleaner. Seems these old Dyson vacuums are a bitch to fix once the motor goes. The Wickes vacuum paper filters were useless from day one and the optional cartridge filter doesn't work too well now. Currently I'm using a bit of old carpet wrapped around it as the primary filter and this works well.

I did all my grit blasting at the bottom of the garden in the greenhouse to keep all the leaked dust away from my workshop. I also used the full length of all my hozes to distance my compressor. There was a lot of dust. The down side was the sudden pressure loss as the air dragged in the long hose. A secondary local reservoir would have helped.

The other struggle was using the reinforced plastic pressure hose inside the cabinet. It made using the gun very difficult and inflexible. Replacing this with a flexible rubber pressure tube solved this one.

Hi Steve,
Yes, the exhaust air is a problem. If you want the blaster to work tolerably quickly, you need plenty of grit, and it's hard to see what's going on. I initially used a vacuum cleaner hooked up to it, but the bag got blocked very quickly. The 3D printed cyclone filter stops almost all of the grit getting to the vacuum cleaner, and the amount it collects is astonishing. I just emply the plastic sweet jar back into the cabinet. I reckon there was about 1Kg in there after an hour of blasting.
I use the cabinet outside, with a cloth over my head else I can't see anything, even though there's ample lighting on the inside.

[SteveW]

Roger,

Being a little careful with resources I tried recycling the used grit but with mixed results.

I used a magnet to reduce the ferrous payload and the kitchen sieve for the lumps. I think a lot of this ferrous was the gun nozzle which went from a relatively small hole to a big one and the character of grit blasting evolved quite a bit. There was also an awful lot of dust too fine to reuse. Best anyone trying this buy a spare nozzle.

I used the cheap Spot Blaster from Machine Mart and later sourced spares just in case I got dragged screaming back into this, sort of an insurance policy. So far I've not needed them.

The issue that cost me more money to resolve was a sort of concretion of the used grit into nodules that couldn't be reused. Turned out moisture in the air was gluing the grit into these little lumps. I had to go buy a water trap to remove the water. This did work, think I used two water traps in the end.

I also went big time into a proper breathing filter system not just those simple face masks. The clue is you can taste what you're doing and it's not good for you.

[SteveW]

Roger,

It would interesting to hear about any little flecks of plastic turning up in your cyclone exhaust grit.

[Roger]

Nov 19, 2024 0:05:48 GMT SteveW said:

Roger,

It would interesting to hear about any little flecks of plastic turning up in your cyclone exhaust grit.

So far, the dust is incredibly fine and I put it all back. I haven't noticed much of anything in there, but I ought to seive it really and see what's in there. I'm using a very fine grit because it's mostly used to prepare clean metal for painting.

[SteveW]

Roger, Guys,

Just remembered ...

The other trick that helped a lot was to replace the crappy little output tap on the compressor for one with a bigger hole and select pipe couplers with the biggest through holes. I got my compressor, an 1.5hp thing, from Machine Mart and the original output tap's through hole was quite small. Thinking about it now I've never needed to turn it off so could have chucked the bloody thing away on day one.

When you are consuming a lot of air, as in a grit blasting, any restrictions in the air feed system, however small, add up and to reduce the available pressure at the gun.

[Roger]

Fortunately, I have the Hydrovane compressor from the factory that we used to take to Trade Shows back in the day to run the Air Bearing Spindles. The only restriction I have is the amount of current it can draw from the single phase variable speed drive which limits me to about 40Hz. It's enough to do the job, but running it at top speed would be even better. I ought to contact Control Techniques and find out why it folds back. It looks like the specification ought to handle it, but it might be due to me having to use a single phase input out of the possible three. The current and power ratings look ok otherwise.