What do I need to start Part 4 Nozzles & Guns

Hi

Not the best couple of days for my re- learning the etching game as my cutting machine has given up the ghost, I have been trying to cut templates for my etching cream tests but something has gone wrong and I can't get it to respond to commands. It is an old GCC Jaguar JR61 and an excellent machine around 15 years old. I have had it for about 7 years and never had a problem until now, I have tried 2 different computers and 2 different parallel port cables but no luck on any of the COM or LTP ports so have sent for a Parallel to USB cable and will give that ago. If it doesn't work then its a new machine, will stick with GCC as they are very good at a reasonable price. I have decided on a basic model GCC Expert 24 and have got a company down to £700 and comes with a stand and software, hopefully I will get my machine working.

Well you have your compressor, cabinet and media but how do you get the media onto the glass, this is where the guns and the nozzles come in.

There are a myriad of guns / nozzles out there so what do you choose; well basically you may require one for each application. I have 3 different types 

A syphon gun.

Nozzle end's

A Sand Carving gun

This is not by any means the full selection of guns, just what I have.

I guess the Syphon gun is the most common with a range of prices depending on design and quality. Mine below cost around £30.

These guns are generally supplied with most cabinets you buy these days and need a large amount of air to operate as they have to suck up the media and blast it out in a stream through a relatively large nozzle approx 5mm 1/4" across. 

If you haven't already done so then have a read.

AZ Glass Classes on CFM v/s PSI on Nozzle size

This type of Syphon gun consists of a pickup which is buried in the hopper, and has an negative air pressure tube that must be above the media to create a negative pressure allowing the media to rises up the tube and prevent clogging. Attached is a short hose which is pushed onto the front of the gun. Care should be taken with the negative pressure tube as it is generally screwed into the pickup body which leaves the tube very thin in a very small area, I must be cack handed as I broke both of the ones I have and had to drill the hole larger to glue the tube back in place.

The air comes in at the back to the trigger and is held until the trigger is pulled, it is this trigger function that makes these guns widely used as it saves having a foot pedal to activate the air.

I have had to buy a new gun as my original would not work and I could not figure out why until I bought a new one and compared.

My original gun.

These guns pick up the media using suction caused by air passing through the venturi tube in the end of the gun, the air exits very fast causing a reduction of pressure, partial vacuum in the chamber around the venturi tube thereby sucking up the media.

This is the tube and chamber on my new gun, the nozzle is screwed on tight to the end .

You can see the opening under the tube and the hose pickup connection where the hose is attached, the pressure drop as the air passes out of the gun reduces the pressure in the chamber and pulls the media up the tube where it is mixed with the air and is thrown out.

In this photo of the chamber of my old gun you can just make out the possible reason why this gun is not working.

Difficult to see but the ventui tube has been worn thru on the underside by the media passing over it on its way out. I guess that the reason why I had to fork out another £30

These guns of course do work and are great for frosting large areas but not for carving where you require control over the media for cutting very small areas but and a big but is that they use / require a lot of air.

Just look at the size of this hole.

Another and possibly better option for a syphon gun is the direct hopper pickup used in conjunction with a foot pedal. 

The pick up is situated at the bottom of the hopper and draws the media directly to the gun.

Although I do not yet own one of these guns probably because there are approx a £100 each, I have made provision on my cabinet I have built for when I do buy one.

I have fitted a tee with one side to the gun and the other blanked off but able to fit a negative pressure fitting, I have not gone for the air foot pedal but the air solenoid method using an electric foot pedal.

I am using a large 1/2" 12 volt solenoid with a pressure controller, the foot switch will be wired to the junction box so the power is directed to the foot pedal,so air on air off.

My foot pedal

The guns are readily available and come with the larger cabinets.

The working is very similar to the trigger gun in that it works on the venturi method of suction.

In this type the whole of the handle act as the suction chamber and the media is mixed with the air as it comes in contact with the jet of air.

These are basically the 2 main syphon type of guns (that I know of)  the other guns that I know of require a single hose attachment with the media being forced along the tube and out of the end. This in itself required 2 different arrangements to start stop the flow of media.

One being a pinch valve arrangement either in line or in the gun itself or a manually operated valve.

The method of forcing the media along a single line is by the means of a pressure pot which I shall look at in another post.

There are a number of guns on the market.

This is a squeeze handle gun, the media is kept in the gun by means of a blanking plate, squeeze the spring loaded handle and the nozzle is uncovered. These are available on eBay and cost around £30.

There are a number of different models.

Unfortunately they do have some drawbacks, the main one is that squeezing them for more than a short period hurts like hell, well it does me (arthritis) and the other, well here's mine.

Looks ok but have a closer look at the blanking plate.

There is a hole blown into the plate, this is caused by not fully squeezing the handle and allowing the media to cut into the plate, useless now so beware if you go this route.

This blanking type is not exclusive to this in-line design but an easier right angled trigger type is available although I have only seen one photo before.

My other gun is a PAB (Pickard Artistic Blasting)

This is a 1/4" model with a 3/32 tip and works on pinching the suction hose as it goes through the gun, it may look like a very cheaply made plastic child's toy, but its not, it's a very expensive cheaply made etching gun which I have used to do around 80% of all my work and I think its great. 
It cost $225 but a few spares should also be bought at the same time.
Gun inserts @ .50c
Spare hose @ $18
and if you are feeling extravagant then a different size tip $39.99, add in delivery and import tax then it is a very expensive bit of kit.
I bought this around 7 years ago and apart from a little wear on the brass section and a burst hose by using to much pressure then it has stood the test of time, although I haven't used it much in the last few years.

A simpler and a lot cheaper option is the valve / nozzle combination.

I have also used this system a lot but not for glass carving but more for light etching and deeper etching for adding colour.
Different nozzles are available in either ceramic or TCT.

These are mine and I buy them from Ace Engineering who sell pressure pots and accessories for blasting. I use the 2.5 mm and the 3mm venturi and they cost around £15 each, I have fitted the 10mm to 1/4" threaded pipe connectors which screw into a 1/4" ball valve for control, unfortunately the valves don't last long as the media eats them away in no time.
The venturi nozzle is the one I use for large area etching as it blasts like a shotgun so instead of a concentrated stream you get a much wider spread.

You can see the difference between the ends of these two, you will also notice the difference in hole size between the syphon gun's huge nozzle and these, now you know where all your air is going.

This by no mean's a comprehensive list of gun's and nozzles but I have found these useful over the years and no doubt I shall end up with the £100 syphon gun but may have to buy a new cutting machine first.

Paul