I am constructing a nitrogen burst development tank for 4x5 negatives. The design I have considered requires drilling tiny holes (#76) in 1/8" or 1/4" acrylic (these are the passage for the flow of nitrogen from the plenum into the bottom of the tank, Gordon Hutchings). I am having difficulty in this department with breaking the drills.
I am looking for a solution to this problem, or possibly an alternate method within the nitrogen burst development realm.
Thanks for any advice. Dave
I am on a similar journey. Have you tried to use water to cool your bit?
Planning to use a plastic fabricator to accomplish this objective, but I have heard that these small bits get real hot and melt the acrylic and break when the material cools down and bonds with the bit. Control the temp and you should be fine.
What are you using for your hangers?
Onward!
I machine a lot of acrylic and it can be troublesome. It expands a lot, so even mild heating can bind up tool bits and drills. #76 will typically break if you use it by hand- drill press required. #76 carbide circuit board drills will break if you even look at them the wrong way- stay with HSS (high speed steel). Try adapting a needle to a soldering iron and poke the holes through with that. You may have to put a dimmer or motor speed control on the iron to keep the temperature low.
Acrylic cuts just fine if the drill is designed to drill plastic. Most of your problem is the design of the drill cutting tip. To properly cut acrylic you need the drill to scrape the plastic, not cut in the conventional sense. If the drill tries to cut, as it will with a conventional tip, it tends to dig in. With larger drill sizes this usually results in the plastic breaking. Trying to drill holes with very small drills might result in the breakage you are seeing when they dig in and bind. For the most part, any expansion due to generated heat should be taken care of by the cutting surfaces along the drill shaft.
You can buy special plastic cutting drills, but they aren't always very easy to find locally and a #76 is pretty small. You can, however, easily make your own. Unfortunately, I can't find any decent drawings to help you.
In general, use your grinder to lengthen the point so it looks more like a pencil point than the normal, flatter, drill point. If you do this without concern for grinding the normal rake into the cutting edge, you should find it ending up at about zero rake - just what you want to scrape the plastic without digging in. Then drill slowly, using a drill press so you don't wobble things around and bind it up with side loading. Drill without much pressure to keep the heat and expansion to a minimum and it should work just fine. Good luck!
Using a light cutting oil like kerosene when drilling will lubricate the bit and keep it from melting the plastic and binding. Also the cutting edges of the drill must be very sharp, using a fine grit wheel and if you know how, make a split point on the drill. Drilling plastic by hand is difficult because the bit wants to dig in, better to use a good drill press to control the feed. I have 30 years owning a precision machine shop and made many parts from all types of plastics. Paul
Wait a minute. This sounds like a design problem. I think of acrilic as a hard plastic. What are you doing - making an acrylic box as the plenum? All this stuff was worked out decades ago. Don't reinvent the wheel.
I'm glad to hear you guys are trying to keep this procedure alive. It is so simple and easy to do, and the results from the even agitation so good, that I'm continually amazed more people don't use it.
Anyway, back to the design. Use flexible plastic pipe. Small, like 1/4" OD. The piping is heated and bent into a winding design which is attached to the bottom of a rack [not the tank]. That way, you can move it from tank to tank. Use a #40 rack for 3 1/2 gal tanks, or smaller rack for smaller tanks. I normally use a small Leedal rack in a 4x5 HR tank to conserve chemistry. I can easily do 5 sheets for one processing. In the large tanks, using 4-ups, you can do 48 sheets per session.
The holes are drilled on the underside of the pipe [relative to the top of the tank] at about 45 deg. from vertical.
Use items made for compressed air tools for the connections. They just slip on. I got mine at Woodworker's Supply of New Mexico. I also used their piping to get from my tank in the garage to my darkroom. That pipe is too thin skinned for the plenum though. Step down the pressure at the tank to 25 psi and then on down to 15 psi going into the timer. There are gauges which incorporate the value into them [again for compressed air, although you're using very low pressures].
You need to be able to disconnect the plenum easily because you'll occasionally get crystalizing of the Nitrogen in the plenum, clogging up the holes. The old timers used Nitrogen humidifiers to avoid this, but I've not seen one in 40 years. Today, you just soak it in alcohol to dissolve the crystals, and get back to processing. It doesn't happen too often, but it does build up.
Hope this helps. Let me know if you have any more questions.
Alec
For nitrogen burst, you don't need to drill holes in hard plastic. Use a flexible silicon pipe in which you just pull holes with a needle. I know many big dip and dunk processors in custom labs where this conversion is done to achieve more uniform burst of bubbles.
David, I found this old post and wonder if your design worked and if you had any further input.
I have read a little about nitrogen burst systems but have never seen/used one. I understand the argument for using nitrogen,(no oxidation), but in reality, when using 1 shot developers, for around 8-15 mins or so of development.....is that really a problem?
It would seem that using a cheaper source of gas (compressed air in a scuba tank let's say) would be more logical? Correct me if I am wrong.
Thanks John
www.johnshuptrine.com
The basic reason for NB agitation has less to do with minimizing oxidation than having fast, efficient, repeatable, automated agitation. Whatever reduced oxidation that may happen is a side benefit.
Originally Posted by jrshupper
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