Terry's Top Ten Tips

On the website: mikefranklinconsulting.com

In remembrance of and as a tribute to Terrance G. Bowyer (1932-2008), model maker/machinist, and his helpful design and mechanical advice. Terry always practiced the Golden Rule: "Thou shalt love thy neighbour as thyself" -- Matthew 22:39 KJV or "Do unto others as you would have them do unto you" (cf. Matthew 7:12), and was an encouraging friend and mentor to many. The italics phrases below are an attempt to summarize the premise behind each of his tips, and sound a lot like Terry. Some practical examples of each tip are given.

1.  Metals are a little like rubber!  Metallic Properties: Metals should be thought of as having a plastic, rubber, or even viscous liquid-like character—not as a completely rigid solid. Fasteners for pressure/vacuum containers must be located close to each other and tightened to uniform force to seal properly (fasteners can be over-tightened and cause leaks)! There is no substitute for mass, but if round or box tubes can be kept in-column by proper bracing—strength can be maintained with reduced mass. (adding a trailer hitch to a vehicle greatly increases rear end crash strength by keeping the frame rails parallel—in column)

If enough force is applied quickly, a metal slug will flow and can be molded or drawn. A 95% aluminum 5% magnesium slug is formed using lots of pressure into an MDI can using this technique.

2.  Cool it to rule it!  Temperature and Materials: Changing the state of matter by changing its temperature enables machining of elastomers in a solid state to higher tolerances This tip was used in making Metered Dose Inhaler (MDI) seals that are superior to conventional "cookie cutter" stamping and contributed to the success of two MDI Valve patents which are as follows:
  • L. Barger, T. Bowyer, L. Britto, M. Franklin, "Flow-through Metered Aerosol Dispensing Apparatus and Method of Use Thereof, U. S. Patent # 5,921,447 (July 13, 1999)
  • L. Barger, T. Bowyer, L. Britto, M. Franklin, " Metered Aerosol Dispensing Apparatus and Method of Use Thereof," U. S. Patent # 5,421,492 (June 6, 1995).

EPDM rubber washer-like MDI valve seals were first cooled to dry ice temperature, (-109F) then the inner seal surface was drilled with a sharp drill. The seal sides were parallel and sealed better with less compressive crimping force on the sliding Delrin hollow stem than the conventional commercial rubber seals. This was because the commercial seals were stamped from a rubber sheet at room temperature using cookie cutter dies. This stamping process compressed the rubber during cutting and caused the inner sealing surface to be tapered rather than being parallel. Since the orientation of the washer-like seals was not preserved during mechanical assembly of the MDI valves, extra force needed to be applied during crimping to ensure a reliable seal and extra silicone oil lubricant was required to reduce sliding friction. (a tapered washer seal in one orientation helps seal the pressure from the metering chamber to the sliding stem, but in the other orientation the pressure makes defeating the seal easier)

Metal surfaces can be locked together by making an interference fit between the two surfaces, by first heating or cooling the appropriate piece—then quickly fitting them together for a shrink or expansion fit as they reach room temperature. Remember you only get one assembly try, so a jig to ensure correct fitting is a good idea.

3.  Hydraulic forces are stronger than friction!   Hydraulics: Liquids/greases are not compressible and can be used to disassemble or assemble mechanical systems. (A broken tablet punch was removed from a multi-station tablet press by drilling a hole through the punch, filling it with heavy oil, placing a gauge pin in the hole, and making one hard tap on the gauge pin with a hammer. (This saved Glaxo Inc. thousands of dollars in replacement costs and time and was done in about an hour) A tractor wheel in Canada was easily removed from an axle by installing a zerk fitting and using a grease gun to apply a uniform force of several thousand pounds per square inch into a blind cavity. This was accomplished after over an hour of unsuccessful pounding on the wheel with a sledge hammer and the use of pry bars in an attempt to remove it.

4.  Everything is abrasive!  Paper and Abrasives: Paper can be used for many shop applications: as a fine abrasive for removing tiny machine marks from Delrin plastic MDI valve parts, to prevent marring a surface clamped in a vice or chuck, as a shim/gripper inside a chuck or collet etc.

Sandpaper should be folded in such a way that only a fresh uncontaminated part of the abrasive surface is used at one time to provide a uniform surface for each application without the abrasives becoming loaded with the material being removed. Use of the right size abrasive is important—too large a grit puts scratches into the work not take them out.

5.  O-rings really seal!   Elastomers/seals: The O-ring seal patent (a torus shaped elastomer) was commandeered by the US Government during WW-II to solve the problem of hydraulic fluid leaking during both high pressure and especially LOW pressure service particularly for aircraft. The O-ring needs to be captured in a groove or channel to that it cannot fail by extrusion through a gap. It can hold pressures of several thousand pounds per square inch. Super glue can be used to make a special size rubber O-ring from nitrile, butadiene, EDPM, etc.) or reduce a larger diameter one to the right diameter if the correct size is not available. Making a jig to hold the O-ring stock in exactly the same size and shape as it will be used helps to get the angle correct when making the razor blade cut. Some O-ring materials containing fluorocarbons = Viton or polyethylene, polypropylene, etc. cannot be super glued.

6.  There is a world of tape out there!  Tape Tips: Some typical examples:

  • Teflon coated tape can be used to reduce sliding friction on chutes or surfaces. The thin Teflon layer provides the reduction in friction, while the hard metal or plastic backings provide mechanical stability.
  • Tommy Tape (rubber elastomer tape) can be used to repair a leaking car heater/radiator rubber hose or make a watertight electrical seal over electric wires by stretching the tape about 50-70% and allowing it to cure for 24 hours.
  • Double-sided tape can be used to mount metal or plastic pieces to a milling machine table. The tape mastic side-ways shear-force is high and can hold the piece without marring it as a mechanical clamp might do.
  • Duct tape-Duck tape comes in a variety of forms that are extremely useful. Aluminized duct tape can provide a surface that reflects radiation heat and reduces the temperature under it of material in direct sunlight. Placing it on a plastic surface such as a plastic trace-metal free hood vent on a NC building roof, protects the polyethylene plastic from sunlight UV degradation.
  • Reinforced tapes shipping tape, is many times stronger that the plastic polymer mastic surface alone. Many of these tapes have the strength in only one linear direction, so be sure the tape is installed so that shear stress does not split the tape apart.
  • Metal tapes (aluminum or stainless steels) can be used to quickly add metal to a flat surface or large loose pin. Grind or sand a car body rust patch and place a piece of stainless steel tape over it, spray some touch –up paint on it and you are "good to go" for a 20 footer repair (step back 20 feet and take a look at it).

7.  It's all about speeds and feeds!  Metal-Tool Interface: The interaction of the metal-tool interface is critical as to the turning speed, amount of material being removed, and the hardness and sharpness of the tool surface. Think of it is plowing the metal away from the turning surface. These cutting speeds-and feed rates are important for best machining. For most stainless steel and mild steel, a SLOW cutting speed is necessary using a tungsten carbide tool. For titanium and bronze, a MEDIUM cutting speed is preferred. For aluminum and brass, go FAST. See speeds and feeds in Wikipedia.

8.  It's what's up front that counts!  Surface Treatments—Plating & Coating: The surface property not the bulk property of material determines the interface effects. If you make a part from 6064 T6 aluminum, then coat it with a couple of hundred micro inches of electrodeless nickel (EN = nickel phosphide) the surface become harder, more lubricious, and chemically resistant. We referred to these parts as our "light weight stainless steel!" due to their similarity of appearance. Remember, the smoother the aluminum surface, the smoother the coating will be. Possible other applications: EN coating of classic car steel brake wheel cylinders to resist corrosion and rust.

Coating the interior of MDI aluminum cans changed the surface free energy as measured by water drop contact angle. Micronized drug in 134a propellant did not stick to the special Teflon coating baked onto the inner surface, allowing GSK aerosol drugs to be formulated without ethyl alcohol-oleaic acid co-solvents which are irritating to inhaled aerosol patients = a superior inhaled MDI product in our view. The patented solution was to apply the PTFE coating by adding PES (poly ethyl sulfone) in the coating as well to get good coating adherence to the metal can and a graded high-concentration of Teflon on the inner surface to give the "non stick" drug performance. (Remember, nothing sticks to Teflon—so how do you get Teflon to stick on the smooth interior aluminum can? Our answer was add PES and bake it on)

9.  There are so many plastics available nowadays, they are as numerous as metal alloys!  Plastic: Composites that have fiberglass or harder material added to softer plastics may be considered for some applications.

Smelling plastics and observing how they behave during turning can help identify them. There is a slight formaldehyde smell during Delrin = PolyOxyMethylene, POM, also known as polyacetal or polyformaldehyde machining. There are stringy fibers from polyethylene machining. PE comes in many different densities UHMW, HD, MD, LD, etc. It is the cheapest and most used plastic. It can be welded, but has no known organic solvent as is the case of the higher melting and tougher polypropylene which can also be hot-air melted-welded.

List your requirements: strength, chemical resistance, hardness, melting point, frictional properties, price, etc. and search some databases to locate the type of plastic best meeting your need.

10.  Use that tool as stock material!  Tool Adaptation: Use shop precision components as replaceable stock materials to speed or complete a job. Gage pins can be used as an exact fit pin. Remember to replace them in the measuring gage pin set—most are only a few dollars each. A precise polypropylene MDI 0.5mm diameter actuator nozzle solid-drug packing-tool was created by using a brass metal backing tool and a 0.025 inch diameter gage pin attached to a manual spring force gage. This tool was used to pack about 40 shots worth of micronized drug into the MDI actuator jet tube at 1000 lbs per square inch force to develop an MDI actuator jet stoppage clearing procedure. An Environmental Scanning Electron Microscope (ESEM) was used to image the plastic jet without sample charging before, after packing, and after clearing the plug. These data satisfied the regulatory agencies in UK and US, and the MDI aerosol product went forward to approval.

Metric and English tools (even drills and taps) can be used interchangeably in some cases. Some examples: A 13 mm socket would tightly fit a ½ inch rusted (rust increased the nut size slightly) shock absorber nut when the standard ½ socket would not. Cut a wrench down to the right size to do the job. Wrenches are cheap to replace, time lost is time wasted!

The Terry Bowyer Memorial Service was held on 12 January 2008, Swift Creek, NC. As I quoted there, the Christian hope (confidence) is: "For God so loved the world, that He gave his only begotten Son, that whosoever believeth in Him should not perish, but have everlasting life" – John 3:16 KJV Bible. I trust that all readers of this information will find these advice tips practical and helpful! mlf Terry's picture follows:

Terry Bowyer Picture