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    • CommentAuthordavid
    • CommentTimeFeb 7th 2009
     
    I posted some work in progress photos for Jay Rich and his distributor problem.
    I think the distributor is too small. It is nice to scale everything down but for the most part we are using ignition coils that are very automotive the voltages are high and they need the big clearances as in a car. Not everything scales well.
    Have you ever experienced the spark preferring to jump over half a inch on the outside of the plug rather than jump the .015 gap in the cylinder? Electricity likes to “creep” along surfaces rather than jump a “clearance” gap. That’s why utility pole insulators have multiple convolutions, it increases the crepage distance along the surface and the gaps between them is the clearance.
    Crepage is very sensitive to moisture and dirt on the surface. A coating of Acrylic automotive spray insulator often does wonders in high voltage problems.
    Another method might be a coil per cylinder and use 2 sets of points and avoid the problem.
  1.  
    Hello All.......Just a note to tell all of the distributor builders.....I have a "bunch of 1.250" clear acrylic rod, and if anyone needs any please get in touch with me, and we will work on getting some of the rod out to you.....It can be turned and then polished to a clear finish......Thanks.......Dale Detrich
  2.  
    Hello Dale, long time no hear, time is on my side again and I will soon have some more shop time on my hands as well.
    The little ones are well and things are simmering down a bit.... enough to keep my head above water anyways.... LOL.

    Here is my question:

    Could you enlighten us all on how you polish the akrylic so nice and clear.... mine turns a bit "foggy" after machining ect.....



    Thanks

    Jan
  3.  
    Hello Jan....The way that I polish the acrylic starts with the cutting .....I try to use a round nosed cutting tool, which leaves you with a smooth surface (still foggy)....Then I do the polishing......I start with automotive wet or dry emery paper about 400 grade.....I.D. work, I use a 1/4"metal rod with the slot to hold the emery paper....And I use progressive finer paper down to a 1000 or 2000 grade....After the paper work, I then use a liquid or paste rubbing compound, and polish the turned and papered surface until the acrylic is almost clear......Then take a good auto polish and apply it to your part....Your part "should" be almost clear.....If it needs more work, use the rubbing compound and polish until you are happy with the finish...There is no "magic" to polish the part, just your effort......Dale.....
  4.  
    Hi Uncle Dale

    You did'nt mention that if you rub to hard the acrylic will heat up and smear. Make sure you use a light touch or you will be back to the 400 grit for round two.

    I only went down to 1000 grit and then touched the part with a clean cotton rag and it clears up nice but not crystal.

    Steve
  5.  
    Hello Steve......I guess that the bottom line is that there is "no" easy way to get the part clear , except to keep at it until you are satisfied with the finish........Dale .....AKA.....UD
    • CommentAuthorjay rich
    • CommentTimeFeb 11th 2009
     
    i got a trick as you cut acrlic use alchol rubbing 91% works for me and then rub off the fog ....jay
  6.  
    Hi Dale & Jay,

    There is a technique that will give you a clear finish but it is bit risky. It's called flame polish. I have used an acetylene torch, but if the flame is too rich, you may get some black carbon on your surface. The professionals use a hydrogen and oxygen flame or torch. The process is to use a very hot flame and pass it over the surface to be polished without melting the adjacent areas. The flame is passed over the surface very quickly and melts the surface, leaving it crystal clear. This is the process that you see in display cabinets that are fabricated and some prototype parts that are machined and used for display. I would recommend practicing on some samples first. Its really amazing how nice it works. It might work with propane with a very hot flame with a blue cone, not a blow torch. I've have never tried that, however.

    Bob Verhaeghe
  7.  
    I have flamed parts. I would never use the torch on a part that size is important. A distributor cap would tend to warp and oval at the opening. If the part is just for show, the torch works very well.
    • CommentAuthorjay rich
    • CommentTimeFeb 13th 2009
     
    i got a good one for all of us and dale i think i am cursed i wa looking at my cap and seeing if there was any large archs well i saw one that carcked the cap from cylinder one to cylinder two contact point on the cap i tell you guys i think its the chep acrlic that ace hardware by me sell or i got bad luck i think the model engine gods are pised at me ....jay
  8.  
    Jay: Sorry to hear the god's may have a curse in you, I have used some material called Polysulfone, it is a plastic used for some machining samples in CNC initial or fine tune runs, machines like acrilyc, it has better dielectric characteristics than Acrilyc, bad part is not really clear, it is more of a yellow/ brown tinge, if you would like to give it a go, I can send you a piece for you to try.

    Else if you are willing to spend money, Turcite or Delrin, Turcite is great but not cheap.

    Jaime.
    • CommentAuthorjay rich
    • CommentTimeFeb 14th 2009
     
    the acrlic works i think its a old problem that bakealite had and water or dirt with water will crack it but yea i would love to try it i got one for all of you useing corian great stuff but stick to a solid color i tried it for my plugs and it failed realy bad i got t0 get the pics to david so for fun i found some stuff from a art shop called plastruct 3/16 clear tube i make some custom 10/32 plugs and the are hot and work great trying to have fun ....jay
  9.  
    Helo Jay...Just reading back through the notes about the acrilyc, and read your note about the crack in your dist. top....I have found that the acrilyc "does not" like to be stressed..If you try to tighten it down too tight, it will stress crack....What ever you are doing with the acrilyc, to not tighten it too tight.....I have had to replace a few dist. caps because I tightened it too tight....Just assemble your parts, and just "snug" the parts....it will keep the acrilyc from cracking......Dale
    • CommentAuthorjay rich
    • CommentTimeMar 10th 2009
     
    hey dale i have all of the parts lose and i found out it was the spark was cracking the top of the cover dont know how but now i have a neat star shape cark form the center out if it breaks i have a stick of polycabinte ill try tha next ....jay
    • CommentAuthorgary hart
    • CommentTimeMar 10th 2009
     
    Had drilled and tapped some acrylic and about 2 weeks later had cracks around the drilled holes. Copied and posted what had read on the internet (afterwards). Think oil base cutting oil and or heat caused the delayed stress cracking.

    "Acrylic is a brittle material. It is therefore important that only light machining cuts are taken and feed rates are kept slow. Various coolants can be used including water and water/air mists, soluble oils and compressed air. Soluble oils must be oil-in-water emulsions and must not contain solvents which may cause stress cracking.

    When machining, drilling or cutting acrylic, the heat build-up can generate stress in the final work piece which can induce “stress-cracking”, a phenomenon common to many plastics materials when stressed. The risk of crazing can be reduced or eliminated by the process of heat annealing."
    gary
    • CommentAuthorjay rich
    • CommentTimeMar 11th 2009
     
    ok gary ill try heat annealing but heres my ? time and temp whts funny is when i first saw this happen the spark jumped from the coil wire to both contacts and it jumped to ground i tryied a ballst and no luck the spark jump stoped but the fire in the plug was not enought to fire the mix i did fit a happy place i put a small fan and hooked it up to the main wires that feed the coil its power so the fan was on a impluse the points woulf turn it on and off this worked well till the fan failed but the problem went away i think i got gremlins now if i can rember where i put that can of gremlin be gone ....jay
    • CommentAuthormiller
    • CommentTimeMar 10th 2010
     
    Electricity is very hard to tame so you cant scale down electricity