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A DIY blog dedicated for those whose believe the journey is more interesting than the destination.

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The Cajun two steps

I set out trying to do a diy project to convert the US turn signal assemblies to Euro style turn signal assemblies.  This has been done before by others.  However, I wanted to accomplish the following:


1)  In the original design, the lens were first molded then heat formed to conform the plastic lens to the lens frame both from outside and the inside.  This is as good a seal that can be made between plastic and metal.  Obviously, my diy project can not completely follow the original production methods.  The new lens will be applied from the outside and sit on the lens frame.  The new lens will likely be epoxied or siliconed to the lens frame.  

2)  The original euro lens has a crease line that follows the crease line on the fender.  I want to be able to duplicate this line.  Also, the fender has a slight concave curvature.  I also want to duplicate this curved surface,


The challenges are many.  Below are a few:


1)  Don't have a 3D model of the lens nor the lens assemblies.  That would make things like forming and trimming out the lens afterwards much easier.

2)  Select the correct plastic materials that would survive the extreme heat and cold cycles that a car would be expected to operate in.  Also, the material should be able to survive UV exposure for as long as possible.

3)  Available plastic that comes in clear amber/orange.  Ideal but does not exist to a diy'er: amber/orange prismatic material.

4)  Production methods that would allow for as good a seal as possible with the lens frame, and produce both the crease line and the curved surface.  I do not have the skills nor the knowledge to 3D scan the lens, 3D print the lens, build a mold/cast from the 3D printed lens....  So, I have to rely on the two things I can do: sketch to cut on a CNC machine, and thermoform plastic parts.


I tried making the molds for thermoforming by one method or the other.  I also attempted to make female/basket molds in the hope of pressing and vacuuming  the heated and softened pieces together.  To make the tasks even more difficult, different plastic materials available to me shrank/expand at different rate and at different temperatures.  Attached is a picture of all the lenses that were cut and tried on various plastic types.  None of them met my expectation for form and fit...  In trying different methods in cutting, forming, fitting, tweaking the lens, I realized one thing:  There were subtle differences/variation in the lens frame.  Any lens forming attempt must be made directly to the exact frame to be fitted.  That was the eureka moment.   So, I spent hours the last few days trying to make the lens molds that fit perfectly with lens frame.  The molds took so long to make because the process required many trials and errors to build up with wood filler, let dry, sand, check fit and repeat. The last iteration were really close with the lens frames fitting snugly over the molds.  The idea now is to cut out the lens shape, heat the lens material and the lens frame at the same time.  Once the lens material is sufficiently softened, both will be  placed over the mold.  The lens material will be hand formed to the heated lens and will conform to the mold and the lens frame at the same time.  Since the lens frame will also be heated, the lens material should conform much better to the lens frame.  


There is one other modification.  I added a "step" to the inside edges of the lens.  The prismatic material is around 0.130".  The step is 0.060".  The idea of the step is to enable:  1) The use of prismatic material directly as the lens itself, instead of using one color/clear lens on the outside and clear prismatic on the inside.  .  2)  The thinner 0.060" material will act as a lip and will conform much better to the lens frame.  BTW, the lens frame itself also has a receiving step that the lip will fit right over and form a seal - a kind of rabbet joint.  The last picture is a back side of the prismatic lens with the .060" step around the edges.     


Stealing one comment on the blog:  "Kind of like the Cajun two-step without the great food but with the beer."  I will have that beer now.






So close....

I ran out of materials to continue experimenting with the lens.  So, I ordered more stuff and the lens project will have to wait.  Naturally, I started to look at the US bracket to see if it can be converted.  (I am sure this has been done before, but, I've got to do it my way.)


The challenges:  1)  Once the US lens is removed and is replaced with the euro style lens, the lamp socket and reflector stick out and will need to be moved in.  2)  There is no room for the bracket to move further in.  In the picture with the three lens assembly, the one at the bottom is the one I tried to push the bracket in so that none of the reflector is outside of the lens frame;  The bottom of the bracket moved too far in and will not fit into the  well/cavity for the turn signal assembly.  

Potential solutions:  1)  Fashion a new bracket and find a compatible dual contact socket.  Trade offs:  Too much work to make a new bracket.  The original bracket is very well designed and rigid.  It will be very tough to improve.  Also, the reflector lamp socket combo can not be reused.  2)  Relocate the existing socket assembly, chop down the reflector to fit.  Trade offs:  The spring contacts and the brass terminals will be very challenging to remove and relocate.


The first step was to remove the US lens.  4 minutes in my toaster oven at 300 softened the gasket enough to remove without tearing it to heck.  Then, 5 minutes more at 350 soften the plastic lens enough for me to yank out (Do not do this if you want to save the lens!).  With a wire cutter, cut off the three plastic nubs at the back of the bracket where the plastic reflector is heat staked through:  Two of these are at the bottom of the reflector on the other side; One is at the back of the bracket near the contacts.  Eyeball the bottom of the reflector and cut about 1/8" away from the flat rib that runs the length of the bottom of the reflector.  The reflector/lamp assembly is now free and is only retained to the bracket via a bronze strip (ground).  Swing the whole thing out of the way to get at the spring contacts and brass terminals.  These are secured by a bifurcated feature that is a part of the brass terminals.  Use a pair of fliers to pinch them and pull them out from the back. 


Back to the reflector.  Cut two channels to allow the bottom of the reflector to sit on the two side rails.  Drill a new hole at the back of the bracket.  Eyeball the little remaining stub and fit it in the drilled hole.  Slide the reflector all the way back and make sure that the little stub fits in the newly drilled hole.  Drill another hole at the bottom of the reflector.  Screw in a self tapping screw right up to the bottom of the reflector.  This screw will hold the reflector in place and pushes it against the little stub in the back.  The whole reflector/lamp assembly is now held securely to the bracket.  Grind off any part of the screw that sticks out the back.


The modified bracket can be secured back to the lens frame using 3/16" 1/4" shank eyelets.  The outer edge (toward the lens) may have to be trimmed down.  But, the whole thing will fit. One of the pictures show an actual euro lens assembly on the left and the mod US lens bracket on the right.


The one remaining problem is to find a new set of spring contact and brass terminal...  Any suggestions?


Update.  I've found a suitable solution for the contact/terminal solution.  Brass standoffs.  The old square holes for the brass terminals just happen to be directly in line with the new socket.  So, if I can spring load the brass standoffs, they should work both as terminals for the wires as well as contacts for the bulb.  









So, I have an idea, hare brained, but an idea none the less.


The goal is to duplicate the curved surface of the lens in a female mold so that the heated/softened plastic lens can be pressed and cooled/frozen to shape consistently.  Without a 3D model, the only available option is to make a mold from the real part itself.  I tried different ways to do this and failed miserably.  The main problem was that the clay/putty material I used kept sticking to the assembly itself and could not be removed without deforming the clay.  So, I thermo/vacuum formed the lens assembly to copy the shape of the lens.  Left the lens assembly in place protected by the formed sheet.  Use Crayola Air-dry-clay (if it is good enough for 5 year-olds, good enough for me) to form the mold, sticking to the thermoformed plastic shell.  Trimmed off the excess shell material.  Used clothe pins (they happened to be the right thichness) to center the softened plastic lens in the mold.  Heat up the lens cut out and pressed into the new mold with my other wooden mold.


The result is good, not excellent.  There were some lens details that did not come out as well as I had hoped.  The top ridge/crease was formed consistently along most of the length of the lens but not the full length.  As a concept, it is feasible.  I will continue to fine tune the processes, material and techniques until the formed lens fit precisely into the lens holder and continues the shape of the fender.






While waiting for the polyurethane to dry, and for something to pop in my head as to how to form the female molds, I decided to cut some 1/8" polycarbonate.  Up until now, I have been using PETG and acrylic.  They both have their pros and cons.  Polycarbonate is likely better for the signal lens application.  It is stronger, much less likely to crack, much stronger against harsh chemicals...  So, got to test it out.  Right off the bat, my plastic router bit broke!  I had to slow the feed rate of the router way down.  The polycarbonate lens did not form well at the recommended 375F.  I may have to play around with the temperature and soak time as I really want to be able to use polycarbonate.


For those who likes to watch grass grows, watch the video here.  Make sure you turn the audio off.  That spindle is really loud, and I only ran it at 1/3 of the maximum speed to cut plastic.



Making the molds

Once the thermoformed pieces cooled off, I traced the outlines of the lenses and cut them out.  Even though these pieces were only 1/32" thick, they were sufficiently stiff to use as templates to help me judged and tweaked the wooden molds.  The concave curves proved to be very difficult to duplicate with a wood rasp.  Then, it occurred to me to lather up wood filler onto the molds, cut up an old Visa to match the curve on the lens, use the curve Visa card to shape the wood filler very much like dry walling.  Once the wood filler is dried, I will sand lightly to smooth them out.  Add a few coats of polyurethane and they should be fairly solid.


 Next is to use these wooden molds to make a set of female molds.  Still have to figure how to do so...








I've been trying to make a pair of wooden molds to form the lens.   They were close, but, not good enough.  After thinking about it, I decided to use the actual assemblies to make the molds themselves.


I already built the vaccuum table from another project.  For this purpose, I use some 1/32" PETG plastic sheet stock.  The sheet is held in place using a wooden frame.  The pocket knife happened to be the correct height to support the lens assembly.  I also rigged up a space heater to use to heat up the plastic sheet  (Yes, at the bottom of the heater box is a cut-up turkey roasting pan to reflect the heat up).  Once the sheet is sufficiently pliable, it is placed over the turn signal assembly and formed in place.