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Monday, March 2, 2020

Catching up 2019 into 2020


Absolutely no excuse or apology for a quiet 2019 into 2020 with little blog update.  Frankly, the blog is a very labor intensive endeavor to cover progress especially when there are numerous things moving at the same time.  My “go-to” update medium is Instagram (and Facebook as a surrogate) and those that follow the project there will have been updated almost weekly on the many things that have progressed on the project.

Secondly, I have been rather sick of the “internet” in general and the B.S. that many of the popular Mustang forums allow from individuals and vendors and the “some are more equal than others” mentality makes me want to puke.  So much so, I plan to spend little time updating my “build” threads on most of the forums and just get on with working.  The Instagram updates seem to be well received and provide positive feedback and that’s pretty well fine with me.  Thank God I don't watch TV......  However, for those that continue to follow this blog, I thank you and will try to get things caught up.

Rear Bumper Scanning – Stuck Between Gears

A lot of folks have inquired on how the rear bumper project was going, so here goes.  First, I was able to produce a composite rear bumper from the molds as originally planned.  A rather nice piece actually and it will work fine as a one-off.  However, as I have mentioned before, the goal is to take this further such that I could reproduce the mold and the part with CNC machinery.  Ultimately, I wanted to produce a billet aluminum copy of the rear bumper that could be finished and chromed like a factory part.
This project has become a much bigger frustration than I counted on.  To date, I have the scanned surface data but no ability to bring it into a “working” format that would allow an “A” surface to be created and modified in something like SolidWorks.  I have asked a number of folks I know in the industry for help, but no one seems be able to help pull this together.  It’s been almost a year and I am pretty much no closer to a solution than I was the day the scanning was complete.  I really don’t have time to teach myself the nuances required to get this done, so it sits in limbo until “something” happens that’s useful.  While I continue to work that problem, I have redirected most of my energy into work that moves the project forward.

And the Rest…….

Honestly, there have been too many things accomplished in the past year to list and detail them all here.  So I am going to rely on the “picture-is-worth-a-thousand-words” mantra and dump a load of pictures here that I ripped from my Instagram feed to visually catch the blog up to where we are today.  If you have any questions on any detail in these images, send me a note!  Otherwise:  Until next time!


Slick Ron Francis light sockets installed in the freshly powder coated turn signal housings.


Gapping doors is very labor intensive and rather iterative, but makes a world of difference!


Take Note:  EVERY Dynacorn 69-70 roof is wrong in the top driver's side corner.  I made this special form tool to correct the contour of the metal for a perfect fit of the windshield trim.



Eliminated the front side marker lights.  Pretty serious pucker factor when modifying original 70 Boss 302 front fenders!


The sad day I was forced to endure the use of the latest SHIT paint strippers.


Just about as nice as an original 70 hood can get!


Cleaning up the inboard details on the LF fender before coating with SEM Rust Shield.


You know you're loved when your family gives you a top-of-the-line DeVilbiss Tekna Pro-Lite spray gun for your birthday!


Truing up the rolled fender edge that came standard on the 70 Boss 302.  They were pretty crude from the factory and needed a little tune-up.


LF fender ready to be fit to the body!


RF fender ready for fitting.


Always enjoy when dents and dings can be floated out with no filler required.


Another metal finishing job requiring no filler.


No license plate warts on this front valence.  No sir!


Underside of the hood slicked up pretty nicely.


As much as I bitch about the cost, a well made billet hinge is light years ahead of even the best replacement hood hinges.  Worth every penny.


Absolutely HATE the repop doors that are available.  Over 200 hours in preparing this pair and probably another 50 left before I'm happy.


PSA:  A lot of people wonder how T5 shifters compare to an original Boss 302 Hurst shifter handle.  There are 3 popular choices:  538-4106 (shown), 538-7436 and the 538-8022.  This is the 4106 and it ain't even close.  The 8022 is the closest available.  More to come.


Best available reproduction grille support installed and NOTHING fits.  However, it's the front latch support (the part the hood release bolts to) that is off and it's the only version available.  What to do?


Section the grille support by 1/2" and watch every part damned near fall into place.  That's what.


Front spoiler installed and looking pretty decent.


Front sheet metal fitted, aligned and indexed.  Several more hours required on the doors and a few on the hood corners to blend them into the fender extensions to cure the notorious hood misalignment that 70 Mustangs were infamous for.  Once that's done, the "conventional" bodywork and priming can begin!






Wednesday, April 10, 2019

Rear Bumper Scanning, Door Gapping, Harley Headlight Install, Etc.

It’s been another good while since my last update but we have definitely been busy with several different projects going on all at once (almost).  While the rear bumper project remains the dominant work in the shop, the latest work on that particular project has allowed windows of “sown time” that enabled a fair amount of other work to progress.  So this update will be covering a lot of very different details but exciting stuff nonetheless!  Here we go!

Rear Bumper Scanning

As the rear bumper project continues, I have been able to ponder what to do with all of the “master” parts that were created to produce the composite bumper.  The life span of a master buck and mold is rather finite and the thought of losing these details started to really bother me.  Also, I have considered that I may find myself needing to produce another example, but custom fit to a totally different car for example.  In consideration of this and the fact that these cars vary rather considerably in build tolerance, I needed to have a way to custom tailor a bumper to another car’s exact dimensions to ensure it fit that car as well as it does mine.  Also, I have fielded a number of inquiries on producing this bumper in a format that would allow it to be fully chromed to render a more “factory” look than the painted version I needed.  So, with all of these considerations on my mind, I decided to seek out a local resource to digitally scan the surfaces at very high accuracy to preserve the shape indefinitely as well as provide a model that could be easily manipulated in almost any modern CAD/CAM design software and reproduced in any volume desired on modern CNC machining centers.

Digital 3D surface scanning is not especially new, but the technology has become infinitely more accessible to this type of market than ever before.  However, the market still varies by an enormous degree as to what is necessary and appropriate to a project like this versus complete overkill.  Price, of course, varies equally wide and suffice it to say that most “commercial” scanning providers that offer mobile services are rather exorbitant in cost in most cases.  And generally speaking, they don’t especially cater to one-off “small” jobs like this either.  So, after much thought, I decided to try to find a fellow enthusiast that was as excited about 3D scanning as I am about car building, and who wasn’t tied to the “Big 3” local mentality and commensurate cost as the “commercial” providers are.

I set off by shaking the vines on of the local “hot rodder jungle telegraph” and after a few weeks, I was put into contact with a very local young gentleman who is “our” kind of people.  He is as much an enthusiast in 3D scanning as I am about this project and we seem to see eye-to-eye on many things.  After a very energetic conversation, it wasn’t long before we had come to terms with the project scope and he was in the shop with his scanning equipment and the process of digitally “documenting” the rear bumper buck in position on the body was begun.

The process is called “structured light scanning” or “blue-light scanning” and involves a projected series of light patterns applied to a targeted surface and recorded by two different precision color cameras at different incidence angles.  The images spliced together and analyzed in a sophisticated software suite that is able to very accurately reproduce the surface contours in 3D space.  In our case, the surface was accurate to 50 microns (0.002”) without a single contact made to the surface!  That’ll work just dandy!

In just a few hours, the entire surface of the bumper buck and surrounding body work was digitally rendered in 3D space and ready to pull into the design software to smooth and correct any imperfections and prepare the “shell” for the rest of the scanned data to be paired.

The next step will be to remove the bumper buck from the body and scan the underlying sheet metal to accurately generate the critical surface and edge details of the body as well as the mounting locations so all of this information can be combined into a single rendered shape that can be reproduced as many times as desired with incredible precision and in almost any medium we choose.  And while I’m not yet prepared to endure the expense of whittling a 510-pound piece of billet aluminum into a 15-pound bumper (yep…..no kidding!), we could at any time do so with the data this technology has enabled us to gather.  Cool stuff!  More to come!


Here, Alex is calibrating the 3D scanning head in preparation to scan the bumper buck mounted on the car.
The bumper buck get an interesting combination of reflective "targets" applied to the surface and a coating that eliminates the reflective surface of the polished buck.  The targets allow the scanning software to accurately overlay the various scanned "snapshots" into a single continuous image.  The dulling spray (actually cheap dry shampoo spray!) kills any reflection off the scanned surfaces and allows the structured light pattern to cast cleanly over the surface without distortion caused by reflections.


I snagged this shot while the light pattern was cast on the corner.  The camera flash really lit up the targets and made for a pretty interesting shot.

Structured light patterns are designed to show deformations in the line shape very accurately.  These deformations are analyzed by the scanning software and are displayed as an accurate copy of the shape.  Essentially, if the surface bends, the structured light lines bend in direct proportion to the surface curvature.  Pretty cool tech!

This is essentially the first surface Alex produces from the scanned data.  It's pretty exciting to see hundreds of hours of handmade work preserved on the screen in all its digital glory like this (and it's not even done yet)!

Pretty proud of this shot!  Total surface deviations are exceptionally small based on this image and any clean-up required will be very minor.  The scanning accuracy using the reflective target method is 50um (0.002")!  Plenty good for this kind of work for sure!

Door Edge Gapping

In the opportunities to return to some “normal” shop work, we were able to pick back up with the final stages of gapping the reproduction doors to the body.  With both ends of each door already gapped to the factory production original fenders and the b-pillar post edges, the only remaining gaps to tweak were the lower door edges as they meet the rocker sills.  These gaps were notoriously wide in production Mustangs to accommodate the rather wide tolerances in fit of an assembly line vehicle.  To the casual observer, the lower door edge is the least likely to show a gap mismatch than either end gap, so the factory naturally gave itself the most leeway there to fit doors into often irregular openings.

Unfortunately, to a builder, the lower door edge must fit just as well as all of the other gaps and this often calls for an extensive amount of material addition and massaging to get the sill gaps tightened up and looking good and this project was no exception.

In the case of this particular door pair, both sill gaps were rather wide and allowed for the entire bottom edge to have a 1/8” welding rod to be welded the full length of the door to fill in the sill gap as much as possible.  We are shooting for a target gap of 3/16” (4.8mm) along the sill which is very slightly larger than the end gaps.  This allows for a small margin of safety when the doors are finally hung and all other play in the hinges is accounted for in “real world” operation.  The difference is imperceptible to the eye but allows just enough cushion to help avoid damage to the painted sills and door bottom edges.

As work continues, the driver door will get final sill gapping completed and then work will move to the passenger door for the same treatment.  Once the doors are fitted, we will be coming to the end of the “major” metal work on the body and we can start to concentrate on the sheet metal forward of the firewall.  Fortunately, with the exception of the front lower valence and stone guard, the entire nose of the car is factory original metal.

Here's a little shop secret:  For doing certain types of body sheet metal welding with a MIG, I cut the gas collar back to expose about 3/16 to 1/4" of the MIG tip.  This creates a more gentle plume of shielding gas around the weld and allows you to see and maintain the perfect wire stick-out for this kind of work.  It works best to run the heat and wire speed slightly on the higher side for the material thickness you are welding and make sure you are welding in absolutely still air.  No breeze, no open shop doors, no A/C or heat blowing over your work area.
Lower door edge receives a stick of 1/8" mild steel welding rod tacked along the entire bottom edge of the door.  In this case, this allowed for about .040-.060" of working stock along the entire lower edge.


With no gap to the original door edge, the welding rod is welded fully along the inside and outside edge of the door.  Note how clean and tight the weld bead is using the aforementioned MIG torch modifications and settings.

Weld seams are finished with a 36 grit Roloc disc and the door is ready to bolt back on the car to begin the gap refinement by hand.  Target is 3/16" gap along the entire lower sill edge.

Here you can see how tight the lower gap has become with the addition of the welding wire along the lower edge.  With a little precision hand shaping, the door sill gap will be a perfect 3/16" in short order.


Harley Headlight Conversion

Some keen followers of this blog have inquired as to what headlight combination is shown in the designer rendering of the car on the title page.  I have played that a bit close to my chest all this time, mainly because I had not fully worked out how to make the conversion a reality.  Well, after untold hours noodling it all out, I am very happy to show the new headlight combo that matches the rendering exactly.

This tricky little setup involves installing a modified pair of Harley Davidson dual-beam headlight assemblies into a heavily modified set of factory headlight buckets and modified fender extensions.  The end result is a very tidy and effective modern headlight installation that is slightly “edgy” in style but doesn’t take away from the “production” look of an original glass headlight without the nasty appearance of LED bulbs that look “too modern” and out of place on a vintage Mustang (IMO anyway).

The end result of the conversion allows the factory retaining rings and adjusters to remain intact and fully functional with the convenience and infinitely better lighting quality of a modern quartet of halogen “twist-lock” style bulbs.  And being motorcycle derived, the light dispersion will be much broader than conventional auto headlights which are a very welcome upgrade for older eyes like mine.  This might not be particularly welcome to oncoming traffic, but it has the side benefit of being a guaranteed “win” if anyone decides to try a “high-beam showdown”.


Another unusual modification I am particularly proud of is the installation of Harley Davidson "dual beam" halogen headlights.  This is a concept proposed by our designer that I fell in love with.  Here, you can see SOME of the modifications made to the factory headlight buckets as part of this conversion.


Fully mocked up, you can see how very tight this adaptation is.  However, the end result is a system that uses ALL of the factory retention and adjustment hardware.

A quick trip through our powder coating booth for each bucket and the conversion was complete!

I really love the look that this headlight conversion makes!  I threw some old trim pieces in the fender extension with the headlight mounted up to show the idea.  I think it perfectly matches the theme of the car in every way!


Antenna Hole Filling

The final quick update was to fill the radio antenna hole in the right fender.  This car will not have a radio installed (at least not one with a visible antenna anyway!), so the need for a heinous looking, fender mounted “flag pole” of an antenna is non-existent.  With that, a simple disc of sheet metal was created and given appropriate contour to match the fender shape surrounding the hole and welded into place.  Nothing fancy required!

With that, we are off to finish up the rear bumper/bodywork scanning and finishing up the door fitting.  Once that is done, we will look to get the doors stripped and in primer, the rocker panels cleaned up and straightened and start work on the cowl panel mounting modifications.  Should be a busy Spring!

Factory antenna hole just couldn't stay.  I made a filler piece on my lathe then formed the curvature to match the fender contour.  I used a 1/4" bolt to hold the plug in just the right spot while I tacked it in as ween here.


Here, the tacks are completed and ground smooth before welding the entire plug in place.  No idea why I didn't take more pictures of the process, but that's all I've got!

Friday, February 15, 2019

Rear Bumper Fabrication Project – Part 4: A Good Part & Critical Decisions


Since the last update, we have had the opportunity to explore using alternative reinforcement materials and, more importantly, a completely different resin chemistry (vinyl ester) in the vacuum infusion molding process we use to produce our composite rear bumper.  After a number of scout procedures, the end result was molding characteristics I simply didn’t like and would not commit to trying any further.  So, not much to report on that front as it’s not got much to do with making a bumper!  Suffice it to say that in any future endeavor, we will stick to our first low viscosity epoxy resin choice and basic combination of reinforcement fabrics and not look back!

With that, the update is rather anticlimactic.  After extensive consideration, we have decided to stay with our 0.137” bumper molding as it is visually almost perfect and will allow greater ease in mounting than a thicker molded copy.  Now the focus will be shifted to developing a robust mount system that can be bonded into the bumper shell with panel bonding adhesive.

Work has begun to craft an aluminum mount that will add good structure to the bumper and provide a solid mounting base that can be easily bolted to the stock mounting locations with a full range of adjustability to allow optimum fit.  At the same time, this strategy will allow the bumper to be fit to the body with simple gap shims that will allow the bumper to be quickly and easily placed in position and aligned on the mounts with perfect body gaps maintained and little to no induced stress into the part while the panel adhesive cures.  Once we’re on top of this series of details, the remainder of bumper work should be relatively conventional insofar as confirming fit and edge finish followed by preparing the part for primer.  Feels good!

In the meantime, work will continue on completing the final bumper trimming, taillight bezel and bucket prep and fitting, backup light housing modification and fitting and final gapping of the doors with the hope of Spring weather allowing a deep-dive into the cleaning and metal prep work on the front sheet metal.  Feels like it’s getting traction again…….




Thursday, November 29, 2018

Rear Bumper Fabrication Project – Part 3: Process Development & Test Parts!


It’s been a long time between blog updates again, but I will blame social media (and getting married!) as a major contributor to this condition as I have posted numerous quickie updates to our Instagram and Facebook project pages as progress has been made on the rear bumper.  The lure of easy, on-the-fly updates has really put a damper on conventional blogging and somewhere, I need to find a better balance.  Also, I have been getting more and more video requests and I continue to contemplate that with more seriousness.  In the meantime, let’s get caught up!

In Part 2, we left off with a polished mold that was ready to begin the process of molding our first test parts.  I was under no allusions whatsoever that I would sacrifice a few test pieces to learn the intricacies of molding such a complex part.  However, a few of the more important lessons learned along the way had more to do with choices in materials options than technique.  More on that in a bit.

For the first test parts, it was decided to target a finished part thickness of 0.125” using a composite laminate matrix of fiberglass cloth, Soric infusion core material, and infusion grade epoxy resin.  This combination laminate would be produced using the vacuum resin transfer method of molding and results in a compression-molded part of near perfect resin to laminate ratio with very little waste and almost no odor or mess.  Under a near perfect vacuum, the laminate stack is under about 7 TONS(!) of compression force over the surface of the mold before the infusion resin was introduced!

Like anything scratch built, there are numerous ways to approach the creation of a composite part like this.  Rules are rarely “hard-and-fast” and it is likely that several attempts and techniques will be needed to arrive at the best overall manufacturing solution.  Our little bumper project has certainly been no different.  Along the way, we have made some rather unexpected materials discoveries along with a number of small (and some not-so-small) setup and process details that make huge differences in the quality of the finished part.  And of course, we have had a few failures along the way as evidence of our steep learning curve.

Molding the First Part – Success in Failure


Someone once said: “Success is a terrible teacher.”  The longer I live; I have come to understand this concept more and more.  If we were immediately successful at everything we attempt, there would be no growth.  No improvement.  No evolution of a craft.  We would be effectively stagnant.

With this idea firmly in mind, the transition into our first molding trials was much easier as we were predisposed to accept the inevitable failures as our most valuable teachers.  In this, the evolution of the molding process and techniques has been quick to develop and our part quality has improved very quickly as a result.  But as I have committed in the past, I will share the “ugly” so anyone who follows this work will know just what was involved should they ever endeavor to do something like this themselves.

Like most endeavors, research into the processes and materials involved is a place that demands discipline and time.  Around our shop, I am most often accused of “overthinking” most things.  However, I am reasonably confident that do so has saved untold thousands of dollars in wasted materials on many aspects of our projects.  However, it may be true as well, that I have cost considerable time in my rather slow evaluation process.  In any case, I am sure the argument will rage long after I’ve been sent to the shed and handed the “noodling” off to someone else.

As it goes, our research into our desired molding process had many aspects pinned down with certainty.  For example, we knew exactly what laminate components we would use (e.g., epoxy resin, reinforcements, layup order, vacuum pump and resin trap setup, general vacuum bagging configuration, etc.).  These details are relatively easy to confirm as there is a large database of experience out there to tap for this type of thing.  However, we discovered that there are equally numerous “intricacies” in this realm that seem to be left to your own discovery.  This became disturbingly obvious on our first attempt to mold our first bumper sample.

From the beginning, we committed to using the best available materials we could get our hands on to avoid having issues as much as possible.  In that, we chose the top-of-the-line vacuum bagging materials based on recommendations from respected suppliers and seemingly objective reviews by users.  This ended up being our first and most critical mistake.

Our first mold preparation and composite stack layup went particularly well and we were able to get into the vacuum bag assembly phase with everything looking textbook perfect.  The vacuum bag assembly went well from all aspects until we reached the point where the actual vacuum bag material came into play.  We chose a bag material with the highest available stretch properties (Stretchlon 200) and was advertised as being compatible with all typical infusion resins available (particularly epoxy resins).  From the off, we had difficulty chasing down vacuum leaks that were extremely small but had to be fixed to allow a proper cure.  This involved many hours of careful leak detection effort before we could achieve full vacuum integrity and could move on to the infusion process.  This should have been our first warning with this particular bagging film as later investigation showed numerous “micro-perforations” in the film as it stretched to conform to the part. 

However, there was one unexpected reaction that doomed our first try in a major way.  Specifically, when the moment came to introduce epoxy resin into the mold under vacuum, the bagging film adversely reacted with the epoxy infusion resin, turning into a rather greasy sheet of cling wrap that lost all physical integrity at every single location where an even moderate feature was positioned.  In the course of about 20-30 seconds, about a dozen massive holes opened up in the vacuum bagging film and the entire mold was fouled after being roughly 75% through the infusion.  At this point, there was really no choice but to let it cure off and hope there was no damage to the mold. 

Fortunately, when the resin had fully cured, the failed part pulled from the mold (albeit with fairly considerable effort) and gave us an opportunity to inspect the surfaces that did see full saturation and we were thrilled with the results.  With this result in hand and the experience well documented, more “noodling” ensued in the quest for root cause of the bagging film failure.  It was discovered that others had experienced similar issues with resin compatibility with this particular bagging film despite of the manufacture’s insistence that resin intolerance was not an issue.  After considerable research, we found a different bagging film (Stretchlon 800, same manufacturer) that ended up working well with our resin choice and was much easier to seal.  MAJOR lesson learned.

Mold preparation is the first step in any composite layup.  Since we had a very nice, Class "A" mold surface, we were able to apply chemical mold release to the mold and begin our layup for our first part trial.
In our first layup stack, we used three different types of fiberglass cloth.  here, two identical patterns are being cut from a roll of fiberglass fabric.



We included a hexcel core material called Lator Soric in the layup.  This material build thickness into the part while allowing fast resin infusion through the honeycomb channels.  When the part is fully cured, the remaining hexcel structure is an excellent strength enhancement.

Here is a closeup of the Soric core material.  The honeycomb channels made into the material allow resin to flow more freely through the material, providing faster and more complete wet-out of the entire reinforcement stack.
While not as "drapable" as fiberglass fabric, the Soric is quite conformable and worked well in the bumper mold.  Here, we have trial fit the Soric over the bumper buck to see how well it would conform to the mold cavity.



In this shot, all of the fiberglass fabric and Soric core material is in place and the mold is ready for the polyester fabric peel ply to be added.
here, the peel ply layer has been applied over the laminate stack.  Peel ply is a fabric barrier between the laminate stack and bagging consumables.  When peeled away from the cured part, it leaves a textured surface that requires no sanding before bonding additional elements (like mounting hardware, etc.

The red screen in this shot is the plastic infusion mesh that is placed on top of the peel ply layer.  This mesh allows even distribution of vacuum across the entire mold surface and allows the resin to flow through the media evenly across the entire part during the resin infusion process.
This is the completed first mold trial with the vacuum bag pulled down under full vacuum and ready for leak check.  It tool far too many hours to chase down every micro-leak we encountered using this particular bagging film and that was our first indicator that things would soon unravel on this attempt.
After all vacuum leaks were addressed, we were able to pull the vacuum bag down to full vacuum in preparation for the resin infusion.
We used an excellent epoxy infusion resin formulation from Composite Envisions.  This resin is extremely easy to work with and has a viscosity that is perfect for the resin infusion process we use.  Unfortunately, our first trial was spoiled by a bagging film choice that did not live up to its advertised capability on a number of critical levels.
In all its ugliness, you can see in this shot how the first trial was on it's way to success before the bagging film failure.  In only about 35 seconds, almost 75% of the laminate was infused before the resin flow stopped.

A closer inspection showing the transparency of the laminate stack and where the infusion line stopped.  For reference, there are three full layers of fiberglass fabric between the camera and the Lantor Soric hexcell core material.  Top shelf materials are key!
 
Up close inspection shows massive bubbles in several different layers of the laminate.  This occurred immediately when vacuum was lost due to the failure of the bagging film.  However, it is interesting to note how the facing layers of fiberglass fabric can be seen within the laminate ahead of the Soric core material.

Even as a failed, incomplete part, the strength of the cured composite matrix cannot be denied.  This is my fat, well-over-200-pound ass standing on the failed first trial part with it straight on the shop floor and the deflection in the part still keeps the edges comfortably off the floor at the lower edges by a solid 5/8" to 3/4".  This was eye-opening to say the least!

Molding the Second Part – Success Can be Bittersweet


In preparation for our second molding trial, we collected all of our notes and decided to apply all of what we learned (a good thing) and a few theoretical remedies we thought might help (not always a good thing).

One very helpful change was to modify the vacuum infusion fittings that allow resin and vacuum to be applied to the laminate through the vacuum bag.  This allowed better vacuum distribution prior to introducing resin into the bag and similarly, it allowed for better resin transfer into the mold during the infusion process.  Go team!

Next, we reversed the pathway the resin would flow across the mold to allow the mold to saturate more evenly.  This was another great move as the improvement in resin flow was obvious.  Score!
Our third improvement involved the method of laying up the fiberglass fabric into the mold.  We used smaller, more tailored pieces to assemble the fabric stack and this allowed for easier conformability to the more intricate mold surfaces and made for an overall easier and quicker layup.  We’re on fire now!

The final (and nearly fatal) idea was to not rely entirely on the chemical release agent to prevent the part from sticking to the mold.  Based on our first de-molding attempt, it was surmised that the release agent wasn’t quite up to the task and perhaps the application of an extra release mechanism might be a worthwhile step.  So, we waxed the mold using the same release wax we used to pull the mold off the car based on its demonstrated success.  Bad idea!

As it turned out, the mold infused beautifully and we were quite ecstatic that out new bagging film was on point and the resin flow through the laminate stack was much improved.  For that moment, we were ROLLING!

The next day would prove to be extraordinarily bittersweet.  The mold was stripped of the bagging materials rather quickly and we were rewarded with the early indications of an absolutely bubble-free and uniform composite thickness of about 0.137”.  However, when it came time to pull the part from the mold, the bottom of our program dropped right out. 

The “sweet” part was that the bumper we ultimately produced was near perfect after trimming.  Even though it is technically “useable”, its total thickness is a bit too thin for our liking and we will need a thicker laminate in the final part.  But the endgame here was that the mold and part it produced, along with the bulk of the vacuum resin infusion process was an overall success.

The “bitter” came about as a result of some simple errors during our mold surface preparation.  As it turns out, in preparing the mold surfaces for the second trial, we cleaned the mold a bit too well and essentially removed the “base” of the chemical release agent from the flanges of the mold.  Then, it was discovered that the vacuum bagging sealant tape was placed about ½” further outboard from the original molding position leaving a thin strip of exposed mold surface without enough mold release.  This was compounded by the discovery that the petroleum solvents in the release wax we chose to add had reacted negatively with the water-based chemical mold release, rendering both agents much less effective than either would have been by itself. 

The end result was a part that was even MORE difficult to remove from the mold and due to the adhesions that occurred around the outer mold flange where no mold release was present, the gel coat was damaged as the part was pried from the mold.  Fortunately, however, the polished mold detail surface was not damaged other than to have a very light etching, similar to water spots, permanently affixed to the mold surface.

This simple shot is very telling relative to a failure in our second molding trial.  The mold was cleaned very thoroughly just prior to this picture being taken and this effectively removed most of the chemical release agent base we had established from the first trial.  The masking tape indicated that we moved the bagging tape about 1/2" further out on the flange edges.  The areas under the masking tape would eventually have too little release agent applied and this allowed resin to adhere to the mold surface during curing.
Our second trial layup was improved by using smaller pieces of fiberglass fabric that allowed better conformability to the mold details.

Here, the peel ply, infusion mesh, and resin feed tube and fittings are in place for the second trial.

The new vacuum bag film worked very well on the second trial and was much quicker to verify perfect vacuum than the first bag film selection that plagued our first molding trial attempt.  The photo above shows the second mold setup ready to be infused with epoxy resin.

This picture shows the mold about ten seconds after the infusion was started.  The resin front is just visible as a darker, edge across the bottom edge of the mold and as a larger dark spot in the center around the resin inlet point.  The resin supply cup can be seen just at the bottom of this image.
A close-up of the mold after being completely infused with resin.  The composite materials are fully saturated with absolutely no bubbles.  This method of construction achieve a near-perfect laminate to resin ratio and ensures the lightest and strongest part possible.
This shot shows the second mold trial completely infused with resin with both the feed line and vacuum line clamped off for curing.  After 24 hours, the mold was opened and the part removed (albeit with a few new issues we discovered as covered in the text above).


Trail 1 & 2 together for comparison.  The lower sample (Trial 2) is in rough trim and looks very much like the bumper we want!  While technically two failed attempts, the evolution is undeniably positive.

What Now?


With a host of additional notes collected and many, many problems solved, the next steps are rather clear and somewhat laborious.  First, the mold flanges are being repaired to restore the smooth molding surfaces.  This requires careful sanding and preparation of the flanges to allow additional gel coat to be applied to restore the surface and allow it to be sanded and re-polished. 

Second, the mold detail surfaces will be stripped and the entire mold wet sanded and polished, starting with 800 grit and progressing all the way out to 2000 grit and then polished to a fresh “Class A” surface.  This will restore the entire mold to “as new” condition and we will get on with our third molding attempt while incorporating all of our lessons learned.

The biggest differences we will make are a move from epoxy resin to vinyl ester resin.  This will allow the use of a much wider variety of fiberglass materials (like CSM) and is much cheaper and more impact resistant than epoxy.  It is also less “reactive” than epoxy which should help in overall materials compatibility as well.  Also, we will be modifying our laminate stack to produce a thicker overall part that will be easier to work with in terms of body fit and it will be stiffer and more temperature stable in the elements.  And finally, we will stick to the chemical release agent exclusively and quit trying to outsmart ourselves.  Fingers crossed! 

Until next time!

Here is the bumper pulled from the second trial in rough trim.  Even after weeks of trial fitting to the body, the part fits the mold perfectly!
We have been using the second trial bumper sample as a crude masking device to protect the mold surfaces while we begin repairs to the mold flanges that resulted from our mold release faux pa during the second trial.

Here is where we are today:  The damaged mold flanges have been sanded smooth and the voids that were created in the gel coat have been filled with fresh tooling gel coat and allowed to cure.  We will finish these flanges with 800 grit paper and them proceed to wet sand and polish the entire mold to return it to Class "A" finish specs before we attempt another pull.