This is Part Two of this article. Click here for Part One.

After the last section had setup I drilled 1/4" diameter locator holes (8) through the vertical separator flange. This absolutely must be done prior to any release of any of the three molds. The bolts are used to join these halves back together for part lay-up.

Now that the molds were cured and locator holes drilled I was able to pop them off the part. This was, as always, THE moment of truth. I always like to start by using a hammer to tap the outside of the mold. I then go around the flanges with the wedges to release them. Once they are released I keep moving them further out into the piece. At some point the mold will literally 'pop' off the part. Knock on wood; I have never had a part stick when using PVA. Before I used PVA I did and it wasn't pretty. From my experience and from everything I have read using PVA is simply the most foolproof product on the market for release. Most people I have spoken with will tell you that a seasoned mold (one that has been used a number of times) will release easier than a new one and may only require wax or PTFE to release. As I have only made a limited number of parts from my molds I have not attempted to eliminate PVA from my process. Given the amount of time and effort involved in making the molds I don't like the thought of destroying one.


After the molds were released from the part it was time post finish. I have yet to have a mold come off a part ready to lay-up. I always have a blemish, pit, dimple, high spot, surface irregularity, etc. to fix and this part was no exception. The majority of the work on the door surrounded the surface irregularity at the door handle and lock areas. While these spots were both filled with clay and smoothed prior to molding, my experience is that a smoothed clay surface will always have to be sanded to match the surrounding area.




For sanding I like to wet sand with blocks and sponge pads as shown above. The surface finish left by 400 grit is plenty smooth. There will be no discernible difference between 400 and 2000 grit on the finished part if PVA is used so I find no reason to go to the trouble. This is a good time to address the downside of using PVA. PVA does not go on perfectly smooth or perfectly uniform regardless of how much effort is put into the its application. Therefore these irregularities will transfer to your parts and molds.





You may remember the outward dimple on the stock part that I mentioned earlier. In the above picture you can easily see it as an
inward dimple on the mold. At this point I simply filled this depression with body filler and sand smooth. The difference in surface texture of this small area will be every so slightly noticeable on the finished part but light sanding of the will eliminate most or all of this variance. Note: My experience is that it is easier to address surface depressions than high spots. Therefore I chose to always address depressions. If there is a depression on a part I will fill it prior to making the mold. Also, I should mention that hardened polyester resin is very tough and takes a long time to sand. If you have a high spot of gel coat that you need to sand down it will take 10 times more effort and time than sanding of body filler.




Above you can see the sanded mold with filled dimple. You can also see that I filled a depression on the mirror extension that will not be needed or wanted on the finished part. Notice that the door handle and lock area are no longer noticeable as they have been completely sanded smooth with the surrounding profile. This part was now ready for mold release and carbon/honeycomb/carbon vacuum bag lay-up.


Part IV: Preparation of Carbon Fiber Lay-up
Alright, I have completed the long, messy task of making the mold(s) and I was now ready to churn out a 3 lbs. race part. This is the fun part. It is also 1/100th the mess that mold making is. The first step of this process was to organize and pre-cut all of my materials. As I mentioned in the opening of this write-up, I will not go into excess detail on how many layers of material are or how much if any core is required to make a part. I will only address the part I am making.

For this part I chose to make the outer skin from three layers of 5.7 oz. 60" wide 2x2 twill carbon fiber and a single 1/8" 3.0 sq. foot Nomex honeycomb core. The topology for the outer door skin was 2x1 or two layers on the outside (mold side) with a core and one layer on the inside. Obviously a single layer carbon was required on both sides of the core. The lightest possible cored parts are 1x1 but I wanted more impact protection for the doors. I know, I know, I can here it now, "What is a single layer of carbon going to protect." The answer is itself. A single layer is pretty darned easy to damage with a slight impact. I can just see the door swinging open into a jack handle and cracking. 2 layers on the outer skin of the doors will definitely make them more resilient. With this said, I have made a bunch of 1x1 parts (my roof, C pillar covers, etc) and they are very structurally strong, just a little fragile.


Ok, on to pre-cutting. I have found that it is much easier to cut the fabrics, core and vacuum bagging materials on a flat table. This keeps the fabric nice and clean and keeps the edges of the mold from making runs in your carbon fiber. I will say that one of the great frustrations in dealing with carbon is keeping it from snagging on stuff. Think of it as a panty hose from hell. You must be VERY careful at all times when measuring, cutting, moving, and wetting out carbon or you will get a run, pull, or tear. A simple hangnail will pull a carbon piece apart. For this reason and to keep any oils off the fiber, I always wear nitrile/latex gloves when handling the fabric.



Since I was cutting the fabrics on a table I made a template of the part. For this I used the white breather ply material as shown in the picture above. I just made sure that the template followed the curves of the parts and that it was NOT UNDERSIZED as this was the size that $150 worth of carbon and a $75 core was going to cut to.



After the template was made I then laid it out on the table on top of the carefully unrolled carbon fiber. I then took the 3/4" masking tape and traced the outline of the part. This had to be done very carefully as well as it would pull the carbon weave apart if I attempted to remove or relocate. Once the template outline had been transferred to the carbon fiber I then cut out the template by cutting the tape in half. This left both sides of the cut with have of the width of the tape. Above you can see a picture of the "Peel Ply" being trimmed to fit the taped and trimmed section of carbon fiber. BTW, only the carbon fiber needs to be traced with tape.


Right now you are asking, "Why use tape?" The reason I used tape was that the carbon loves to fray. Much like a woven basket, if it starts to unravel it will become a HUGE MESS. The tape 'helps' keep this from happening. As you can see in the picture below, it doesn't totally prevent it. Now that the first layer of carbon fiber was cut I repeated the process for the other two layers and the peel ply (slightly oversized).




Cutting of the core was only slightly more difficult. My preferred method of doing this is to lay the core on the mold (this is why we haven't applied mold release yet, btw) and mark it. Again I must make sure that the core follows the profile of the part before marking. I often put something on the core to insure that this is the case. For marking I made dots with a black Sharpie marker to show me where to cut. I should mention that the core must stop prior to the edge of the part. I like it to stop no closer than 3/4" from the edge. This give the inner carbon layer a good chance to bond to the outer layers. It also makes it easier when bagging – more on this later. For this outer door skin I have stopped the core well away from the edges as that is where I am going to bond the inner structure.

After the core was marked I then moved it to the layout table. To cut the core I used a pizza cutter like circular fabric cutter and simply followed the dots. This worked extremely well as the core cut very easily. If I am using a core thicker than 3/16" I bevel the edge by angling the cutter 45 deg. Cutting the core was not difficult to do as the markings were correct.


Now I apply mold release:





Now that the carbon, core, peel ply, and breather ply were cut, it was time to apply mold release to the mold. For this I followed the exact same process as before. The only addition to this process was that I ran 2" wide blue painters tape completely around the outer edge of the flange as show in the above picture where I am spraying PVA to the mold. I did this so that this area received no mold release. Why? Because this was where the bagging seal tape is going to go. I have made the mistake of trying to get this tape to stick to the release agents and it is a challenge. I am much better off with it sticking to the bare mold.

Finished Part Lay-up:





As with the mold lay-up, I like to get all of my supplies out and ready. Above is a picture of them. In addition to the two parts of the epoxy, I have my .1 oz resolution scale, nitrile gloves, cups to mix the epoxy, tongue depressors to stir the epoxy, composite rollers, and spreaders. I also have the bagging sealing tape rolls ready.

Now it was time to start wetting out the part. Once I began this phase I was back into a time sensitive area. The epoxy resin I used starts to cure in the cup in about 20 minutes and on the mold in 3-4 hours. Obviously this is quite a bit longer than the polyester resin used in the mold lay-up. I still proceeded with diligence as the vacuum bagging process requires the resin to flow from the part to the breather ply.



Above is a picture of the first layer of the carbon on the mold. A couple of notes, here you can see the tape along the trimmed edges of the carbon and the outer edges of the mold. They are still there for a reason. DON'T CUT OR REMOVE THEM YET.

Once the carbon was in place it was then time to mix and add the epoxy. The epoxy I used requires a 3:1 mix ratio. For accuracy I always recommend using the scale. Most composite shops sell 'ratio' pumps. I have several and don't like them. They are messy and inaccurate. I definitely would not use them without a scale to confirm the ratio. For this part I began by mixing 12 oz. of epoxy. BTW, I usually don't mix up more than that even if the part needs it as it prevents it from sitting in the cup.



In the above picture I was adding the epoxy to the mold. I began by using the soft spreader (make sure it is clean and free of anything that could snag the fabric) and working the epoxy around. I have no problem seeing what was wet and what wasn't. The beauty of the vacuum bagging process is that it will remove almost all of the excess resin from the part. Knowing this I usually will error on the side of too much epoxy as too little will ruin the part.

I continued spreading the epoxy mixing and adding more as necessary. Once I got the part wetted out I lifted the carbon exposing the interior of the mold. I did this one corner at a time to prevent movement of the fabric. If I ever notice an area that is dry I add a little epoxy. This is usually not needed but this was the time to check. After this I went over the fabric with the composite roller. This roller does a great job of two things. One, it gets rid of any air bubbles/pockets under the fabric, and two, it fixes cosmetic blemishes to the orientation of the fibers.


Once this layer is fully wetted with epoxy I preceded with the second layer. As this second layer was not cosmetic I used the least perfect of the three layers I cut. The wetting of this layer followed the exact procedure as above except I did not lift the carbon to check underneath. This layer takes less epoxy to wet out as it will pick up from the layer below. After this layer was completely wet I went over the entire surface again with the composite roller.




Now it was time to wet out the inner carbon layer. I am sure you are asking, "You skipped the core?" We will get to that in a minute. The inner carbon layer was wetted out first on the layout table as shown in the picture above. The procedure for this was simple; I laid out the fabric and wetted it completely with epoxy. I definitely wanted this layer of fabric to be 'oversaturated' with resin.




Now it was time to lay the core on the outer two layers of carbon. I had to be very careful here as I didn't want the core to snag the carbon. When the core needed to be moved, I picked it up and laid it back down. I did not attempt to shift it. Also, the core did not stick to the carbon underneath nor did it perfectly follow the contours of the part (and it won't unless the mold is perfectly flat). I just located it as best I could and followed the rule of getting the core to no closer than 3/4" from the finished edge.



Now I transferred the pre-wetted carbon layer from the table to the mold. Special care was taken here and for this operation I required an extra set of hands. The fabric needed to be laid out as evenly as possible and centered all the while not disturbing the location of the core. This might not sound like a big deal but it was the most challenging part of this lay-up.


Given the fact that the core did not follow the form of the part, the third carbon layer also did not follow the contour of the part. The key here was to make sure that the carbon was not stretched or folded. As you can see in the above picture, there was plenty of excess material around the edges to be taken up by the vacuum.

Once this layer was applied it was time to trim the excess carbon. This is pretty simple as the edge of the blue tape is the line I use to cut to. I just make sure I have good sharp scissors and take my time as I did not want to disturb the fabric and core. Note, trimming the excess carbon also trims of any remnant masking tape that was left on the edges of the carbon. Once the excess carbon was trimmed I then removed the blue tape from the flange.


You will notice that you now have a perfectly clean (no epoxy, no mold release) flange. The first several parts I made I did not use tape and would have to clean the flange edges. This added a lot of time and effort to the process. Definitely use tape. It not only leaves a clean flange but it also 'smoothes' the rough trimmed fiberglass mold edges which reduces the chance of snags on the carbon and bagging film.



I now made a final pass around the part making sure that all of the carbon is nice and smooth, particularly around the flanges. Once that was completed it was time to apply the peel ply as shown above.

There are a couple different options to transfer resin off the part. The first is perforated release film. This is simply a sheet of polyethylene with tiny little holes spaced at about 1/4" from each other across the entire surface. This I have used for all of my parts up until this one. It works pretty well and is very easy to remove from the cured part. For this part I used nylon peel ply. This is a simply tight nylon fabric that has been treated to prevent it from sticking to the part. Unlike the perforated release film, this fabric does not have holes rather the resin will flow through the entire surface. Also, the peel ply is advantageous in that it leaves a fabric imprint on the carbon which is great for adhesion. This is important for this part as I am going to epoxy the inner door structure to the inside of this panel.





Neither the perforated release film or nylon peel ply are that flexible. Therefore it is important that these layers drape across the part and do not 'span' the contours. If they span a section of the lay-up they may pull the carbon and core when the vacuum is applied.

I now applied the breather ply. The breather ply is used to absorb the excess resin that is pulled through the peel ply/perforated release film under vacuum. The only trick here is to make sure that the breather does not touch the carbon fiber. If it does it will seriously stick to it. Therefore I want the peel ply to be slightly larger 1/4" than the carbon fabric to prevent this. Also, I want to determine the location of the vacuum bagging attachment fitting at this time. The fitting is approximately 2" in diameter and must be placed directly on top of the breather ply. Also, I greatly prefer to have this fitting off of the finished section of the part. The flange is excellent for this but you can also use a fold in the vacuum bag to serve the same purpose. I will usually use scrap strips to make vacuum channels for larger parts. This prevents the possibility of resin blocking areas of vacuum. You can see how this was laid out in the picture above. I also ran this extra strip down the part and to the vacuum fitting location.




Once the breather ply is on it is time to put down the bagging adhesive. BTW, this is some unbelievably sticky stuff. To install it I start in a corner and proceed around the perimeter of the mold. I don't peel off the outer covering of the tape until the bag is installed. When I come to a corner I simply twist the tape around it as shown in the picture above. The outer cover of the tape will break but the tape will be a continuous run which will GREATLY reduce the possibility of leaks. After I have laid down the tape I go back over it with a lot of pressure to insure a seal.





I now lay out the bagging film. As with the release film, there are a number of options for bagging film. I LOVE the green high elongation bagging film and highly recommend it. It will stretch a ton and is very easy to work with.

I start by rough cutting a piece and laying it on the part. BTW, this film does not have to be trimmed to a perfect size. It just needs to be bigger than the part. Once the film is cut and placed it is now time to stick it to the bagging adhesive tape. I like to start in the location that I am to place the vacuum fitting. In this case it is right behind the mirror extension on the flange.




Now for a tricky part. The key to getting a great vacuum seal is getting the bag smoothly adhered to the tape. This took me a few tries to get down and you may want to practice on a workbench or table. This is also a process that is dramatically easier with two people as I really need three hands. One hand will be necessary to pull the cover off of the tape, another is needed to lightly press the bag on to the tape, and a third is needed to pull the bag tight to prevent wrinkles. I can't stress enough how important it is that this is perfectly smooth with no even tiny wrinkles. In the picture above of the process you will notice that there is about to be a small wrinkle in front of my finger. Here I pulled the bag film tight to eliminate it as it would be a source of a leak otherwise.




I am much better off with one big fold vs. a bunch of small ones. As you can see in the picture above I ended up with a big one. To remedy this I stretched and folded open the seam and pressed in a section of tape.

I now have 95% of the bag taped down except for the area right next to the vacuum fitting. The vacuum fitting is two parts, one that goes under the bag and another that attaches to it on the outside. Therefore I made a small incision in the bag, inserted the bottom section of the fitting into the bag, and connected the two parts. It is better to make a small cut (1/4") and stretch the opening than one that is too big and will leak. I also make doubly sure that the hole is in the exact place that I want the fitting.

Once the vacuum fitting was installed and put together I finished taping the bag down. Now I can turn on the pump. For my pump it takes a minute before the excess air is out of the part. At first I always wonder if it is working. Then, all of the sudden, the bag will contract to the part. If it doesn't, I check the pump. If I am sure that it is working then I have some major leaks. To find them I call on a good set of ears and some chunks of the bagging tape. I simply go around the parameter listening for leaks. When I find them, I stuff in some tape and squeeze it around. Then I go looking for more. This is where having a quiet pump is very nice to have as it is easy to hear air moving into the bag.


My DIY pump will pull 28.5" of vacuum which is awesome and higher than many $250 pumps will pull and it is 1/1000th as loud. This is made even better by the fact that I have $20 in it. If I am not pulling 28.5" on a part then I need to go looking for leaks. I personally regard 20" as a minimum for acceptable vacuum bagging carbon parts. Less than that and you will need a new pump or you will need to do a better job sealing your bag. BTW, A part the size of a hood is what I consider the maximum for my pump.

12 hours and a six pack later…









It was now time to release the part. First I turned off (unplug) the pump and removed the vacuum fitting from the bag. I then pulled the tape (not real easy to do btw) off the part with the bag attached. Then I peeled off the peel ply as shown above – also not easy to do. BTW, with the peel ply I pull back parallel to the part instead of up.





Once this was off it was time to pop the part from the mold. As with popping the mold from the original part, I began by working the wedges all the way around the flange. I always have to be careful not to get in a hurry even though I am dying to see the finished part. In a way it is kind of like opening a Christmas present. With this part I then ran the wedges into the short end of the mold and it popped almost instantly. With other parts this can be a long process that requires sticking wooden yard sticks way up into the mold. Hopefully yours will pop out as easy as mine have. All hail PVA.


Above is the finished outer skin after I washed off the thin layer of PVA. BTW the PVA will stick to the part and not the mold. This makes moving on to the next copy of the part easy but requires washing of the finished part. Fortunately PVA removes easily with water. The hotter the water the better but I will usually just hose my parts off and then wipe down with a soft sponge.




Here is the inner panel. The nylon peel ply left a very nice textured finish to the interior of the part. It is now ready to bond to the inner door structure.


At this point I exposed the part to an extended post-cure. I did this by laying the part out in the sun for a day. 12 hours at 160 deg. flat did it. Post curing makes the finished part 10-15% stronger than not post-curing.





The stock gutted door skin (no glass, no mirror, no interior panel, no lock, no handle, no speaker, no switches, no side impact door beam, no interior skin, etc.) weighed 30.5 lbs. The stock door with all of the stock stuff in them probably weighed 100 lbs. each. This carbon, honeycomb, carbon reproduction is 3 lbs. 5.6 oz. Not bad as it should be right at 3.0 lbs. when trimmed.
To trim this part I simply used a Dremel tool with a fiberglass reinforced cutoff disk. Carbon fiber this thin cuts easily, almost too easily. The flange that I put on the mold leaves a nice line where to cut. This part of the process was not hard but I had to be careful, steady, take my time and definitely wear eye protection and a respirator as it made a TON of dust.


Appendix:
DIY Kentucky Redneck Vacuum Pump!


Many people have asked about my vacuum pump and here it is in all of its DIY glory. Keep the redneck jokes to yourself. BTW, full credit for this idea goes to my good friend Gene Young so point the redneck jokes at him.

This pump started life as a drinking fountain refrigerator compressor. I have converted it from compressing Freon to vacuuming air. This setup is so simple it is comical to think of spending $350 for a rattle trap to do the same thing.

Here is what you do:
1. Go to a local refrigerator repair guy and buy a used compressor. I got mine for free.
2. Bolt it to a piece of wood.
3. Wire it up to plug strait into the wall – screw an on/off switch
4. On the 'suck' line, attach with a worm clamp a 1 foot section of 1/4" section of vacuum line
5. At the end of that worm clamp on a $3.00 fuel filter (needs to have 1/4" barbs) to prevent epoxy from getting into the pump.
6. Then run another foot of vacuum line to a shutoff valve (optional)
7. 'T' into the line a vacuum gauge as show. I got mine from McMaster-Carr for $8.
8. To it attach a 15 foot run of vacuum line. This will give you a ton of placement flexibility.
9. To the pump outlet, attach a cheap filter as shown to prevent oil from spraying out of the pump.

Every once and a while you will want to lube the pump with refrigerant lube that you can get at AutoZone. Also, I run a fan over my pump to keep it from overheating. This probably isn't a potential problem but they do it on refrigerators so I do too. Eventually I am going to add a fan to the mounting board. This is why it is oversized.


Parts list:
1 Small refrigerator pump
1 12 ft. electrical cord
1 1'x2' piece of wood
4 small lag bolts to bolt the pump to the wood
1 cheap fuel filter with 1/4" barbs
1 cheap filter to keep the pump from making a mess
1 1/4" NPT female to female shut off valve
1 1/4" NPT male, female, female 'T' fitting
1 vacuum only 2" gauge w/ 1/4" NPT male fitting
2 1/4" NPT male to male barb fittings
1 1/4" NPT female to male barb fittings
1 Six pack of your favorite beer to enjoy while watching your $20 pump for 12 strait hours while waiting for your part to cure.


By: Paul Bird, contributing member of TheTurboForums.com
Copyright Paul Bird 2005