Jerry Feather

As many of you know I appear to have been dragging my feet on this project for quite a while; and the fact is probably consistent with that appearance. I can probably justify my inattention to this project in my own mind, but I am sure that is of little interest to those hoping that something worthwhile will come of this Replacement Wheel Well Liner project.

Sometimes it seems strange, even to me, the kinds of things that put me off of one endeavor in favor of another, or in favor of no other endeavor at all, but I seem to find that outside input from others (you guys) helps to get me re-focused. I think that may be happening here. Too, what I kind of thought might be someone else's independent effort, has not materialized, at least not to this point.

I think the "tooling" or development for this project is not nearly so complicated as many others seem to imagine. The offer, I think, to purchase a new GTS liner is certainly appreciated by me, but it is both unnecessary, since I have a decent enough set now from Tony, and it is only minimally helpful since my forming method will not lend itself to a duplication of the originals. The original liners, however, do help greatly in setting some basic parameters for the replacement versions I am developing.

Although I have dabbled in plastics off and on over the last several years, it has only been lately that I have devoted so much time and mental effort to the things you have seen me work on. Because of that I always seem to hold a reservation with each project that sounds like "if it works at all!" On the other hand, so far I have not had to abandon a project because it failed. I admit that I did abandon the Hatch Latch Liner project, not because it failed, but because it was superceded. Nevertheless, at this point I feel confident about the potential success of this WW Liner Project.

There are some lingering considerations and ideas going on in this topic that I will try to address as this thread develops.

Jerry Feather

Jerry Feather

I have learned that there are various ways to fabricate things with plastic. Some time ago I had an acquaintance in the Air Guard who was in the plastic injection molding business. It was very interesting and educational to see his operation and how that kind of stuff was made. I doubt that I will ever be invloved in that process.

Not too long after that I became acquainted with the process of "vacu-forming" where heated plastic sheet is pulled down over a form in the desired shape. Actually, since air does not suck--it can only blow, the force used in vacuum forming is ambient air pressure pushing against the plastic when a vacuum is formed under it. I made a form then for a pair of wingtip position light covers for a TBM bomber and had them formed. Recently I had some more of them formed from the same form, and have been devoting a little time to finishing them since the original batch has been used up.

Then a few years ago I became invloved in the process of what I call "blow forming" where plastic is heated to soft then held around the edges in a somewhat air tight fixture and simply blown into a bubble. This method of forming is used extensively by my plastic supplier to make plexiglas domes for acquariums and the tops of Yerts, and for other applications.

A variation of the free-forming-by-blowing process is to limit the "freedom" of the plastic by use of what is called "bridging" over the area the plastic is going to be blown into; and that is the process I am going to use for the new WW Liners.

Another process you have seen me work with now fairly extensively is a purely mechanical process where I force heated/soft plastic sheet through an opening with a particular shape form. Someone recently mentioned that this is called "compression molding," but since I don't call it a mold I refer to this as compression forming.

Finally, for my purposes, a similar process I am using to form windows for my airplane involves my making a form the shape of the window then heating plexiglas to soft and pulling is with some force over the form. Its a little more complicated that that, but not much.

Jerry Feather

Herman K

I did send you an e-mail...

Jerry Feather

Got it. Thanks Herman. Jerry

EspritS4s

Jerry,
You are an interesting bird, but I love your initiative and willingness to share your design processes.

Jerry Feather

The WW Liners that I got from Tony are actually in much better shape that I had expected when he sent them to me. In fact I think they are much better than many of you are still trying to get by with until something better come out of this project. What I am going to get out of them is a determination of just how "deep" upward I need to make my new ones. I need to reach the original GTS upper two mounting points, but not beyond. I can come a little short of that given the anticipated design of the mounting bracket I have in mind. Then I can also determine the limits in front and in th rear, but which I can also determine from one of my cars, I think.

What will be different is what the shape is in between. For that I expect to make mine more rounded, but somewhat elongated front to rear. Mine are not going to be quite so boxy looking. As soon as I get the blow oven set upright I'll start on the final shape of these liners.

As to getting the oven set upright, I have made some progress in clearing out the space I will need for this set-up. I made a bunch of shelve brackets that I am going to use to get my surplus stuff up out of my way. I have about a dozen of the brackets painted, so I can start getting the shelves up soon.

I am going to try to get my neighbor over here to help me with the wiring of the oven. I understand electrical a little, but I am puzzled a little by how these 240 volt AC oven coils should be wired. Actually, I think I know how they should be hooked up. but I just can't understand how they work when hooked up that way. I think one positive goes to each end of the coil and the ground goes to the body of the oven. I just don't understand how the electricity travels in this set-up; and I am troubled in having the oven assembly itself being part of the circuit. I'm sure there is a simple way to look at it, but just need to find out.

Jerry Feather

Jerry Feather

Thanks Gary. That actually mean quite a lot to me. Jerry

jon928se

Strangely I derive more satisfaction from the description of your labours Jerry than I do from the fruits. I have a couple of your hatch receiver liners here that I have yet to fit - A whole lot of more important stuff (more than I could go into here) has happened over the last year. Suffice to say when my father was on his last legs in the Hospice a year or so ago, reading about Jerrys efforts to form the hatch liners kept me close to reality.

S4ordie

Jerry I too like many others appreciate the documenting of your process. I wish I had some of your innovative skills.

Regarding the shape of the WW liners, perhaps the reason the orginal liners have more of an elongated box shape is to make sure the tires do not rub. Many of us run wider than stock and sometimes diameters greater than stock tires that just fit inside the existing liners. Would be unfortunate to mount up your product to find there is an interference issue.

Jon - Sorry to hear about your father. It is interesting how things like Rlist can help keep you more emotionally grounded when enduring something so serious as family member with a grave illness. My sympathies and condolences.

M. Requin

Jerry, you're right, that's a bad old practice- get a 4 conductor pigtail and receptacle and separate the ground and neutral circuits. If your friend is a wireman he'll understand.

Jerry Feather

I'll look further into the wiring. Thanks for the suggestion. However, when I went to bed last night thinking about this it occured to me that the Porsche 928 is wired in just that way--the whole car is the negative circuit for the electrical system. The difference is perhaps in the level of voltage?

Jerry

Jerry Feather

Thanks Dan, for the thoughts about shape. Based on what you say and my own intuition I would say that the ideal shape or the shape to allow for the maximum tire space would be to make them as tall as possible within the car body constraints, to make them as far foreward and rearward as the car will allow, make them come all the way out to the outer body at the wheel opening, and then make everything in between match the shape of the biggest tire that might be put in there and moved around in any direction up the the limits set inward, outward, frontward, and backward.

Guess what? That happens to be just about exactly how the final shape will be determined.
The funny thing is that based on that method of shaping these, if it had been followed by the factory the liners would not look squarish like they do. That's why I suggest that mine will not look much like the originals.

On the other hand, I think the originals were designed almost solely as a means to hold the sound deadening material away from the tires. I think they probably determined how much sound deadening material was needed or desired, put it the approximate locations and then designed the liner is such a way as to hold it there. All they needed to do was keep the stuff away from the tire. I think that's why the are squarish. Anything in between will serve the same purpose; and I like my design idea better because I think it makes more visual sense.

I hope that doesn't sound glib. I don't mean to be glib when I respond to various ideas; and I don't want to sound glib and put anyone off especially from making suggestions. Sounding glib is unfortunately my nature; but being glib is not.

I want to thank Dan and all of you for your input on this and the other projects, because it really is what keeps me motivated.

Jon, I too am sorry to hear about your father. I'm very pleased to feel like I played some small part in helping you through that time in your life.

Jerry Feather

Jerry Feather

Gary, I read your post to my wife and she said "did you tell him yes, and I have all the feathers to prove it?"

Jerry

M. Requin

The basic practice is that the neutral and ground circuits in a standard residential 220/240V service are ONLY tied together in the main panel. At first (and even to some electricians) it appears that since they are tied together, they are the same throughout all the wiring. The important difference, which does not apply of course to DC circuits in a 928, is that this makes sure the ground circuit is not a current conductor, only the neutral. For years the three-wire appliance circuit was standard, but because in that arrangement the ground is a current conductor, it was basically unsafe.The NEC, which is pretty dense reading admittedly, makes this very clear. Knowing you (at least from this list) I'll bet it will only take you a minute or so of reflection to see how this is so. Took me a bit longer, but I do all (include service entrance) wiring on our farm, and I follow the NEC like a bible, so I studied it hard, since it's the only way to be safe.

Jerry Feather

Thanks Martin, for the help. You are giving me much more credit than I deserve. When it comes to electricity I am pretty much out of my element. I think my problem with electricity is that I cannot see it, so I just fail to understand it enough. I can do the mechanical part of electrical stuff and can wire things like houses and perhaps 928s, but fully understanding it is somewhat above me.

Here is what I have with the oven: The oven coils (two of them) are designed for 220/240V. They have a wire core and what appears to be a ceramic lining around the wire core and then are covered with a metal outer shell or covering. Each end of the coil has a simple tab with a screw hole to fasten a wire; and I assume that the wire is continuous throughout the coil. I have changed these before in an oven in our kitchen and simply fasten what I think is one leg of the positive to one end of the coil and another to the other end. That is also what the appliance guy said I should do with these when I bought them.

I am pretty sure that the two positive legs are going to alternate with each other through the coil, but I can't quite figure out where the electricity is going on the negative side. So, I have mounted these coils in the wall of the oven blow chamber in a solid copper mounting devise that is screwed to the wall of the chamber. The mounting devise is solid around the outer jacket of the coils. I am assuming that the electricity is somehow passing from the wire core through the ceramic lining and into the outer jacket of the coil and int to oven body. I assume that the resistance involved in this is what creates the heat that turns the coils red. That also tells me that the oven chamber now needs to be connected to the neutral wire to complete the circuit.

The only way I can isolate the oven chamber from the neutral function is to redesign the mounting of the coils so they are on something seperate from the chamber. My problem is that I have to also make this mounting air tight because the oven chamber has to hold the air pressure that will be used to blow the heated plastic into the form. That makes it a real challenge since in addition to being air tight it will need to be isolated electrically and further it will need to be very heat resistant.

With a four wire circuit, which, as you point out, is more common these days with 240v appliances, if they are joined at the box, what are the doing at the other end? What is the difference between the neutral and the ground. My best guess is that the neutral, in my case, will be the outer shell of the heat coil, if my assumptions are correct about the circuit, and the fourth wire, or ground, will be affixed to the oven body.

It that is all correct, I can't figure out what the safety factor is with four wires? However, that brings me back to my intuition and concern about having the oven itself being part of the 240 volt circuit, doesn't it?

Thanks again for your input.

Jerry Feather