Body Plug Construction Methods - CLAY

[Ian McMurdo]

Do any teams have experience using Chavant modeling clay for constructing their body plugs, then using MDM to make female molds? This is the process that is shown quite often on TLC's Rides TV Show, being used by all the prototyping companies around Detroit. We would build an armature for the clay that is close to the final shape, cover it in clay, then have it milled into the right shape. Some final smoothing off by hand would required, but I think this would be less work than sanding.

In the past we have always had plugs milled from sheets of insulation foam, then stuck them together, and covered it with fibreglass and bondo. The prospect of not having to do so much sanding is VERY appealing. Anybody wish to share their experience? I'd love to hear what methods other teams are using to construct their plugs.

[Ian McMurdo]

Do any teams have experience using Chavant modeling clay for constructing their body plugs, then using MDM to make female molds? This is the process that is shown quite often on TLC's Rides TV Show, being used by all the prototyping companies around Detroit. We would build an armature for the clay that is close to the final shape, cover it in clay, then have it milled into the right shape. Some final smoothing off by hand would required, but I think this would be less work than sanding.

In the past we have always had plugs milled from sheets of insulation foam, then stuck them together, and covered it with fibreglass and bondo. The prospect of not having to do so much sanding is VERY appealing. Anybody wish to share their experience? I'd love to hear what methods other teams are using to construct their plugs.

[HenningO]

In 04 we built our master using a rough foam core and put clay on it. We didn't mill the clay but did all the shaping by hand, a lot of work but still a lot more fun (actually) then using filler and sanding.

[Chace]

Come on. Sanding is a rite of passage for underclassmen. Who here doesn't have fond memories of the smell of bondo at 3 in the morning? Wait, what am I talking about? Clay would be way cool. How difficult is it to get a smooth even surface?

[RiNaZ]

Ian, do you know the episode where they showed the process? I need to go watch it. I made a lot of plugs/molds, and not having to do any sanding-like you said, is veryyy appealing.

What kind of final smoothing by hand are we talking about? how do you smooth out the clay? Is it comparable to an A-class finish?

When i do plugs, it's the old fashioned insulation foam (sometimes those really cheap foam you can get from the roof). Just like how you do yours ... glass and metal glaze/bondo, fillers and such. And i used to have a lot of trouble trying to pull the parts out of the mould, either bad gel-coat or just cheap wax. So now, whatever plugs that i do, i always go for A-class finish ... it just saved a lot of headaches afterwards.

[HenningO]

I've got some more time to write now, so I'm going to fill in some info I left out in my earlier post.

We used clay from a german company named Kolb (http://www.kolb-technology.com/studioline/index.php?content=e_2_3_1).

A rough master was built using foam and cutting sections after the CAD model, glueing them togheter etc. etc. But instead of putting filler on that, we drilled 10 mm holes on the entire master. Then we started putting the clay on, the clay is quite hard at surface temp, so in order to apply it to the master you heat it up in an oven to about 60-70 celsius. Then you put it on your body. This has to be done in several layers as you can put on up to 10 mm at a time.

This took us about a day (3 people working). Then the fun part started, shaped the clay by using steel rulers in different sizes and shapes. "Shaving off" clay in some places, adding in other to get the design. We didn't have a final body design, instead we designed the body on the fly. Here's were the clay is so handy, you can easily model a part of the bodywork in say 5 minutes, you get quite good surface finish and you can evaluate the looks. If you're not happy, you put on some new clay on that area and you can start all over. So you can test out small design changes with a cycle time of less then 10 minutes. This makes the whole process much more fun compared to putting on filler, waiting for it harden and then sanding it.

When the actual design is done, you put small amounts of hot water on it and go over with a rounded plastic ruler. This gives you a class A surface. You get reflections in the body and that makes it easy to find faults.

After that, it's just a matter of putting on enough wax / release agent before you laminated your mold. We didn't, so when we removed our mold we had a whole bunch of clay in the mold which was quite time consuming to get rid of.

Overall though, I'd recommend everyone to use clay if you got the possiblity. I'd say it takes about as much time as doing it the bondo/sanding way but you have so much more fun doing it!

[Ian McMurdo]

Henning,

Thanks for the info. How thick on average was your layer of clay? Is there anything wrong with doing a fairly thin coating, say 1/2"? We will probably have the body design at least 95% finalized before milling the clay, or foam, depending on what we end up doing. What material were you using to make your female molds?

[Mike Claffey]

How difficult was it to achieve symmetry between the two sides of the car HenningO? I'm assuming there was 30mm of clay between your master and the surface - any tricks in getting it to look right?

[HenningO]

Symmetry is easier to achieve since it's much faster to change the design with clay compared to bondo/sanding.

We had some areas where the clay thickness was very thin, we had no problems with that. However it's a bit harder to get a good surface with thin clay thicknesses, as the clay can come of the foam while you're working on the clay.

I just realized that two of the guys I worked with wrote a report about the work, and it's still online.

There's plenty of pictures in there of the actual process. As you can see the shape of the body wasn't very complex because we were not sure how hard the modelling was going to be. Afterwards we realized that a more complex shape wouldn't make the plug building process any harder.

http://www.md.kth.se/body/edu/mme/4F1560/Formula%20Stud...%20Racing%202004.pdf (http://www.md.kth.se/body/edu/mme/4F1560/Formula%20Student%20vt%202004/4F1542/Bodywork%20Report%20-%20KTH%20Racing%202004.pdf)

[RiNaZ]

HenningO, how do you achieve class-A finish with the clay? Im thinking it's going to be hard just by using scraper and such.

Also, how do you apply your gel-coat on these surfaces? Does the surface work just like regular bondo/metal glaze?