Getting the perfect wheel well shape.

[notnilc20]

One very nice technique is to take photo of each wheel well, perpendicular of it and from at least 2-3 meters distance. Then, put the photo in some image editor program or 3d program, and draw an arc or Bezier curve (aka spline). For the 2d image editing way, put the photo in a lower layer and draw the curve on the upper layer. For the 3d program way, put the photo as a texture to a plane (must have exact scale of width and height!) and draw the curve relative to the plane (usually it's the side view). You may want to make the layer or plane of the photo semi-transparent, or adjust the brightness, in order to make the drawn curve easier to view. Hopefully this heps.

 Here is an example of doing the 3d method in Rhino4 using the command "Picture frame". I set the transparency to 80% to make the colours less vibrant. Notice how the wavy shape of the wheel well is easily recognisable. Working in 3d for this particular task has one great advantage - you can quickly zoon-in or zom-out the image to the desired size, so it's really easy to spot even small imperfections of the shape of your wheel well.

Wow, never would have thought this up. Good info.

[plans4sale]

 One very nice technique is to take photo of each wheel well, perpendicular of it and from at least 2-3 meters distance. Then, put the photo in some image editor program or 3d program, and draw an arc or Bezier curve (aka spline). For the 2d image editing way, put the photo in a lower layer and draw the curve on the upper layer. For the 3d program way, put the photo as a texture to a plane (must have exact scale of width and height!) and draw the curve relative to the plane (usually it's the side view). You may want to make the layer or plane of the photo semi-transparent, or adjust the brightness, in order to make the drawn curve easier to view. Hopefully this heps.

 Here is an example of doing the 3d method in Rhino4 using the command "Picture frame". I set the transparency to 80% to make the colours less vibrant. Notice how the wavy shape of the wheel well is easily recognisable. Working in 3d for this particular task has one great advantage - you can quickly zoon-in or zom-out the image to the desired size, so it's really easy to spot even small imperfections of the shape of your wheel well.

[Iwanagofast]

Just keep looking at it from all angles, put your ear to it and eyeball it. Same thing applies I wouldn't be using a DA, use a sanding block with vacume attachment. Also run your palm around it to feel for uneveness. DA's are best used for keying a surface for paint, I also use them with 40 or 60 grit for taking down high spots very quickly with filler or fibreglass, then finish with block. Back to the question, I would also suggest putting the wheel on when you are doing this as it will help you to see any irregularities. Just cover it to save having to clean all the dust from it later.
Hope that helps

[notnilc20]

Good info. Thanks everyone and for others feel free to chime in with any other ideas. Thanks.

[lance345]

As with anything you can start as coarse as you want. If it's really rough starting with 80 is a time saver for sure. You can start wherever you want really (36 grit if you want) just make sure to get out the scratches as you go finer. A guide coat is nice for this but it takes longer (spray bomb works, diluted paint, you can buy powder guide coats)

As a rule though (and every product is different, but for the most part this holds true to every product I've used) a primer won't fill scratches coarser than about 180 and it usually needs <400 to stick well. I go 180 on big problems (like cold filler) 320 where I think my primer will be, and 400 for the overspray area.

CAN primer fill coarser? yes, but you will save yourself so much time and aggravation by just going over it with something finer.

CAN you prime over 600 or 800? yeah, and it will probably stick forever, but if it does peel won't you feel silly. Primer is designed to be thick, so it needs a larger tooth to bite.

I'm not trying to be a know-it-all or whatever. Just trying to save you time from my experience. I have prepped thousands of cars working at a high quality shop.

Side note - please wash your gel coat with soap and water. Release agent is used to get parts out of molds and if there is any on still and you start sanding you just grind it in. It may only cause a problem 1% of the time, but that 1% is worth the 1hr to wash the kit imo.

[rodrieguz]

Dura block makes a nice blocking kit with a radius block that would work well or any round hard object you can wrap paper around.
I would block gel coat with 80 grit first and work up from there to get the panels nice & flat.

[notnilc20]

Sorry, i guess i didn't explain it too well. What i'm talking about is the wheel well opening itself. I'm still shaping it to get a relatively nice looking radius b/c on the edge, the gel coat was chipping so i had to grind some away to re work it.

Another question, with gel coat what grit do you block with to get it ready for primer? Thanks.

[Robert]

Is there any special techniques used to get a nice even line on the wheel well opening? Right now i'm just using the edge of my DA but didnt know if there is a better way that the pros use?  Thanks.

Never use a DA to block! You will end up with a wavy paint job. Taping your feature line is the way to keep a consitant line. Quality means using your hands to sand!

[lance345]

I agree with the above post. To make really nice lines you want to mask under the line and block above it, then mask above the line and block below it. This really defines the line and makes it sharp and precise. Just keep an eye on your tape, you will sand through it especially if you are using a coarse grit like 320 or something. Just normal masking tape works, but again watch going through it.

[Iwanagofast]

Sanding block would be better than a DA in this case. Masking tape can be used to form lines or prevent them from being sanded away.

[notnilc20]

Is there any special techniques used to get a nice even line on the wheel well opening? Right now i'm just using the edge of my DA but didnt know if there is a better way that the pros use?  Thanks.