fabrication pointers

Pint · 12-11-2007, 05:05 PM

hi,

I'm looking for some pointers on my fabrication -
the best way to cut a striaght line in Plastic. I've tried to use a dremmel but my had is not steady enough and the result is a bit wonky.

In the past I've used an epoxy resin to fill in the gaps. this didn't work that well becuase the finshed result looked clumpy.

I also have had other problems with epoxy resin. When I have sanded it smoth. It's texture is different to the plastic which shows when I've sprayed it.

I've used a aerisol can spray which only seems to apply heavy coats and not light ones.

Maybe I should just get a professional to do this. Who should I approach? A body shop?

monkeyracer · 12-11-2007, 07:54 PM

ok, here's some pointers for you:

Take your time.
Follow all directions on the products.

More specifically related to your project:
- Straight lines are impossible by the hand, a jig or ruler is needed to guide the tool.
- Gaps should be filled in with the same material as what was cut. Example: ABS plastic should be filled back in with ABS. Other materials of similar properties can be used in place of the original if necessary, but BONDO is not a "fix-it-all." BONDO is designed to fill small dents and cracks to make a smooth surface, and should not be used for any structure.
- The best surface is achieved after a lot of sanding. I really mean a LOT. You'll also want to use a sanding block, or something other than your hand.
- There are a lot of techniques to try and match the texture. Some textures and patterns are not achievable with home-made tools, and a different texture will need to be used. There are spray on texture paints available in varying textures.
- Spray Paint (sometimes called Rattle-Can paint) can be used with great results. Hold the can a little further from the area that's being sprayed, start to spray beyond the project, and use brisk sweeping motions to apply a light mist. Wait for the light coat to dry (most paint takes a few minutes with light coats...) and apply the next light coat, and repeat until the paint is the way you want it. Keep in mind that the first coat may start the curing process within an hour, and applying a fresh coat might cause wrinkling. Check the can for info on when coats can be applied. My Krylon says additional coats can be applied within 3 hours and after 7 days. Heavy coats are bad, the paint will drip, the surface will be uneven, etc.

Hope some of this helps.

Pint · 12-11-2007, 09:56 PM

monkeyracer, thanks. I'll give your hints a try.
I will probably get a an air brush to improve the quality of the paint finish.

GoHybrid · 12-11-2007, 10:05 PM

a method I use to get dead accurate cuts in plastic or foam of any shape is to mark out the line first with tape or a sharpie or whatever you want that's going to stay in place. Use your favorite tool to rough cut the hole you're trying to make. How steady you can keep the tool will determine how close to the line you should get. At no point though should you ever cut right up to the line. When you have your hole rough cut, use coarse sandpaper like 60 grit to start finessing the shape. Use the sand paper to get to the line. Not only will you have a much nicer edge, but you have a constant reference point as far as when to stop sanding a particular area.

For your keypad - if you can procure a new part to cut into, try this. Take the keypad apart and use the casing as a template to trace from. If you are patient and remember that the only accurate cutting you're doing is with the sandpaper, I would bet that you could get it tight enough that you could just press the keypad in and not even need glue. (definitely secure it, i'm just trying to illustrate a point).

There is an example of this in my foam thread (see sig) where i use a crappy air dremel to hog out a bunch of material, draw a line and then use sandpaper to capture all the contours of my curvy dash and get it perfect.

Pint · 12-11-2007, 11:18 PM

Quote: Originally Posted by GoHybrid

At no point though should you ever cut right up to the line.

I can confirm this is what I did and it was a mistake.

I like your idea of taking the keyboard apart and using it as a stencil. However the keybaord is flat and I'm trying to fit it onto a curved surface. I tried making a stencil by tracing the shape of the keyboard out on paper and then using the paper as a stencil - That did not work very well.

Are there any other methods?

pRoFiT · 12-12-2007, 12:22 AM

Curverd surfaces are hard to transfer flat parts too. I've never done it, but i would probably start with some calipers and try to transfer overall measurements from the keyboard to the center console. Then do an inside cut and see how close you are. use sandpaper to open it up where needed.

You could also center the keyboard where you want it then trace top and bottom to the center console. Then under gestimate where the left and right would be and then cut close to top and bottom but way under on the left and right sides. Then sand top and bottom to let the keyboard slide in. Center keyboard and make new trace marks where it hits on the left and right. repeat until it slides in all the way. Maybe there is a better way. thats just my first thought on it.

The texture? is it the same on the entire car? Depending on how much work you wanted to do you could sand away all the texture where the keyboard is going and replace with a spray texture paint. That way you would get a uniform look.

GoHybrid · 12-12-2007, 12:47 AM

maybe try taping the bezel down where it touches the console to help steady it, then use the flat side of an x-acto knife to keep yourself perpendicular to the flat bezel and just lightly score in a line in the console, moving the knife up and down to make sure you are in contact with the console.

If you are going to paint this thing anyway, you might try using a high contrast color, like in that case it would be black - get the bezel where you want it and lightly tack it in place with some hot glue or whatever on the inside making sure the outside edge is clean, and from maybe 12-18" away and directly above the bezel spray light little mists and let gravity carry the paint straight down. It will create a sort of shadow where your cut lines should be. I've used this relatively successfully when transferring bolt patterns or cutting outlines of complex parts that I just don't want to or can't trace quickly.

Pint · 12-18-2007, 09:42 PM

I looked into getting a new part to cut into but it was way to expensive. So I decided to fill in the gaps, sand and then spray. I covered the keyboard in masking tape and cut around the edge.

I then taped a pen to an allen key to use to mark an even distance on my dash around the keyboard

I now need to do some sanding.....Lots of it.

I have got hold of an airbrush to use for painting, but my question is what sort of paint should I use for a plastic surface?

I'm guesing that if I use the wrong type it will crack and chip easily?

Profozone · 12-19-2007, 11:53 AM

I think that if you prep and do a really good job of painting with rattle can paint, you can do a reasonably good job of painting something, but to me the stuff is just too fragile for anything that is touched. It rubs off way too easily.

What I have done in the past to get a nice fine texture is sand blast it. I don't have a sand blaster, but it wasn't that costly to have someone else do it. The cool thing is, there is no paint involved, just the natural color of the plastic.

Hope this helps.