Cutting old plastic

[denise 20352]

  I need to make rectangular holes in a speedometer back plate, to install a digital tach and speedometer.  This plate is clear plastic, laminated with a layer of black stuff that has the numbers on it in white.  It is backlighted in such a way that the numbers glow, and backplate is nearly invisible at night.

  What is a safe way to cut the hole?  Im guessing that this stuff is going to be really brittle, 30 years of age, and the stuff that they used is not very plastic in the first place.

  Any ideas, or should I just fabricate a new back plate from scratch?

  Why couldnt they just make them out of metal, like the Cadillacs?

thanks

-d

[Dave Leger CLC #19256]

Hi Denise,

    I have had some luck cutting things like that using a Dremel or flex-shaft with a thin cutting disk at high speed, and going slowly a bit at a time, so you dont overheat and melt the plastic.

Dave

[Bill Gauch]

If the black stuff is a "coating", I definitely wouldnt start out with a rotary tool. Actually, I am inclined to think that the rotary tool will likely vibrate the piece into oblivion. Personally, I would get a brand new blade in a utility knife and very slowly score a cut down into it. You should be able to cut the whole hole out with enough patience. If you can make some sort of template to guide you, you will get much better results. Also, if you can sandwich the piece flat onto a board with just the area of the template exposed, you will reduce the vibrations even further. If you do decide to use a powered approach, I would still score it initially and then drill a series of small holes just inside the line.

[denise 20352]

  If I decide to drill it, any recommendations on what speed and bit angle to use?  I would be using a press.

thanks

-d

[Bill Gauch]

I would definitely go slow. You want to shave the plastic not melt it. Also, make sure the piece is fully secure. You dont want the part to walk and snap the bit. I am unsure about the angle. A 135 deg. point may work better, but I am only guessing.

[Rhino 21150]

Use a bit for aluminum (135) and around 400 rpm, light pressure. Finish cutting the hole with a coping saw from Home Despot, around $8. Use the finest blade they make. Arrange some sort of support near the cut line. Scoring with the box cutter is the right idea. I score plastic laminates before cutting with a Skilsaw to minimize chipping. With arthritic hands this will be uncomfortable (experience).
There will be no NOS plastic pieces as they will age as badly as the original. Witness the dash piece on my La Salle.

[John #22631]

Denise,
You might try using one of the Dremmel or Roto-Zip bits in the press. Lock the press down where the bit is inside a predrilled hole and then you would be able to guide it around the area to be cut. This way you can go as slow as you want while maintaining control of the cutting process.
John

[denise]

  OK, now I know that Im going to make a template, lay it out on the material, and score it all around with a hobby knife.  Im  fairly sure that Im going to finish the hole with a swiss file set.  The steps in between, I have lots of things to try now.

  I do have an extra plate, in case I screw one up.  Ill post a picture of it all lit up when I get it done...I think its going to look cool.

-denise

[Bruce Reynolds # 18992]

Densie,

The best places to find the correct items to cut the plastic with is the Model Shops.

Then treat the piece as a delicate irreplaceable plastic Duesenberg, take time, and all will come clean.

Doing conversions makes one take time, and as mentioned before, dont move too fast as the plastic will simply weld itself back together behind the cutting tool.

Bruce,
The Tassie Devil(le),
60 CDV

[Fred Garfield 22310]

Having read all the suggestions, Im going to play the contrarian and advise you to forgot about this stupid piece of plastic.

Get yourself a nice piece of anodized aluminum plate at a machine supply or well-stocked hardware store. Scribe your cut lines and punch your divets for pilot holes with a scratch awl. Then you can use a fine metal cutting blade on a jig saw and regular speed bits to finish the job. Remove any burrs with a fine-tooth file and youre done.

[denise 20352]

  Well, I gave it about three hours of my time, and finally decided to accept it.  What takes forever is the final finishing of the holes.  I could have spent three days and still not had it perfect.

  What really sucked, though, is that I got the whole thing together only to find that the numbers on the gauges are not the same fracking size!  These were from a matched set, so it never would have occured to me that they wouldnt be.

  This is it, subject to having the holes trimmed of excess glue.  Does it look as bad to you as it does to me?  I was thinking maybe of putting the oil pressure gauge where the tach is, and moving the tach somewhere else, so that I would have the same sized numbers on both gauges.

http://www.americansoapbox.org/chrysler/digpanel.jpg TARGET=_blank>http://www.americansoapbox.org/chrysler/digpanel.jpg

-denise

[denise]

  Thats not a bad idea at all.  What I wanted was to have the original analog speedometer, with digital gauges behind tinted panels.  I would have to put the whole panel together to really see the effect, and maybe rearrange the gauges so that they have the same fracking sized numbers, but I dont think that it is going to look as good as I expected.  In fact, it looks pretty crappy.

http://www.americansoapbox.org/chrysler/digpanel.jpg TARGET=_blank>http://www.americansoapbox.org/chrysler/digpanel.jpg

  I really do like your idea.  My only problem is that I dont have the skills to put the analog numbers on there and make it look nice, and I really do want to keep the analog speedometer.  Im going to have to give this some more thought.

  Another thing that I should do is to get a good digital picture of the panel and try things in a paint program.

-denise

[denise 20352]

http://www.americansoapbox.org/chrysler/chrysler_panel.jpg TARGET=_blank>http://www.americansoapbox.org/chrysler/chrysler_panel.jpg

When I look at it this way (amateur artists rendition), it actually looks pretty good.  I may have to stare at this in various states of mind before I decide if I like it or not.

Anybody have an opinion?  You cant possibly hurt my feelings, so go for it.  Suggestions would be good.

-denise

[Bruce Reynolds # 18992]

Gday Densie,

What I would suggest is that you replace the whole plastic piece, reposition the electronic displays, one above the other, that is the larger one on top, then reconstruct the original dial on the replaced face with Letracet stick-on numerals and lines.

Or, with your computer, seeing as you are pretty good on such things, recreate the dial and print it out on clear plastic film, as though you were creating an overhead projector sheet, and stick that on the face.

This way, you could choose the colourings desired.

Another way to reproduce the face would be to scan the good face that you have, (but close your eyes first as the light is very bright, ha ha), and then computer manipulate the requirements, then print.

Bruce,
The Tassie Devil(le),
60 CDV

[denise]

  I wish I could reposition the displays, but there are only those two places in the panel where they can fit, unless I scrap the whole thing.  They have circuit boards and junk on the back of them.

  What I might do is to bring the whole panel out flush with the bezel.  That would require making a new panel, but it would give me a lot more flexibility in where to put the gauges.

  Now I have to go try to find a sheet of tinted acrylic plastic, and that isnt easy.  It should be, but it isnt.

-denise

[Rhino 21150]

To create a new panel from metal use Bruces idea and several others. Cut a blank piece of sheet metal to match your dial. Scan the face of the dial. When you have adjusted the positions of the numerals and other stuff to your taste, print on overhead projection film. Its pricey (about $4 per 8.5 X 11) but it also comes in colors. I think it works with laser printers only. This will slice nicely with a razor. If you warm it it should stick to the metal. Look in your yellow pages for sheet metal shops or metal fabrication. What you want may be a scrap for free. I get free rubber roof material in small pieces all the time to make custom body gaskets. ASK! Go around closing time, they are eager to help you leave.
Some day Ill show you how to do the same thing with the technology that came before LEDs, Nixie tubes. http://www.ominous-valve.com/images/bignix1.jpg TARGET=_blank>http://www.ominous-valve.com/images/bignix1.jpg

[Fred Garfield 22310]

I think there are online companies that do custom laser printing, etching, etc. on metal media using your template, layout, and specs. Some of them take small orders and dont charge too much.

Get your layout done with the appropriate software. Then make a mock-up or two out of hobby shop balsa, cardboard or whatever is convenient. Print your saved layout to scale with the background color you plan to use and paste it to the balsa or cardboard. When youre satisfied with it, contact one of these online companies.

Youre likely to get a very professional, durable result.

I recently used a similar web-based company to reverse-print some quality vinyl window decals in custom script. Cost was low and the result is excellent.

[denise 20352]

   I can see a dash with those vacuum tubes for displays, sort of a 3D thing with different sizes of tubes everywhere.  Maybe some external wires running around.  It might work in an old hearse.

   It looks like doing away with the analog speedo is a possibility, if for no more reason than that it makes noise.  Im still meditating on it.

-denise

[Fred Garfield 22310]

Tap Plastics has pulled my bacon out of the fire more than once.

http://www.tapplastics.com/ TARGET=_blank>http://www.tapplastics.com/

Their stores are in CA, OR and WA, but you can shop them online and they have an 800 number as well.

[denise 20352]

  I discovered something kind of cool last night.  One of the things that I tried was using reflective tint film on clear acrylic.  It makes a panel that looks like a mirror, and the numbers from the displays show up on it, like they were inside the glass.  I really liked the effect.  It looks kind of like a liquid crystal display, but of course you can put different colored lights in it.  Im going to experiment with this a little more.

-denise