Ever tried to cut a taillight lens?
 

Can it be done (cleanly)?

I have two broken w123 wagon tail lamps that I would like to make into one for the moment....

I once experimented, years ago, on one off a volvo using a dremel with a cutting wheel but it just melted the plastic into a mess.

This is extreme make over.
 

Never done it as I would try to pull one from a JY. I would expect it can be done with a good hack saw. Can you do a test cut, just cut away the broken part, but not the intended line and see how it looks? You probably need to sand the cut line then glue the 2 halves together. Interested to see the end result.

Good luck.

I have a variable speed Dremel and an adapter that allows to use of a HSS circular saw blade about 1 1/4" in diameter, I'd bet that such a tool could be slowed just enough to prevent it from melting the plastic but still rotate fast enough to reduce the chance of kickback that a slow turning blade does.

The saw adapter has a spring loaded guard so it's pretty easy to expose just enough blade to get the cut done without having a crasy spimming blade waiting to amputate a finger!

Agreed, the melting is caused by the tool spinning too fast or if it were a band saw, same idea but in a straight line.

i would be tempted to use a fine-toothed blade, maybe a masonry blade, on a chop or miter saw. leave enough room for the kerf to be melted and messed up and when you get the burned plastic piling up at the edge it can be wirebrushed off before gluing. paramount would be cutting a straight line, which is what i think would be hard to achieve using a dremel.

You would have a better chance of cutting a straight line with a Hack Saw using a fine tooth blade. Also you wouldn`t get the plastic hot.

I think Acitone would work to attach the two pieces together. that would depend on the type of plastic I would guess.

Charlie

I wonder if he is waiting on the free 300TD rear passenger tail light lense from me to attempt this procedure.

Melting plastic is due to high cutting speed. Cutting by hand with a fine tooth hacksaw would work, make the cut further towards the bad section allowing you to finish sand. ( A hack saw will give you a straight cut where the rotary tool won't )

The plastic is very brittle so don't put too much pressure on the cut.

If you were using the brown / black abrasive cuttings wheels, they cut by abrasion rather than cutting chips increasing heating.

those tiny saw blades work great for plastic. I use them routinely for interior trim modification, and even used them when repairing my Euro headlamps and for the HID retrofit in my Sebring. I use a generic set from Horror Fraught, and this leaves me with no safety guard, so I use only my cordless Dremel with them because it lacks the torque of the corded beast.

Also, anyone that thinks a straight line can't be cut with a Dremel just hasn't learned the trick, yet. I do it all the time, and consistently, at that. You have to keep your eye ahead of the cut, Kinda how you watch down the road as far as possible while driving. (Unless you just stare at the tail lights of the car in front of you, in which case you are probably doomed to never make a clean cut with a Dremel.)

Water jet will cut just about anything, initial cost is probably a bit high. If you go to home cheapo, you should find a coping saw set, about $10, will get you a coping saw and several coarse to fine blades. Mark your cut, take your time. Seen lots of failed attempts to bond to taillight plastic. Might scuff a spot and use JB weld or some epoxy. 5 minute epoxy will yellow, I don't know if polyester resin will.

at this point, just buy a good used one. Your time should be factored into the cost and if my time spent hacking a part together is more than buying a good used part or new is more then I just buy the new part.

Good grief... those lenses are turning into gold by this point. Upon my return to the US I may coordinate a group purchase at $50-$70 a piece brand new. If that does not drive the prices down, nothing will!

Teye-eye-eye-ime IS ON MY SIDE! Yes it is
 

I get the impression he has the time to invest. One could sink just as much time trying to hunt down a "good" used example. Unblemmed originals are AKA unicorns.

I second the fine toothed hacksaw followed with the sandpaper. Much more control over everything. It only takes one misplaced oversized tooth to catch the plastic and ruin your donor piece. Tool and piece in a fixed position to help with straight edges. Think meat slicer here. Belt sander on low speed sounds perfect. Can they be run slow enough?

MBZ123

Ever the devil's advocate =>

Has anyone tried using heat to cut these lenses before?

Something like this might work

Hot Knife thermocutters for all your plastic cutting needs

I would not want to try heat.

as for Joe (TheDon) comment, I have several broken lenses I have kept in case I needed at some point to cut them and build a new one. When I first started with the 123s twenty or so years ago, parts were pretty expensive, now they are still fairly plentiful but eventually all the cheap used parts will get used up and unless someone builds new parts the old ones will become more expensive and make the repair more worthwhile.

OTOH the OP may just enjoy the challenge of repairing a part.

When the Mrs. PT Cruiser was still pretty new we backed into another of our cars and broke the taillight lense into about 15 pieces. A new one or good used one was over $150 so I picked up the pieces and glued them all together, thinking before I sold it I'd just get a good used lense. eight years later we traded in the car sight unseen so the mended lense stayed. $100+ saved and some satisfying time spent mending something broken like Humpty Dumpty.