Drilling plexiglass

LloydGT40 · 03-06-06, 11:00 AM

Guys/ladies

Anybody have any issues drilling plexiglass. I just cracked my rear window. I drilled a small 1/8 hole arround the outside edges. When i went back to elarge the hole with a bigger bit it dug in and crack the window. Do lubricants help. I was using a very slow speed that might have attributed to drill binding up I read the technique was to start with a small hole and gradually increase to the size you want. My next thought was to find a dremel bit the right size and try that. I'm sure the window is not going to be cheap to replace. Don't want to break it a second time.

LLoyd

**J What?** · 03-06-06, 12:28 PM

Lloyd,
The problem with using a steel drill on plexiglass is it digs in and does exactly what it did to you. There are plexi drills which help. I don't know about a pilot hole but I would think it would dig in more if you use a pilot hole. If you don't use a plexi drill, use a dull drill of the size you need and don't drill it slowly. If you have to buy a new window, have it made out of scratch resistant Lexan (polycarbonate). It does not crack like plexi.
Bill

Rob · 03-06-06, 01:50 PM

Hey Lloyd,
Yep.. it's a tricky one. I have always done it in tedious steps of single bit size increments and found if drilling multiple holes dipping the bid in a cup of cold water helps to reduce gummning of the bit. Or if you have a third hand available, I guess pouring the water as a coolant would work too. I'm always working alone, so never tried it. Regarding speed, I found that spinning the bit as fast as possible without melting the plastic is the goal, reduced the chances of the bit biting to big a bite. Cup of water trick helps here too. Hope this helps.

Ron Earp · 03-06-06, 02:35 PM

Search and ye shall find...

http://www.gt40s.com/ubbthreads/show...0/page/1#13816

might help some, although a back glass window would solve the problem and are readily available.

R

LloydGT40 · 03-06-06, 03:56 PM

You guys are a wealth of knowledge.

I have already found a lexan place locally. He carries lexan but wasn't to keen on the scratch resistant variety. We means he knows his business or can't get it. Any experience between the two.
Many techneques for drilling. I just did all the wrong things.

Thanks

Lloyd

LloydGT40 · 03-06-06, 04:24 PM

Ron
Whats this about a glass back window. How is it held in.

who sells it. How do they handle the variation between cars.

My car is already painted.

Needless to say i'm very excited about a glass window.

LLoyd

Ron Earp · 03-06-06, 04:59 PM

LLoyd, every manufactuer uses glass windows now. They are simply held in with adhesive and a bonding trim strip, like any window, and work well. I imagine that they'll drop right in an ERA since there is little variation in the window size or flat plane of the rear clip. Paint doesn't matter much. Have a look around at CAV, RF, Tornado and other replica pictures, you'll find lots of glass back windows.

I'd give Fran a call at RCR and see if he can get you one or direct you to a source. I can see using plexiglas for an exact replica, but for normal use I want glass since it doesn't distort with heat or discolor with fuel and chemicals. It is hard enough to see out the back without adding wavy and opaque plastics in the mix.

LloydGT40 · 03-06-06, 05:51 PM

Thanks Ron

I feel exactly the same about the glass. I will do some investigating

LLoyd

Phil · 03-08-06, 12:19 AM

LLoyd
If you can find a Lawson rep near you they sell a really neat set of cutters that go from 5/16 to 3/4" in the small set. They look like minature hole saws, and as was mentioned they don't put side pressure on the bore but cut straight thru. I use them regularly on plexi and polycarbonate, and they will also easily cut all types of sheet including stainless with no problem.
Good luck
Phil [img]/ubbthreads/images/graemlins/twocents.gif[/img]

FRPGUY · 03-08-06, 07:56 AM

Phil,
Tell me more about Lawsen.

LloydGT40 · 03-08-06, 12:28 PM

Phill

I'm drilling #10 holes arround the perimeter. I've got a new plexi rear glass. I was discouraged on the glass. Issues were brought up about the thickness of the glass on top of the adhesive would sit too high.The car was not designed for glass. The chances of another car manufacter glass fitting mine are pretty remote

I have the old rear window which will look like swiss chesse when i'm done. I plan on practicing on the old piece before going at the new piece. I worked with the guy that builds the turn key units. He showed me his technique and claimed he has never broke a piece yet

thanks for the support

LLoyd

Rob · 03-08-06, 01:10 PM

So Lloyd,
What was "his" technique. Always looking to improve my process'

LloydGT40 · 03-08-06, 01:39 PM

Drill fast and put your finger under the hole light pressure. As you feel it start to come through go VERY light on the pressure (as it comes through it has a tendency to grab). Do not drill a pilot hole. Once all the holes are drilled in the plexi. Put the glass in the car. Put the drill through every hole and dimple the fiberglass. Then remove the glass and drill each dimple with appropriate size for the self taping screw. I also found if you counter sink the fiberglass it reduces chipping

Lloyd

Mike Dozier · 03-08-06, 01:54 PM

With my skill I'd drill through my finger 1st hole...
Good idea about drilling while the plexi is in place...
but have to make sure it doesn't shift while drilling.
I think'd first drill through at each corner and screw down.

MikeD

LloydGT40 · 03-08-06, 02:26 PM

Mike exactly on locking the window down with a couple of screws. I shim the window to center it and masking tape the window to the body. I like to work from the center out. Put one top center and one bottom center. Word of CAUTION the stripe is not always center of the car. Place center screws to line up with the stripe and don't pay attentention to the center of the window. Don't ask how I know. But it won't happen on new window.
Lg

Chris Simpson · 03-09-06, 03:39 PM

One of the main rules when drilling plexiglass without cracking it is to make sure it is not too cold. Ideally it should be at room temp so if your workshop is cold, a few careful passes with a heat gun prior to drilling would be advisable. Also drill the required diameter in one go - no stepping up in drill sizes unless you want the excitement of cracking noises as you drill the hole larger and larger. Finally drill the hole slightly oversize to allow for slight movement and in the surrounding fibreglass. Otherwise I endorse everything stated before except I would always drill slow (about 150 rpm) as the plexiglass tries to climb up the drill as it breaks through.

Hope this helps.

Chris

LloydGT40 · 03-11-06, 09:49 PM

update on drilling plexi. Spent a lot of time with the old window. I now know what works and what doesn't. First the finger under the glass works well as indicator of when its coming through. Neither slow or fast drill speeds work. As Chris stated there is a tendency to pull through as it comes through the backside. Highspeed makes it uncontrollable and can cause a break as it pulls through. Slow speed causes the bit to bite more.
Bottom line practice on a spare piece of plexi. Its better to break a scrap than a window. A lot has to do with the feel. Slow take your time. Mistakes happen when you're tired or in a rush.
Chris also makes a good point on temperature
Last thing is dimple with a small drill bit to mark the hole. THe larger drill bit has a tendency to drift. The dimple stops this.
good luck

LLoyd

Howard Jones · 03-12-06, 12:13 AM

Check out www.cyro.com. Everything you ever wanted to know about lexan. Go to Techknowlogy Center page.

Polycarbonate and lexan are the same material. Lexan is a brand name.

Mark Worthington · 03-13-06, 11:36 AM

When I installed my headlight and parking light covers, I used crystal clear packing tape on both sides of the edge and used high speed and very low pressure. It worked fairly well, but I stall managed to crack one of the parking lamp covers. I noted in the McMaster Carr catalog that they sell special drill bits for plexiglass and laminates; these bits have a sharper 60-degree tip angle which is supposed to reduce cracking.

Problem was that I couldn't get these bits in the exact size I was looking for. My wife gave me a Drill Doctor for my birthday present and one of the things it can do is sharpen a drill bit to a sharper or flatter angle than standard jobber bits. I still have to install my door windows so that's what I was going to do.

Are we all on the same page that a sharper drill bit is better for drilling lexan? It seems some of the posts I've read above suggest a flatter bit would be best.

LloydGT40 · 03-13-06, 12:19 PM

Another point to drilling plexi is the drill clutch. Put it in the lightest setting. As the bit starts to grab the clutch disengages.

Mark I found the same issue on plexi drill bits. Too small or too big not a lot of options. ERA ground a drill bit to use on plexi. Not much noticable difference. The best advice is tack a piece of scrap plexi of equal thickness and practice how close you can get to the edge with out breaking. Once you establish the feel it works great.

LLoyd