Drilling Plexiglass

[Elmo Rodge]

Rex, that would probably be PETG. I went to Aircraft Windshield in Los Alamitos, California to have my canopy formed. That is what they suggested to me. It has the basic properties of Lexan with better optical clarity. I got excellent service from them too. To save me an extra trip down from Utah, they did the job over the weekend. I are happy.   Wayno

[4-barrel Mike]

Wayno:

   How's about a picture or two?  It's been a LONG while since you've shown us anything.

Mike

[Elmo Rodge]

Mike I'll try to take some pictures this week.  Wayno

[interested bystander]

Have not have difficulty drilling and countersinking Lexan personally -haven't done anything like that since last Tuesday. Drilling  using a plastic drill -extreme sharp point - available at Home Depot -and Cleco-ing completely and, as yrs truly has done for years, and advocated above, then  REDRILLING for some "breathing" room.

 I think it's important and seems to work.

Forming's out of my league, but what impressed the daylights out of me was the Buckeye Bullet fuel cell car's w/s and the way the clever young LADY aerodynamicist integrated it into the bodywork.

Looked optically correct from outside!

[Elmo Rodge]

I'm going to try a "Dreamer" on a piece of scrap. That's a drill/reamer. Straight flutes with pretty good lead. I'll try it on PETG And plexiglass. Maybe tomorrow. Wayno

[saltfever]

Rex and others: I need to form my lexan windshield. I was going to make a insulated hot box heated by a two burner propane heater. I would place my glass windshield inside, supported by wood ribs, contour-cut to rest exactly against the inside glass shape. I figure if heated slowly the glass should be able to get to the proper temp (see below). Then lay the Lexan on top of it and let it slowly take a set against the glass. It will be done outside because of fumes. Lexan drooping temperature is 140-150^o C according to the data sheet in the link.
http://www.theplasticshop.co.uk/plastic_technical_data_sheets/lexan_polycarbonate_9030_technical_properties_data_sheet.pdf

Do you see any problems with this approach?  TIA

[Dean Los Angeles]

Is this installation ok?



When you are forming your windshield don't forget to flame polish or hand polish the edges. It looks MUCH nicer if the edge is exposed.

[Rex Schimmer]

Saltfever,
Let us know how your forming works, a friend of mine has a pile of lexan windsheilds for his car that were done by several "professional" shops and if you look thru any of them you get sea sick. If you look at 90 deg. at them they seem clear but when you look at the angle that the driver would look they are terrible.

Rex

[Elmo Rodge]

I went to great effort to make my mold smooth. The first thing they did was rough it up with 40 grit so the felt wouldn't slide around.  Makes sense now. Wayno

[roygoodwin]

Here's something on thermoforming polycarbonate that I haven't seen mentioned.  These are some quotes from the manufacturer's (MAKROLON) documentation because the document is too large to attach.   I expect that this would be generally true for all polycarbonates, regardless of brand.

"MAKROLON Polycarbonate Sheet must be dried before thermoforming because polycarbonate absorbs moisture at a high rate. Trapped moisture forms vapor above 250°F, and the vapor expansion creates bubbles in the sheet."  & "Sheets of MAKROLON Polycarbonate sheet should be placed in a dehumidifying air circulating oven for predrying. Temperature should be 250°F and monitored with controls.
Recommended predrying time periods are shown below."

DRYING TIME (HOURS)
THICKNESS         250°F    180°F
.093˝                4            8
.118˝                 6           14
.150˝                 8           20
.177˝                12          30
.236                  24          50

Hope this will help someone

roy

[wobblywalrus]

Try clamping the plexiglass tightly between two hardwood wood scraps and drilling through the sandwich.  Go easy on the pressure when you are going through the plastic.

[saltfever]

That is good information about "drying" the Lexan. I wouldn't have thought of it but Lexan certainly absorbs water. Now I have to add even more complexity to the oven to regulate temps . . . bummer!

Agree, Rex. I imagine distortion is a problem for Lexan no matter what I do. It doesn't have very good optical charasterstics unless it is the high-index eye glass variety. Can you imagine the cost of a sheet of optical grade! I was hoping the distortion-free surface of a standard glass windshield would transfer that characteristic to the Lexan if allowed to droop long enough onto the glass. I don't know if it will work. Also, temperature and "droop-time" may be critical.

Received rule book today. What thickness should the Lexan be for 200mph?  No mention of thickness in rule book.

[redrock_2003]

   In the past I have built many dragster and funny car windshields out of lexan (3/16" - 1/4" thick) and for the most part not had any problems drilling them. I do have a couple of tips that I would like to leave with you.

Use a sharp bit
Let the bit do the cutting (don't push to hard)
Drill the holes slightly larger than the screws to prevent stress cracks
Leave ample tear out (the distance between the center of the holes and the edge of the lexan) to reduce the chance of the hole cracking out under stress.
 
Just my 2 cents
Dave

[Jeff Brock]

Great info guys , Thanks .

What about recommended thickness for LSR ?
And is tint recommended ?
My opening is about 10"x 62" . I have 1/4" Lexan lined up , but if I could use 1/8th safely , it would be much easier.

[jimmy six]

I used 1/8" on my roadster. I made a pattern out of thin cardbord holes and all. Laid the pattern on the poly and drilled the holes making sure all holes were at least 2" fron any side. After the holes were drilled I cut out the pattern/windshield out. Even poly can split and crack when close to an edge...I also believe "Plexiglass" is specifically forbidden in our rulebook.....At least it once was.....JD