MGA Off Season Folly & Misadventure
11-20-2016, 09:40 AM
#1
Thread Starter
MGA Off Season Folly & Misadventure
Episode 1 – Bending Polycarbonate - Lexan & Makrolon
My cockpit style windscreen needed some tender love to address serious cracks that had developed over the last two seasons. The windscreen was made of 1/8” thick material – clear plastic.
Research on the Web revealed that a polycarbonate replacement would be the material of choice. It also revealed that this stuff was expensive. Moreover, polycarbonate has a tendency to yellow with sun exposure and to scratch, and given my application, I was worried about these issues. It seemed like Lexan Excell D, or Lexan XL-10 were my best choices, but I couldn’t find these materials readily available in small pieces. Eventually, I elected to use Makrolon AR. “AR” stands for abrasion resistant. I ordered my piece from TAP Plastics. It was about $40 with shipping.
The Makrolon was bendable, but seemed too stiff to use for the windscreen. The Internet has many articles and videos about how to bend polycarbonate with heat, but all seemed to relate to straight 90 degree bends. Some home gamers used a heat gun or hair dryer, but I didn’t think that would work for me. I felt that I actually needed to bend my piece in two planes. After scratching my head for a few days, it seemed like the oven would be my weapon of choice.
Afraid to rip apart the windscreen, I attempted to make a template for cutting my piece. With rubber cement, I glued some paper to the inside surface and then marked my lines and cut the template. But when I laid it on the outside of the windscreen, it seemed too small. So I followed the same process – rubber cement and paper – on the outside and made a second template. When I laid them over each other, I came up with a new form!
Initially I used this combined template to mark out my cut on the Makrolon.
I planned to use a jigsaw to cut my piece and I wanted a sharp blade. Went to Home Depot and picked up a 36 teeth per inch metal cutting jigsaw blade. While there, I also picked up a small 6” x 8” piece of Lexan to use as a test mule.
My initial efforts were promising. The saw blade worked fine and left a smooth cut on a 2” strip of Lexan. I heated up the oven and worked my way up in the temperature range. At about 325 degrees, the Lexan became pliable, but still too stiff. But at about 350 degrees it was easily bent. I pulled it out of the oven and draped it over the side of my wife’s biggest pot covered with a cotton towel and ended up with this.
Very promising indeed!
I was still uncomfortable with my template, and decided that it was time to dismantle my windscreen. This was riveted together and required that I drill out the rivets. Once apart, I made a new template using the rubber cement and paper technique.
I laid out the new template on my piece of Makrolon. Because the bottom and the top were so similar in shape, I left a “tab” along the bottom surface that I would later remove once the piece was shaped.
In my search for a bending form, I found a stovepipe thimble that I had ripped off my roof decades ago. It was a little rusty, so I put a protective piece of paper on it and marked the location where I would bend my piece. I set this up in the kitchen next to the oven.
Now it was do or die. I felt I had only one shot to form my piece, so I experimented some more with the Lexan and with the scrap piece of the Makrolon. I wasn’t sure if the Makrolon would react the same way as the Lexan since it was “abrasion resistant”. I would lay my piece on an upside down cookie sheet for the heating process. .
Of course, it was important to remove the protective sheeting on the Makrolon before heating!
Experimenting, I determined that heating to 325 degrees for more than 5 to 7 minutes simply wasn’t enough for the polycarbonate pieces to become pliable. Heating to 375 degrees for the same amount of time caused internal bubbles to form and ruined the piece.
With a big caveat, a preheated oven at 350 degrees seemed to be the sweet spot.
Experimenting with smaller pieces cut from the Lexan and Makrolon, however, revealed that 5 minutes at 350 degrees was too much, causing the internal bubbles and ruining the piece. But at 3 minutes, the pieces became sufficiently pliable to bend over my form.
I took the decision to heat my windscreen piece to 350 degrees for 3 minutes. Aargh! That didn’t work. When I pulled it out of the oven, the piece was still too stiff to bend. I let it cool down for about 10 minutes and started over.
This time I heated to 350 degrees for 4 minutes, all the time worried that bubbles would form and ruin my piece. But at four minutes, the piece was pliable enough to drape over my form with some pressure from my hands (I draped a cotton towel on my form and flipped up the excess over the hot plastic as it cooled.) This is the result.
I returned the protective sheeting back onto the surface of the Makrolon and I now needed to do some drilling along the bottom and some sanding of the top edge.
Here you can see the little tab that I left to identify the bottom.
I cut that piece off and remarked my piece for fitting. I lined the piece up with the front piece of the aluminium frame and started drilling my holes from the outside in, one at a time.
Once I had a few holes drilled, I lined up the rear piece of the frame (which didn’t fit so well).
Once the pieces were all test fitted, I scribed a line so I could cut off the protective paper from between the aluminium.
Then I put back together. I was going to use flush rivets like originally attached, but when I went to check my “supply”, all of my rivets were too short. So for now, I just screwed back together with 10-32 1/2 “ machine screws, using blue Loctite on the nuts.
Once everything was back together, I pulled off the protective paper to reveal the final product.
My cockpit style windscreen needed some tender love to address serious cracks that had developed over the last two seasons. The windscreen was made of 1/8” thick material – clear plastic.
Research on the Web revealed that a polycarbonate replacement would be the material of choice. It also revealed that this stuff was expensive. Moreover, polycarbonate has a tendency to yellow with sun exposure and to scratch, and given my application, I was worried about these issues. It seemed like Lexan Excell D, or Lexan XL-10 were my best choices, but I couldn’t find these materials readily available in small pieces. Eventually, I elected to use Makrolon AR. “AR” stands for abrasion resistant. I ordered my piece from TAP Plastics. It was about $40 with shipping.
The Makrolon was bendable, but seemed too stiff to use for the windscreen. The Internet has many articles and videos about how to bend polycarbonate with heat, but all seemed to relate to straight 90 degree bends. Some home gamers used a heat gun or hair dryer, but I didn’t think that would work for me. I felt that I actually needed to bend my piece in two planes. After scratching my head for a few days, it seemed like the oven would be my weapon of choice.
Afraid to rip apart the windscreen, I attempted to make a template for cutting my piece. With rubber cement, I glued some paper to the inside surface and then marked my lines and cut the template. But when I laid it on the outside of the windscreen, it seemed too small. So I followed the same process – rubber cement and paper – on the outside and made a second template. When I laid them over each other, I came up with a new form!
Initially I used this combined template to mark out my cut on the Makrolon.
I planned to use a jigsaw to cut my piece and I wanted a sharp blade. Went to Home Depot and picked up a 36 teeth per inch metal cutting jigsaw blade. While there, I also picked up a small 6” x 8” piece of Lexan to use as a test mule.
My initial efforts were promising. The saw blade worked fine and left a smooth cut on a 2” strip of Lexan. I heated up the oven and worked my way up in the temperature range. At about 325 degrees, the Lexan became pliable, but still too stiff. But at about 350 degrees it was easily bent. I pulled it out of the oven and draped it over the side of my wife’s biggest pot covered with a cotton towel and ended up with this.
Very promising indeed!
I was still uncomfortable with my template, and decided that it was time to dismantle my windscreen. This was riveted together and required that I drill out the rivets. Once apart, I made a new template using the rubber cement and paper technique.
I laid out the new template on my piece of Makrolon. Because the bottom and the top were so similar in shape, I left a “tab” along the bottom surface that I would later remove once the piece was shaped.
In my search for a bending form, I found a stovepipe thimble that I had ripped off my roof decades ago. It was a little rusty, so I put a protective piece of paper on it and marked the location where I would bend my piece. I set this up in the kitchen next to the oven.
Now it was do or die. I felt I had only one shot to form my piece, so I experimented some more with the Lexan and with the scrap piece of the Makrolon. I wasn’t sure if the Makrolon would react the same way as the Lexan since it was “abrasion resistant”. I would lay my piece on an upside down cookie sheet for the heating process. .
Of course, it was important to remove the protective sheeting on the Makrolon before heating!
Experimenting, I determined that heating to 325 degrees for more than 5 to 7 minutes simply wasn’t enough for the polycarbonate pieces to become pliable. Heating to 375 degrees for the same amount of time caused internal bubbles to form and ruined the piece.
With a big caveat, a preheated oven at 350 degrees seemed to be the sweet spot.
Experimenting with smaller pieces cut from the Lexan and Makrolon, however, revealed that 5 minutes at 350 degrees was too much, causing the internal bubbles and ruining the piece. But at 3 minutes, the pieces became sufficiently pliable to bend over my form.
I took the decision to heat my windscreen piece to 350 degrees for 3 minutes. Aargh! That didn’t work. When I pulled it out of the oven, the piece was still too stiff to bend. I let it cool down for about 10 minutes and started over.
This time I heated to 350 degrees for 4 minutes, all the time worried that bubbles would form and ruin my piece. But at four minutes, the piece was pliable enough to drape over my form with some pressure from my hands (I draped a cotton towel on my form and flipped up the excess over the hot plastic as it cooled.) This is the result.
I returned the protective sheeting back onto the surface of the Makrolon and I now needed to do some drilling along the bottom and some sanding of the top edge.
Here you can see the little tab that I left to identify the bottom.
I cut that piece off and remarked my piece for fitting. I lined the piece up with the front piece of the aluminium frame and started drilling my holes from the outside in, one at a time.
Once I had a few holes drilled, I lined up the rear piece of the frame (which didn’t fit so well).
Once the pieces were all test fitted, I scribed a line so I could cut off the protective paper from between the aluminium.
Then I put back together. I was going to use flush rivets like originally attached, but when I went to check my “supply”, all of my rivets were too short. So for now, I just screwed back together with 10-32 1/2 “ machine screws, using blue Loctite on the nuts.
Once everything was back together, I pulled off the protective paper to reveal the final product.
Last edited by blueosprey90; 11-20-2016 at 09:48 AM.
11-22-2016, 05:37 PM
#6
Nice job! When I made one for my TR3 I used a helmet face shield. They are already curved and are polycarbonate. It is not nearly as tall or wide as your windscreen, but I did not need it any specific size.
11-23-2016, 05:04 AM
#7
Community Organizer
Impressive.
Trending Topics
11-23-2016, 04:10 PM
#8
Thread Starter
Random thoughts!
NASA-NE schedule posted by freq on Track Days: What a looser am I? I only did two HPDE events this year. (I bought insurance for three!)
Aashish bumped himself to Advanced and is talking "instructor". Leaving his old friend behind in Intermediate!
I wonder if British John still has his Corvette badged as an S.
Looks like the VSCCA is curtailing the vintage racing. Too many old guys! Too many old cars! Too expensive track rental!
I need to get my act together with some other clubs - or else hill climbs. Our friend Eric (Aashish & me), with the '64 Formcar /a/k/a Darth Vader, had a brake failure and crashed into a tree at the Hershey Hill Climb. He too thought he was going to die!
Nancy' is planning a Volga River cruise in August. I told her the trade off was racing down south in late fall. Summit Point, Road Atlanta - and what's that track outside of Savannah?
Third Saturday of July - Solidarity Drive - that's the plan. Come Hell or High water this year! We won't be diverted by Shiv's grandiose plans!
Got some MGA parts (mostly unwanted) last weekend, including another engine block. Might start a race engine. Ordered parts to build an engine mount today. Shipping more expensive that the parts.
Need to learn to weld!
Heading to Lake Placid for Thanksgiving! Up there I can't do much Black Friday shopping! Hope all have a good holiday.
NASA-NE schedule posted by freq on Track Days: What a looser am I? I only did two HPDE events this year. (I bought insurance for three!)
Aashish bumped himself to Advanced and is talking "instructor". Leaving his old friend behind in Intermediate!
I wonder if British John still has his Corvette badged as an S.
Looks like the VSCCA is curtailing the vintage racing. Too many old guys! Too many old cars! Too expensive track rental!
I need to get my act together with some other clubs - or else hill climbs. Our friend Eric (Aashish & me), with the '64 Formcar /a/k/a Darth Vader, had a brake failure and crashed into a tree at the Hershey Hill Climb. He too thought he was going to die!
Nancy' is planning a Volga River cruise in August. I told her the trade off was racing down south in late fall. Summit Point, Road Atlanta - and what's that track outside of Savannah?
Third Saturday of July - Solidarity Drive - that's the plan. Come Hell or High water this year! We won't be diverted by Shiv's grandiose plans!
Got some MGA parts (mostly unwanted) last weekend, including another engine block. Might start a race engine. Ordered parts to build an engine mount today. Shipping more expensive that the parts.
Need to learn to weld!
Heading to Lake Placid for Thanksgiving! Up there I can't do much Black Friday shopping! Hope all have a good holiday.
11-23-2016, 05:14 PM
#10
Former Moderator
Random thoughts!
NASA-NE schedule posted by freq on Track Days: What a looser am I? I only did two HPDE events this year. (I bought insurance for three!)
Aashish bumped himself to Advanced and is talking "instructor". Leaving his old friend behind in Intermediate!
I wonder if British John still has his Corvette badged as an S.
Looks like the VSCCA is curtailing the vintage racing. Too many old guys! Too many old cars! Too expensive track rental!
I need to get my act together with some other clubs - or else hill climbs. Our friend Eric (Aashish & me), with the '64 Formcar /a/k/a Darth Vader, had a brake failure and crashed into a tree at the Hershey Hill Climb. He too thought he was going to die!
Nancy' is planning a Volga River cruise in August. I told her the trade off was racing down south in late fall. Summit Point, Road Atlanta - and what's that track outside of Savannah?
Third Saturday of July - Solidarity Drive - that's the plan. Come Hell or High water this year! We won't be diverted by Shiv's grandiose plans!
Got some MGA parts (mostly unwanted) last weekend, including another engine block. Might start a race engine. Ordered parts to build an engine mount today. Shipping more expensive that the parts.
Need to learn to weld!
Heading to Lake Placid for Thanksgiving! Up there I can't do much Black Friday shopping! Hope all have a good holiday.
NASA-NE schedule posted by freq on Track Days: What a looser am I? I only did two HPDE events this year. (I bought insurance for three!)
Aashish bumped himself to Advanced and is talking "instructor". Leaving his old friend behind in Intermediate!
I wonder if British John still has his Corvette badged as an S.
Looks like the VSCCA is curtailing the vintage racing. Too many old guys! Too many old cars! Too expensive track rental!
I need to get my act together with some other clubs - or else hill climbs. Our friend Eric (Aashish & me), with the '64 Formcar /a/k/a Darth Vader, had a brake failure and crashed into a tree at the Hershey Hill Climb. He too thought he was going to die!
Nancy' is planning a Volga River cruise in August. I told her the trade off was racing down south in late fall. Summit Point, Road Atlanta - and what's that track outside of Savannah?
Third Saturday of July - Solidarity Drive - that's the plan. Come Hell or High water this year! We won't be diverted by Shiv's grandiose plans!
Got some MGA parts (mostly unwanted) last weekend, including another engine block. Might start a race engine. Ordered parts to build an engine mount today. Shipping more expensive that the parts.
Need to learn to weld!
Heading to Lake Placid for Thanksgiving! Up there I can't do much Black Friday shopping! Hope all have a good holiday.
We can build the BRZ and share it at events. Think about it. Maybe do the One Lap next year. We can loop Shiv in and go as Swami Racing Team
I haven't left you behind. You've just had a busy schedule this season. Too bad about Eric's car but I am glad he is fine. Since it is a Vee I am hoping he will be able to put it back together.
I'm not sure how 'advanced' I am, but I'd say we are at the same level and you have wheel to wheel experience that I don't. As for instructing, its been a back of the mind thing. But coaching teens or autocross newbies is not the same as being in the right seat at triple-digit speeds.