Rick6a
Well Known Member
I have a confession to make. As I read through many of the comments submitted by builders frustrated by causing a crack when countersinking Plexiglas, I simply did not make a crucial connection. Every time I read one of these posts, I ask myself...."Why do folks continue to insist on using a regular countersinking bit?" "That's crazy." All I know is I have worked with a lot of Plexiglas over the years and as far as RV's are concerned, have drilled and installed two canopies with nary a crack. I never obsessed over causing a crack or otherwise gave it much thought. To me the canopy is just another sub-assembly, no better, no worse than any other in the assembly process. So I hope you understand that when I see photographs of builder induced cracks in the 'glass caused by an inadvertent momentary side load on the countersink cutter pilot, I tend to consider that as a wholly unnecessary consequence of using an "improper" tool. I further confess that when it came to drilling the many holes through the canopy, I felt no need to refer to the written instructions feeling quite familiar and comfortable with Plexiglas' characteristics. Heck, when I installed the (slider) windshield portion on my -6A in the unheated hangar, I felt comfortable enough to drill and countersink through the 'glass and into the rollbar amid an ambient temperature of 65? although I certainly do not recommend anyone try it.
But after reading so many comments, some sounding rather huffy that so-called "experts" thought they knew better, I felt compelled to dig out the good old RV-6A builder's manual for review. Sure enough, I found what I was looking for and here is a direct quote from Van's: "By countersinking before enlarging the holes, you can use a countersinking bit with a standard pilot."
I see now. Certainly, I am not going to challenge the wisdom of Van's advice so I thought I would submit this post merely in the spirit of a "builders tip."
May I humbly submit an alternative way to easily countersink Plexiglas with very little risk of cracking the 'glass REGARDLESS of how large or small the hole is? I use a 100? no flute countersink bit, a type of countersinking bit sometimes used in the production environment to countersink graphite composite skins. Because there are no flutes, the countersink it produces will not chatter and is high quality. In composite work, the use of a standard 3 flute sheet metal countersinking bit is verboten. I cannot recall where I specifically learned to use this type bit on Plexiglas, so I guess I found out on my own. A no flute countersink bit works just as well on Plexiglas. The only way you might crack the Plexiglas using this type of countersinking bit is if you haul off and throw it!
http://www.skygeek.com/ats-zfc01.html
This type bit does not cost very much and also serves double duty. Perfectly suited for deburring holes, I routinely chuck it in a cordless drill and have at it. Let me suggest you buy one one of these inexpensive bits to use as a deburring tool. Then take a scrap piece of Plexiglas and drill several different size holes through it. Finally, use this bit to countersink those various sized holes. I do not think you will be disappointed. Nevertheless, good, bad, or indifferent, be sure to share your own findings with us.
One thing is clear to me. In a VAF poll "Has Your Canopy Cracked?," over 35% of the 211 respondents reported that their canopy had at some point, cracked. Over ONE THIRD of RV builders who participated in the poll have already experienced a significant problem with the canopy 'glass cracking. Those stark numbers speak for themselves. For sure, the poll only accounts for a tiny number of all RV's out there. Even though two thirds of the respondents reported no problems, if those percentages are anywhere near representative, that alone speaks to underlying quality control issues that beg to be addressed. Countersinking Plexiglas need not be a contributing factor in the overall number of canopy cracks that do seem to occur.
http://www.vansairforce.com/community/showthread.php?t=23509&highlight=poll+canopy
But after reading so many comments, some sounding rather huffy that so-called "experts" thought they knew better, I felt compelled to dig out the good old RV-6A builder's manual for review. Sure enough, I found what I was looking for and here is a direct quote from Van's: "By countersinking before enlarging the holes, you can use a countersinking bit with a standard pilot."
I see now. Certainly, I am not going to challenge the wisdom of Van's advice so I thought I would submit this post merely in the spirit of a "builders tip."
May I humbly submit an alternative way to easily countersink Plexiglas with very little risk of cracking the 'glass REGARDLESS of how large or small the hole is? I use a 100? no flute countersink bit, a type of countersinking bit sometimes used in the production environment to countersink graphite composite skins. Because there are no flutes, the countersink it produces will not chatter and is high quality. In composite work, the use of a standard 3 flute sheet metal countersinking bit is verboten. I cannot recall where I specifically learned to use this type bit on Plexiglas, so I guess I found out on my own. A no flute countersink bit works just as well on Plexiglas. The only way you might crack the Plexiglas using this type of countersinking bit is if you haul off and throw it!
http://www.skygeek.com/ats-zfc01.html
This type bit does not cost very much and also serves double duty. Perfectly suited for deburring holes, I routinely chuck it in a cordless drill and have at it. Let me suggest you buy one one of these inexpensive bits to use as a deburring tool. Then take a scrap piece of Plexiglas and drill several different size holes through it. Finally, use this bit to countersink those various sized holes. I do not think you will be disappointed. Nevertheless, good, bad, or indifferent, be sure to share your own findings with us.
One thing is clear to me. In a VAF poll "Has Your Canopy Cracked?," over 35% of the 211 respondents reported that their canopy had at some point, cracked. Over ONE THIRD of RV builders who participated in the poll have already experienced a significant problem with the canopy 'glass cracking. Those stark numbers speak for themselves. For sure, the poll only accounts for a tiny number of all RV's out there. Even though two thirds of the respondents reported no problems, if those percentages are anywhere near representative, that alone speaks to underlying quality control issues that beg to be addressed. Countersinking Plexiglas need not be a contributing factor in the overall number of canopy cracks that do seem to occur.
http://www.vansairforce.com/community/showthread.php?t=23509&highlight=poll+canopy
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