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Source for 100 deg C'sink for Plexiglass/Acrylic

Girraf

Well Known Member
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Need a recommendation/vendor for a no flute 100 degree countersink cutter to use on leading edge landing light lenses. I don't think I'm looking for the type with a single hole cutting edge. I'm having trouble sourcing what I need and of the threads I found on this subject, they have broken links to avery tools and sky geek.
 
Need a recommendation/vendor for a no flute 100 degree countersink cutter to use on leading edge landing light lenses. I don't think I'm looking for the type with a single hole cutting edge. I'm having trouble sourcing what I need and of the threads I found on this subject, they have broken links to avery tools and sky geek.

A traditional three flute counter sink cutter works great as long as you use low speed and light pressure. The key is that you avoid a lot of friction induced heat. Using a relatively new cutter that is real sharp is also beneficial.
 
A traditional three flute counter sink cutter works great as long as you use low speed and light pressure. The key is that you avoid a lot of friction induced heat. Using a relatively new cutter that is real sharp is also beneficial.

The Authority Hath spoken. I'll give my three flute a chance to show me what it can do. May pick up a fresh one too to better my chances of success.
 
Or one of these - must be plenty of suppliers in the US
https://www.permagrit.com/large-countersink-100-degree-no-nipple/

I just went through the same predicament. After searching through the normal channels, I wound up ordering the entire countersink kit directly from PermaGrit in England. Shipping took about a week, the kit contains a number of different sized countersinks as well as a pilotless version, all of which should come in handy when working on the fiberglass parts as well.

https://www.permagrit.com/kt2/
 
Success!

I happened to find a new-ish 3 flute #6 countersink cutter among my tools. I cleaned up the backside of each hole and then using a hand deburring tool with light pressure and some boelube got some great looking countersinks!
 
Take a hard look using a 10x magnifier. A lot of the time, countersunk plexiglass which looks fine to the naked eye is a mess of stress risers under magnification.

Agree with grinding the CS for final finish. Light touch please.

BTW, I was able to discourage edge cracking on highly bent Lexan by sanding the cut edge, then wiping the edge with a Q-Tip soaked in methylene chloride, aka dichloromethane. Melts away all the potential stress risers, leaves an edge as smooth as the faces. Use only in a well ventilated place.
 
Despite all my care in cutting the countersinks, I still developed a crack in one hole after installing it. I was installing the 6 lens screws gently with a hand screwdriver and got them all snugged up. Everything looked great. When I removed the lens after checking for fit, I noticed one hole had cracked. I took some scotch brite and rubbed all 6 countersinks in hopes of trying to further polish them which is why they now look more opaque than clear. The crack is highlighted among some superficial scratches from my polishing attempt.

I'm a bit lost on how to prevent it from happening again. Should I be polishing the countersinks with emory cloth or SB after cutting them in an attempt to really smooth them out? The chemical treatment with methylene chloride is a new one to me. Not even sure where to buy that.

The permagrit tools seemed like a neat idea but pretty costly for this small job. I'd like to hear more about why Scott doesn't recommend them.
 

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Stuff

The comment about methylene chloride got me curious and I have some paint stripper that is 87% of said chemical, so tried it on a piece of scrap plexi. The result? I sure ain't gonna be getting that stuff anywhere near the canopy! (It turned the plexi surface opaque)

As for Scott's comment about the Permagrit, I'd say the reason it's not suitable for plexi is that it will leave a rough finish, whereas plexi likes smoooth as in 2000 grit and I'm guessing the Permagrit is nowhere near that fine.
 
The permagrit tools seemed like a neat idea but pretty costly for this small job. I'd like to hear more about why Scott doesn't recommend them.

Look closely at the surface texture of a permagrit counter sink. To my eye it looks about the same as 80 grit sandpaper. Far too course for the finish that we desire on cut acrylic edges.
 
3 flute countersink bit with pilot nipple. Back up the plexi with a piece of wood drilled with a pilot hole. Go light & slow as mentioned before & this job will be done in 3 minutes (quicker than it took to tap out this note)
 
Look closely at the surface texture of a permagrit counter sink. To my eye it looks about the same as 80 grit sandpaper. Far too course for the finish that we desire on cut acrylic edges.

Thanks for checking back Scott. Your comments are appreciated. I'll stick with my 3 flute cutter for now. Maybe I'll come back and try to polish with some very high grit (2-3k) paper and hope for better results on the other lens.
 
Aircraft Tool has single flute 100 deg countersinks, I got two and it was very easy to make clean CS in plexiglass.

https://aircraft-tool.com/shop/search.aspx?qid=6391&page=3

The link appears broken, but they have several options for 100-degree zero flute countersinks. Sadly no 120-degree options.

Search for "zero"
https://aircraft-tool.com/shop/search.aspx?keyword=zero

Or just browse through the "cutters" category
https://aircraft-tool.com/shop/search.aspx?CATEGORY=CUTTERS
 
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