CriCri MC-15 in NZ

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MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
I finished up skimming the forms with filler a couple of days ago, the photo comes out quite dark since its near the end of the day and it's winter here. I 'could' put more lighting in my workshop but it's easier to just go home when it gets cold and dark.
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I want to get on with the finish pass on these but first I have another job to do.

The cheap 50mm Ebay roundnose cutters I have are quite out of round (the left one in the picture below) so I decided to make a machine to sharpen them to the correct profile. The cutter on the right is ground to cut a true half circle, the left cutter cuts closer to an elliptical cut. It also has a very flat section and no back rake near the center of the cutter.
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I cut a round circle of acrylic and then used the freshly re-ground cutter to mill a slot through some foam to check the fit. Looks much much better.
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And here is the machine I made to regrind the cutters. It uses an old treadmill motor and variable speed with a 600grit diamond wheel. I made a custom fixture for holding the cutter from scrap acrylic. I made use of a couple of ice cream containers, one to keep any water off the electrics and the second to hold a small amount of water to lubricate the diamond wheel. A small piece of seat foam runs against the diamond wheel to transfer the water to it (seems to work ok and if I fill the water up too much it really flings everywhere)
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The acrylic mechanism for grinding the cutter sits in a slot on the plywood base and is held in place to do the cutting and manually moved around against the wheel the grind the cutting edge.
I have two main adjustments, I can slide the whole mechanism closer to the diamond wheel to change the cutter nose radius (A machine screw acts as a stop to set the outside diameter) and another machine screw to feed the cutter forward in the pivoting block, setting how much is ground from the nose of the cutter. The tricky part was the the cutting edge isn't mounted completely parallel to the shank of the tool and if I clamped the shank in the fixture the cutting edge would be out of round after grinding. To compensate I had to make a brass support that keeps the cutting edge at the same height as the cutter is ground, the cutter rotates around its shank a small amount as the fixture is rotated and gives a true spherical cut to the finished cutting edge. Quite fiddly to use and would really be best made from something like cast iron due the flex in plywood :( but to get a couple of cutters sorted it is no problem if a consistent touch is used. Not really a machine for the ham fisted.
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Hopefully the explanation makes some sense!

I CNC cut the foam for the forms with the cutters as I purchased them since the variation from round doesn't matter quite as much when everything is getting filled over but now I have a true ball nose cutter I can make some progress on the finishing.
 

JonMiller284

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Apr 5, 2021
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15
Shannon! Your progress is Looking good! I hope you don’t mind me sharing a couple pictures here. My rudder is 75% done! So far I’m pretty happy with the way it’s turning out!
 

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MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
Shannon! Your progress is Looking good! I hope you don’t mind me sharing a couple pictures here. My rudder is 75% done! So far I’m pretty happy with the way it’s turning out!
No problem at all! Good to see you moving along. A few more thousand parts to go and you will have them all made ready to assemble :cool: :p
Keep us updated on your progress.
 

MadRocketScientist

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Used the CNC to finish cut one of the canopy form halves today. Came out so much better than the previous canopy form that I made. The lead in on the flanges looks really neat too.
There were a few cosmetic pinholes and small air bubbles that need filling so I will fix those before sanding out the tool marks.
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MadRocketScientist

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Stuck the two form halves together with even more filler. One half had some distortion along the join line so the large sash clamp was used to tweak it into place. I mixed up a slow batch of filler and carefully made sure that the join stayed aligned until the filler set enough that things no longer moved. Ended up with a very slight misalignment but it sanded out with no issues.
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I sanded the join smooth, using light coats of matte spray paint as a sanding guide. I will sand the radius at each end after the final sanding, since their shape isn't all that critical.
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As I now had the form in one piece, I used some cardboard to make up a template for the plastic starting shape. I will easily get two attempts from a 4'x8' sheet of plastic.
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After some searching both at my workshop and then at home I finally found the large piece of felt I purchased for lining the form. The piece is only 90cm wide but it will stretch to the 110cm needed to cover the inside of the form. Interestingly the felt stretches easily across the sheet and not very much at all length ways.
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Then it was onto Ebay and ordered some 1mm thick self adhesive foam for sealing the hot plastic around the outside edges. The Déjà vu is almost over :p
 

MadRocketScientist

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After some thought about the thin rubber strip I had ordered on Ebay, I was starting to think it might be affected by heat, then I remembered I had some thin rubber sheet in amongst all my stuff. It has a slight texture so I considered that it may leak air but after testing against some clear plastic it seems like it will seal well enough. It should also handle the heat being solid rubber rather than foam.

I marked and masked out the edges of the form where the rubber was to be installed. I used some high strength contact spray glue to hold the rubber in place using the masking tape and some cardboard to stop over spray. I am happy with how this came out and it is now ready for the felt.
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JonMiller284

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After some thought about the thin rubber strip I had ordered on Ebay, I was starting to think it might be affected by heat, then I remembered I had some thin rubber sheet in amongst all my stuff. It has a slight texture so I considered that it may leak air but after testing against some clear plastic it seems like it will seal well enough. It should also handle the heat being solid rubber rather than foam.

I marked and masked out the edges of the form where the rubber was to be installed. I used some high strength contact spray glue to hold the rubber in place using the masking tape and some cardboard to stop over spray. I am happy with how this came out and it is now ready for the felt.
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Man! I wish it were cheaper to ship stuff across the pond! I’d have you make me a canopy! Sweet looking mold!
 

JonMiller284

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Apr 5, 2021
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I may have a way of getting a canopy or two around the place without too much shipping cost, I will ask around and see what is available.
the company Starplast in France quoted me $5000 usd just for one canopy including shipping… their canopy with out shipping if you were to pick it up at their shop in person is only$1250
 

MadRocketScientist

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WOW that is insane, I guess they are now one off piece and they realyl don't want the hassle of making them. From memory I think the PET costs me around $25 NZD per canopy attempt so they won't cost anywhere near that price.
the company Starplast in France quoted me $5000 usd just for one canopy including shipping… their canopy with out shipping if you were to pick it up at their shop in person is only$1250
 

Jim_MC15

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Oct 30, 2018
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I contacted Airplane Plastics.... They wanted $10,000 to make a mold and $1,000 per canopy. Also contacted Mecaplex in Switzerland per Airplane Plastics recommendation.... They didn't have a mold for a CriCri either. I will be attempting to make my own shortly.

Can't wait to see how yours comes out!
 

MadRocketScientist

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That is also crazy! and Yes I can't wait to see how mine come out.

I contacted Airplane Plastics.... They wanted $10,000 to make a mold and $1,000 per canopy. Also contacted Mecaplex in Switzerland per Airplane Plastics recommendation.... They didn't have a mold for a CriCri either. I will be attempting to make my own shortly.

Can't wait to see how yours comes out!
 

MadRocketScientist

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Location
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And lined with felt.

I used a reposition-able spray glue for most of the felt but it doesn't really have enough stick and tends to lift. I stuck the edges down with some permanent spray glue once I had the middle stretched out neatly. If I end up gluing it again I will thin down some contact glue with mineral turpentine so that it dries more slowly and use that for the sticking down.
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