mtnman, where did you get the metal 'countersink reinforcements', and how are they fastened/implanted in the outer tube/nosecone?
Pem nuts are real handy, and very durable compared to plastic rivets. I'd be interested in a set of each of those sizes.2-56, 4-40, and 6-32? Or is 2-56 too small in your opinion?
How many are you planning to have with each kit?Last call folks.... finalizing order to McMaster this week.
25 or 50, depends on what quantity said thread/size is sold by Mcmaster. I don't plan to split up quantities if that makes sense.How many are you planning to have with each kit?
Depending on the cost I would be interested in the sizes mentioned in a previous post.25 or 50, depends on what quantity said thread/size is sold by Mcmaster. I don't plan to split up quantities if that makes sense.
Didn't see your previous post...? What are you needing please?Depending on the cost I would be interested in the sizes mentioned in a previous post.
25 of 2-56 and 25 of 4-40. If 50 is what is in a kit I'll take that.Didn't see your previous post...? What are you needing please?
Pem nuts are cool and I have used them to hold payload sections to the AV bay. I don't think they will add any significant strength to you fin attachment. Theses pictures are of large headed rivets on a 6" BlueTube tube fin, it shows they had little if any effect on the tube fins leaving.I use PEMs for a variety of things on a rocket.
As Justin noted, they are primarily used to fasten two parts that you do not want to separate in flight, but do want to separate on the ground. Most commonly, this means fastening the ebay coupler to the payload bay instead of plastic rivets:
4-40 PEM on a 3" rocket:
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I also use them for a similar purpose to attach the coupler to a nosecone when I want to put electronics in the NC Bay:
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Another thing I use them for is to attach tube fins. I have a 4" Neon upscale with 6 Tube Fins and 6 straight fins. The tube fins are all held on by 2 x 6-32 screws with a PEM in the airframe and they are also epoxied to three points of contact (each adjacent fin and the body tube). One set of the tube fin PEMs is 10-32 to accommodate 1515 rail buttons inside the tube. In addition to the PEMs I used for the ebay and nosecone, this rocket required the use of 17 PEMs of various sizes. I am currently working on 6" and 8" versions of this rocket, each needing a similar number of PEMs up to 1/4-20.
View attachment 460176
Pem nuts are cool and I have used them to hold payload sections to the AV bay. I don't think they will add any significant strength to you fin attachment. Theses pictures are of large headed rivets on a 6" BlueTube tube fin, it shows they had little if any effect on the tube fins leaving.
Sorry mtnmanak most definitely not done on impact. About 3 or 4 seconds into an M2020 tore the fins off. Landing was soft and smooth!!! Rebuilt it and still take the boy Scouts out and launch it. Mostly with 54mm IMAX L's or small M's since thenThose pictures show fins fully breaking off on impact. It doesn't matter what you attach fins to a rocket with - if they break off, what's the difference?
I used #6 stainless steel bolts as well as 3 points of epoxy contact for each tube fin. Each tube fin is a 4 inch fiberglass thick wall coupler. If one of those fins breaks, I am seriously doubting my problem will be with the attach points. This is a 25 lbs rocket. On one flight at Red Glare, the deployment bag wrapped around the main causing a total collapse. It burned in on a 15" drogue right onto the fin can. Paint was scratched, but the fins were fine. I flew it again that day on an L1090, no problem. I have also flown it above Mach 1. Flew it again this weekend, perfect flight. I am very confident the PEM nuts and stainless steel bolts helped assure none of my fins have budged on hard flights and hard landings.
Nothing is going to help you if you crash a bird hard enough with blue tube fins.
You can see the scuff marks on the bottoms of the tubes from the hard landings:
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I have also used PEMs and #10 screws to both secure the tube fin and install the 1515 rail buttons inside the tube. Works perfectly every time.
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Sorry mtnmanak most definitely not done on impact. About 3 or 4 seconds into an M2020 tore the fins off. Landing was soft and smooth!!!
Correct. A couple bolt's, Rivets or Pem Nuts won't make a difference on fin attachment unless you click your heels 3 times and you really believe.Point is, the fins broke. If your fins break, who cares how you adhered them to the frame?
I'm needing to go way back teepot. It was a local Santa Barbara / Ventura surf band from the 90's called Phantom Riders. Mostly saw them playing at the local concerts in the park. With all the distortion, they might have used PemNuts to hold the amps togetherWho did the music. It sounded like Dick Dale surf music.
Well, I got the surf part right.I'm needing to go way back teepot. It was a local Santa Barbara / Ventura surf band from the 90's called Phantom Riders. Mostly saw them playing at the local concerts in the park. With all the distortion, they might have used PemNuts to hold the amps together
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