DavieRockets
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Sometimes you get a fibreglass kit where the nosecone shoulder will not go into the airframe tube. The usual way to deal with this is to sand off the two mold lines and then keep sanding the shoulder until the nosecone can slide into the airframe. This usually works on smaller diameters but once into the 4" and larger airframes this can be very tedious work. There are also some other issues with this method:
1) It sometimes take a lot of sanding which wastes HOURS of your time and lots of sandpaper and makes a dusty mess.
2) If the nosecone is really oversize, you can easily sand through the nice smooth gelcoat exposing rough fiberglass cloth or roving and make the shoulder very thin and weak. This can lead to time consuming reinforcement methods and extra material (fiberglass cloth and epoxy).
3. Once the nosecone is reinforced, you still have to repair/fill the damaged gelcoat to get a nice smooth surface again. It will never look "factory" and painting the shoulder is not a great idea.
I just started building a Performance Rocketry Gizmo XL (Extra Large) kit. This is a stubby 8" diameter kit. with a 24 long nosecone and a 25" long G-12 filament wound airframe tube. The tube is very thick at 1/8". The nosecone would not go into the tube at all. A slight chamfer on the tube and nosecone only afforded a tight fit for the first inch. Clearly this was going to take a lot of sanding and a lot of time and elbow grease. Then I thought of using a large diameter drum sander on my electric drill to reduce the INSIDE diameter of the airframe. I just finished doing this and it worked superbly well.
I started by hand sanding off the two opposing mold lines on the shoulder of the nosecone using 280 grit paper on a flexible sanding block. I did not sand any other part of the shoulder, leaving the shiny white gelcoat untouched. Next I used some 150 grit paper to form a slight chamfer on the inside edge of the airframe tube. This will help funnel the nosecone into the tube. Likewise I rounded over the nosecone shoulder's edge with 280 grit paper. I measured the shoulder length of the 8" diameter nosecone and used a felt pen to mark a reference line on the airframe. The sanding procedure inside the airframe would have to go a bit further than this mark to ensure no binding of the nosecone.
Next I placed the airframe in a cradle and chucked my 3" diameter x 3" long rotary drum sander into my variable speed drill with an 80 grit sleeve installed. I made an index mark where my sanding would begin at the bottom of the lip of the airframe tube. I began sanding the inside face of the tube with a slow side to side motion making sure the drum sander was making full contact from front to back so as not to cut grooves into the fiberglass. Without stopping the drill I pushed the sander in further to overlap the originally sanded area until I was just passed the index mark. Then I rotated the airframe tube about 15 degrees and repeated the same action; side to side and front to back. I did this over and over until I met the original index mark on the lip of the tube. This meant I had gone right around the complete interior of the tube. I test fitted the nosecone and it slide in much further than before. I repeated the complete procedure 2 more times and now the nosecone slid in all the way. I cleaned up the roughened, interior surface of the airframe by hand sanding using sandpaper wrapped around a flexible foam backing plate. I used 150 grit, then 220 grit. Finally I wet sanded using 400 grit including the chamfer on the airframe lip. I also used the 400 grit to clean up the area on the nosecone shoulder where the mold lines were previously sanded. The nosecone now drops right into the fuselage with minimal friction and no side to side play is detected when it is in all the way.
This method took about 30 minutes and saved HOURS of hand sanding the gelcoat on the nosecone and it's associated problems. (No messy and costly shoulder reinforcement using epoxy and glass needed.) Now I can epoxy in the nosecone's bulk plate making sure it is not so tight so as to deform the nosecone shoulder.
This method worked so well I may even try it on my smaller diameter builds instead of hand sanding nosecone shoulders. I picked up the 3" diameter sander at an ancient hardware store for $15.00 including 2 sleeves. I knew it was a deal so I grabbed it knowing I would find a use for it one day. It seemed huge at the time and weighs about a pound. The owner said it had been sitting there for at least 10 years and it was made in USA to boot! I also find it great for enlarging centering ring holes that are 3.5" and larger because it is easy to control because of its large diameter and mass. The second photo shows me enlarging a rough cut hole for a 4" glass tube that will go into my 8" nosecone.
I know that Sears has a similar sanders HERE. Rockler also has one HERE. Hope this helps some of you with tight fitting nosecones.
1) It sometimes take a lot of sanding which wastes HOURS of your time and lots of sandpaper and makes a dusty mess.
2) If the nosecone is really oversize, you can easily sand through the nice smooth gelcoat exposing rough fiberglass cloth or roving and make the shoulder very thin and weak. This can lead to time consuming reinforcement methods and extra material (fiberglass cloth and epoxy).
3. Once the nosecone is reinforced, you still have to repair/fill the damaged gelcoat to get a nice smooth surface again. It will never look "factory" and painting the shoulder is not a great idea.
I just started building a Performance Rocketry Gizmo XL (Extra Large) kit. This is a stubby 8" diameter kit. with a 24 long nosecone and a 25" long G-12 filament wound airframe tube. The tube is very thick at 1/8". The nosecone would not go into the tube at all. A slight chamfer on the tube and nosecone only afforded a tight fit for the first inch. Clearly this was going to take a lot of sanding and a lot of time and elbow grease. Then I thought of using a large diameter drum sander on my electric drill to reduce the INSIDE diameter of the airframe. I just finished doing this and it worked superbly well.
I started by hand sanding off the two opposing mold lines on the shoulder of the nosecone using 280 grit paper on a flexible sanding block. I did not sand any other part of the shoulder, leaving the shiny white gelcoat untouched. Next I used some 150 grit paper to form a slight chamfer on the inside edge of the airframe tube. This will help funnel the nosecone into the tube. Likewise I rounded over the nosecone shoulder's edge with 280 grit paper. I measured the shoulder length of the 8" diameter nosecone and used a felt pen to mark a reference line on the airframe. The sanding procedure inside the airframe would have to go a bit further than this mark to ensure no binding of the nosecone.
Next I placed the airframe in a cradle and chucked my 3" diameter x 3" long rotary drum sander into my variable speed drill with an 80 grit sleeve installed. I made an index mark where my sanding would begin at the bottom of the lip of the airframe tube. I began sanding the inside face of the tube with a slow side to side motion making sure the drum sander was making full contact from front to back so as not to cut grooves into the fiberglass. Without stopping the drill I pushed the sander in further to overlap the originally sanded area until I was just passed the index mark. Then I rotated the airframe tube about 15 degrees and repeated the same action; side to side and front to back. I did this over and over until I met the original index mark on the lip of the tube. This meant I had gone right around the complete interior of the tube. I test fitted the nosecone and it slide in much further than before. I repeated the complete procedure 2 more times and now the nosecone slid in all the way. I cleaned up the roughened, interior surface of the airframe by hand sanding using sandpaper wrapped around a flexible foam backing plate. I used 150 grit, then 220 grit. Finally I wet sanded using 400 grit including the chamfer on the airframe lip. I also used the 400 grit to clean up the area on the nosecone shoulder where the mold lines were previously sanded. The nosecone now drops right into the fuselage with minimal friction and no side to side play is detected when it is in all the way.
This method took about 30 minutes and saved HOURS of hand sanding the gelcoat on the nosecone and it's associated problems. (No messy and costly shoulder reinforcement using epoxy and glass needed.) Now I can epoxy in the nosecone's bulk plate making sure it is not so tight so as to deform the nosecone shoulder.
This method worked so well I may even try it on my smaller diameter builds instead of hand sanding nosecone shoulders. I picked up the 3" diameter sander at an ancient hardware store for $15.00 including 2 sleeves. I knew it was a deal so I grabbed it knowing I would find a use for it one day. It seemed huge at the time and weighs about a pound. The owner said it had been sitting there for at least 10 years and it was made in USA to boot! I also find it great for enlarging centering ring holes that are 3.5" and larger because it is easy to control because of its large diameter and mass. The second photo shows me enlarging a rough cut hole for a 4" glass tube that will go into my 8" nosecone.
I know that Sears has a similar sanders HERE. Rockler also has one HERE. Hope this helps some of you with tight fitting nosecones.
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