Monday, November 17, 2014

Inlay of Aka Washers

One of today's small tasks was routing out the bulkhead beams to allow inlaying the carbon plate washers.

The template was made with a 3 inch hole saw.   This was slightly bigger than the 75mm washer and it left a bit of room for glue.  The template was aligned/centered by "stacking" the components.  The G10 tube went in the hole, the washer went over the tube and the template around the washer.

The washer dry fitted.

A flush trim bit removed the material from the beam.   This is another task that an experienced build would have knocked out straightaway, but it took me a little head scratching until I came up with the solution.

Task time: 3 hours
Total project time: 334 hours

Saturday, November 15, 2014

Mainsheet Beam in Vacuum Bag

This is just an extra shot I had of one of the many vacuum baggings of the beams. The envelope is made of plastic packing tubing.  Only the ends need to be sealed on the tube, simplifying matters and reducing the potential for leaks.  I have been sealing the ends of the tubes with these plastic snap-together flanges from ACP Composites.  They are cheaper and more consistent than bagging tape.

The packing tubing can be found at ULINE and other places.

Thanks to Dan Newland at Pegasus Aeromarine for turning me on to packing tubing.

Main Bulkhead Work

I have been trying to do several small projects in parallel.   One of the recent projects are the main bulkheads that are at both ends of the main cabin.   These stations have reinforcing planks where the aka cross beams will bolt through the hull.

The unfinished area in the middle gets cut out of the companionway after the bulkhead is in the hull. Until then, it is an extra bracing support.

The bulkheads are large enough that they came from two pieces of plywood.  After gluing the puzzle joints, I have coated both sides with three layers of epoxy.  The epoxy then got sanded back as smooth as I could get it, so it is now ready for final finishing.

The reinforcing planks will get epoxied to the bulkheads before being placed on the strongback.  The planks were shaped from templates that I had made a few months back.  I recently dry-fitted them to the bulkheads with screws through the back.  This allowed me to get the alignment correct and bore holes for the aka bolts.  The screw holes will get filled with epoxy later.   They will mar the less visible surface of the bulkhead a bit.   The screws will be used to accurately locate the planks when they are slick with glue and to help with clamping.

I left the epoxy coating off of the gluing surface of the bulkheads.  This will give an area for a primary wood to wood bond.  Probably not that critical, but it can't hurt.

The hole through the bulkhead gets a similar treatment to the akas.  A G10 tube is inserted and then there is a 75mm cplate washer that the bolt will tighten against.

Task time: 20 hours
Total project time: 331 hours

Monday, November 10, 2014

Mainsheet Beam Carbon Layups

Each side of the mainsheet beam gets about 12 layers of carbon.  These include uni, bi-directional and plain weave cloth.  It seems quite easy to wrinkle the cloth as it goes around the compound curves in the vacuum bag. As I learn, I tend to get less of this.  It is definitely not good since to get a smooth layer a wrinkle must be sanded a little bit, causing a small area of reduced strength.

A pattern for cutting cloth.

A typical layup applied to the beam before going into the vacuum bag.

I had to cleanup the nubbins with a router after a few layers that did not lay well into the groove.
Above, I am putting a few layers of scrap carbon back into the groove.  The dowel matches the size of the router and is used a clamp to compress the carbon.  I lashed the ends of the dowel around the beam to pull it tightly into the groove.

The dowel was removed after cure. I used packing tape to keep most of the new material off the surrounding beam. 

The  excess cloth has been trimmed and sanded.  This beam needs three more layers all the way around.

Each layup has quite a few steps including cutting the cloth, peel ply and breather, setting up a vacuum bag, wetting out and applying the cloth, peel ply and breather and getting it into the bag.

I have been wetting out the cloth on a piece of plastic.  I spread the epoxy over a layer and squeegee it back and forth.  Another layer of cloth goes on top and more epoxy.  At about three layers maximum, I  stop.  The plastic gets folded over the cloth.  I then squeegee the whole stack very firmly on both sides of the plastic envelope.  This forces air out and epoxy in.   The stack is then peeled off the plastic and laid on the beam where it is smoothed down tightly before the peel ply is smoothed over the top.  I tend to error on the side of too much epoxy.  The bag squeezes out the excess and you really want the carbon well wet out.

I am getting to the last layer which will be a bidirectional woven sleeve.  The sleeve should conform well and leave no seams.

Task time: 20 hours
Total project time: 331 hours

Monday, November 3, 2014

Boring Beam Mounting Holes

The Akas are attached to the main bulkheads with 18mm bolts.  The bolts are carried through the beam holes with a 20mm (3/4 inch) G10 tube liner.  I needed to bore the holes through the solid interior of the beams before the first layer of carbon cloth.  CNCed holes are marked on the plywood sides and I did not want to lose the reference marks under the cloth.

This is one of those seemingly simple tasks that takes a lot of pondering and worry.  The holes must be perpendicular to the beam all the way through and be accurately located so that they will mate properly with the bulkheads.

All kinds of little issues arise for consideration:

- How do you level an 18 foot beam with one end across a drill press table?
- There is not enough throw on the drill press without shifting the tables and re-leveling in the middle of a hole.
- How do you drill an accurate hole without using a drill press?
- The forstner bit is not long enough.
- The forstner bit extension does not fit a metric forstner bit correctly.
- The collar on the bit extension does not fit down into the  hole.

Finally found a drill stand for a hand drill, but would it be accurate enough?

G10 (Garolite) Tube

Setup that allowed a hole "almost" deep enough.  It would not reach the last millimeter, but the point of the bit went through for reference.

A 3/4 inch hole that has been sanded slightly with a dowel covered with sandpaper.  The 3/4 inch tube fits snugly through most of the hole.  There is a little extra room at the top where the original hole in the plywood is slightly bigger (2mm), but the tube is squared in all directions.

All you can say when you drill that first hole and it is OK is whew.

Task time: 2 hours
Total project time: 311 hours