Sunday, April 17, 2011

More Blades and Brackets

A little bit here, and a little bit there, and progress is still being made.

I sanded the brackets, using both the piece of sanding belt and the drum sanding bit on the end of a flexible shaft connected to a Moto-tool. I quickly discovered that holding the hose of the shop vac in one hand and the Moto-tool flexible shaft tool in the other was the best way to keep the work area clean and to reduce the amount of airborne dust. I also discovered that the Moto-tool drum sander was very effective in removing unwanted material in tight places around the support brackets.

After the sanding was completed I then applied fillet material where there were still gaps under the receiver tubes from the first application, and around the tubes on the outside of the brackets.

Several more strips of saturated 12 oz. biaxial cloth were applied to areas that were missed the first time. Some 6 oz. cloth was applied over some of the bare wood at the center of the brackets and some of the 12 oz to help flatten the material and smooth it out.

A couple of areas on the top of the stabilizers where the wood had appeared due to too much sanding were also glassed over.

Finally, while waiting for the resin to set, I spent some time grinding the first set of propeller blades. Instead of using a hand-held grinder I used an 8 inch bench grinder. It took many passes on each of the four four edges, with care being taken to keep the edge of the blade appropriately aligned with the edge of the wheel as the blade was drawn along the tool rest.

After the rough shape was formed I polished it using a 100 grit flapper wheel on the drill press. It took a while, but that managed to remove almost all of the grinding wheel grooves as well as the bumpy surface of the bar stock.

The first propeller hub still needs to have the slot cut into it for the blades. A local machine shop said they could do whatever I wanted, at a cost of $80 per hour. While it probably is worth it to get a professional job done I would still like to see if it could be done using fairly basic tools such as a drill press and a band saw. My neighbor suggested getting a larger cutting disc for my Moto-tool to cut the slot, but that would still leave a section of the waste material attached preventing it form being easily removed. We'll have to think about this further.

Now that the resin has set I went back and sanded the brackets again. The stabilizers were vacuumed and flipped over, and strips of 3.9 oz cloth was cut to cover the bare wood edges where the sanding had been too vigorous. In addition, the rudders were sanded in preparation for glassing, as were the two wooded pieces to hold the central mounting bracket for the stabilizer akas.

So, no, the boat won't be ready for next weekend's Jetty Island Race. The Escapade will have to fill in again for my photography platform.

Friday, April 08, 2011

Attaching Brackets to Stabilizers

The original plan was to apply resin to the wooden bracket pieces, assemble them with the outrigger receiver tubes and place them on the stabilizers. Following this I was going to fillet the joints and apply 12 oz biaxial cloth up the sides, over the top edges and back down the insides of the brackets.

Well, I should have known better than to try to do this all in one go.

The resin application to the wood was fine, as was assembling the brackets and tubes and mounting them on the stabilizers. Using an aka tube to keep the bracket tubes properly oriented worked well, too. However, trying to apply fillet material didn't quite work as the brackets kept moving about.

I ended up scraping off all the fillet material and cleaning it from the brackets and tubes.

I had spread out a number of 12 oz strips of cloth on the plastic covered workbenches. Prior to working on the wood I poured resin poured on the strips to allow it to soak in and saturate the strips. The idea was that I would apply the cloth on the filleted brackets and things would be just fine.

Now there was no fillet material to round out the joints, and I had cloth saturated with resin that would shortly set. What to do?

Well, I applied the strips to the brackets anyway. The longer strips wrapped over the top edges of the brackets and down the insides. With the biaxial weave the cloth was able to bend over the 4mm plywood fairly well and stay flat against the inside wall. It even managed to make the 90 degree turn where the brackets meet the top of the stabilizer.

Once the cloth strips were in place the wooden bracket pieces were fairly well fixed in place, so I decided to fillet them and the tubes with the remaining fillet material. This was still rather messy, and the results were nowhere near as clean as I would have liked. Sigh....there will be a bit of cleanup work needed once this stuff hardens!

In addition to the stabilizer brackets I applied some patches to areas on the stabilizers where I went a bit too deep with the sanding, and to similar places on the edges of the top of the main hull.

As I was running short on mixed resin I decided to not coat both sides of the main hull mounting bracket pieces. Instead, I coated one side and let it set with the bracket in its position on edge with the bottom piece.

Checking on the cloth on the brackets I noticed some of it was pulling away from the wood. After pushing it back in place I covered it with plastic and used small plastic clips to hold it in place. This generally worked, but some of the shorter fibers along the edges escaped. They will just have to be removed after the resin hardens.

There will be a bit of sanding this weekend, followed by a bit more filleting and glass application.

Monday, April 04, 2011

Blades and Brackets

The metal for the propeller blades and hub arrived. They were purchased from Online Metals.Com, which turns out to be located maybe 20 miles from my house. Their prices were reasonably competitive, and their price to cut the metal to the proper length was acceptable, too.

I bought 2 sets of 304 stainless bar, and one set of 316 stainless cut from plate. If worse comes to worse I have spares with which to work on or to replace a prop if one gets lost.

I also purchased round aluminum bar stock, enough for three hubs, and 3/4 inch round Delrin stock to be used for plain bearings.

Following Rick's instructions, I carefully measured and marked the grind lines on both sides of each bar. I then marked the grip lines, the pivot points and the zero angle lines. All was ready for bending them to shape.

Rick's instructions described how one mounts the blades vertically in a vise, with a right angle ruler to ensure the blade was truly vertical. He then used a protractor and a stationary reference to make sure that when the blade was twisted that is bent to the correct angle.

I decided that this was too much work. Anyway, I didn't have a fixed protractor like Rick's, but I did have a nifty angle measuring tool I picked up years ago from Sears. It is a 360 degree dial protractor that has one flat side which one applies to the surface to be measured, and the gravity driven plum bob need swings down to the lowest position against a marked dial. You then read the angle directly from the dial.

In the past this tool has been invaluable for measuring bike frame angles and the like, and measuring the stuffing box angle on the boat.

For the propeller blade situation I merely rotated my vise 90 degrees so the jaws were in the vertical position, and clamped the blade in place. One quick measurement of the blade made certain that it was horizontal. Grasping the blade at the grip line with a large adjustable wrench with one hand and countering the weight with my other hand, I was easily able to bend the blade to the desired angle.

Repeating the process with the blade inserted at the other end and the job was done.

All in all, it took maybe 5 minutes to bend the 6 blades.

The 316 stainless, being about .005 inches thinner than the 304 bar, definitely was easier to bend. Hopefully this won't be a an issue when those blades are called upon to push water.

Putting the blades aside for the moment I then began work on the mounting brackets for the outriggers.

At first I planned to do something along the same lines as the Cadence outriggers. That boat uses UHMW plastic blocks drilled and sliced in half with mounting holes drilled on either side to clamp the two pieces around a short section of larger fiberglass tubing to the top of the float.

The problems with this are 1) the blocks are somewhat heavy, 2) I couldn't find a reasonable and inexpensive source for it, and 3) this requires some sort of threaded receiver on each stabilizer.

I had already purchased T-nuts for this purpose. However, having second thoughts about mounting them, the weight of the bolts, the lack of adjustability and reduced strength, and the extra work needed, I decided instead to mount the brackets directly to the top of the stabilizers.

The hull mount will still use the T-nuts, though they will be the longer ones with wider bases. This will still allow vertical adjustment.