Vodkaman

Good post Mark. The problem of switching from pounds to Kilo's and inches to centimeters, is not about the numbers. If it was, everyone would change over in a flash. There cannot be any arguement that metric, base 10 units are much easier and meaningful than imperial, multi base units. Hell, the base number changes within the one subject, example: ounces, pounds, stones are the imperial standard measurement of weight, I need not say more. The problem is 'the FEEL'. When you change over, you loose the 'feel' for a measurement. Example, 14st to me or 200lb to an American means a sedentary life style with a few too many burgers. It takes a long while to 'feel' that 90Kg means the same. This uncomfortable position of not being in control of the numbers is why the change is resisted. If a conscious effort is made to change or it is forced upon you, the change happens very quickly. The secret is not to mix and match. When I post, I usually post both units, placing the imperial in brackets. But some subjects just don't belong in imperial, the numbers are just too cumbersome. Density is one of them. If you don't want to change, I can respect that and will rejuvinate my efforts to publish in both units.

Mark and Pete, both good, simple practical solutions. Just what I was looking for. Thanks for the feedback.

The balsa seems to have advantages and disadvantages. On the one hand it gets ripped up by the process, but it is very quick and easy to clean up. I have been considering pouring a block of polyester resin and machining that to make a positive master. It drills OK, so I am assuming that it will be suitable for machining, but I don't know for sure. It is fairly cheap and obviously no grain to take into consideration. Have you considered other materials? The end result looks very good. Many thanks for sharing. Keep posting as the job progresses.

I guess my digital dexterity needs enhancing. It's like trying to perform brain surgery with hands like a pound of pork sausages. I just need practise. I was just wondering if anyone uses any specific technique for positioning. I have read of the technique of drilling a lateral hole through the body at the eye position, to aid alignment, here on TU.

Mark, both specific gravity and density in what ever units are equally useful for determining the relative buoyancy attributes between wood types. But the clear advantage of measuring the density in gm/cm³ is that the density of water is 1gm/cm³. Therefore, you have a direct indication of the buoyancy of the wood. This figure is far more useful. It is an amazing coincidence that 1cm³ of water weighs exactly 1gm. It is almost as if the weight system was arranged specifically for lure design!

Impossible? I love a challenge.

Rofish, you are correct. I made a mistake, used the weight from the 36 inch board for the 9 inch weight. Sorry about that. Density = 0.137 is a much more realistic value!

Yes it is. In fact that is the information that PB has provided above. But as usual, I went over the top. The beauty of this method is that it can calculate the density of any scrap of wood or any other buoyant material. The method reads complicated, but once you have done it once, it is quite simple. I think the method was worth bringing to the table. The principles used in this method can be applied to other aspects of the lure, such as: Calculating the buoyancy of an existing lure, in order to duplicate the buoyancy characteristics in the next lure. Improving repeatability in production. Calculating the effect of a top coat on the buoyancy. Another example: you want a suspending bait. In the bath tub, you hang the lead to achieve suspension. Drill a hole, fit the lead. But the resulting suspension does not happen. The above method will help explain the error and allow you fix it.

I developed this technique for predicting the ballast for a lure, long before I get to the painting stage. I would shape the body, seal it to prevent water ingress and then do the volumetric calculation to obtain the density. If the test is to be performed on unsealed wood, it would probably be a good idea to weigh the wood sample by itself before the buoyancy test.

As it happens, I have just been working on a future thread, of which this is a part of. To calculate the density of an unknown sample of wood: Chop off a sample piece. Size or shape is not important. However, the larger the sample, the more accurate the data. Attach pure lead to achieve neutral buoyancy (just below the surface). 1. Accurately weigh the sample+lead, in grams. 2. Accurately weigh the lead only, in grams. One gram of water occupies a volume of one centimeter cubed. Therefore, the volume of the sample can be calculated, knowing that the density of pure lead is 11.389gm/cm³. 3. Calculate the volume of the lead by dividing the weight of the lead only by 11.389 4. Calculate the volume of the sample by subtracting the volume of the lead from the weight of the sample+lead weight. 5. Calculate the weight of the sample by subtracting the weight of the lead only from the weight of the sample plus lead. 6. Calculate the density of the sample by dividing the weight of the sample by the volume of the sample. Now I've got a headache, as I suspect anyone else reading this has. But from the information you have given above, I calculate a density of 0.55gm/cm³. To calculate this, convert all your figures to metric (grams and centimeter cubes). Divide the weight by the volume. This figure is very high for balsa, which is normaly about 0.12gm/cm³.

Looks good here. Thanks for all the work Jerry. Dave

That is going to be quite some mould. A vertical split for the tail and a horizontal split for the claws and legs. Those skinny legs are going to take some pouring too!

As long as you don't start going on about pink skirts, you'll be OK. Welcome to the fray Seargent.

Having created half a tin of frogs spawn, I thought I would complete the job and mount a couple. I cast a plaster body for experimentation. I tried to glue the eyes, slightly high, just running into the back curvature, as a good test. This thread should have been about gluing eyes, as making them is so easy compared to fitting them. Maintaining symmetry and keeping the edges glued down and gluing fingers to the paint job is a nightmare. How do you guys do it? I can feel a special tool design comming on.

Palmetto, absolutely.

Just a really picky side note. Two identical lures, built to have the same buoyancy etc, one cedar, the other balsa, they will both weigh the same. The lure is looking really good.

Just an amusing interjection, again I apologise, no inference intended. Looking forward to reading your progress reports.

The insignificant comma can have such huge consequences of interpretation, or mis-interpretation. For example: Sorry, couldn't resist.

There is an article in the left side menu called, 'what happened?'. This explains everything.

Running scared!

Humour is a very necessary part of my threads, otherwise no one would read them!

The black dot would be a drop of black plastic, rather than card.

Jim. Thanks for your input. Yes, there are a lot of materials to try out. I will continue to experiment with what I have available in my local stores. If I were a plastics user, soft plastics would be a very good solution. Using a shiny PoP mould, black blob, clear lens and white latex paint backing. This would be a very cheap, simple and effective solution.

Could you post some close-ups of the negative mould when you've finished. I'd like to see the state of the m/c finish before any tidying up, if you don't mind. The reason I like the idea of a positive mould is that it would be easier to clean up the surface finish after machining. This is all good stuff. Go for it and let's see.

I suspected TU was addictive, but the withdrawal symptoms kick in pretty quick!