Wednesday, August 29, 2012

First slingshot for the law professor

Recently, I received an email from a professor who teaches at a US law school. Turns out he grew up in Brazil, and loved his slingshot! Now, at pretty much the same age I was in when I got back into the sport, he feels the same urge...

He asked me about the recommended shooting style (hammer grip vs. finger support), and I said it comes down to personal taste (mine strongly runs towards the hammer grip).

So I offered to make two slingshots for him, as a gift!

So I was left with the task to design a slingshot for a law professor, who is a beginner (again). I settled on a variation of the lead launcher, as the slightly higher fork works good for beginners and experienced shooters alike. But I wanted more "3D" for the handle, and also a "butt" that swings out like my hammers.

For the details, I decided that I want to have as many analogs to a good law as possible.

A good law needs a solid base, so I chose a Multiplex core.

US courts often use oak panelling, so I chose oak for the handles. But in this case I used moor oak, as the tree it came from probably grew at the time of Hammurabi, when one of the oldest written legal codes were established (in Babylon).

I settled on the paragraph sign for the handles. Sawed them out of the oak and later filled them with light grey putty, for the contrast.

A good law is what I call watertight, so I covered the whole frame with polyurethane varnish.

Later on, I will wrap the fork with rubber, so the occasional fork hit won't damage the finish.

Next, the finger support shooter!

Friday, August 24, 2012

Gemini for a friend

Made a Gemini for a friend from the US today, maybe the start of a new exciting project. His zodiac sign is Gemini, but that is just a coincidence!

In this case noble wood wasn't suitable, form was more important. I used Multiplex. Had to repair it on one spot as there was a huge void in that piece, but it worked fine. Shoots great!

Oiled in in linseed for the color and hardness, then coated it in four layers of polyurethane. This will last a long time for sure.

Banded it up with a single layered untapered target band (long lifetime) and a fairly strong double layered tapered hunting band.

Will send this out on Monday!

Thursday, August 23, 2012

New high speed camera ante portas

Finally ordered a new high speed camera today!

The Olympus i-speed LT. 1000 frames per second at 800x600, max. 2000 fps, full color!

Check it out on the Olympus website

The sales guy from Olympus was here today. Great service! He brought two cameras and we did actually slingshot test shots. Of course I loved the TR model even more (1280x1024, with a huge sensor) - but it was waaayyy out of my price range.

Delivery time will be about four weeks - can't wait! The biggest investment in my channel so far, but much needed.

Sunday, August 19, 2012

"The Snail Shell"

Made another slingshot over the course of the last few days.

It took that long because this may be the most work and material intensive Hammer Howitzer variation I ever came up with.

It may not look like a Hammer Howitzer, but it is...

It actually is a fully encapsulated "safety" slingshot, made from a total of 8 layers of Multiplex (birch plywood). Each plywood layer cosists of 13 layers of wood, which means this slingshot is made from 104 layers of wood. It looks like a mixture of a sculpture and a piece of pottery!

The whole thing is laquered with yacht polyurethane (three layers), which makes it watertight and very shiny. Even though it offers total protection from handhits and band slaps, the motion of the hand is not hindered at all.

This was a lot of work and sawdust galore, but I think it was worth it. One of my favorites.

Thera Tube: New recipe?

I haven't bought any Thera Tube rubber for a long time, as I mostly use the flat type. But the new launchers I recently made work well with tubing, and my stash was dwindling away quickly.

So I ordered some new silver, black and blue tubing. I put the silver on my Blunderbuss, and was immediately stunned by the stretchiness - and the speed of the shot.

I compared the old and new types, and the difference was totally obvious. The new tubing is much thinner. See the new and the old silver in comparison:

I weighed it, and the data confirmed the visual impression. The old silver tubes weigh 0,875 gramms per centimeter, the new type just 0,535 gramms -  just 61%!

I measured the draw resistance, and it was identical (about 17 kg at full stretch). This means that the new tubing is 39% more efficient!

I then looked at the black type. The same thing! See the old and the new:

Same thing - the old type weighs 0,57 gramms per cm (actually more than the old silver), whereas the new black type is 0,43 gramms per cm only. 25% less! Same draw resistance (7,5 kg at full stretch). #

I tested the weight of the flat type (Thera Band Black) and 0,49 gramms per cm. This means that the new tube is 12% lighter than the flat bands - which used to be 13% heavier! The weight ratio has been completely reversed.

I will do some chrony tests today. But my experiences so far have been very promising. Maybe we will see a comeback of tubular bands for performance oriented shooters.

Here is one more pic, the new silver compared to the old black:

Thursday, August 16, 2012

Watermelon Woman - why she failed

The watermelon fail video, published by the CBS show "Amazing Race", has received over 4 million views by now, and counting.

It has a rather negative effect on the slingshot hobby, as many people are now afraid of returning balls.

I have looked at the video another time and found that the pouch design and - mostly - the grip technique the poor woman used were the cause for the epic fail.

Returning ammo is - from my point of view - always caused by a twisting pouch. These twists can have several reasons, and a shooter is well advised to avoid all of them.

a) Bad pouch design, with basket or bowl shaped pouches
b) Bad rubber/pouch attachments, using attachment points at the pouch corners rather than in the middle
c) A release technique that releases the upper or lower side of the pouch first

The (still) biggest forum for slingshots (I no longer use it) recommends a narrow fork, but I disagree - the fork width has no influence on such issues. I have slingshot crossbows that feature 70 cm fork width, and no such issues ever occured. I think this theory is scientifically unproven and more like a superstition than a fact. 

In the case of the watermelon woman, a), b) and c) have caused the fail.

Let us look at the pouch first.

This pouch consists of a piece of raw hide or textile (hard to tell) with eight holes, two in every corner. The thick rubber bands (I estimate 12mm industrial rubber) have been put through the top left/top right holes (upper band) and, respectively, the lower left/lower right hole, with the rubber bands running through on the back side of the pouch. Like this (view of the backside):
This pouch design and band attachment are both rather bad. They create a "tobacco pouch" effect, as the bands will tighten the pouch edges until they touch each other. And they won't open at the end point of the acceleration either.

The band attachment is also very dangerous because it twists the pouch easily. If you pull out slightly off center, the upper and lower bands won't be stretched evenly, and this leads to twisting. Look at the shot, taken right after the release, with the bands still swinging.

You can see the twisting - and that was a SUCCESSFULL shot.

She did in fact draw out nicely, for the most part. See her draw before the success shot:

She holds the pouch in the middle, and both bands are evenly stretched. It worked.

Now see how she drew out when the shot failed:

You can clearly see the difference. The upper bands are stretched more than the lower ones, and the melon is totally off center. This no doubts caused the pouch to twist, the melon did not release - but came back at her.

Now let us look at a much better pouch design - employed by my slingshot cannon.

As you can see, it is longer, but narrow. And it has a generous center hole, so the ball will always be in the middle. The bands are centered, too - not much room for twisting. And it works - see the bands after release!

No twisting, just a totally clean release.

If course, it is harder to draw out a pouch like this with your bare hands. A mechanical release makes a lot of sense. Just an upscaled version of this here would do the job just fine:

So - I think I have demystified the video just nicely. I may make a small scale model and record the effects in slow motion, someday soon - it is on my list of future projects.

Monday, August 13, 2012

A sabot for the blunderbuss!

Made a cup sabot today... fits ten 20mm steel balls (.79"), or many more smaller BBs.

Plugged with a bit of tissue, this works REALLY well. I am amazed how tight the groups are.

Saturday, August 4, 2012

Shooting range: Shipshape!

After the last shooting weekend with the boys from Knittlingen, I had to sort all of the ammo, and also repair my trusty old catchbox. We shot thousands of round against it, and it looked like heck. Twisted, deformed, broken. Fixed everything, it is ready for a lot more action!

While I was typing these words, this scene happened right in front of me... kind of cute, don't you think? Smile

Asgard equipment: Thor's training Mjölnir

In order to be prepared when Toast comes to Germany, I made "Thor's practice Mjölnir".

Total weight 45 kg, 35 kg (head) and 10 kg (handle).

Toast is right, this is a monster to play with. I can lift it over my head of course, but it will take lots of practice to be able to effectively use it. Which must be the goal, of course!

Thursday, August 2, 2012

Texan Persimmon Natural

Some days ago, John from Texas (close to Austin) sent me four great, fat forks from Persimmon. The tree was felled by a storm, and supplied plenty of very nice wood.

Persimmon is an interesting wood, it is a kind a ebony. Subtly brown, great grain, and very dense.

As always I will send John one completed slingshot back in return, and have made the first one the last few days.

A Hammer-Howitzer, what else, it is the best design I found (so far). A great cooperation between me and Tobias brought out this shape, which I think is hard to beat.

The wood was fresh and is known to crack easily, it took many careful microwave sessions to dry it.

It may seem a waste to start from such a thick fork, but the HammerHowitzer shape requires a very thick and wide piece. The raw "board" has to be thicker than 2 full inches, otherwise the handle won't reach this sweet depth which makes the frame so controllable.

Sanded, wetted, resanded, oiled (linseed), and polished.