Can odd parts be bought through Caswell individually

[george]

Hello Again

I was wondering if it is possible to buy Lexan Tubing for specific submarines from Caswell and the End Caps, bulk heads etc?

Just wondering.

Thanks

George

[He Who Shall Not Be Named]

George,

We used to sell discrete parts for our line of SD's. But the problems of inventory control and sizing (there is a wide tolerance between Lexan tube dimensions for any given size) made that practice unprofitable.

M

[Subculture]

I've made three films (part three is currently uploading and should be online very shortly) on the subject of DIY end cap construction. It involves the use of a lathe, so you'll need one of your own or access to a machine through a friend, school, work etc. It doesn't have to be a large lathe like the one shown, however.

For a few cents of material you can make parts for whatever size of cylinder you want, no casting parts or other fuss, you just need plastic sheet of suitable thickness and a length of tubing. The calculation for o-ring sizes may throw some a little, but it's very logical when you sit down and think about it- just simple subtraction, but take you time and double, no, triple check to make sure you have the right dimensions before you chop away at any material.

There is more to making a complete functioning WTC than presented in these films, however if you can get the caps and cylinder built, then you can buy in the shaft seals and add them fairly easily, and a tech rack for the R/C and batteries isn't that tough to build.

[Subculture]

[He Who Shall Not Be Named]

This is a great resource, Andy. Thank you so much for the presentation. Good stuff, pal.

David

[george]

Hi Subculture

Thanks for posting the videos. I have learned a few extra tips that I did not know before. I even see that you have the same plastic string effect as I do on my lathe. I thought it was due to a dull cutting bit because of my raw limited lathe experience.

I wonder if you would be willing to come up with a General Formula sheet to cover ALL the math you did to determine the end cap start to finish including the o ring?

George

[Subculture]

Basically 10-15% cross sectional compression (best to work to the 15% figure) and 1 to 5% of the of o-ring diameter (inside diameter remember) for snap/stretch of the ring. All other dimensions are going to depend on the pipe you are using.

Third and final part of the film

[Subculture]

So in written form for o-ring calculation. I'll use imperial units this time, to make life a bit easier for US readers.

Assuming radial compression, you need to know three things-

1. The inside diameter of the tubing you are using, I recommend measuring this with calipers like I show in the videos, as the tolerance is variable. Take the measurements in different spots, and go by the lower figure. So for arguments sake we'll say we are using 3" tubing with an internal diameter of 2.75", and we'll say that figure varies plus or minus about 5 thou- not unreasonable for plastic extruded tubing I find. we would want to note our working diameter 2.745".

2. O-ring cross section. Now I'm not 100% au fait with the o-ring standards in the US, here in the UK they conform to British Standards. lets assume that we wish to use a 1/8" thick o-ring or 0.125" in decimal. This is the cross sectional diameter.

3. How much squeeze or compression we want to put on our o-ring. We want to squeeze that cross sectional diameter about 15% to effect a water tight seal on our tube, so 15% of 0.125" is about 19 thou, we can easily go for 20 thou for a nice round figure, especially as our tubing tolerance is far from perfect.

So to calculate out groove depth we sub tract 20 thou from the o-ring cross section 0.125"-.02"= 0.105"

So our groove depth is 0.105".

The last step is to factor the 'snap' for our o-ring, which is basically a requirement to have the o-ring stretch a little when it is in place on the groove. This helps it stay in place.

The figure we use is 1-5% with an optimum being about 2%. So we take out earlier inside tubing dimension of 2.745" diameter subtract 2x cross sectional o-ring diameter, which gives us a figure of 2.495". Take off 2% of that which gives us a figure of 2.44" which is o-rings inside diameter- remember from part one that o-rings are measured on the inside diameter not the outside. In fact an o-ring diameter of between 2.37-2.47" would be perfectly acceptable.

The last stage is to work out our groove width for the o-ring, as it extrudes as we squeeze it. I would take the 1/8" o-ring cross sectional diameter, add on the squeeze which is 20 thou, and add on 25-50% so 25-30 thou, which gives us a figure of 0.15-0.155" groove width minimum. You can go higher than this, but not lower, but don't go crazy.

Is that easy to understand, or still clear as mud?

[Kazzer]

So in written form for o-ring calculation. I'll use imperial units this time, to make life a bit easier for US readers.

Andy

Let 'em suffer. The USA is the only country still using this rubbish system. No wonder we're going backwards here!

[greenman407]

You made it easy for us Andy. Thanks

[Subculture]

You made it easy for us Andy. Thanks

Have I? Good stuff.

Here's a little test then for anyone that wants to take it. Found a really good US based website for o-rings, and they have a chart.

http://www.oringsusa.com/html/o-rings.html

On the far left of the chart, there is a column of numbers relating to AS568, which I would take a guess is your equivalent of our BS (ahem,that's British Standards btw, not the other 'bs'!).

Tell me me what AS number you would order for the end cap spec I detailed in my last post, also if I reduced the pipe to 2.5" diameter with 1/8" wall thickness and about the same internal tolerance, what size o-ring would I order then?

[He Who Shall Not Be Named]

Andy

Let 'em suffer. The USA is the only country still using this rubbish system. No wonder we're going backwards here!

How the hell did we let all these Brit's in here, anyway!?....I WANT ANSWERS, damit!

M

[greenman407]

Rubbish System??? In 1826 in Seven Sisters, London, the British themselves crafted the present units of measure that the US uses today. If I am not mistaken the United Kingdom still ,by law, still uses the Imperial system of measurement as well as the Metric System.
I dont know,.........the Metric System seems......so............so, I dont know..........foreign?:pop

[He Who Shall Not Be Named]

I don't know about you guys, but I feel that any base number system founded on the count of human extremity digits (male genitalia don't count) is just plain cheating!

Real men use the Imperial number system. It ain't supposed to be easy!

M

[Kazzer]

Bin there -- dun all that! It sucks!

Try this - add these up Pounds shillings and pence - the fractions are farthings


4/2/93/4
5/9/111/2
7/17/61/4
7/0/11/4
19/11

Next - price out 12 @ 2/91/4


You should be able to do these in your head.