End caps

[petn7]

I have a polycarbonate tube. OD: 1.5"; ID: 1.375" (1 and 3/8 inch). I'm making a new WTC for my 1/200 Alfa sub (pic of it in my avatar)

I would like some o-ring end caps for it, but I can't make them on my own. I imagine machined nylon with nitrile, EPDM,or Viton 0-rings would suffice. Or because of the small size, would alumilite work as well?

Anyways, Is there anyone out there that can recommend the best technique and be able to make 2-4 end caps for me? I'd be willing to pay $45-$55 per endcap, depending on the method used to make it and the quality of the work.

Any advice, referrals, or possible "bids" would be appreciated.

[raalst]

Fung Pang has described a

Fung Pang has described a way to make end caps.

http://home.att.net/~cheap-sub/endcap.html

[petn7]

Fung Pang has described a

Fung Pang has described a way to make end caps.

http://home.att.net/~cheap-sub/endcap.html

I know, but I don't have his equipment, that's why I'm trying to "contract out" the manufacturing of end caps.

[redboat219]

why not do it the

why not do it the way Meriman does with his shaft seals. Cast the endcap with the o-rings in place. Or you could just try axial sealing. Here you cast the endcaps the usual was but you no longer need to make the grooves. You just need your o-ring to be the same diameter as your WTC. Water pressure pushing on the endcap ensure sealing.

[tmsmalley]

I know, but I don't

I know, but I don't have his equipment, that's why I'm trying to "contract out" the manufacturing of end caps.

Fung Pang uses a Dremel Mototool in a drill press stand and a few bits. These are pretty basic tools you might want to get anyway. It would cost about what you would pay to have the work done for you and you'd have the satisfaction of learning a new skill that will come in handy.

Here is a slightly expanded writeup on FP's method that might help.

The "How do I make endcaps for my WTC without a lathe?" is a perennial question for new sub guys. Either they
don't want to buy a set from the usual vendors or they have an odd size tube for which there is no standard endcap available.

Long time SubCommittee guy - Fung Pang - has a nifty
(and CHEAP) way to make endcaps without a lathe. I
have copied his instructions to the best of my memory
below. (FP - if I messed up, please chime in here!)

He cuts a length of the WTC tubing to act as a mold (he puts brass tubing over the tang of the bits to act as a spacer.)

Note - when he took the photos he didn't have his usual Dremel bits (#199, #198) in the chuck - so he stuck one
of his others in there, but you get the idea.

Here are his instructions.

++++++++++++++++++++++++++++++++++++++
How to make an odd size end cap

Why an odd size? You could buy a standard one, why make it?
I need a cheap WTC to go in my cheap sub! That means I have no lathe! Not everyone knows how to use one - I know I don't!

I use part of the pipe as a mold to cast an endcap, so any size pipe can be used.

For how to make a mold and casting, goto "smooth-on's website" but remember, most castings shrink; not too much on the small pipe, but the big pipe is a bit on the loose side.

Another thing to remember - the inside of most PVC pipe is not round.

All these end caps are made for pvc pipe you find cheaply in a plumbing store. And it could be any type of pipe.



Small one is 2", the big one 3".




The taps (ears) are to make removing the end cap easy (I copied this from another Subcommittee member's idea )

Making the mold...

One ring goes on top of the other.

Outside ring made from card stock, about ½ inch tall,
center ring is made from pvc pipe end cap, with cut out for taps (ears), about ½ inch tall

note]http://home.att.net/~cheap-sub/endcap4.jpg[/img]

Cutting the end off a PVC pipe cap with saw in Dremel drill press



This is a setup on a dremel drill press, a real drill press will do even better with lower rpm and more torque.

I set this up to take a picture, but it is a bit misleading.

The cutting bit should move in to the chuck little more, the spacer should be on the cutter.

Think of it as a router table, I start up on the Dremel router table setup with the stopper, it works very good on the end cap, until I try the taped end cap!




This doesn't show the pins that go on the baseplate of the drill press that you push the endcap up against to get an even depth cut.



I use the drill press as a upside down router, use brass tubing on the cutter as a spacer to adjust how deep it cuts and move the drill up or down to cut the width of the O ring, or just as Deep Sea Designs shows at http://www.deepseadesigns.net/wtcplans.html

Cutters - Dremel #199, #198 and spacers [brass tubing] to cut the grove for the 'O' ring

The brass tubing goes on to the shaft of the cutter, one after anther to build it up, so it will not cut too deep,
or the Dremel will jam to a stop. I like to run my Dremel at low speed, if i can, don't want to smoke it.

The cutter is thinner than most of the “O” ring that I find.

To fix this set the first cut at the high point of the cut, turn the end cap as the cutter cut in to it, when finish cutting around the end cap.

Put some paper under the end cap, this will adjust the end cap higher for next cut, check for size.

Add paper, cut, check, add paper, cut, check, remove brass tubing., cut remove paper cut, check, remove paper cut check.

Put a vacuum next to the cutter so it sucks up all the PVC cut out of the groove to stop the indoor snow storm!



Here is a view of the jig used for cutting the groove.

++++++++++++++++++++++++++++++++++

Thanks FP for the great idea!

[wingtip]

I imagine machined nylon with

I imagine machined nylon with nitrile, EPDM,or Viton 0-rings would suffice.

I recently made my own endcaps as the ones i recieved from mikes subworks had lots of holes and airbubbles and i was worried about drilling and tapping into this..
after talking with an engineer here at work ( we use nylon, delrin, g10 etc etc alot) and he said nylon absorbs water and can change something like .010 per inch as i recall... anyways i used delrin instead.

http://www.indyhelis.com/junk/sub/endcap03.jpg

http://www.indyhelis.com/junk/sub/endcap01.jpg

[Guest]

Just use PVC sheet. Acetal

Just use PVC sheet. Acetal (delrin) , polycarbonate or polystyrene will also work well, acrylic will also do, but this needs care when machining.

Nylon is water absorbent as mentioned, and as the cost is about the same as the other plastics mentioned, it makes little sense to use it.

Andy

[petn7]

Thanks for the insight guys.

I

Thanks for the insight guys.

I have someone making me some end caps.

[petn7]

I imagine machined nylon with

I imagine machined nylon with nitrile, EPDM,or Viton 0-rings would suffice.

I recently made my own endcaps as the ones i recieved from mikes subworks had lots of holes and airbubbles and i was worried about drilling and tapping into this..
after talking with an engineer here at work ( we use nylon, delrin, g10 etc etc alot) and he said nylon absorbs water and can change something like .010 per inch as i recall... anyways i used delrin instead.

http://www.indyhelis.com/junk/sub/endcap03.jpg

http://www.indyhelis.com/junk/sub/endcap01.jpg

Can you elaborate? I have Mike's endcaps as well, and except for the o-rings being a little too thin (or the o-ring groove being too deep) the end caps seem well made. What risks are you afraid of? When I drilled into the endcap, it was solid material with no bubbles.

Although, I admit, those delrin end caps look mighty fine...

[wingtip]

his endcaps work just fine

his endcaps work just fine and seal great, but my gearbox assembly and electronics chasis all "hang" from the endcap and is quite heavy. the standoffs i have are small and have a 6-32 thread and I just wanted a good solid material for peace of mind(and the experience of making my own) and to tweak his oring groove..
His groove is a bit wide by our standards here at work and we deal with oring stuff on a daily basis.. the footprint on my caps seemed to be a bigger footprint ... the footprint meaning when the cap is in the tube and you look thru the clear material at the oring you can see a dark shadow in the center of the oring where its actually making the physical seal... his seemed to be about 1/16th thick where my footprint is like 1/8th... whether or not that is desireable i dont know for certain but im guessing it is lol..

[petn7]

Yeah, I noticed the "footprint"

Yeah, I noticed the "footprint" issue, but I feel that in order to get the optimal footprint, one must make each endcap specifically for the particular tubing. Or, just use some teflon tape to make the o-ring sit higher in its groove and therefore creating a thicker footprint. I've done this as necessary.

[wingtip]

that method wont always work

that method wont always work depending on the width, and as i said i tightened the groove on mine... look at http://www.indyhelis.com/junk/sub/endcap01.jpg again... apologys for it being out of focus.. but notice the pink cap and the gap where the oring curves down and the flat surface of the cap diameter.... when that is slid into a wtc that oring gets pressed and most of the oring gets squeezed into that gap, even if you put tape under it, which im guessing is why the big difference in footprints... compared to the one i made where i narrowed that gap slightly...

also his oring groove is a rounded groove where mine, like everything we use here at work, is squared... i am not sure why its done like this but they do it like that here on everything and they seal to extremes here..

[skip asay]

The reason for using square

The reason for using square grooves instead of round ones is that, contrary to popular opinion, rubber does not really compress but rather it extrudes. With a round groove which is sized to the O-ring, the rubber has no where to go except above the groove and below the tube itself.....which isn’t very much. This then requires either 3 men and a boy to install/remove the end cap or a substantially smaller end cap diameter.

Skip Asay

[petn7]

The reason for using square

The reason for using square grooves instead of round ones is that, contrary to popular opinion, rubber does not really compress but rather it extrudes. With a round groove which is sized to the O-ring, the rubber has no where to go except above the groove and below the tube itself.....which isn’t very much. This then requires either 3 men and a boy to install/remove the end cap or a substantially smaller end cap diameter.

Skip Asay

My finger nails thank you for that explanation.

[petn7]

that method wont always work

that method wont always work depending on the width, and as i said i tightened the groove on mine... look at http://www.indyhelis.com/junk/sub/endcap01.jpg again... apologys for it being out of focus.. but notice the pink cap and the gap where the oring curves down and the flat surface of the cap diameter.... when that is slid into a wtc that oring gets pressed and most of the oring gets squeezed into that gap, even if you put tape under it, which im guessing is why the big difference in footprints... compared to the one i made where i narrowed that gap slightly...

also his oring groove is a rounded groove where mine, like everything we use here at work, is squared... i am not sure why its done like this but they do it like that here on everything and they seal to extremes here..

With enough teflon tape, the "gap" can be filled. The tricky part is not using too much tape where the endcap becomes impossible to install/remove. Also, if the cap is removed too often, the end cap needs to be retaped.