2 part epoxy vs silicone II

[Charlie Knighton]

i am turning my 1st urn for a cousin

i will be using a threaded pvc shutoff valve for the bottom opening

i would like to coat the inside of the urn and glue the pvc shutoff valve to the bottom opening

major concerns is wood movement (using dry Amboise maple) as the weather changes. also there is a precaution on the epoxy box. it says "Not suitable for polyethylene, polypropylene, flexible materials or prolonged immersion in water."

any suggestions or precautions ???????????

 

[Joe Greiner]

Whatever the exact details of the "pvc shutoff valve" may be, you will probably get best results from dissimilar material combinations by making a mechanical connection for structural integrity (nuts & bolts or screws), and using glue or sealant for sealing. Polyurethane sealant works well in adverse environments, and it's generally available in two or three colors at the Borgs. The mechanical connection can then be loose enough to accommodate movement.

If you can post a sketch of your proposed detail, some better ideas might follow.

 

[Charlie Knighton]

the urn has not been hollowed, will do that today, the tenon top and bottom have not been turned away

i got the idea from post about a month or so ago from mm

Short answer - no. Some are not urns, some have slide fits on top, and some have removable bottoms.

The cremains are normally delivered in a plastic bag, so I wouldn't make the neck of the vessel too narrow or you'll be decanting. Leaves out most of the brass type threads you can purchase from turning places. If you want threads, get some 4" PVC pipe fittings, male and female, and glue them in. That way you can open and close often, though why, I do not know.

Just a taper twist fit is fine for a spreading ceremony. You can modify it with a parting tool and hydraulic O ring to get a nice tight fit that way too.

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[john lucas]

I use Clear Silicone caulk to glue my hand mirror glass to the wood. It works incredibly well and doesn't suffer from any wood movement problems. It does not dry solid like epoxy but should work well for what your doing. I will say that I have not glued something that has to be unscrewed. I don't think the forces would be a problem but it could be.

 

[Richard Baker]

Will there be enough room and wall thickness to drive a few small screws thru the pvc and into the wood in the radial direction? These in addition to the clear silicone caulk/adhesive, to resist torque when screwing/unscrewing the plug. Might also want to roughen the pvc surface to give the silicone a better grip.

 

[Charlie Knighton]

wall thickness

Will there be enough room and wall thickness to drive a few small screws thru the pvc and into the wood in the radial direction?

yes, but...

i can drill from the outside of valve all the way through the pvc, but i need the screw head on the inside with the threads and i do not see how to make the hole bigger on the inside threads so the screw head will be below the threads. i can use a finishing nail and get below the threads into the wood as i have plenty of wall thickness. i am leaning towards using the finishing nail, unless someone can explain to this confused woodturner how to easily and frugally do that

i will rough up the outside, good idea

 

[Richard Baker]

Good point. You would almost have to drill at an angle from inside the pvc in order to countersink for screw heads. Maybe no workie. And screws or nails, might still want to pilot drill the wood to prevent splitting. Thought I knew the answer, but maybe not. Might consider making a test piece with silicone only, let set up well, and give it a torque test. Might be ok.

 

[Mark Warden]

How bout drilling from the outside and glueing brass rods in and fininshing the end of the rod to leave an accent.

 

[Charlie Knighton]

might still want to pilot drill the wood to prevent splitting

i believe the finishing nail will work without splitting the maple, the maple is pretty soft wood and i should be able to nail it in, the outside dimension of the shutoff valve is 4" so i have enough room to nail it from the threaded side i will probably have to let the silcon set up on the sides of the pvc before nailing, not sure i will have enough room to drill pilot hole, but will try

 

[Charlie Knighton]

How bout drilling from the outside and glueing brass rods in and fininshing the end of the rod to leave an accent.

good idea, but i have a cove at the foot of the urn, it might hide it
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[john lucas]

Charlie Just cut vertical grooves in the wood and some grooves in the plastic. They can be shallow. The epoxy or silicone caulk will fill the grooves and keep it from twisting. I do this with the tenon on my mirror handles. These joints are often cross grain joints and will weaken with wood movement over the years. The epoxy I use for my handles never really shrinks but can break the bond over the years. The grooves make sort of a mechanical dowel joint with the epoxy acting as a dowel. I think silicone caulk would do the same but to a lesser degree.
Scratching or heavily texturing the outside of the plastic will also increase the mechanical strength of the joint. I don't know if I described that very well. Think of what happens if you put a dowel in a hole and then drill a small hole right at the joint of the two. Then you fill this hole with a small piece of wood. The wood keeps the dowel from twisting. That is what the epoxy does.

 

[Joe Greiner]

First things first: The pvc fitting is usually called a "cleanout plug," not a valve of any sort.

The screw heads do NOT need to be inside. You could pre-drill (undersize) pilot holes in the wall of the plug body for wood screws from its outside, and let them (temporarily) extend into the interior, with the screw heads well proud of the exterior. Then use a small cutoff wheel in a Dremel (or equivalent) to grind below the threads of the plug.

With a generous-enough wall thickness in the wood, rout pockets to mate with the screw heads, undercut if you think necessary. This can, and should, be a very loose fit.

Fill the pockets and the annular gap with sealant.

All of this might be over-engineered, and John's suggestions could also work quite well.


Another option, really, really strong, is sometimes used on boiler heads and ship engine heads, a variation of John's grooves. With both parts assembled, drill holes along the boundary, to create half holes in each material. It's advantageous to deliberately make one of the hole spacings unequal to the others, for accurate final assembly. Fill the holes and the annular gap with sealant. Press a piece of (slightly smaller) all-thread into each hole. On locomotives and such, the holes are also tapped for the threaded fasteners - obviously overkill for your application.

 

[Charlie Knighton]

Charlie Just cut vertical grooves in the wood and some grooves in the plastic. They can be shallow. The epoxy or silicone caulk will fill the grooves and keep it from twisting.

good idea John, i saw you demostrate your hand mirrors at concord a year or so ago, i started useing the silicone you suggested

Then use a small cutoff wheel in a Dremel (or equivalent) to grind below the threads of the plug.

good idea, Joe

i am still a little worried about splitting the wood, i prefer to drill hole on inside pvc and into wood, i may predrill pvc and then after sealant setup use vise grips to hold small size drill bit and hand drill if possibe

 

[Joe Greiner]

At this stage, you can still use a variation of the boundary holes, maybe even stronger:

Start all holes perpendicular to the bottom to establish their locations. For about half of them, continue to the target depth. For the rest, drill at a slight outward angle to engage more of the wood. Put some of the same sealant on short pieces of slightly smaller all-thread, and place in the holes. The combination will create wedges, in effect, almost impossible to separate.

BTW, your camera's date setting seems to be off by a year.

 

[Charlie Knighton]

good idea, Joe, the silicone has not dried yet, must be the humidity

i will change date,thanks

i had precut holes in pvc, here is my hand threading hole with bit, vise grips, and knife to put pressure on bit

 

[Jim Keenan]

If you really want some to stick and never plan to remove it, go to the marine section of your local Ace hardware or to a marine chandlery and get 5200 sealant. make sure you are wearing disposable gloves when you use it.

 

[Bill Boehme]

First things first: The pvc fitting is usually called a "cleanout plug," not a valve of any sort.

I sure am glad that you cleared that up, Joe. I had a mental image of an urn with a spigot at the bottom like a coffee urn. When I read that it was a cremation urn, I was getting really confused about the whole thing.

Now that I think that I know what is going on, why is a screw top needed? Couldn't you just solvent weld plugs with slip fittings to a section of PVC.

There are very few things that will actually bond to PVC and neither epoxy nor silicone sealant will truly bond to it, but will usually do well enough for all practical purposes. Something that actually will stick to it is butyl rubber caulk and possibly also latex caulk. Fill the space between the wood and PVC with the caulk and it will be an effective seal. With any caulk -- including silicone caulk, it needs to be added in very small increments and built up over a period of time because it needs air to cure.

 

[Joe Greiner]

Here's a recent discussion about threads in cremation urns: http://www.aawforum.org/vbforum/showthread.php?t=5968

The threaded fasteners in tapped holes are sometimes called "shear pins." Many variations possible. I've used them to repair cracks in cast iron pulley spokes for restoration.

 

[Charlie Knighton]

There are very few things that will actually bond to PVC and neither epoxy nor silicone sealant will truly bond to it, but will usually do well enough for all practical purposes. Something that actually will stick to it is butyl rubber caulk and possibly also latex caulk. Fill the space between the wood and PVC with the caulk and it will be an effective seal. With any caulk -- including silicone caulk, it needs to be added in very small increments and built up over a period of time because it needs air to cure.

i agree, i am finding the sealant II is not drying

sometimes i take step backward on learning curve before moving forward again