Sourcing 3in, polished 316 stainless Flanges?

[Chotu]

Originally Posted by CassidyNZ

I mentioned it in an earlier post, you probably already know this but. . . . When you put set screws in to hold the tubes firm in the footings, you should drill through the side of the tube where the threaded hole in the footing is then use a long enough set screw to go all the way through to the other side of the tube.

This way the set screw can be turned firmly against the inner wall of the tube without any distortion to the tube.

Actually now that I think about, on your application it calls really long set screws, maybe it won’t be that effective. I use the process on my tubing but size never exceeds 50mm (2”).

Ok. Thank you for that information and technique.

I could just through bolt the set screws too. If I’m willing to look at the set screws on one side of the piece. Maybe tap and thread the far end’s hole to avoid a nut on there.

[Ken Fry]

Originally Posted by Chotu

Found them! In FRP.

3” ID so I can put the support column inside.

3lbs each! About $50.

I’ll paint them for looks.

Some issues with these:
1.) 3 lbs is heavier than a 3" version of the 2" stainless fitting you started the thread with. Even if you cut off the excess length, you will be heavier than the stainless version. This thing is quite massive, owing mainly to the weakness of the fiberglass. (150 PSI rating is a very low bar -- no pun intended.)

2.) The 8" diameter 7/8" thick flange is so large that it will luck "clunky".

3.) The wrong side of the material is the mold side, so the side you see is not finished -- a lot of sanding and filling will be required to make them nice looking and ready for paint.

4.) Drilling and tapping fiberglass can be problematic unless you are the only person who will ever touch the screws that go into the fiberglass, because you cannot torque them to standard torques, due to the 2:1 or 3:1 difference in strength between the fiberglass and the steel fastener. If you go this route, better to use a through bolt than a set screw or anything that threads into the fiberglass.

So:
If I were doing this, I would make some anodized aluminum fittings. You could do these yourself, if there is a "maker's lab" with a metal lathe near you. If you wanted, these could be shaped like the stainless flange. You'd use a piece of plate for the flange, and piece of tube for the tube. Machine the hole in the plate and the outside of the tube to an interference. Depending upon the anticipated pullout load, the interference would be about .002" Make one and test it in a press. Then make the rest.

Satin finish them on the lathe (with emory cloth, etc) then get them anodized some nice color like blue or gold.

Even simpler: just use a flange without the tube protrusion (a 1" tall, 3" id, 5" od ring). Counterbore or counter sink the mounting screw holes at 6 locations. Counter bore the holes for the retainer bolt, so the both the head and nut are recessed.

Either of these would be lighter and better looking that the fiberglass plumbing fitting version.

Before doing any of this, you would want to quantify each potential load on the fitting. If there is any significant cantilevering at the fitting because of structural deformation of your davits under load, then you'd need to rethink things, because these flanges (of any type) should not be asked to deal with anything more than a relatively large, substantially pure side load (as in a short stiff tube fixed at both ends by flanges) and a relatively small pullout load.

[Chotu]

Well, I already got them. BUT, they are bases and tops for support columns.

The columns they hold in place are under compression loads.

Tensions loads possible if I’m at a dock and a 70mph wind from a thunderstorm comes up from aft of the boat.

Otherwise this is all in compression.

And I forgot one thing. I forgot to mention my interior support columns are frp. The exterior support columns are 3” aluminum with 1/4” wall. Beefy AF.

These flanges are to just hold those columns in their vertical position under compression.


These beefy support columns are the point at which the davit beams (3in x 3in by 1/4” wall square frp tubing) rest. It’s the starting point of the cantilever. 0 on the x axis.

These hold the roof directly below the cantilevered davits which are through bolted to the roof as well.

This is probably WAY overkill in all actuality, but I calculated all the loads for a dingy full of water, engine on, 12ft long, heaviest RIB and still left a big safety factor.

I’ll see soon when they arrive, but all the frp parts I’ve got so far as perfectly smooth and ready for paint.

Do you buy a lot of that stuff? I’ve got about a dozen pieces so far and they are already perfect finish.

However, that’s a cool idea about making them from aluminum at some kind of public machine shop. I’m not aware of one, but very good thinking.

I already have these arriving shortly though. Also, the less I have to make the better. Off the shelf is the way to go.

Originally Posted by Ken Fry

Some issues with these:
1.) 3 lbs is heavier than a 3" version of the 2" stainless fitting you started the thread with. Even if you cut off the excess length, you will be heavier than the stainless version. This thing is quite massive, owing mainly to the weakness of the fiberglass. (150 PSI rating is a very low bar -- no pun intended.)

2.) The 8" diameter 7/8" thick flange is so large that it will luck "clunky".

3.) The wrong side of the material is the mold side, so the side you see is not finished -- a lot of sanding and filling will be required to make them nice looking and ready for paint.

4.) Drilling and tapping fiberglass can be problematic unless you are the only person who will ever touch the screws that go into the fiberglass, because you cannot torque them to standard torques, due to the 2:1 or 3:1 difference in strength between the fiberglass and the steel fastener. If you go this route, better to use a through bolt than a set screw or anything that threads into the fiberglass.

So:
If I were doing this, I would make some anodized aluminum fittings. You could do these yourself, if there is a "maker's lab" with a metal lathe near you. If you wanted, these could be shaped like the stainless flange. You'd use a piece of plate for the flange, and piece of tube for the tube. Machine the hole in the plate and the outside of the tube to an interference. Depending upon the anticipated pullout load, the interference would be about .002" Make one and test it in a press. Then make the rest.

Satin finish them on the lathe (with emory cloth, etc) then get them anodized some nice color like blue or gold.

Even simpler: just use a flange without the tube protrusion (a 1" tall, 3" id, 5" od ring). Counterbore or counter sink the mounting screw holes at 6 locations. Counter bore the holes for the retainer bolt, so the both the head and nut are recessed.

Either of these would be lighter and better looking that the fiberglass plumbing fitting version.

Before doing any of this, you would want to quantify each potential load on the fitting. If there is any significant cantilevering at the fitting because of structural deformation of your davits under load, then you'd need to rethink things, because these flanges (of any type) should not be asked to deal with anything more than a relatively large, substantially pure side load (as in a short stiff tube fixed at both ends by flanges) and a relatively small pullout load.

[Ken Fry]

Originally Posted by Chotu

Do you buy a lot of that stuff? I’ve got about a dozen pieces so far and they are already perfect finish.

However, that’s a cool idea about making them from aluminum at some kind of public machine shop. I’m not aware of one, but very good thinking.

I already have these arriving shortly though. Also, the less I have to make the better. Off the shelf is the way to go.

Re the fiberglass, I was going by the picture.

I am always weighing the cost benefit of making/buying stuff. Sometimes it can get silly, as in this burner for an alcohol stove. It is one of two that can be slid into position under one pot or separated for use under two. The machined part is a venturi and is pressed together from a a plate and a cylinder, then finish machined. Fun project, not cost effective, but probably worth it in amusement value. The alcohol container is a cat food can.


Running a lathe is like crocheting: relaxing, slow, vaguely meditative... until you screw up and something flies out of the chuck.

[Chotu]

They are here! Incredibly strong, lightweight and smooth for paint. Excited!