How to machine a tube 'hinge'

[dansawyer]

I am machining a ring hinge similar to this one. Mine will have an id of 4.19 inches. I have everything down except for the hinge. To make a long story short this started out trying to take astrophotographs and I ended up buying a Bridgeport BOSS CNC kit, completing getting it working, writing G - Code, and createing a solid blank of the hinge like the on in the picture. Cutting a slot and creating the closing side should be straight forward. However I am stuck on the hinge.
Does anyone have directions or pointers on how to machine such a hinge from a single piece?

 

[seasicksteve]

Google hinged scope rings and take a look how they are made it may provide some design ideas

 

[Nutfarmer]

Make the hinge first out of two pieces, then bore the Id with the two pieces clamped together. The hinge pin can be a dowel pin. Use over and under size reamers on the hinge pin hole.

 

[homebrewed]

Your clamp looks a lot like these. The hinge is made with a plate that joins the two main sections. It fits in a slot milled in the arc sections. Two pins join the arcs and the plate. If I recall correctly, the plate is reamed so the pins are a friction fit, but they are free to rotate in the arc sections.

Sorry, not a one-piece solution but something to consider. These are designed to draw two pieces together for vacuum applications so possibly could be simplified for your purposes (or perhaps useful in terms of stopping light leaks). One advantage of this approach is that the two arc sections are identical at the hinge portion, unlike a classic hinge. Obviously, the other end(s) are different to accommodate the screw IF you want one end captured. I've seen designs that make those ends the same as well, but they are a PITA to tighten up -- you will find yourself juggling too many degrees of freedom: two wayward clamp pieces, two pipes to join, a screw that is free to go its own way, a nut to tighten (how many hands do YOU have)......possible but not fun. Trust me, I know. If you go this route, make sure the screw is captured on the end of one of the arcs, you will be happy you did.

 

[JimDawson]

I don't think it's possible to make a hinged clamp as a single piece. We make some similar devices and they are all two pieces.

Here is a steady rest that I built that has the same type of hinge, should give you some ideas on design and work holding. https://www.hobby-machinist.com/threads/steady-rest.45980/

 

[Mitch Alsup]

Make the hinge first out of two pieces, then bore the Id with the two pieces clamped together. The hinge pin can be a dowel pin. Use over and under size reamers on the hinge pin hole.

This, and if the ID is critical, perform the boring operation using the joint already pinned together.

On telescopes, we often line the inner surface ID with felt (or similar) to avoid marring the tube and to allow some rotation and translation of the tube under moderate forces.

 

[homebrewed]

For a really quick and dirty solution, make or buy a pipe with the right ID. Split it in half, line with felt. Put a pipe clamp or two around it and tighten down. Who needs a friggin' hinge

 

[extropic]

I have used roller chain master links (size as appropriate) as the pivot for hinges. That way, the pair of clamp parts can be machined from a single piece of stock. Leave bosses for the master links to pivot in.