best way to mould a hollow cylinder with flanges both ends ?

[Merlin]

Hi,

How do I go about moulding a hollow cylinder which has flanges at each end flaring outwards and wont pull out vertically if in pillar box orientation in the moulding box due to these and another item on one side. Item is about 5 inches long and 1.5 diameter.

 

Forming clay round the outside for a two part mould does not address the problem of the centre. The inner diameter must be exact same as the master. I also dont want to waste a lot of silicone inside the tube as its expensive stuff, inside the tube at the 'top end' is a 2mm step which is ragged whilst the other end is perfect.

 

Maybe I have the inner anti wastage core rod running through both ends of the box, box lying down coffin mode !  Cylinder attached to 'coffin' at cylinders bottom good end. I form a clay barrier at the top end, around entire rim there, that also acts to support cylinder at that end.  create two channels using rod to the cylinder end, one resin in the other air out, rods attached using humbrol maskol. Treat maskol and tubes to mold release agent.  I pour silicone in between 'coffin ' and the  clay barrier and it travels down the inside only, stopping at the other end wall as the cylinder is fixed to that.

Then I remove the clay barrier and the cylinder is now suspended so it cant rise, apply mold release agent over the silicone, pour in the silicone to encompass the cylinder totally, then when cured , remove box, cut along sides in a wavy fashion to extract cylinder. Jiggle the 'T' end of the iner silicone plug to break the two tubes free (maskol should allow easy freeing up !) , pull rods out of silicone.

Remove cylinder then reassemble box , laying the lower silicone part in first, add walls and sellotape shut, with the inner core and its outer layer of silicone re-attached to box ends, but now gravity is a pain, as it will sag the upper silicone maybe ?  With my pouring vent at small end of coffin I stand 'coffin' on end and pour via end spout that will minimise that chance if silicone sag I hope.

 

Clear as mud no doubt, hope you can visualise this. any better ideas welcome.

 

Merlin

[Rob G]

3 hours ago, Merlin said:

 The inner diameter must be exact same as the master.

 

There's your first hurdle - if you're casting in resin, the likelihood of shrinkage (ooh errr missus!) is pretty high. Casting undersize and finishing with drill/broach etc is the only way to be sure of 'exact'.

 

If you only need one or two, is it easier to just make them out of plastic tube?

 

If you must cast, do as the kit manufacturers do, and split the tube longitudinally, then cast the 2 halves. Before making the mould, you will of course need to add back whatever you lose in swarf.

[Merlin]

Hi,

after much thought, I decided to CAD model it out, hope to spot any errors in method this way. Its about 5 inches long.

 

As it will or may prove useful to folk faced with molding such hollow interiors, attached is the story board of how it should go.

 

Let me know if you see any problems.

Cheers

 

Merlin