On 19-Mar-18 9:51 PM, Joseph Gwinn wrote:
On Mar 19, 2018, Perry wrote
(in ):

On 19-Mar-18 12:19 AM, Joseph Gwinn wrote:
On Mar 18, 2018, wrote
(in ):

On Sunday, March 18, 2018 at 3:03:49 AM UTC-4, Perry wrote:


The part is about 2"/50mm wide and just over 1"/25mm tall.
The bottom face is say 6" x 2" = 12" squared.

If the vacuum pump sucks down to say 1/2 of atmospheric then I should
see 12 Sq Inch x 7.5 Pounds/Sq Inch = 90 lb down force.

The angled sides of the mold should prevent the part being thrust
sideways when flycut.


As all four sides are sloped I had thought of using a second aluminium
mold as a vacuum chuck. I would have to machine 5mm machined off the top
to expose the top face of the casting that needs to be machined back.
chuck.
Wouldnt it be quicker to simply use a sharp X-acto knife to cut the
flashing away?


---

That would remove the flashing but we want the bottom face to be
completely smooth. It's one of those jobs where aesthetics count.

How abouts using a belt sander to flatten the surfaco and remove the flash.
If the aesthetics are okay it would be a bell of a lot faster.

Id be tempted to wet sand it on a submreged metal plate with coarse
wet/dry sandpaper glued to it, facing up. The sloshing water will keep the
plastic cool and wash the swarf away as you go. Ive used this approach
many times.

Joe Gwinn

The belt sanding (or a jig and a 'bobbin' or disk type sander) is
something I've thought about.

I'd like to maintain the finished part both flat and not tilted - if
that makes sense.

Machining under a mill makes this easier to attain.

The water aspect is interesting. The down side of the epoxy is that when
sanded it changes from black to a whitish grey colour.

The whitish gray color is the frosted surface due to the coarse sandpaper.
Wet sand using a series of finer grits and it will go to a mirror finish,
which will be black when dry.

One can also or alternately varnish the coarse-sanded surface.

Joe Gwinn



Thanks - worth considering.