I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

On Sun, 18 Mar 2018 14:36:46 +0800, Perry wrote:

I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

Wouldnt it be quicker to simply use a sharp X-acto knife to cut the
flashing away?


---
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On 18-Mar-18 2:49 PM, Gunner Asch wrote:
On Sun, 18 Mar 2018 14:36:46 +0800, Perry wrote:

I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

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.

On Saturday, March 17, 2018 at 11:36:55 PM UTC-7, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.

So, mount a similar mold to a lathe faceplate, apply pressure on the
workpiece center with the tailstock, and face off the outer rim of the gizmo.
Then apply clamps, retract the tailstock, and complete the cut.

Fly cutting something that I can't hold in a vise makes me nervous.

On Sun, 18 Mar 2018 15:03:41 +0800, Perry wrote:

On 18-Mar-18 2:49 PM, Gunner Asch wrote:
On Sun, 18 Mar 2018 14:36:46 +0800, Perry wrote:

I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

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.


Ah! One of "Those"

(Grin)


---
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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.

Dan

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

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.

On 18-Mar-18 5:30 PM, whit3rd wrote:
On Saturday, March 17, 2018 at 11:36:55 PM UTC-7, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.

So, mount a similar mold to a lathe faceplate, apply pressure on the
workpiece center with the tailstock, and face off the outer rim of the gizmo.
Then apply clamps, retract the tailstock, and complete the cut.

Fly cutting something that I can't hold in a vise makes me nervous.



Yeah I'm not so keen on the fly cutting myself. Actually I may have
misled you. As you've probably guessed I am not a machinist.

Facing would be done using a tool like this but with only 4 cutting inserts.

http://www.machiningnews.com/wp-cont...1.-560x534.png


It cannot be machined in a lath chuck as the cast part has a long cable
attached to it.


Cheers.

On Sunday, March 18, 2018 at 2:36:55 AM UTC-4, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

I've been doing a lot with vacuum work holding lately. It sounds like your plan is pretty good. If you have a reasonably close fit around the sides, you are safe from the part flying out of the fixture.

What I would do is machine slots for the vacuum to spread around and also machine a groove around the periphery of the bottom to place a seal. I use 1/8" neoprene round cord from McMaster. Make the groove about 3/32 deep and 1/8 wide and the neoprene will just sit in there and make a very good seal. If you have irregularities larger than that will absorb, go to a thicker seal - I also have 1/4" material, but haven't had the need to try it yet.

If you are using a refrigeration pump and you have a good seal, you are going to get a LOT better than 1/2 atm, much closer to 1 atm.

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

On 3/18/2018 9:06 PM, Perry wrote:
On 18-Mar-18 5:30 PM, whit3rd wrote:
On Saturday, March 17, 2018 at 11:36:55 PM UTC-7, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.

So, mount a similar mold to a lathe faceplate, apply pressure on the
workpiece center with the tailstock, and face off the outer rim of the
gizmo.
Then apply clamps, retract the tailstock, and complete the cut.

Fly cutting something that I can't hold in a vise makes me nervous.



Yeah I'm not so keen on the fly cutting myself. Actually I may have
misled you. As you've probably guessed I am not a machinist.

Facing would be done using a tool like this but with only 4 cutting
inserts.

http://www.machiningnews.com/wp-cont...1.-560x534.png



It cannot be machined in a lath chuck as the cast part has a long cable
attached to it.


Cheers.

A face mill.

Is there any reason you can't put the face mill in the lathe chuck and
fasten the piece to the cross slide? Perhaps held tightly in stiff foam
rubber?

Paul

On Monday, March 19, 2018 at 2:28:56 PM UTC-4, Paul Drahn wrote:
On 3/18/2018 9:06 PM, Perry wrote:
On 18-Mar-18 5:30 PM, whit3rd wrote:
On Saturday, March 17, 2018 at 11:36:55 PM UTC-7, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.

So, mount a similar mold to a lathe faceplate, apply pressure on the
workpiece center with the tailstock, and face off the outer rim of the
gizmo.
Then apply clamps, retract the tailstock, and complete the cut.

Fly cutting something that I can't hold in a vise makes me nervous.



Yeah I'm not so keen on the fly cutting myself. Actually I may have
misled you. As you've probably guessed I am not a machinist.

Facing would be done using a tool like this but with only 4 cutting
inserts.

http://www.machiningnews.com/wp-cont...1.-560x534.png



It cannot be machined in a lath chuck as the cast part has a long cable
attached to it.


Cheers.

A face mill.

Is there any reason you can't put the face mill in the lathe chuck and
fasten the piece to the cross slide? Perhaps held tightly in stiff foam
rubber?

Paul

What would be the advantage to that over doing the same in a mill?

Perry - do all as you describe but skip the vacuum and use two hold down
clamps on the surface you're cutting. Use the clamp on the left while you
surface the right side and the opposite. If too costly timewise, you'll at
least get a look at the finished appeareance.

Hul

Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

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.

On 20-Mar-18 2:28 AM, Paul Drahn wrote:
On 3/18/2018 9:06 PM, Perry wrote:
On 18-Mar-18 5:30 PM, whit3rd wrote:
On Saturday, March 17, 2018 at 11:36:55 PM UTC-7, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.

So, mount a similar mold to a lathe faceplate, apply pressure on the
workpiece center with the tailstock, and face off the outer rim of
the gizmo.
Then apply clamps, retract the tailstock, and complete the cut.

Fly cutting something that I can't hold in a vise makes me nervous.



Yeah I'm not so keen on the fly cutting myself. Actually I may have
misled you. As you've probably guessed I am not a machinist.

Facing would be done using a tool like this but with only 4 cutting
inserts.

http://www.machiningnews.com/wp-cont...1.-560x534.png



It cannot be machined in a lath chuck as the cast part has a long
cable attached to it.


Cheers.

A face mill.

Is there any reason you can't put the face mill in the lathe chuck and
fasten the piece to the cross slide? Perhaps held tightly in stiff foam
rubber?

Paul


I'm worried about holding the work piece. The sloped sides make holding
it difficult.

Thats not a bad idea Hul. Maybe some of those toggle type clamps would
make it easy to do. Thanks.


On 20-Mar-18 5:54 AM, Hul Tytus wrote:
Perry - do all as you describe but skip the vacuum and use two hold down
clamps on the surface you're cutting. Use the clamp on the left while you
surface the right side and the opposite. If too costly timewise, you'll at
least get a look at the finished appeareance.

Hul

Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

On 19-Mar-18 8:32 PM, rangerssuck wrote:
On Sunday, March 18, 2018 at 2:36:55 AM UTC-4, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy part.


The part is cast using epoxy into an open top aluminium mold.
When the part is removed from the mold there is a meniscus type sharp
flashing along the edge.


What I want to do is flycut about 1mm of material off this face to
remove the sharp casting flashing and to create a smooth surface.

The only way I can think of holding it is in a vacuum chuck of some sort
as the four sides are sloped (like an inverted flat top pyramid).


Part side view is as below;


Need to flycut this top face
----------------------------------------------------
\ /
\ /
\ /
\ /
-------------------------------------------


-----------------about 7"/175mm long-------------

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.

I could plumb a vacuum line into the base and use a refrigeration style
vacuum pump to hold the part down and then flycut the top.


Will it work?

Should I use a die grinder to run a few slots for the vacuum to spread
around in the bottom of the mold base used for clamping?

I've been doing a lot with vacuum work holding lately. It sounds like your plan is pretty good. If you have a reasonably close fit around the sides, you are safe from the part flying out of the fixture.

What I would do is machine slots for the vacuum to spread around and also machine a groove around the periphery of the bottom to place a seal. I use 1/8" neoprene round cord from McMaster. Make the groove about 3/32 deep and 1/8 wide and the neoprene will just sit in there and make a very good seal. If you have irregularities larger than that will absorb, go to a thicker seal - I also have 1/4" material, but haven't had the need to try it yet.

If you are using a refrigeration pump and you have a good seal, you are going to get a LOT better than 1/2 atm, much closer to 1 atm.





Thanks. I was thinking of buying an eBay refrigeration vacuum pump. I
can get a 6 or 12 CFM unit for a couple of hundred dollars. I've got a
fridge compressor pump but its small and pumps a low volume.

Thanks for the info on the sealing bead.

"Perry" wrote in message
...
On 19-Mar-18 8:32 PM, rangerssuck wrote:
On Sunday, March 18, 2018 at 2:36:55 AM UTC-4, Perry wrote:
I need to flycut the top face of an irregularly shaped cast epoxy
part.


Thanks. I was thinking of buying an eBay refrigeration vacuum pump.
I can get a 6 or 12 CFM unit for a couple of hundred dollars. I've
got a fridge compressor pump but its small and pumps a low volume.

Thanks for the info on the sealing bead.

https://www.ebay.com/sch/i.html?_fro...+pump&_sacat=0

Mine pulls 26".