[SpacedCowboy]

I'm planning on buying a home injection-moulding machine, and a CNC mill to generate the moulds. What I'm not entirely certain of is the software to make the moulds.

I was looking at this page and it doesn't look too hard to make a mould, but it needs a few things:

• The ability to create very fine structures - 0.005" by 0.05" for example - channels of this sort of dimension are used to allow air to escape from the mould as the plastic is injected
• The ability to model something then split it in half (for the upper and lower parts of the mould)
• The ability to create "negatives" of the model. Essentially a boolean subtract, but it would be nice to not have to worry about alignment etc.

I was hoping to get the Alibre design package for the CAD part, and then possibly use meshcam to import (from STL or DXF) the design that Alibre created, and mill it out.

Anyone got any comments, help, guidance etc.? I've used CNC before (I've got a 3D printer, and a PCB "engraving" machine) but I've not got into milling parts before, so I'm all ears

Cheers
Simon

[ben_jackson]

Alibre's strength is not "surfaces". It does have "lofting" but if you want to make complex "organic" 3D shapes then Alibre may not be for you. It does support "draft" (tapering for mold release) on extrusions and some other operations. It does have boolean operations. I have not tried them to know if they retain associativity to the parasolid geometry.

It has STL export (only) and 2D (only) DXF import/export.

Although I have never used it, I think people recommend Rhino (or, of course, Solidworks) for complex smooth shapes. Blender could also do that but it has a learning curve all its own.

[SpacedCowboy]

Alibre's strength is not "surfaces". It does have "lofting" but if you want to make complex "organic" 3D shapes then Alibre may not be for you. It does support "draft" (tapering for mold release) on extrusions and some other operations. It does have boolean operations. I have not tried them to know if they retain associativity to the parasolid geometry.

I guess I'm not after "organic" shapes, but I was looking here and those seemed to be about the sort of complexity I'm thinking of. The first things I want to make are brackets to fasten some LEDs onto some extruded aluminium. There's some complexity in the "star" shape of the LED heatsink, but I'm thinking more like the first of the three images in...

It has STL export (only) and 2D (only) DXF import/export.

Although I have never used it, I think people recommend Rhino (or, of course, Solidworks) for complex smooth shapes. Blender could also do that but it has a learning curve all its own.

[shudder] I've tried Blender; rather I should say that I have been tried by Blender. On the other hand, I have got 3d models working quite nicely in Sketchup, but it doesn't have the precision required for the mould. I guess it *was* designed for building-scale models, not 1/1000" scale models [grin]

Thanks for the insight

Simon

[HuFlungDung]

I'd advise that you need a NURBS modeller to get models that are smooth enough for precision machining. I've never worked with an stl modeller to know what the options are, but suffice to say, you need a lot of very small triangles to simulate a sphere, but only one NURBS surface to do the same thing.

A NURBS model is also something that you can do useful Boolean operations upon, and this is handy whenever you need to make male-female offsets for molds. You can also fabricate surfaces, extract edges from NURBS surfaces, and this is very much necessary to do precision machining or to add features to an existing model.

I won't say it is easy to make organic NURBS surfaces, because I don't run into that need in my work. But I make all sorts of engineered shapes such as your samples above.

I use OneCNC. This makes sense to me, since it is necessary to have a CAM system that can do something with your model. So if it comes with solid modelling capabilities (which it does have available in certain versions) then, why not use it to its maximum capability? I do and so far have not needed to look further.

There are other NURBS capable systems out there as well. I don't know if any of them are budget priced like Alibre, though. Darn it anyway!

[HuFlungDung]

You might need to check the various export options from Alibre. I'm sure that guys are exporting NURBS models using that software. The default file type that Alibre saves into might be an STL, but it may have other options.

[SpacedCowboy]

Not wishing to argue with those who know a lot more about this than I, but also wanting to clarify my requirements...

I don't really want or need curvy surfaces - I'm happy with flat, boring, plain ole squares If I could round-off my cube-like straight edges into quarter-round edges, it'd be a bonus, but it's not necessary.

Here's an image (hot off the 3D printer, and still with the printing-raft semi-attached [grin]) of the first prototype of the part I'm thinking of:



It's about 1/3 the size now (lengthwise), and slightly more "shaped" underneath, but it's still angular, flat, and geometric, not curved. Does that make a difference with needing NURBS ? Or would you recommend I use a NURBS modeller anyway ?

I'm trying to do this on a budget (aren't we all [grin]), so the cheap price of Alibre Design appeals. I went to the oneCNC website, but there's no details of any pricing anywhere I can find [sigh].

Thanks for the help

Simon

[HuFlungDung]

As the infamous owner of Practical Machinist forums once quipped something to the effect: I'm having trouble seeing the individual atoms in that picture. Could you make it bigger?

[DIYaholic]

HuFlungDung,
Careful there, watch what you say! I here that if Practical Machinist is mentioned here on the "Zone", the post gets deleted!

My bad! It's the other way around.

Randy,

[SpacedCowboy]

As the infamous owner of Practical Machinist forums once quipped something to the effect: I'm having trouble seeing the individual atoms in that picture. Could you make it bigger?

I sort of expected the forum s/w to thumbnail it down [grin]. It does rather look like what a scanning tunneling electron microscope produces, doesn't it

Perhaps I ought to have used links:

Here's the model of what it was supposed to look like on top, and here's the underside. That turned into this for the top of the bracket, and this for the underside.

What I was trying to show though was that all I'm after is relatively straightforward 90 degree angles...

Simon

[Edit: I ssh'd into the server from here at work, did 'sudo port install netpbm' and resized the images. Isn't unix great ? :-]

[tobyaxis]

I make molds with Alibre regularly. Of coarse the surfaces made aren't free form or organic it is fully capable of making mold models.

A correct plan of attack will allow you to make just about any shape.

Look through the Tutorials, the answers are in there.

[SpacedCowboy]

I make molds with Alibre regularly. Of coarse the surfaces made aren't free form or organic it is fully capable of making mold models.

A correct plan of attack will allow you to make just about any shape.

Look through the Tutorials, the answers are in there.

Cool - that's encouraging. Thanks

To be honest, I'd not thought it would be an issue for a CAD program to do what I wanted, but then I tried Sketchup, and it fails to render or cope with the tiny-resolution (0.003" x 0.05") channels I'll need to allow the air out of the moulds when the plastic is injected. Hence the questions

I'll have a look through the tutorials when I get my PC (for the first time in my life, I'm buying a PC to run windows...). I'm guessing I could probably run the s/w under VMWare, but I'll need an actual honest-to-god parallel port for the CAM part, so I figured I might as well get a dedicated PC...

Thanks for the help,

Simon

[ben_jackson]

To be honest, I'd not thought it would be an issue for a CAD program to do what I wanted, but then I tried Sketchup, and it fails to render or cope with the tiny-resolution (0.003" x 0.05") channels I'll need to allow the air out of the moulds when the plastic is injected. Hence the questions

That's surprising to me. Sketchup can definitely work in precise units. Where Alibre is better than Sketchup is when you change your mind about a dimension of some part way after you've drawn it. Alibre's method of operation remembers how you created your 3d part from a 2d sketch and when you go back and change your very first operation then everything else "replays" on top of that. In Sketchup if you change your mind later about the shape of a hole you cut through something you basically have to nuke the hole, redraw it to your new specifications and then cut it again.

(obviously it does other things better than Sketchup too, but that's probably the main thing when it comes to moldmaking)

You can download Alibre and try it for 30 days. Do the tutorials and see if you like it!

For what it's worth, I think the idea of going to STL files (or NURBs or whatever) for rectilinear shapes is a bad idea. If you really want a rectangular pocket you're better off drawing a rectangle and milling it with a conventional 2.5D cutting path. The results will be much better (and much faster) than milling a 3D mesh surface that happens to define a rectangular pocket.

[SpacedCowboy]

That's surprising to me. Sketchup can definitely work in precise units.

Me too - but when you get down to those sort of resolutions, the OpenGL renderer just shows large triangles. Zooming out once jumps to about 10 steps of zoom-out, and you can't "push" the rectangle to create the surface.

Where Alibre is better than Sketchup is when you change your mind about a dimension of some part way after you've drawn it. Alibre's method of operation remembers how you created your 3d part from a 2d sketch and when you go back and change your very first operation then everything else "replays" on top of that. In Sketchup if you change your mind later about the shape of a hole you cut through something you basically have to nuke the hole, redraw it to your new specifications and then cut it again.

(obviously it does other things better than Sketchup too, but that's probably the main thing when it comes to moldmaking)

You can download Alibre and try it for 30 days. Do the tutorials and see if you like it!

I will do, as soon as the PC turns up I'm not sure how a 2D sketch could transform into an asymmetric outline, but the examples on their sites are way more complex than I want, so I'm sure it's possible [grin]

QUOTE=ben_jackson;753430] For what it's worth, I think the idea of going to STL files (or NURBs or whatever) for rectilinear shapes is a bad idea. If you really want a rectangular pocket you're better off drawing a rectangle and milling it with a conventional 2.5D cutting path. The results will be much better (and much faster) than milling a 3D mesh surface that happens to define a rectangular pocket.[/QUOTE]

Well, I have a lot to learn about... Perhaps I'll end up doing it in 2.5D after all

Cheers,
Simon

[mactec54]

Hi SpacedCowboy

One of the most important things for your cad to be able to do, is doing the parting line,(split the mold in the right place) not many cad programs do this, without it there can be a lot of extra work to make your part come out of the mold, this is something you only get one shot at when making/cutting the steel for your mold

[tobyaxis]

Cool - that's encouraging. Thanks

To be honest, I'd not thought it would be an issue for a CAD program to do what I wanted, but then I tried Sketchup, and it fails to render or cope with the tiny-resolution (0.003" x 0.05") channels I'll need to allow the air out of the moulds when the plastic is injected. Hence the questions

I'll have a look through the tutorials when I get my PC (for the first time in my life, I'm buying a PC to run windows...). I'm guessing I could probably run the s/w under VMWare, but I'll need an actual honest-to-god parallel port for the CAM part, so I figured I might as well get a dedicated PC...

Thanks for the help,

Simon

Are you calculating for expansion and contraction in the solid model???

[tobyaxis]

The ability to create very fine structures - 0.005" by 0.05" for example - channels of this sort of dimension are used to allow air to escape from the mould as the plastic is injected

• The ability to model something then split it in half (for the upper and lower parts of the mould)
• The ability to create "negatives" of the model. Essentially a boolean subtract, but it would be nice to not have to worry about alignment etc.

I was hoping to get the Alibre design package for the CAD part, and then possibly use meshcam to import (from STL or DXF) the design that Alibre created, and mill it out.

Anyone got any comments, help, guidance etc.? I've used CNC before (I've got a 3D printer, and a PCB "engraving" machine) but I've not got into milling parts before, so I'm all ears

Cheers
Simon

First thing Alibre will handle 6 places after the decimal. (.000001)
Second STL and DXF aren't the best for machining purposes. You should be using STEP or IGES Models for Machining.

The STL's are good for Importing Solid Fixtures, Bolts and Clamps into the CAM Software to check tool/tool holder clearance.

[SpacedCowboy]

Hi SpacedCowboy

One of the most important things for your cad to be able to do, is doing the parting line,(split the mold in the right place) not many cad programs do this, without it there can be a lot of extra work to make your part come out of the mold, this is something you only get one shot at when making/cutting the steel for your mold

That's what I was trying to get at in the second point of the original post...

I thought it was just a matter of aesthetics and practicality, but are you suggesting there's a "right" (for some definition of 'right') place to do it on the mould ?

If 'tobyaxis' makes moulds using Alibre, I assume it can do this - I guess you just want to intersect a plane with the model and delete anything above/below the plane... But it'd sure be nice if there was a built-in to do it for you I found some mould-making CAD s/w, but it was horrendously expensive for the hobbyist like me - about $6k. Yeah, I know, par for the course in CAD/CAM s/w but still a chunk of change.... I've just paid my tax-bill [sigh].

Are you calculating for expansion and contraction in the solid model???

Not yet... I'm going by what's on this page for the air-release channels (which are the tiny scales I was talking about. None of my part dimensions are anything like that small). On my parts, if it's within a few mm, it'll be fine - I have a lot of tolerance here

I'm fine with having to do a few iterations of this, and I don't expect to get it right first time - it'd be nice [grin], and I'll certainly try to, but I doubt it'll work out that way

Cheers
Simon.

[tobyaxis]

Simon you have a PM

[BurrMan]

Sketchup is a polygon modeler. Alibre is a NURBS modeler. The last time I looked, Alibre used the ACIS modeling kernel. Did they change something?

A polygon modeler only makes little flat planar surfaces that "represent", at some resolution, a curve. A NURBS curve or surface is a mathematically precise definition of the curve or surface. For machining, you will always want to choose the NURBS option. For 3d printing, you would still want to use the NURBS option to model, then Mesh your object to a polygon format, at the required resolution. If Alibre is saving to STL, then it is doing this conversion then. The Ideal would be if Alibre is allowing you control over this meshing to Polygons, or if it just doing something "automatically" and presenting something to you in the end.

FYI.

[BurrMan]

You can make the solids and do what you are asking to do in Alibre, with a few things added to qualify this. When you start talking "Molds," it can become very complicated and this is a very complex task. Though as a hobbiest, you can probably get some results with simple model splitting and making "air holes", true mold designing is a very complex operation (Especially injection) and the 6K software have built in tools for helping this stuff out. They will calculate flow+time and know that this little corner will not get filled before the plastic cools., kind of thing. Others here have mentioned drafting qualities that would be required for proper results, but the hobbiest can get by with prying stuff apart too.