How to create negative impression of machined stock model?

[Corp6]

I use almost exclusively vacuum fixtures for small one-off parts that are made of specialized materials, and often these parts have reasonably complex 3D surfaces.

I generally machine the first side from a solid block, then flip it over and machine the second side while the first side is held in a vacuum fixture that is a negative image of the first machined side.  I would like to be able to take the first side machined surface and (in MasterCAM), flip that over and use it as a cutting tool on an extruded block to create the vacuum fixture.

I know I can use the original solid model, but this is often less accurate than using the actual machined result.  I am already using the Stock Model feature, so what's an easy way to do this?  I can't seem to use the stock model to actually do anything.  I have also tried exporting the verify results as an STL file and importing that, but I can't use it either with the impression tool or as a boolean cutting surface on an extrude, so I am not sure how to make this work.

Any tips?  It seems like there must be a much easier way to achieve this.

[Guest]

What exactly are you trying to accomplish?

I use the Impression Tool for making electrodes....it should be quite useable for vacuum fixtures from what I have seen in my use

 

[JoshC]

It sounds to me that you are looking to remove one solid from another and if that is the case mastercams Boolean found on the solid tab should do the trick.

Create your vacuum block as a Solid, Place your finish part into that solid exactly where it will sit, then Boolean remove the Tool body (the part) from the vacuum block that will be holding the part. Make sure to either copy your original solid first onto another level or turn on the non-associative option that Boolean has so your original part does not disappear.

[lowcountrycamo]

You can import Stl in Solis works and export as stp

[JoshC]

6 minutes ago, JoshC said:

It sounds to me that you are looking to remove one solid from another and if that is the case mastercams Boolean found on the solid tab should do the trick.

Create your vacuum block as a Solid, Place your finish part into that solid exactly where it will sit, then Boolean remove the Tool body (the part) from the vacuum block that will be holding the part. Make sure to either copy your original solid first onto another level or turn on the non-associative option that Boolean has so your original part does not disappear.

After I read through this again I see you are using a stock model for this task so my idea will not work for Boolean since that tool only works with solids. If you can make a solid and not use the stock model / STL that would be ideal in my opinion. 

[Müřlıń®]

46 minutes ago, lowcountrycamo said:

You can import Stl in Solis works and export as stp

I wouldn't......the solid is HUGE and quite unusable....

tried it many times without success....

Way easier and faster just to build a solid.

 

[crazy^millman]

7 hours ago, Corp6 said:

I use almost exclusively vacuum fixtures for small one-off parts that are made of specialized materials, and often these parts have reasonably complex 3D surfaces.

I generally machine the first side from a solid block, then flip it over and machine the second side while the first side is held in a vacuum fixture that is a negative image of the first machined side.  I would like to be able to take the first side machined surface and (in MasterCAM), flip that over and use it as a cutting tool on an extruded block to create the vacuum fixture.

I know I can use the original solid model, but this is often less accurate than using the actual machined result.  I am already using the Stock Model feature, so what's an easy way to do this?  I can't seem to use the stock model to actually do anything.  I have also tried exporting the verify results as an STL file and importing that, but I can't use it either with the impression tool or as a boolean cutting surface on an extrude, so I am not sure how to make this work.

Any tips?  It seems like there must be a much easier way to achieve this.

I did what you are asking to do 20 years ago and never used STL I always made solids from the parts I was cutting. You are thinking wrong here and using the part you are cutting with the the correct process will always yeild better results than taking a stl file that by nature is not any near as accurate as a solid is. STL is a bunch of triangles meant to loosely represent a shape not make an accurate shape. You start off in that direction and you better get a super computer with 10K cores and 1000GB of memory and 20 Video cards. STL files become huge quick the more accurate you make them. I have done my share of reverse engineering with point clouds and STL files and Solid make seem like more work, but end of the day Solids will always be your best bet.

[crazy^millman]

Found a computer to work with the STLs to make reverse molds.

Oakridge Supercomputer.  

[gcode]

2 hours ago, C^Millman said:

Found a computer to work with the STLs to make reverse molds.

Oakridge Supercomputer.  

I got a stock model from a customer this week.

Its an STL file created by a 3D laser scanner

The part is a stainless steel casting 70" x 55" x 37"

I asked for a casting model and they sent me the stl file.

It's 890 meg..  I haven't even tried to open it.

I'm afraid my PC would catch fire and burn the place to the ground

[huskermcdoogle]

1 hour ago, gcode said:

I asked for a casting model and they sent me the stl file.

This type of crap from customers always makes me chuckle. 

"Yeah we have a solid model, it's exactly what we want."

You receive the model, it's total crap, boss says cut it anyway.  You cut it to the model, customer gets it and goes, "WTF is this".  This isn't any good, it doesn't match the other parts here, here, and here.  You must not have followed the model...

Or my favorite, and I bet a few beers to whoever reads this that crosses paths with me first, the parts I sent out today will fall into this category.

Customer sends you physical part to reverse engineer.  They tell you that they want them exactly like they are, that they are perfect.  You end up looking at them, and notice a number of "defects" that look like crap, and given the aesthetic nature of the parts, should be fixed.  Boss says just get them scanned and cut them.  Customer gets the parts and goes, hey can you fix this, this, and this.  Then complains when they have to pay for another scan because its a highly complex organic surface that needs tweaking, and it isn't as simple as just push and pull here and there.  It is usually far fast and easier to just bondo it up and rescan.  I wish I had the time, software, and hardware to scan and reverse on our own.  In these cases I would just fix the stuff as I went.

UGGGGHHHHH

I feel for you g.

[Corp6]

It's not simply an issue of the solid model being more or less accurate than the STL file of the machined verified stock, it's also the fact that the part file from the customer is a finished part but as the part goes through the multiple steps of machining, it will transition from raw material to that finished part - and I will want to mount it in a vacuum fixture at some intermediate point at which it will not have all the features of the finished part.

That means I am modeling features which do not exist for no reason other than to use them to create my vacuum fixture - and there's no reason I ought to have to do that, when MasterCAM has already figured out what that intermediate stock will look like.  It exists both in the form of the stock model as well as an STL file exportable from the verification tool.  

It seems like MasterCAM simply lacks the power and capability to use the stock model as a reference for any sort of modeling, and also lacks the power and capability to use STL files for the same.  I can't say I am surprised, but I was hoping I was wrong. 

[Colin Gilchrist]

39 minutes ago, Corp6 said:

It's not simply an issue of the solid model being more or less accurate than the STL file of the machined verified stock, it's also the fact that the part file from the customer is a finished part but as the part goes through the multiple steps of machining, it will transition from raw material to that finished part - and I will want to mount it in a vacuum fixture at some intermediate point at which it will not have all the features of the finished part.

That means I am modeling features which do not exist for no reason other than to use them to create my vacuum fixture - and there's no reason I ought to have to do that, when MasterCAM has already figured out what that intermediate stock will look like.  It exists both in the form of the stock model as well as an STL file exportable from the verification tool.  

It seems like MasterCAM simply lacks the power and capability to use the stock model as a reference for any sort of modeling, and also lacks the power and capability to use STL files for the same.  I can't say I am surprised, but I was hoping I was wrong. 

I know you think Mastercam has "figured out" that intermediate stock, but that's not how the Stock Model works. STL Files, and Polygonal Mesh Entities are all faceted models. They are not canonical geometry shapes, but are collections of triangles. As such, they cannot be scaled without losing resolution. The bottom line is that you are correct that Mastercam will not do what you are asking for with an "easy" button. That doesn't mean it can't be done.

Since you can import a STL File as "points", this gives you physical Point entities that will represent the STL stock. You can then use these points to build lines, arcs, or splines, and construct surfaces from there.

A poor craftsman blames his tools. A good one figures out how to get the job done with what they have on hand.

[Corp6]

3 minutes ago, Colin Gilchrist said:

I know you think Mastercam has "figured out" that intermediate stock, but that's not how the Stock Model works. STL Files, and Polygonal Mesh Entities are all faceted models. They are not canonical geometry shapes, but are collections of triangles. As such, they cannot be scaled without losing resolution. The bottom line is that you are correct that Mastercam will not do what you are asking for with an "easy" button. That doesn't mean it can't be done.

Since you can import a STL File as "points", this gives you physical Point entities that will represent the STL stock. You can then use these points to build lines, arcs, or splines, and construct surfaces from there.

A poor craftsman blames his tools. A good one figures out how to get the job done with what they have on hand.

 

I don't think MasterCAM has "figured out" that intermediate stock, I *KNOW* they have.  That is the only way they could have generated the STL file.  The fact that they have chosen to represent that information to the user in STL format and the fact that the software lacks the capability to subtract an STL from a solid isn't a limitation of what I am trying to do, it's a limitation of the software.  There's nothing preventing the software from doing some sort of averaging of the triangles to generate a planar surface or warning the user that a shape generated from this method lacks accuracy, but it's not a technological limitation in terms of something that cannot be done in the realm of possibility.  It's just that MasterCAM can't do it.  I don't require an easy way to do it - just to know whether it can be done within this software or whether I need to process some models in other software.  

I can certainly get the job done with what I have on hand.  It just means I have to use more capable software to do it.  I was hoping to do it right within MasterCAM, but I realize the software is exceptionally limited, especially when it comes to any sort of drawing - so I wasn't expecting much - and wasn't disappointed! 

[jlw™]

I have to agree and disagree.  I totally agree, I wish I could export a step file from stock model - even a faceted one.  I however disagree that the software is not powerful.  I have used Esprit, Edgecam and Mastercam professionally.  Mastercam may not appear as "powerful" because it is more difficult because it requires more input.  All that user input is literally power of the programmer/engineer.  Given the choice today, I would pick Mastercam every day.  I am sure there are members of this forum who remember how adamantly I wanted to stay with Esprit.  Having said all that, give me a step file from my stock model and the software is as powerful as you make it!