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MachinistBlog.com

Plans, projects and how-to's for home machinists

Casting Lots of Small Parts

I spend about half of my time writing CAM software, and the other half doing product development for a bunch of companies.  Usually my prototypes are one-off, sometimes I have to make lots of them.  I happen to be in the middle of just such a project- I need to make about 50 of these:

Luckily, they’re not very big, only the size of a dime.  I tried using our CNC mill to machine one but it quickly became apparent that it was going to take too much time like that since it would have to be machined from two sides and with a good finish.  I decided to turn to one of my favorite techniques- casting the parts.

Other people have written very extensively about casting techniques, my favorite is at http://lcamtuf.coredump.cx/guerrilla_cnc1.shtml .  For the time impaired, the basic idea is that you make a mold of the part that you would like to make and fill it with a two-part resin to make the finished product.  The mold can either be a soft silicone, as the site above shows, or a hard mold that you machine directly in a CNC mill.  For small parts like this one I like to save a step and directly machine a hard mold.  Since I only need to make 50 pieces, I decided to machine them from Delrin- a very strong plastic that happens to be relatively non-stick.  The non-stick part ends up being a huge benefit here to make it easier to remove the finished parts.

Making the Molds

The fist step was to reopen my part in SolidWorks and design a mold to produce the parts.  Since the part is symmetrical, I only need to make half of the mold and machine them in multiples of two.

 

The mold shows a lot more stuff than the original part that are worth an explanation.  A big part of designing a mold, whether it’s for casting like this one, or injection molding for high-volume production is making sure you provide a way for the material to flow freely into the mold.  This includes providing a way for any air in the mold to be pushed out.  The flow of resin will be something like this:

Red lines show the path of the resin

The resin is pushed in from the left and eventually overflows out through to the right, hopefully taking most of the air with it.  Any air left in the mold will create a void in the finished part.  Note that without the bottom-most runner, there would be no way to get resin into the bottom legs of the part since air would be trapped in there.  There are certainly better ways to approach this part but this was easy and I was in a hurry to get started.

Machining the Molds

Machining these molds is easy.  I exported an STL file from SolidWorks into MeshCAM  to make a toolpath.  Some users have found the SolidWorks STL export options confusing so I’ve put up a SolidWorks CAM page to show that process in more detail. Continue reading Casting Lots of Small Parts

CAM program D2NC’s new features

This is a very quick introduction to D2NC, the CAM program I use to convert DXF files into G-code for my mini-mill.  It also does conversational CNC programing and it has a “Shape Description Language” for creating shapes and tool paths.  D2NC only costs $79, which seems pretty inexpensive for a good CAM program.  It costs even less if you buy it with a Mach3 license.  There’s also a fully-functional demo version you can try free for 15 days.

The video shows the pocketing, ramping and tab features that were just added to the latest developmental version, which may become the stable version soon.  It also shows how easy D2NC is to use, which is one of the reasons why I bought it.  The excellent videos, well-written documentation and the help that is available from the D2NC discussion group were another reason.

For those of you who aren’t familiar with computer-aided manufacturing programs I’ll quickly explain what they do.  A CAM program takes your CAD drawing and creates G-code instructions for your CNC mill (or whatever) to run.  But to do that it needs a little help from you, especially if you’re working with 2D drawings.

Imagine a CAD drawing of a flange that is a simple square with a circle in the middle.  The CAM program sees the circle but it doesn’t know if you want to cut it out, drill it, pocket it, raise it by milling the material down around it, engrave it or whatever.  Similarly, it also doesn’t know what you want to do with the square portion.  So you need to tell it and also what size and shape cutting tools to use and what feeds and speeds to use.

For me, finding and learning how to use a good affordable CAM program has been the hardest part of learning how to do CNC machining.  So I think I was lucky to find D2NC, which is kind of a well-kept secret even though it’s been around for at least five years.

StickFont – Free software for engraving

StickFont v1.1 is a free Windows program you can use to create single-stroke text for engraving.  It’s very similar to another free program we’ve written about called DeskEngrave.  Both programs will take a line of text and generate the g-code you’ll need to engrave it using a CNC mill, router or similar machine.

Some of StickFont’s features

  • You can engrave text on an angle or around an arc
  • You can mirror text in the X or Y axis
  • You can easily adjust the character spacing and height
  • If you want, you can easily set parameters such as z depth, retract, plunge and feed rate, etc.
  • You can save the output as a DXF file

StickFont can create text using any font installed on your PC.  But working with Windows fonts is not as easy as it is with DeskEngrave because you have to convert them to a “CHR font file” first.  It’s easy, but it’s an extra step.  If you don’t like any of the fonts on your computer then check out the 14 good-looking free fonts you can download from their web site.

I’ve played with StickFont on my laptop but I haven’t been able to try it out because I have a 400-pound jump shear parked in front of my mill while I reorganize my workshop.  If you could try it out and let us all know how well it works I’d appreciate it.  By the way, there’s an older version of StickFont with fewer features floating around the net.

DeskEngrave

Use a negative radius to put text on the inside of a circle. Use a positive radius to put it around the outside.

DeskEngrave is a free Windows program that makes it easy to add engraving to your parts if you have a CNC mill, router or similar machine.  It will create text using any TrueType font installed on your PC, make it the height or width that you specify and put it on a straight line or wrapped around a radius.  It will also create a DXF file or generate G-code that you can run directly on your machine.

You could also use it to make cut-out, raised or pocketed text, although you’ll need the help of a CAM program.  That’s how I’m going to use it to make street numbers for my mailbox.  You can also import its DXF files into a CAD program if you want to create multiple lines of text or add them to another design.

The program couldn’t be much easier to install and use.  It seems to work very well but there are some things you should know.  The size of your text appears to be controlled only by the height and width boxes on the main screen.  Even though you can change the font size on the font selection menu it doesn’t seem to make any difference.  I’ve also noticed that the size of the text is often significantly bigger than what I specified.  So if size is critical you might want do to a test run and either adjust the size until you get what you want or rescale the DXF with a CAD or CAM program.  You can specify only the height or width of your text, not both.

You also need to set the parameters before you try and run the G-code it generates, otherwise your controller program will probably complain about a feed rate of zero.  Also, the “Precision” and “Dec. Places” settings are important.  I don’t know what the optimal settings are yet, but if you don’t the increase the default settings your font will look like it’s made entirely from straight lines instead of curves.  Click on the help button for more information about those settings.

DeskEngrave is from Deskam.com, which appears to be part of DeskCNC, a maker of CNC software and controller boards.  The program hasn’t been updated since 2000 but this CNC newbie thinks it is still pretty useful.

Random Quote

Every accomplishment starts with the decision to try.

— Unknown