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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

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.

Review: DeltaCAD

This is a quick review of DeltaCAD, an inexpensive and easy-to-use 2D CAD program with a short learning curve.  I highly recommend it, unless you need to design and draw complex parts or make 3D drawings.  If you’ve been looking for a simple CAD program then invest a few minutes and take a look at this one.  The fully functional demo won’t take long to download or install, and it will work for 45 days with absolutely no restrictions.  And you can buy it for only $40, which I think is a bargain.

DeltaCAD reads and writes industry standard DXF and DWG files, which makes it compatible with almost all other CAD programs.  It loads almost instantaneously, which makes it a great viewer for looking at CAD files you find on the net.  It has so many features that I’m not even going to try and list them all.  And DeltaCad has been around for a long time, since 1995, and it’s always being updated and improved.

The program’s author claims it is the “world’s easiest CAD program,” which may be true.  I looked at many other CAD programs and none of them come close to matching DeltaCAD’s ease of use.  I’m not an expert, but it seems to me that they shared some common problems:

  • The other programs were really powerful, almost designed to do all things for all people.  In other words, they were bloated with features that many users, especially home machinists, would never use.
  • They often didn’t come with a tutorial or some other way to help a new user get started.  They also typically came with documentation that would be great at telling you the obvious, like “Click on the line icon to draw a line,”  but leave out basic details, like how to make it a certain length or at a certain angle.
  • DeltaCAD just seems to have been designed to be easier to use.  It also comes with a simple tutorial that will get most people started making useful drawings in about an hour.

You’ll find DeltaCAD’s tutorial in the help menu.  The tutorial will guide you step-by-step through the process of drawing a calculator, showing all the different methods you can use.  I think most people will probably be able to complete it in about 30 to 60 minutes.

Unfortunately, it doesn’t show you how to add dimensions to a drawing, which is really easy.  So after drawing the calculator you may want to take a quick look at the “dimension” topic, which you’ll find in help under “drawing.”  Afterward, I think you’ll know enough to start making your own drawings.

If you have questions you can ask them on the DeltaCAD User’s Forum, where you will also find a library of drawings, symbols and macros to download.

There are some good reasons to learn how to use a more powerful and complex CAD program.  For example, I’ve been told that many of the 3D CAD programs will help make certain that the parts you design will fit together properly.  If you make a change to one part they can automatically make changes to the others so that critical dimensions and things like bolt holes will continue to match up.

So someday, if I start designing more complex projects and making them on CNC machines, I may need to learn how to use an affordable 3D CAD program like Alibre or Dolphin CAD.  But so far DeltaCAD has been more than capable of meeting my needs and I’m going to continue to use it.

Related Links

ReviewCentre’s user reviews of DeltaCAD

Random Quote

You miss 100 percent of the shots you never take.

— Wayne Gretzky