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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

Solsylva 25×25 CNC Router Build

 

I’ve started building a CNC router from plans.  It’s something I’ve wanted to do for a long time now but I couldn’t decide how big a router to build or who had the best design.  This article describes why I want one and why I finally picked David Steele’s 25×25-inch dual leadscrew CNC router.  It’s a popular design you can probably build for $600 to $1200, depending on your choice of electronics and leadscrews.  The plans cost $25, or $35 if you buy them packaged with two of his other CNC router designs.  They’re available on his web site, Solsylva.com.

My choice was based on at least 25 hours of Internet research plus what I learned last month at a four-day CNC Workshop I attended in Ann Arbor, MI.  There are many router plans to choose from and it was difficult to determine who has the best design. I was strongly influenced by this router’s size, its popularity and the detailed information I found on the Solsylva web site.  But what clinched it was the many helpful builder’s logs I found, many of which detailed improvements you can make.

Here are some builder’s logs I recommend:

  • Crane’s 25×25 Solsylva Build w/ Pictures – This CNC newbie built a “stock” machine and in the process he got hooked on building CNC routers.  So then he built a heavily modified version using both his own ideas and those of other Solsylva builders.

Why a CNC router instead of a bigger CNC mill

I want to cut out, carve and engrave parts that would be too big for my CNC mini-mill or even Bridgeport if I had one.  A CNC router can’t machine metal as well as a mill but being able to cut out and shape large intricate parts out of wood, plastic and foam will make it possible for me to make all kinds of interesting and useful things.

I also think members of my family will want to use it and it’ll be fairly easy for them to learn how.  They’ll be able to make signs and cut parts out of flat stock using a “2.5D” CAM program that is much easier to use than the one I use with my CNC mini-mill.  They can also take advantage of some of the many free “almost ready to cut” DXF files you can find to make things like signs, toys and even furniture.

Size matters

I don’t have room in my very small workshop for a 4×8 or even a 4×4-foot CNC router.  They would also cost more and they probably wouldn’t be very suitable for a first build.

I almost decided to build a small moving-table type router instead of one with a moving-gantry because I’d be able to easily transport it to demonstrate or teach with.  They’re also the least expensive and easiest kind of CNC router to build.  But most of them are limited to making fairly small parts.  The ones I’ve seen that could easily fit in my car’s trunk usually have a working area of only about 12×12-inches or so, and that’s just too small to be very useful.

So I finally decided that I wanted a CNC router with a working area of at least 18×24-inches because it would be able to make most of the parts needed to reproduce itself or make an even bigger router.  The Solsylva design is a little bigger than that, with a working area of 25×25-inches.  And it includes plans for a table on casters that lets the router fold down so it takes up less room when it’s not being used.  It also serves as a work table you can build your router on.  If it’s too big or too small for you then take a look at their other designs.  They have plans for three other CNC routers with table sizes ranging from 10×9 to 24×48 inches.

Cost matters too Continue reading Solsylva 25×25 CNC Router Build

5-axis machining

I wonder if we’ll be able to buy an affordable hobbyist version of one of these machines in 10 years?

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.

Random Quote

Do well by doing good.

— Benjamin Franklin