My Third CNC Machine


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The picture above shows my latest CNC creation. I’m now on my third CNC machine. My first CNC was replaced because I wanted something bigger and faster, and my second CNC, Joe’s CNC 2006, received the sledgehammer treatment because its accuracy had gone considerably downhill.

My tool collection is rather limited when it comes making accurate parts, so this latest incarnation was “designed” with adjustability in mind. (The word designed is in quotation marks because I didn’t really design it so much as I just made it all up as I went along.)

At the time of this writing, I’m playing the role of the poor college student, so this CNC machine was built using whatever odds and end I had on hand. The expensive parts like the power supply, stepper motors, and leadscrews were reused from the older CNC machines. The only major addition, as far as cost is concerned, was a second leadscrew on the x-axis along with a chain and sprocket to slave them together.

This entire machine is essentially a prototype in that I plan on remaking several of the parts as time permits it. Many of these parts will be made by the CNC itself.

Linear Slides

The accuracy of a CNC machine hinges largely on how well its linear slides are put together. One popular method of making linear slides seems to be to use angled aluminum like what I did with My first CNC. I wanted something with more adjustabilty however because I never seem to be able to make them as accurate as I like, so I decided to try something else.

The design I went with this time can be seen in the pictures below. They still use skate board bearings but instead of the angled metal technique for the rails I went with a design that could be adjusted to fit whatever squarish / rectangularish pieces of metal I had on hand.

One day, when I finally own a drill press, I plan on remaking them out of metal, but for now the wood version seems to work OK. I just have to make sure not to overtighten them to avoid splitting the wood.

Leadscrew Nuts

I’m still using the same leadscrew nuts that I wrote about on the DIY Leadscrew Nuts page with this CNC machine. I also still don’t know what type of plastic it is that I’m using, but I have learned that a plastic called Delrin is sometimes used for making leadscrew nuts.


[bad]

Dual Leadscrew for X-axis

Initially, this machine was set up to only use one leadscrew for the x-axis, but this introduced a great deal of inaccuracy. The y-axis gantry could be pushed and pulled out of square because there was only the one contact point between it and the one leadscrew. Adding a second leadscrew was huge help, and the y-axis now stays nice and square with the x-axis.

Roller chain and two sprockets are used to make sure both leadscrew rotate in tandem. It is also possible to slave two stepper motors together to accomplish the same thing, but if one stepper motor loses steps at some point, the whole thing will have to be re squared.

I bought my chain and sprockets off of Ebay from a supplier called usabearingsandbelts.

Here is the description of the sprocket.

40B13 x 1/2″, 13 tooth sprocket for #40 Roller Chain

Here is one for the chain.

40 Roller Chain,10′ length ,#40-1R Roller Chain

I used a chain breaker to “break’ the chain to the appropriate length. One tip, should you try this yourself, is to make sure you get a master link to go with your chain because it makes putting it back together a whole lot easier.

Router

I’m still using the same router, and it has been great one for CNC machine use.

 

 

More to do

There is more that needs to be done, but as it is now, the machine does its job. So far, it seems to be the most rigid machine I have built, and I plan on making it even better still, but more on that later.

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