Because I’d like to have a bit more of an “analog” feeling when operating my machine I was looking for something like a DRO with a jog wheel or a joystick that works with GRBL.

I didn’t find much like that. What I found was this article about a man in the middle approach, but it was very rudimentary and the implementation of the rotary encoder didn’t really work out well, when I tried it with my high resolution rotary encoder.

For an analog feeling there should be beside a small lag also some kind of repeatability. I mean if I rotate the wheel and move it back in it’s old position, the machine should also end it it’s old position.
I used an Arduino Mega for this, because it has three hardware serial ports and most important, I already had one here.
For the DRO I used LEDs because they are nice and bright and easy to read form each angle – also from far away.

For some reasons I couldn’t manage to daisy chain the LED display with the Arduino library I’m using. So I just connected each one separately to the Arduino. The Mega has for sure more then enough pins for that, but the Library isn’t the fastest. Therefor I had to lower the communication speed to 9600 Baud. Sounds dramatic, but in fact it doesn’t make any difference for me. The buffer is still filled up nicely when I’m running jobs. On a laser cnc this might be an other story …

Maybe it’s worth giving it a try on a faster board then the Arduino Mega. I tried and the code compiles for a Teensy as well. But for me there is no need, cause it’s just doing fine with 9600 Baud.

Here are the parts I used:

• Arduino Mega
• four 8 digit 7 segment LED displays with a max72?? chip
• Rotary encoder with 600 steps per rev (maybe a bit overkill, but it wasn’t expensive)
• Two rotary switches for setting the axis and the resolution for the jog wheel
• Two potentiometers for the overrides – linear with center click (from 1k to 10k should be fine)
  
  

Of course there is some tweaking involved to get it run smoothly. All those parameters are found in the config.h file. There is also defined what to be connected to what pins.
I added some descriptions there, so it should be pretty much straight forward.

The code is still alpha. Use it only if you understand it and if you know what you’re doing.

This is potentially dangerous.

For the first test I’d recommend not to use it on an actual machine. Use an Arduino (not connected to anything) running GRBL with the same settings then your machine for testing.

All on your own risk. Here is the code – have fun!

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Lets start in the beginning. Before I was getting serious on this build I started playing around in CAD and I liked the idea of casting the structure of a machine. There are two ways of easily casting parts at home. Concrete (HPC) and epoxy granite or mineral cast. Somehow I decided to start playing around with epoxy granite. Just out of curiosity.

I think it was in December 2018 when I ordered some epoxy at amazon.
I just picked one that’s supposed for casting with a slow hardener. Slow hardener because I don’t want to work under time pressure and I guess a slower hardening process should also result in less heat and less deformation. But that’s just my guess. I don’t have any professional knowledge of resins.

At a local hardware store I purchased some fine sand (for mixing concrete) and a bag of gravel. The sand came really humid, so I had to dry it first. Did this in a cooking pan in the kitchen (at this point I hope so much that my girlfriend isn’t reading this …).

I used such a Tupperware like plastic container as a mold. They are pretty handy because epoxy doesn’t stick to them and they got and draft angle. Plus they are a little flexible, so the test piece can be easily released.

First I started mixing sand and gravel to see what mixing ratio looks good. I used a kitchen scale and made notes in order to be able to reproduce the results.
First test I made was with 17% of resin. Then I lowered the amount of resin to 15 and 10 percent.

The 17 percent piece came out almost perfect. But there was quite a layer of resin on top (in this pic it’s on the button). That’s a clear indicator that there was more resin then the sand/gravel mix can absorb.

But on the other hand while casting it behaved extremely pleasant. Very thin, almost liquid. That’s the reason why I didn’t find any air bubbles in this cast.

The 15 percent piece looked a bit more rough. Some small air bubbles, the surface not as smooth as the first test.

The 10 percent piece looks pretty rough with a few air pockets and a not very nice surface finish.

My conclusion was that I should use as little resin as possible, but still enough to ensure a good handling and as little air pockets as possible.
Using as little as possible because of less heat while hardening, and even if epoxy is only shrinking a very little, it’s better to be on the safe side here.
Little heat and little shrinking should result in a part with little tension and little distortion.

Little distortion is a time saver later on. As straighter the rail mounting surfaces come out, as less effort is necessary for lapping them flat afterwards.

At this point I’d point out that those results are depending on lots of parameters, the grain of the sand, the epoxy and so on.
Doing some tests is the only way to figure out a working recipe.

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A cnc mill I wanted to build now for quite a while – guess it’s for more then a decade now. Lately I found a bit more time to waste on pet projects, so I finally went for it.
The Idea is to build a cnc machine, that performs well with materials up to aluminum. Because I’m not having lots of space in the garage, it should have a small foot print. In my thoughts I played around with many materials I could handle. Starting from aluminum extrudes to solid aluminum pieces to granite, concrete and finally epoxy granite.
Epoxy granite got this professional aura. Most search results on google are big to huge machines, only a few individuals did it at home in their shop. But also those home made machines are quite a bit more massive then what I had in mind.

So I thought why not scaling this thing down. On a smaller scale everything seems to be easier. This thought was getting stuck in my mind and I started to design a vertical milling machine with an easy to realize building process in mind. At this stage I wasn’t really sure if I’ll go for it or not. At one point I ordered some epoxy for casting and went to buy some sand and gravel.

With that I did a few test casts in small plastic food containers. Already the first one came out surprisingly well. I did two more with less epoxy. So in the end I had three pieces of homemade epoxy granite to play around. Even in so tiny dimensions, they all looked quite stiff to me and none of them broke while playing around with them.

I had the feeling this could actually work. I made a material list. Only for the machine base. With that list in hand I realized that it would be also pretty cost efficient. In the end I spent a bit less then 100 Euro for the machine base. And some of the materials in this list will also last for more parts. Like some of the screws and the gel coat for example. What happened then I showed in the first video I did.

The next step will be bringing the aluminum supports for the rails in acceptable tolerances. I’ll put the whole piece on an old traditional milling machine. This will hopefully happen in three weeks.

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It looks quite technical and rough to me. Usually I like that, but here I had the feeling something is missing. After starring at it for a while a rest piece of aluminum fender in the scrap box captured my attention. I thought maybe this could do the trick. It was already a cut, that almost fitted on the head lamp.

So I taped it to the head lamp and looked at it for a while. Somehow I like it. Also because it would be such a simple solution. I got to admit that working with sheet metal is not really my biggest strength. Can be pretty frustrating, to do everything two or three times and then still not being totally satisfied with the result. But like this it just need to be a little shorter. In front view it should be proportion wise about two third of the diameter of the head lamp. Not sure yet if it should line up with the instrument or if it should maybe a little shorter. I should not rush with that.

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I like to use the jig saw upside down in a parallel vice. That’s really handy for (almost) precise non straight cuts.
The problem with smaller pieces was, that the window around the saw blade in the base plate is so big, that there is not always enough support on both sides. The result is an uncontrolled jumping of the work piece.
To eliminate that I made a simple baseplate out of aluminum. It’s screwed on top of the stock one. So it can be easily removed when I want to use the jig saw in a conventional way.

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