The Quest for Accuracy

Hi All,

I’m working on a tool to aid in my quest for accuracy with the Goliath. I made a template that fits the tower center bases and then affixed both to a board cut 52" x 10 3/4" the back corners of the tower base then sit neatly at 48" wide and 8 3/4" back from the edge (222.25 mm back from the edge). This lets me leave the towers set up and back from my working piece to cut, all I have to do is set the edge of any piece I am actively cutting at 222.25 mm Y coordinate in Slingshot.

I will say, it has taken a little dialing in to make sure that the towers are EXACTLY parallel to the edge of the work piece, however once I’ve gotten it in just the right spot, then I can leave the tower plates attached and remove the towers to pack up, and place them again later with success.

I’ve included the Tower Base Plate file for anyone who would like to experiment with this as well.

I’ve so far had some really good successes in the cuts being exactly the desired cut size, and am fine tuning the cut lining up with the edge of the board. I can confirm that 0,0 X/Y position in Slingshot is in fact the apex of Tower 1.

Tower Base (142.0 KB)


Now that’s exactly what I wanted to accomplish! I guess I’ll try this weekend. :slight_smile:

Nicely done.


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Also I have some pictures from the first test, which I am very pleased with and will be adjusting my jig and trying again tomorrow to dial it in.


So goliath accuracy is based on parallelism. So let’s assume you had a 2 inch thick piece of glass 4 feet by 8 feet as your spoiler board. And than you placed on top a typical 4 ft by 8 ft by 1/2 inch of plywood that we will assume was perfectly flat! Which we all know isn’t! Now on the corners you have your 1/2 inch tall bases… Well.if the bases you had where even height to each other your already off from the software! Why? because you’ve introduced an angle that will decrease the expected accuracy the closer you get to the towers as compared to the software. So you want 2mm accuracy? then spoiler board, work board and everything literally else from the rubber wheel thickness to the weight distribution of the robot at any moment in time must be perfect! Not real life. So want to make a human sized boat frame that works, well bobs your uncle! Want to make a sub millimeter accurate carving of an eagle forget it! This is why million dollar cnc machines cost a million dollars! For the accuracy and repeatability.
I write all this to save you time in your experiments and apologies if you already are aware of all of it! And power to you because it would be terrific to know and share the best way to get accuracy and what it is!
Also remember and Google the cnc difference between accuracy and repeatability! They are both important and very different!
Looking fwd to your future posts!

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Accuracy - Repeatably - Tolerance
it will be very interesting to know what the “limits” are.
And it will be, from my point of view, more then acceptable
that these are not as “narrow” as the specifications of 1 m$ CNC machine.

The test set-up from @Tom can give us at least an idea,
but maybe these specifications are already available from Springa?
@Lucia , is there any information - documentation available?

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All good points. I’ve made the tower base plates separate from the board for the exact reason @Middyeasy has mentioned for keeping the towers’ bases the same height as cutting surface.

For some clarification-my main line of work is stage, one of the things that attracted me to Goliath initially was the thought of little cnc machine, large work area. My dream was that the machine would be wireless, meaning I could place it on a 30’ by 30’ work surface and have it run about cutting very very shallow markings as indicators of where walls, doors, etc would be placed on a floor which would save me time and be more accurate than traditional location of these points by hand. Alternatively, I often have to paint complex shapes, stone work, etc, and having the Goliath be able to “plot” these designs on a large floor sounded excellent. Knowing that the work area is not truly limitless, but still very large, if I can dial in a tower base template that is something like 8’ wide, made with plywood and the holes for the tower bases cut out (like a dog bone?) then I can make my first area markings, move the jig over, line it up and repeat. So I’ll need the ends of cut A to line up with the continuation on B. 1mm accuracy for this sort of large scale application is more than enough.

Even better is this is not the only application I’ll be using this tool for, but just one of which really makes it a win win.

My dream project right now, once I am confident enough with the machine is to make an inlay directly on a wood floor.

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Agreed, I have thus far been impressed and pleased with the accuracy that was described by the creators.