Hi, and welcome! The reason the standard gondola doesn't tilt the pen is practical rather than technical - it's just easier that way. You're right though, a tilted pen would be better.

Pens with liquid ink absolutely _do_ need to be tilted, but anything that's got an ink-soaked felt thingy inside is ok (in my experience) without. The gondola does have a slight tilt on it, but it's probably more to do with the angle of the drawing surface than anything else. As far as I can see, the down-side to tilting is that it biases the movement of the pen. That is, it will be smoother moving up the surface than down the surface. It might tend to judder when it moves down. And the tip will get a chisel worn on it eventually that will mean it won't necessarily draw the same way again in future.

For the spectrum arts drawings I used a gondola that Stuart Childs made for holding big chunky marker (liquid ink) pens, and that can be constructed to hold with a tilt - for that kind of pen it has to.

The standard central-axis Polargraph gondola doesn't naturally like tilting because the stabiliser will lift the pen tip off the paper if it does, but it's easy enough to chop the stabiliser down to let it do so. I did ship a batch of machines back in the day, that didn't have the stabiliser, they just had a small hanger for the servo motor. Personally, I was pretty happy with their drawing behaviour but it took more tuning to get it drawing well, reliably, and the margin for error was smaller. I will dig one of the truncated stabilisers out for you and include it in with your machine - you can experiment!

sandy noble

Welcome TeamTeamUSA - I know your work from Thingiverse, so I look forward to your polargraph contributions!

Since I draw on a board that tilts, I've never felt the need to tilt the pen within the gondola. Also, I can't think of an occurrence when an un-tilted pen failed me because its ink wasn't getting to the nib.

Sharpies and Pigma Microns work fine without any tilt (well, just enough to keep the gondola against the paper). For my ballpoint drawings, I tilt the board quite a bit, say 30 degrees, but that's for weight on the pen tip, not ink flow to the tip.

Like Sandy, I suspect tilting some types of pens might cause differences in line quality between the up and down strokes. I wouldn't want to discourage your experimentation, though, so get to it.

If you're feeling ambitious, I'd love you to design a gondola that caps the pen when a drawing is completed. And can hold 4 pens for CYMK drawings. 😉

Kongorilla, thanks for the welcome, and Sandy thanks for the explanation. 🙂

I see (in my mind's eye) what you did there. A simple use of leverage to induce a tilt; clever!

Last night I hacked the Mr Stu Fat & Fatter gondolas to create another mechanical way to create tilt: a yoke that pushes down on the front of the pen body. I uploaded the designs to Ponoko. They fit on the smallest plastic sheet, P1, and cost about USD$20 for both. http://www.ponoko.com/showroom/TeamTeamUSA/product-plans/free

I ordered a set and will report back when I get them.

Go!

=ml=

Looking good, you've got a ghostly mickey mouse emerging from your lawn 🙂 The servo horn extender for the spectrum machine was just a 50mm machine screw hot-glued on.

Re round vs oval, it looks like a miscalibration - you've told it that your home point is higher than it really is. I guess it was drawn lower than you expected too? In my experience, that distortion can come from inputting the wrong machine width too, if that's wrong then nothing can save it 🙂 Remember that you need to upload machine spec any time that changes.

You could test a fix by homing, and starting the drawing as usual, but then pausing it and physically moving the gondola up a couple of inches and see if the shapes come out more accurately.

good luck!
sn

Oh right, so do you think it was a corrupt SVG somehow?

I added some images to the gondolas at Ponoko; they should help anyone assemble all the pieces into a working Mr Stu Fatter gondola: http://www.ponoko.com/design-your-own/products/p1-mr-stu-fat-fatter-polargraph-gondolas-w-push-it-technology-8886

In addition to the acrylic parts you will need these vitamins:

* 2 @ 3mm x 30mm machine screws
* 2 @ 3mm nuts
* 1 @ 3mm x 12mm machine screw
* 1 @ 3mm nylon wing-nut
* 1 @ spring 6mm OD x 16mm L (or use what works)

Go!

=ml=