I cut a disc from plywood that was supposed to be 7 9/16" which I converted to metric by 7.5625 X 25.4 = 192.0875 so I called it 192mm. Although it seems perfectly symmetrical, it’s 1/16" under no matter which diameter I measure across. I did it in Tinkercad and even though I maxed out the number of sides and segments I can see/feel (but can’t get to show in a pic) traces of a faceted surface around the outer edge.
Since it seems dimensionally equal in X, Y and anything in between I’m wondering if this more characteristic of the way Tinkercad generates circles rather than an issue with the burly?
What if you used Inkscape? If the shape is only 2d, Inkscape might give you more precision? You can make the model with both tools, and then measure them in estlcam, middle mouse button.
I just tried to quickly do that but starting at one point and going along a diameter it lets me go beyond the drawn line. Is there away tom make it snap at both ends? I’ll have to see if I can do it in Inkscape. I kinda suspect Tinkercad, last week I needed to make a shower curtain rod holder and did it in Tinkercad and printed it. Once again maxing out sides and segments it’s more of a gently faceted surface rather than a true circle. And the burly seems to have hit the same dimension in X and Y as expected.
I can live with the piece I cut as it’s more an ‘Arts & Crafts’ project than a ‘Technical’ one, just trying to determine if it’s the software and I need to learn something more accurate should I need it.
Yeah, I’ve played with both a little bit. Reading some of the manual that came with the Inkscape download I’m amazed at it’s complexity when I’d really just be happy being able to do a few signs and engrave some text. 360 too, seems extremely capable, likely capable beyond my needs with the attendant complexity. I’m still grazing in the free CAD field, next up I want to give Qcad a look.
On further thought I have to wonder how much the material being cut influences things? The plywood disc will have a plastic tube passing thru it, I was trying to find the right size to cut the holes made three test cuts in a piece of polar that was on the table which were 0.1mm apart in size. The 33.8mm hole was a perfect, tight slip fit in the poplar but wouldn’t allow the tube to pass thru in the plywood. Only problem is I 'm not absolutely sure I maxed out the sides/segments on both and one of the drawings is gone. I think tomorrow I will fool with some foam just to do some comparisons.
Don’t get me wrong, I use Tinkercad a lot, and I really like it, but there are a few tricks that you can use for dimensions.
Tinkercad makes its “circles”, then measures them corner to corner, by default. This is true for the default (20 sides) and for the max (64 sides) Try making your circle in TinkerCad, get it to 64 sides, and rotate it by 2.81 degrees. (2.8125 to be exact, but TinkerCad will round to 2 decimals.) you’ll see that the reported size decreases. (Not much. A 300mm circle becomes 299.64mm) It’s small, but it’s enough to make the difference between something that fits in a hole and something that doesn’t sometimes.
3D printers quite commonly print circles undersized, I’ve heard lots of handwaving explanations as to why this happens blaming shortcuts that Marlin takes and the fun of trying to translate a circular extrusion (or cutting path) into many short straight lines, though given that there are machines out there that are capable of extreme precision when dealing with cutting bits… I don’t think that this is particularly trustworthy. This is a known quantity in CAM.
Last but not least, I’d also measure the width of the path your cutting tool actually makes in the material. Most of these are pretty accurate, but the difference between 1/8" and 5/32" is pretty small.
Thanks for the explanation. I can live with Tinkercad’s quirks for ‘Arts & Crafts’ type projects. Given the symmetry of the piece I cut I tend to believe the burly did as instructed.
I do the same but printed or cut so far can still see evidence of a faceted surface rather than a smooth arc. I definitely need to learn a more advanced software for anything that needs a more perfect arc, especially when I get brave and start fooling with aluminum which isn’t as easily shaped by hand but I see a place for Tinkercad when you need a ‘quick & dirty’ plan.
How did you generate the gcode? And what is the diameter of your milling tip? I guess the tool traveled exactly on your drawn line, not outside of it, offset by its radius. Maybe?
I haven’t, mainly because I tend to believe the problem stems from he manner in which Tinkercad generates curves. My plan is when i get a chance I’ll see if I can manage a simple circle in Fusion and to cut it in some foam alongside a Tinkercad circle for comparison.
I haven’t figured out how to measure in Estlcam and have it snap to a point but eyeballing seems to show it a bit shy of the 192mm as drawn in Tinkercad.
Well, I just cut the piece again using a sketch I did in Fusion and it’s exactly as drawn so it would seem the issue was with Tinkercad.
Now if I could only find a CAD program somewhere between Tinkercad and Fusion. I’m amazed at the capabilities of Fusion, especially considering it’s free, but it has many capabilities I’ll likely never need and I find it a bit too easy to click the wrong button and get totally lost.
TinkerCad is remarkable for what it is, but has some limitations that are hard to get around. I’ve done some very elaborate projects in TinkerCad (My 3D printer was designed in TinkerCad) so it can be very powerful, but there are certainly times when I’d like to be able to tell it to align something to something else without moving the thing that’s already in the right place.
That’s been pretty much the conclusion I arrived at, I’ve been learning more of it and it’s handy for dashing off a quick object for certain uses, I just need to get a bit further along the learning curve of when to use it and when to use something else.
I think tomorrow I will fool with some foam just to do some comparisons.
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