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Constraining two sets of circles with a common midpoint
dev_scally425
Member Posts: 8 ✭
Hi folks. I hope the title makes sense. I'm not sure to describe what I'm looking for, but hopefully it becomes clear with the aid of a screenshot.
So I get this situation a lot, where I have a pair of circles (small circles), and then I want to draw a second set of circles (bigger circles) but have them constrained to share the same midpoint distance with the smaller set. I know I can draw two lines between both of them and find the midpoints and work backwards but that gets messy with lines on top of lines. I can also just workout the distances i need, but then they are not constrained, so future editing means i have to work out my distances again. I want o leave it so that if I need to change the dimension between the two bigger circles, that they will stay centred between the two smaller circles and vice versa.
I feel there is a really easy and obvious solution to this problem but I cant figure it out. Cracking this would really speed up my workflow.
Please help.
Comments
Use construction lines between the two left and two right circles and set them equal length
eric's suggestion is good but if you want one less line… draw a vertical construction line between the circles. set each circle on one side with a mirror constraint to the other side.
The Midpoint constraint will also work with 3 points (centers and the origin also count). You could make something that looks less cluttered that way, but I just tend to use centerlines. They're easier for another engineer or future-me to figure out what I intended without looking carefully through the constraints.
Awesome. I had a tinker with it and it wasn't working until I realised that I had the far right circle defined with a dimension.
Yep, I had a go at Eric's suggestion and your's and they both work great. I'll be honest, I was sceptical whether the mirror line option would let me dimension centre to centre. I was expecting to have to dimension half my distance from the mirror line to one centre. But thankfully OnShape knows what I'm trying to do and sorts it out for me.
I like this option. It is indeed a lot cleaner. And playing around with it has offered me the opportunity to discover the difference between driving and driven dimensions. Every day is a school day.
For anyone stumbling on this in the future:
Looking at S1mons's drawing, it got me wondering what would happen if I wanted to take it a step further and wanted the spacing between the big circle and the small circle (10mm) to be constant while still being able to dimension my centre to centre distance between the larger circles (40mm). I still wanted a visual dimension for reference between the two smaller circles (60mm) and dimensioning them would over define the sketch. So I changed that reference dimension to a driven dimension (right click the dimension and toggle driving to driven). Now when I change my big circle spacing (40mm) the driven dimension (60mm shaded) should change along with it.
This is child's play for some, but its the small things like these that really slow me down as a hobbyist.
These little things are why the official free training modules are so valuable. Especially if new to parametric design.