Help finding thread on mocking up cylinders with PVC

Colonel Monk · Dec 17, 2014

Another way that makes them simpler to figure out, is to use a 2D CAD software or sketch in 3D CAD to mock up your motion.

You don't need to draw your design, just some lines to represent your cylinder, and mechanism at stop and end point, pivots, etc.

What it does for you, is that it'll solve all the geometry formulas for you, and tell you where to put your pivots for a given length cyl, or vice versa.

Here's one that I did recently for a work-related project:

You're looking at the load in two different positions, horizontal and vertical. I've got the vertical fixed mast and angle brace which has the cyl mount on it. The dimensions in parentheses (x) are being solved by the sketcher, and I input the rest.

Basically, I ended up changing the geometry to spec a standard cylinder, but in that example I solved for the position of that lower pivot. I could have hard dimensioned that pivot and asked it to find the other one, or the angle of the brace, or basically anything ....

Without farting around in the shop making mockups, this is sure an easy way to do it. There's lots of free cad out there that should be able to do this simple problem.

CM

dfkrug · Dec 18, 2014

Colonel Monk said:
Basically, I ended up changing the geometry to spec a standard cylinder, but in that example I solved for
the position of that lower pivot. I could have hard dimensioned that pivot and asked it to find the other
one, or the angle of the brace, or basically anything ....

Whether you use CAD, a ruler and some trigonometry, or a mock-up, designing around a standard
cylinder is the most efficient way to go. This is true for a grapple, or the hydraulic backhoe thumbs
I have written about.

Since you have to cut your jaws and make pivots anyway, why not leave them as variables and fit
to the fixed open and closed lengths of a standard cylinder? Save a lot of time, effort, and cost, and
also make a damaged cylinder easily replaceable.

Scott65 · Dec 23, 2014

Oh my, wonder what happened here. I stopped getting alerts on this thread for some reason. Thanks for all the helpful responses! I've got the grapple redone, and working pretty well. Its still not a pretty thing, but I've been using it quite a bit so I'm happy with it. I'll work on making a new thread over in the BIY section.

As for CAD, its a neat technology. Probably way over my head. But I'd love to take a look at it some day. My problem would likely be replicating whats on the screen into real steel products. But I can't say for sure since I've never used any of the software. I've been slowly (very) collecting up the material to make a front mounted hydraulic post hole digger. Perhaps I'll take some time and try to mock up the bracketry on some of that software