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I'm working on a project trying to combine a pantograph linkage with a four-bar linkage. I'd like to build it out of relatively at-hand materials (AKA, nothing requiring a machine shop), and I'd like to do some educational projects in the future involving students building linkages, too, so low-cost would be great. Relatively stiff and able to run unattended as a display are also desirable.

I'm thinking that bolts and nuts are going to be problematic after it runs for too long. Is there a particular type of bearing that would be easy to use/acquire? ...a good material for the rods? I have a Carvey CNC machine, so HDPE and wood are easy to machine for me. It's mostly the pivots/bearings that I'm having trouble with.

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  • $\begingroup$ Buy metallic dovel pins? $\endgroup$ – joojaa May 9 '17 at 19:42
  • $\begingroup$ How would I hold them in, if they're loosely fit enough to allow rotation? What sort of rod material are you envisioning? $\endgroup$ – DeltaG May 9 '17 at 19:48
  • $\begingroup$ you friction fit the other side and let the other be loose. $\endgroup$ – joojaa May 10 '17 at 4:09
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I have tested linkage models using wood strips with small bearing recesses milled into the wood. Skate bearings 8mm ID x 22mm OD x 7mm width are widely available for about 60 cents if you buy 20 or so. I just milled the bearing recess a bit tight then pressed them in. If those are too large then smaller bearings are also available and may be cheaper in bulk. Be aware that skate bearings are available in some exotic ceramics and other materials that get very expensive, so don't be scared off if you see some for $10 per bearing. I have paid about 40 cents for them when I bought them in bulk.

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  • $\begingroup$ This looks like a great idea. So I press the bearing into one piece or maybe both of the linkage, then use some sort of pin friction fit for the inside of the bearing? $\endgroup$ – DeltaG May 10 '17 at 3:15
  • $\begingroup$ I think I used 5/16" fasteners with a washer or two to keep the linkages separated. I have also fastened one end to plywood with a 5/16" lag screw and spacer to create a fixed pivot point. $\endgroup$ – Entrepreneur May 10 '17 at 3:39
  • $\begingroup$ Thanks! Looks like a good solution, fitting all of the desired outcomes $\endgroup$ – DeltaG May 10 '17 at 3:41

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