The mechanism tutorials seem to always show a crankshaft with block and piston so we've seen this for YEARS AND YEARS and we should all be super proficient at assembling a crankshaft and piston or some variant. This must just be the best thing for a company making crankshafts and cylinders.
Drawer slide units are significantly different And it is sooo easy to make a drawer slide just right but a major pain to get TWO slide units to work together (especially if the are supposed to be the SAME PART!)
The slide itself turned out to be unusually easy, this always throws me! No, seriously they are as easy as assembling a "mid slider" to the base component (housing) as a general mechanism with the appropriate travel limits and then an "inner slider" TO THE "MID SLIDER".
Remember, these are full extension slide units - they have a housing and a "mid slider" as I'm calling it and then what I'm calling the inner slider which attaches to the drawer.
The cool thing is that the assembly just works. The "mid slider" will always move about half the distance of the inner slider when you drag the component. It's as if the Creo "knows" what you want. That was very pleasant surprise.
There is no need for a relation driven dimension to control the two moving parts. That was just too cool - or so I thought.
The funny thing is that these are ALWAYS used in pairs and this is where I'm stumped. We get the usual "you can't drag the ground body" type message no matter what we try.
Last weeks solution involved making two DIFFERENT slide assemblies for the right and left side of the drawer. The goofy thing here is that the slide units should be the same. Literally and virtually they are the same - they are flipped around in almost all cases BUT THEY ARE THE SAME. This would help so that I don't have a goofy "left side slider" as a work-around cluttering up the assembly.
I suggest using rack and pinion gears. What this does is allow you to assign each rail as a rack to a common "pinion" in mechanism. It doesn't matter where you drag the assembly, the "pinion" will keep them all in sync. Technically, each ball bearing in the slide is a pinion that does exactly this. You can also set limits to control end stops.
I use Accuride drawer slides (McMaster-Carr) and I find that they often loose synchronicity. Every so often I need to give them a good pull to reset their position. You can get nice master CAD files at McMaster-Carr. Then all you need to do is set up the mechanism relations.
I modeled these as a single assembly with horizontal, vertical, in-out, and rotational offsets and have parameters for them all to make it easy to be flexible. Of course one slide of the pair could also be flexibly suppressed.
Not sure why the same would not apply to the use of mechanism restraints.
Thanks, I’ll try the rack and pinion trick.
Yes I also got the models from McMaster I used the import data doctor to isolate the parts and I thought it was excellent that the default datum planes were aligned conveniently.
I think we’ve all seen the cage creep with these sliders but, like you say, they’re easily reset with a good pull.
Yes, this morning (Monday) I reassembled the parts and it worked fine. I started with the two slide units and added the drawer constrained to the inner (full extension) slider of one unit AND THEN added a constraint to the inner slider of the other slide unit and it is all happy now.
I still think its great how the middle and inner slide units stay aligned with no rack/pinion or anything other that basic mechanism.
That is to say when the drawer is halfway extended the middle slide unit is extended about half of that travel (1/4 total)
I have seen occasion in both Creo 2.0 and Creo 3.0 where a body becomes grounded because some assembly level is grounded. It drags fine until you do an edit and then it displays the ground body message regardless of what you just edited. Just a heads up that if you think something is weird, it is probably not your imagination. As you figured out, order of assembly is extremely touchy (not necessarily logical).