Making Keys to Connect a Cut Print
I just recently made my Gloomhaven Cave Bear model, which needs to be printed in two pieces because of the details around the bear's teeth. When I was cutting the model to be printed, I realized that I was going to need a post to help guide the head into place (otherwise it was really difficult to line up the fur), which got me thinking about the whole post-and-slot design for situations like this.
When I've done similar cuts in the past, I put the post directly on one half and cut the cavity into the other half... and that worked great, as long as I got my tolerances correct. When I failed to get them right, I was stuck either reprinting the part with the post (after making the post slightly smaller) or the part with the cavity (after making it slightly larger). Either way, I had to reprint a fair amount of the model.
I noticed this problem even more when I was printing a model that someone else had pre-cut. He had cut it with a 5% tolerance, which sounds like a lot, but when your post is about a millimeter thick, that ends up only creating a .05 mm gap around it. My printer is good, but it's not that good! The pieces were quite large and the post/slot were irregularly shaped, so adjusting their size and reprinting wasn't really a good option for me... I ended up just filing the post down until the two pieces would fit, which isn't really a good solution.
So, that .05 mm tolerance must've worked for the original artist, but it didn't work for me. There is a huge variety of printers on the market, with a corresponding variety of printing tolerances... so there's no universal right answer for how much larger a slot should be than the post that's going into it. That left me wondering, how could I deal with that when publishing my Cave Bear, which was going to need a post and slot design?
The best answer I could come up with was to use two slots and a completely separate post. That way, I could make them based on the .2 mm rule of thumb (which works great for me), but other people could easily scale up or down the post if they find that it's too loose or too tight (and the post by itself is like a 5 minute print, so it's not a big problem to print it a few times).
So, that's what I did! The bear works great for me, and hopefully it will work well for everyone else, too!
P.S. On New Year's Eve, one of my friends asked me what I had going on for the new year. I told her that I was thinking of writing a sequel to my 8 paragraph love letter to the trapezoid... here it is!
P.P.S. If you're interested in testing your printers tolerance with posts like this, I put together a quick slot tolerance test model on Thingiverse. It has a post like I use on my minis, and then 6 slots. The first one has 0 tolerance, if your post fits in there, your post probably printed out a bit small :P After that, each hole increases its tolerance by .1 mm, so the final hole has a .5 mm tolerance.
When I've done similar cuts in the past, I put the post directly on one half and cut the cavity into the other half... and that worked great, as long as I got my tolerances correct. When I failed to get them right, I was stuck either reprinting the part with the post (after making the post slightly smaller) or the part with the cavity (after making it slightly larger). Either way, I had to reprint a fair amount of the model.
I noticed this problem even more when I was printing a model that someone else had pre-cut. He had cut it with a 5% tolerance, which sounds like a lot, but when your post is about a millimeter thick, that ends up only creating a .05 mm gap around it. My printer is good, but it's not that good! The pieces were quite large and the post/slot were irregularly shaped, so adjusting their size and reprinting wasn't really a good option for me... I ended up just filing the post down until the two pieces would fit, which isn't really a good solution.
So, that .05 mm tolerance must've worked for the original artist, but it didn't work for me. There is a huge variety of printers on the market, with a corresponding variety of printing tolerances... so there's no universal right answer for how much larger a slot should be than the post that's going into it. That left me wondering, how could I deal with that when publishing my Cave Bear, which was going to need a post and slot design?
The best answer I could come up with was to use two slots and a completely separate post. That way, I could make them based on the .2 mm rule of thumb (which works great for me), but other people could easily scale up or down the post if they find that it's too loose or too tight (and the post by itself is like a 5 minute print, so it's not a big problem to print it a few times).
So, that's what I did! The bear works great for me, and hopefully it will work well for everyone else, too!
P.S. On New Year's Eve, one of my friends asked me what I had going on for the new year. I told her that I was thinking of writing a sequel to my 8 paragraph love letter to the trapezoid... here it is!
P.P.S. If you're interested in testing your printers tolerance with posts like this, I put together a quick slot tolerance test model on Thingiverse. It has a post like I use on my minis, and then 6 slots. The first one has 0 tolerance, if your post fits in there, your post probably printed out a bit small :P After that, each hole increases its tolerance by .1 mm, so the final hole has a .5 mm tolerance.
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