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 Post subject: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 6:03 pm 
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So I got my TIE cube in the mail - I used the grigr core from his learn 3x3x3 model, but the problem is that most of the holes ended up being too big for the M3 screws. The screws would go in, tighten a little bit, but never secure in the core. Now that I've tried a couple of times it bored out the hole, so my core is useless!

So questions - Was it a bad print, or maybe should the holes be a little bit smaller in the core - say 2.5mm?

Any suggestions of fixing the core I have - maybe just fill it with some epoxy?

Has anyone else ever run into this issue?

Thanks!

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 6:14 pm 
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Yes, 2.5 mm is the standard M3 screw size. I suggest you fill in the core with epoxy or some other material then drill a hole.

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 6:25 pm 
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Take a look at:

http://www.tribology-abc.com/calculators/metric-iso.htm

The "drill diameter" is roughly the inner diameter and for M3 screws you want 2.5mm

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 6:25 pm 
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rubikcollector123 wrote:
Yes, 2.5 mm is the standard M3 screw size. I suggest you fill in the core with epoxy or some other material then drill a hole.


I don't think you can epoxy the hole and then drill the epoxy for several reasons:

  • The epoxy will be very viscous and hard to get into the shaft
  • The epoxy will expand
  • The epoxy's exothermic reaction can get so hot that it will deform the nylon
  • The epoxy is extremely hard and the surrounding nylon is very soft so without very precision equipment you wouldn't be able to drill a hole
  • You have a 2.7mm shaft and you want a 2.5mm hole leaving only .1mm of epoxy material on the outside

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 6:33 pm 
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Thanks guys for the quick replies - I'm off to the hardware store to see if I can find a slightly bigger screw for now till I can remake the core! If not it's back to waiting on the UPS guy!

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 7:19 pm 
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I had a very similiar issue with my Multi Gear Cube kits. See my post here:

http://twistypuzzles.com/forum/viewtopic.php?p=284480#p284480

Luke followed up with this reply:

Luke wrote:
As far as I know, Tom uses 2.75mm (diameter) screw holes for his puzzles. I go slightly smaller, with 2.65mm. Slight fluctuation with the screw size can sometimes causes looseness, and 2.65 seems to be a good balance between being too large and too small. Alternatively you could go midway and use 2.7mm. Anything between 2.75 and 2.65 should be fine.
Off the top of my head I'm now not certain what hole size I'm using on Shapeways for M3 screws. I'll check and post again but I'm thinking it is 2.65mm.

If the hole is too small I would think you could deform the part you are screwing into. Oskar, Tom, or other designers do you want to share what hole size you are currently using for M3 screws?

Thanks,
Carl

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 7:31 pm 
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I used 2.52 mm for my recent twisty puzzle. I don't think the extra .02mm actually made a difference so yeah.

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 9:58 pm 
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Since we're talking about it - where do you guys buy your M3 screws, springs etc...? Perhaps what I have is not exactly an M3 after all... It's 3mm wide, but I'm not 100% sure it's an actual M3. What is the standard length for one?

Edit - would this work? http://www.pololu.com/catalog/product/1076

Sorry if all this has already been answered somewhere else!

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:14 pm 
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Ok.... I've checked several of my models. I was using 2.75mm without issue for a long time. My last model I switched to 2.65mm as I had a problem with just a single hole on one print of a model which used 2.75mm. Should I really be using 2.5mm instead?

As for where I got my M3 screws the last batch I purchased I got off Amazon but the seller I bought them from isn't there any more. As for length you should be able to get just about any length you want. I think I'm seen 5mm, 8mm, 10mm, 12mm, 15mm, 20mm, 25mm, 30mm, 45mm, and 60mm.

Carl

P.S. There is the thread where Tom states he uses 2.75mm:
http://www.twistypuzzles.com/forum/viewtopic.php?f=9&t=24319

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:18 pm 
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wwwmwww wrote:
[...]As far as I know, Tom uses 2.75mm (diameter) screw holes for his puzzles. I go slightly smaller, with 2.65mm. Slight fluctuation with the screw size can sometimes causes looseness, and 2.65 seems to be a good balance between being too large and too small.

In my opinion, your screw holes are on the "large" side of things. US size "4" screws like 4-40 are smaller in diameter than M3 screws. I like it when the screw holes will work with either however with your Bubbloid122 puzzles (at 2.65mm?) the screw holes are too big for 4-40 screws and IMO a tiny bit too big for M3 screws too.

I've had a bit of trouble with stripping of the screw holes on both your Bubbloid122 and some TomZ puzzles like the Multidodecahedron. Last year when I assembled the 8 Bubbloid122s I tumbled, I partially stripped a few of the 64 screw holes. This year I was much more careful about tensioning and didn't strip any. I've stripped more than one Multidodecahedron core too.

There probably isn't a perfect size because cylindrical features like screw holes show more print variance than many other puzzle features. Also, there is a fine balance between too tight and "just right" (strip-resistant). I'm certain though that 2.5 to 2.6mm screw holes will work well with M3 screws and the holes could probably even stand to be 2.4mm in diameter and work with 4-40 screws too.

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:22 pm 
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Great info everyone - I think there were two things at work here with me and my errors - I stripped one hole, and on second look, I think maybe I'm not using exactly an M3... Secondly, I think one of the other holes was just slightly bigger due to the printing process...

In hindsight - I think I'm going to go down to 2.6, buy some official M3's, and see what happens from there. Nothing like good old trial and error!

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:34 pm 
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Stop the presses! I just figured out what it was - There is an error in the learn 3x3x3 file that I copied the core from... two of the holes in the core are actually 3.26mm, not 2.7mm. That explains a lot! FYI, if anyone else ever uses this file to base something off of!

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:41 pm 
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jabeck wrote:
[...]two of the holes in the core are actually 3.26mm

I'd expect those to be very tight. How well do the narrow diameter holes work with M3 screws?

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:47 pm 
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bmenrigh wrote:
jabeck wrote:
[...]two of the holes in the core are actually 3.26mm

I'd expect those to be very tight. How well do the narrow diameter holes work with M3 screws?


Tight, or loose? I'm confused... The 2.7 diameter worked fine. It was the 3.26 that were way too loose...

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Mon Jul 08, 2013 10:49 pm 
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bmenrigh wrote:
I like it when the screw holes will work with either however with your Bubbloid122 puzzles (at 2.65mm?)
Just checked... the current Bubbloid122 model uses 2.75mm holes. Only the latest version of the Multi Gear Cube Kit has the 2.65mm holes.

alaskajoe uses 2.7mm. I found that info here: http://twistypuzzles.com/forum/viewtopic.php?f=9&t=25529

I'm pretty sure I've seen the diameter Oskar uses too. Looking for that now.

But yes, I certainly agree that 2.75 isn't optimal. And in the post I link to above alaskajoe had an issue with 2.7mm being too small but I believe that was a printing error.

Has anyone actually used 2.5mm? Trial and error is certainly a great way to learn but I'm after the cheapest way to learn. Considering the number of designers here and how willing most of them are to share I don't see a need for each of us to reinvent the wheel.

Carl

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 12:26 am 
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I usually use 2.9, and it works, so I'm not sure it's a bad print so much as a VERY bad print ^^

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 1:06 am 
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jabeck wrote:
bmenrigh wrote:
jabeck wrote:
[...]two of the holes in the core are actually 3.26mm

I'd expect those to be very tight. How well do the narrow diameter holes work with M3 screws?


Tight, or loose? I'm confused... The 2.7 diameter worked fine. It was the 3.26 that were way too loose...

Ah I read it as "2.26" not "3.26". So the 2.7 worked well?

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 1:14 am 
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jabeck wrote:
Stop the presses! I just figured out what it was - There is an error in the learn 3x3x3 file that I copied the core from... two of the holes in the core are actually 3.26mm, not 2.7mm. That explains a lot! FYI, if anyone else ever uses this file to base something off of!


Thank You
in the model is actually a bug. I will fix it!

it is a model learning. I never printed it!
I did it to show some of the methods of work for my friends.
I do not guarantee the accuracy and tolerances in the elements of this model ...

my friends SpeedCubers suggested me: you can wrap the foil screw and screw it

ps
I use 2.6-2.7mm for holey

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Core + Screws + Springs Set:
http://lightake.com/detail.do/sku.MHZ_C ... s_Set_(New)-29962
http://lightake.com/detail.do/sku.Core_ ... _Set-30525

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 10:46 am 
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Thanks grigr - It is no problem! I should have checked it before I printed it! And thanks for the links...

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 10:47 am 
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Yes, the 2.7 was fine...

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Tue Jul 09, 2013 10:56 pm 
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Just as another reference: I've used 2.4mm diameter holes for all of my puzzles, and I've never had an issue.

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 Post subject: Re: Shapeways cores - 2.7 mm hole was too big
PostPosted: Wed Jul 10, 2013 12:58 am 
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will_57 wrote:
Just as another reference: I've used 2.4mm diameter holes for all of my puzzles, and I've never had an issue.

Your puzzles work with both M3 and 4-40 screws although the M3 screws are a bit tight. Somewhere around 2.4 to 2.5 is the sweet spot for supporting both metric and US sizes.

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