Printed Spools

Re: Printed Spools

Postby Samuel » Mon Jun 23, 2014 4:39 am

Nicholas, I saw earlier you had posted an order for 9x 12mm spools and 6x 16mm spools. Would you mind mentioning your reasons for those quantities and sizes?

I may have the opportunity to get some custom machined spools done myself, and I was wondering which size I should get. If you've had a chance to try them out, I would be interested in the results as well.

*Edit - use Nicholas' actual name.
Last edited by Samuel on Mon Jun 23, 2014 5:03 am, edited 1 time in total.
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Re: Printed Spools

Postby Nicholas Seward » Mon Jun 23, 2014 4:57 am

@Samuel: I will assume you mean me. :-)

I mostly want to have a range of sizes on hand to experiment with. Smaller obviously will result in more force and better resolution.

I am still in the process of designing the new arms. I suspect that these 18mm spools will work great. However, I think smaller will be better. Basically, I need the smallest ones I can get that still store enough string on them.
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Re: Printed Spools

Postby Samuel » Mon Jun 23, 2014 5:02 am

Yes, you're right. I know your name too; it must be getting late...

I take it then that you have not yet received or tested any metal spools?

How much is 'enough string'? And do you mean without having the string layer on top of itself, changing the effective spool diameter?

If you're redesigning the arms, should I print everything else and just wait a few weeks for the new arm design, or should I go ahead with the current ones?
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Re: Printed Spools

Postby Nicholas Seward » Mon Jun 23, 2014 5:35 am

@Samuel: I have not received the spools or paid for them so I will probably go eventually get them made locally.

The triangulation error isn't so bad if you can stay +/-5mm from the center. (The string leaving the spool on the new design travels 180mm before it is redirected which will keep the error under 100um.) If the string is 1mm wide, this will give you 375mm of string travel from the 12mm spools. My new design will need a travel just a bit bigger than that.

I wish I could tell you with certainty when I will be done with my new design. I am not close enough to hazard a guess. I do know that the hub and the arms will be different. That leaves just the shoulders so I might as well rethink them also.
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Re: Printed Spools

Postby UnderSampled » Fri Jun 27, 2014 8:48 am

Hello Nicholas,

I am currently working for a metal shop and was recreating your drawing in Solidworks so I could submit a proper 11x17 print with my work order to make them, and have a few questions regarding it, specifically:

If dimension A is a diameter of 12mm, then the value of [A/4+2.5] is 5.5 for the position of the 2mm vertical through-hole. This results in the edge of that hole being 6.5mm from the center, which is larger than the spool's radius of 6mm. Is there some other equation for that dimension that would work better?

Another thing I wonder is if you think it would be worth it to specify geometric tolerance for the roundness of the spool, as that probably matters more than the actual diameter, and if so what would be the right tolerance. Finally, most prints have a disclaimer on them stating that they should not be reproduced. Since you are the creator of the design, I would like to know what license you are giving it under, and how you would like me to denote it on my version of the drawing.

I am planning on making a few of both sizes for Samuel (He's my brother), and if you would like I should be able to make the ones you requested as well. Just let me know if your interested.
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Re: Printed Spools

Postby Nicholas Seward » Fri Jun 27, 2014 1:00 pm

Sorry, the equation should be [(A-5)/4+2.5] and I would suggest a 1.5mm hole for the smaller spools.

You can license the drawing however you like. I typically go with an MIT or GPL license that essentially says they can do anything they want with the drawings.

I can always make a 11x17 print for you if you need. Let me know.

Don't worry about ordering me any spools. Thanks for the offer.

BTW, this post has an attached pdf that you could just print off on a 11x17 piece of paper.
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