First, I should say that I'm very (very) new to CNCs.
I finished a homemade CNC a few weeks ago (built to my own design from from discarded handrail, old dot matrix printers & Aluminium computer cabinet blanking panels!) ...& just being messing around ever since.
I want to make my own sustainer (wihich is essentially a guitar pickup in reverse ...it generates magnetic flux to actively keep the string vibrating).
Such 'driver's don't need to be as deep as a standard pickup bobbin...& I'd like to surface mount (to saving cutting into my guitar's body), therefore I'm pretty much on my own wrt coming up with a bobbin to wind the copper wire onto.
So I got messing about with some CAD/CAM software & came up with these parts which I intend fitting together to make a bobbin.....
(I'm not sure if you'll notice, the bit marked 'bottom' part has a slight chip at the top left corner, this is because when changed cutting bits ,I had the feed rate too high, the machine went ballistic & gouged into the part a little! The other two parts turned out well though...particularly happy with that middle bit - that's just 1mm between the edge holes & the bobbin edge at each end - esp since my leadscrews are just M8 rod, & my drive nuts are badly homemade delrin ones!
The colour scheme(!) wouldn't be of my normal choosing, but I was limited to those colours because of the thickness of the acrylic (I needed 2mm thickness which I only had as clear acrylic & also 4.5mm which I only had in translucent royal blue!). Here it is as a temporary 'push fit'
those poles sticking up are actually 20mm lengths of Alnico magnets ...they obviously need trimming...they were an *extremely* tight fit. I screwed up with the middle part too! Basically, I read somewhere to get rid of the cutter marks that acrylic can be flame polished along the edge ...apparently, all you need to do is run a butane torch gas flame along the edge - I'm sure it normally works well, but not when the part so small....the acrylic heated the small part up & distorted the acrylic! (shrunk it a fraction...hence a couple of the poles not being bolt upright)
Here it is ready to be wound (I've not glued the top to the middle, because, after the coil is potted, I'd like to see how it looks without the top, hence the large washers clamping the top to the middle for while it's being wound)...
So then, next I wound 150 turns of 0.235mm wire (which is actually 0.27mm if you include the enamel coating! I'm a Brit so I dunno what that is in 'base 8, 16 or 32'!), this gauge is much thicker than I'm used to & is quite a bugger to 'control' while winding on to the bobbin....
....those two large screws atop are simply holding the top part to the remainder (pending potting - after which, they'll eventually come out & the magnets will go in)
Ok, back to the reason for posting - in short it looks a little 'homemade...there's no edging to the parts to give it a more 'pro' vibe (it looks utilitarian, sort of "East European circa 1970!" design). Becuase the coil wasn't as thick as I thought (I will be trimming the top overlap you see for my next attempt).
, & because it looks amateur, I'm going to revisit the design in CAD/CAM.
This is where I'm struggling. Becuase I only work in 2D, I'm having difficulty wrapping my head around how I should do the edging.....in CAD? (wouldn't that be 3D), or in CAM (ie just selecting a suitable cutting tool to run round the edge of the top part?)
If the latter, what cutting tools could I run round the top part to either give it a curved edge or chamfered edge? I'm only using a dremel as the spindle (on account I only inted cutting thin acrylic)
IF it helps, I bought a ballnose cutter a week or two ago...but haven't a clue when to use it...& how to use it! (I've only worked in 2D CAD/CAM software to date)
Edit: Pulled the copper off in the end as it was too loose (I need more tension, but my winding motor - an old DC cooling fan) doesn't have enough torque. I cut those alnico poles down ....bad idea!!! (wrecked my X axis delrin drive nut)
Last edited by HankMcSpank; 06-30-2009 at 05:26 PM.
Very nice work.
If you're just making one of these to put on your own guitar, I wouldn't mess with it beyond the changes you've already noted; it looks like a Sputnik part, yes, but it is a space age guitar gizmo, after all...
If I were having one of those built for me by you, I'd ask you to make the bobbin out of something like this:
I think just swiping the edge with a bit of sandpaper is the solution to go with; I did find a Dremel roundover bit that MIGHT work:
I don't think chamfering it would improve matters much, by the way, so I'd avoid that.
I'm just learning CAD/CAM myself, so I can only speculate that 2d CAD won't work; I THINK you'd have to use the CAM to set the height of the bit so that it removed the desired amount of material. You might even have to run the bit a small distance away from the part profile to allow the roundover bit to intersect with the part in the middle of the bit cutting profile; that piece of acrylic looked pretty thin, and the bit profile looks pretty big.
Last edited by Alvarado1357; 06-30-2009 at 03:13 PM. Reason: superfluous remark about metric system deleted