Coil winder Ideas and traverse devices

[Woodenspoke]

OK so I just spent about an hour reading through the coil winding Idea section and got a headache about page four. I have a cnc mill and still I was getting weary.

I kept hearing about using a heart shaped cam rather than the reversible drive belt mentioned. I did a search but could not find a drawing of a typical heart shaped cam.

I don't want to make this a long rehash of that coil winder post I am just interested in the cam design.

I personally believe a cam would be easier overall even with a CNC solution since you can vary the rate at which the cam spins thus changing the traverse speed. OF course if your coils are different widths then that may be an issue and require more than one sized cam or the movement of the transverse arm forward or backward from the pivot point.

Reversing steppers has always been an issue and unless you can go to a high end servo system I like the cam idea as a starting point better than using a belt driven reversing stepper.

I got the heart shaped cam theory but for some reason I cannot bring myself to put two and two together as to which part of the cam is driving the wire on what part of the wind, if this makes sense.

I guess if it made sense to me, or if I could picture it I wouldn't be asking. A picture, a link or a long explanation would be appreciated.

[David Schwab]

Check this page out Coil Winder

Go to the fourth, six and seventh and pages and see a heart shaped cam.

This winder spins the wire around a stationary bobbin. I've never quite figured out how that works.

[Woodenspoke]

David;

Wow just reread my original post, sorry I sound like an idiot???

Even though your pictures and links make some sense it seems like someone has reinvented the wheel or just likes to add lots of complicated parts. For something that complex you might as well program a CNC machine to do the work without all the little additional cams. Or buy that CNC winder from China for 2.5K I have seen on ebay. which incorporates all the standard winding features you would ever need to make straight neat coils.

My thought was a straight piece of aluminum bar with a set pivot point. Below the Pivot point a motor driven cam would push the bar out and a spring would keep the bar against the cam. The spring would allow the bar to ride along the cam creating a clean transverse winding motion. I realize the trick is is in the reverse motion. It has to be quick enough so the wire will not build up on the bobbin edges. bottom line a fast change of direction

The question I think is at what point in the movement along the heart shaped cam does this quick change of direction take place. Is it in the V at the top of the heart or the outer V point at the bottom?

I can picture the quick wire change of direction where the wire drops into that V portion at the top of the heart but why is it not the same at the opposite end? This is where my confusion comes in.

Here is a rough sketch of my design so this all makes sense. The only thing missing is a spring (not hard to figure that one out) and the motor may have to move along with the cam contact point or horizontal rather than vertical as drawn, I am not sure at this point. Again a rough sketch of a possible quick and dirty design. Now if I can only figure out the cam the design would come together much faster.

[wilser]

I recently got a small DC motor that has a ball screw and nut attached from an electronics surplus store. I'm just waiting for a small linear bearing to complete my auto-traverse! getting guide bearings small enough for 42/43AWG wire was a challenge! Anyway, the motor will change directions by flipping the polarity with a DPDT relay that's driven by a simple flip/flop circuit. The circuit will be triggered by small push buttons (wired for set/reset on the flip/flop) that will be adjustable in position. I hope to have this ready by the time I start making the pickups for a few of the basses I have on order, otherwise I'll have to scatterwind them (which is getting tiresome!). I'll post pics and more detailed specs when I have it working.

[Woodenspoke]

My feeling is if you add switches and other electrical reversing solutions you may add in an unwanted delay. This delay would be the time the switch is actuated until the time the motor changes direction and would be enough to cause build up of wire on the coil edges. I am assuming the bobbin motor is running at a constant speed.

All things equal I believed keeping the transverse motor going in the same direction and having a cam do the rapid movements off the edges would eliminate the possibility of any directional delays. I will also probably experiment with different cams to create a scatter wound type motion as others have done.

Still would like to see some info on the heart shaped cam in action.

[Sam Lee Guy]

Just look at a real old treadle or hand crank sewing machine - one with a cotton bobbin winder on the side that you can engage with the main wheel and you'll see exactly how a heart shaped cam works.

[Woodenspoke]

I'll look for some old sewing machine pictures but why is it so hard to describe its operation in words?

Hopefully I can find something that makes sense, since I cant remember any cams on any sewing machine I have seen others use in my life time. maybe I was not looking too hard.

[Woodenspoke]

I really didn't find anything that stood out in bobbin winding from any sewing machine web page.

I did however set up a computer test using Adobe Illustrator where I took a guitar pick (heart shape) and set up several different points of rotation from center to top edge of the heart all of which rode along the edge of the rod. This shape created weird winding patterns where one fast wind across the bobbin was followed by one slow even wind. Moving the cam pivot point away from the edge made it even worse.

Then I though maybe it would be easier just to use a circle and offset the Pivot point to one side. In this model the rod moved cleanly back and fourth at a steady speed which would result in an even wind in both directions.

I also realized that the point of contact should be the rod and not some pin on the top. But I am still working on a theory about changing the movement to accommodate different bobbin sizes without changing the cam size. So a pin that moves is not out of the question yet but that may be wishful thinking.

With a round cam then you can start making different surface features which could mimic scatter wound pickups but still have smooth traverse motion between the two bobbin ends.


If anyone believes this to be wrong speak up before I wind up wasting time making parts.

Hopefully this makes sense

[John_H]

I really didn't find anything that stood out in bobbin winding from any sewing machine web page.

I did however set up a computer test using Adobe Illustrator where I took a guitar pick (heart shape) and set up several different points of rotation from center to top edge of the heart all of which rode along the edge of the rod. This shape created weird winding patterns where one fast wind across the bobbin was followed by one slow even wind. Moving the cam pivot point away from the edge made it even worse.

Then I though maybe it would be easier just to use a circle and offset the Pivot point to one side. In this model the rod moved cleanly back and fourth at a steady speed which would result in an even wind in both directions.

I also realized that the point of contact should be the rod and not some pin on the top. But I am still working on a theory about changing the movement to accommodate different bobbin sizes without changing the cam size. So a pin that moves is not out of the question yet but that may be wishful thinking.

With a round cam then you can start making different surface features which could mimic scatter wound pickups but still have smooth traverse motion between the two bobbin ends.


If anyone believes this to be wrong speak up before I wind up wasting time making parts.

Hopefully this makes sense

The oblong cam like you describe wont work. It would wind very lopsided coils. A heart shaped cam guides the follower at a smooth uniform velocity, and doesn't dwell at one end or the other.

To me it seems the most difficult part of making a mechanical traverse would be controlling your turns per layer, and being able to easily vary it. Without that all you have is a back, and forth thingy.

[Woodenspoke]

The oblong cam like you describe wont work. It would wind very lopsided coils. A heart shaped cam guides the follower at a smooth uniform velocity, and doesn't dwell at one end or the other.

To me it seems the most difficult part of making a mechanical traverse would be controlling your turns per layer, and being able to easily vary it. Without that all you have is a back, and forth thingy.

Thanks for the picture since at at least you have given me a starting point. I now see heart shaped means sort of heart shaped. It is actually a cross between the guitar pick and round offset cam I ran on paper.

Now I assume this rides along a small pin given the dip at the top of the heart is not that big. You also have it running from a drive gear and I want to mount mine directly to the shaft of the drive motor.

My only question and it might seem stupid at what two points on that cam does the left and right bobbin change of direction occur. This will help me with the location of the shaft position. I see this is also offset a certain distance from center.

Unless someone has a DXF file of a working cam they are willing to part with. Any info I can get will help speed up the process.

Thanks again for the picture you made my day.

[John_H]

Now I assume this rides along a small pin given the dip at the top of the heart is not that big. You also have it running from a drive gear and I want to mount mine directly to the shaft of the drive motor.

My only question and it might seem stupid at what two points on that cam does the left and right bobbin change of direction occur. This will help me with the location of the shaft position. I see this is also offset a certain distance from center.

A follower rides on the cam. It's L shaped, and the other end is the wire guide. The distance of travel can be controlled by the length of the rocker.


The change of direction occurs at the most extreme outward, and inward points. One revolution of the cam moves the lever across, and back.

You say you want to mount a cam to the drive motor. This wont work without some kind of mechanical reduction of the speed of the cam. For example, if you were winding strat single coils and wanted a level wind the bobbin is 7/16 tall (.4375) The wire dia. is approx .0026. That equals 168 turns. At that rate the cam would have to revolve once for every 336 turns of the coil. A different solution is required for every type of coil you would wind. Traverse length, and turns per layer both. I have ideas about how to achieve this rather simply, but would have to build another winder to implement them. Until then I'll continue to hand wind, and learn as much as I can about making good sounding pickups.

[Woodenspoke]

I think what you describe is what I envisioned. However I have not gotten the part of the inner V to outer movement as coming off the bobbin in the opposite direction of where you want the wire to go. I will have to do some building and see first hand.

I planned on changing motor speed to account for the width and bobbin speed. To do the two with equal precision will require some experimentation. or a cnc program and two servos. I also have a mill with the fourth servo in reserve and could create a program which would change the the speed of the motor to match the bobbin. Then just make whitness lines on the bobbin winder motor as to needed speed.

I did get the L shape but the rocker I didn't figure out where that is in relation to the L shaped piece. My picture may be an over design.


I have rushed this reply since I am going out the door but your explanation of the rocker would be appreciated.

[John_H]

I think what you describe is what I envisioned. However I have not gotten the part of the inner V to outer movement as coming off the bobbin in the opposite direction of where you want the wire to go. I will have to do some building and see first hand.

I planned on changing motor speed to account for the width and bobbin speed. To do the two with equal precision will require some experimentation. or a cnc program and two servos. I also have a mill with the fourth servo in reserve and could create a program which would change the the speed of the motor to match the bobbin. Then just make whitness lines on the bobbin winder motor as to needed speed.

I did get the L shape but the rocker I didn't figure out where that is in relation to the L shaped piece. My picture may be an over design.


I have rushed this reply since I am going out the door but your explanation of the rocker would be appreciated.

I should have said rocker arm in the earlier post. Sorry 'bout that. I was referring to the arm that actually guides the wire. Adjusting the traverse length could be done by attaching the wire guide at different points on the arm.

[Woodenspoke]

I kinda thought thats what you were referring too. I see that there is no 1:2 ratio on the cam as you stated. Unless you make a new cam for each coil size or change the speed of the cam it is an issue. I can see why you are hand winding

I wanted to just hand wind at first but then thought about just starting and stopping the process without sitting in front of the machine guiding the wire.

back to the drawing board for now to mill over all the information you have provided.

Thnaks again

[Wrnchbndr]

Hi, this is my first post to this forum. Lots of great info and talented folks here. My spin on this heart shape is to imagine that you need a cam to deliver a linear movement that travels the same distance for every degree of rotation of cam driveshaft. Using just an offset circle won't work because if you start at the high point of the cam, it is comparatively flat per degree of rotation and tranverse travel will be slow. Maximum travel will occur at 90 degrees of rotatation but will slow down again the closer the cam gets toward the 180 point and totally stop while it passes over 180 and then speed up again as it heads toward another 90 degrees. This will cause build up of windings at each side of the bobbin. The solution is to start with a circle. At the zero point (0 degrees, designate the maximum radius. At the 180 degree point designate minimum radius which will be a difference of the intended stroke. Consider that the rotation rate is constant. You divide the difference between maximum and minimum by 180 and you'll acquire a figure that indicates how much less than the maximum radius of material needs to be cutaway from the circle per every degree of rotation. 180 degrees is only half of the circle. The other half will be the exact opposite form for the opposite direction or stroke. The resulting cam will have a heart shape and if you do the math and calculate the radius by ever degree, the resulting transverse motion will yield an even build up of wire.