A Homebrew Coil Winder

[FRANK.C]

I built a coil winder some years ago, it can be seen in this thread. It has served me well, but the time has come for it to be rebuilt as it is showing sings of wear.

The first section I have tackled is the supply reel. I feel the supply reel is the most important part if small diameter wire is to be wound. Most supply reels that I have seen are mounted horizontally, but I like them vertical as this minimizes the effect of any imbalance in the reel or spool.

The spindle is made from 10mm rod with a M10 tread cut into most of it. On it is mounted a brake wheel and a base to hold the spool of wire. Two bearings hold it vertical and it sits on a trust bearing.
It's got two brakes one is the main brake the other keeps back tension on the wire as its being wound.
The back tension brake has a shoe which is felt lined, a spring and screw adjusts the tension.
The main brake is operated by the jockey pulley arm, its shoe is rubber lined. It operates like a wedge in that when the shoe is offered up to the brake wheel, the brake wheel grabs it and pull's the brake shoe tighter again the brake wheel.

There is a spring which adjusts the tension on the jockey pulley the main brake works effectively regardless of the setting of this spring.
I mounted the jockey wheel on a shaft with a bearing at each end. The jockey wheel arm is made from two lengths of box section brass, one fits snugly inside the other and they are drilled so the arms length can be adjusted to suit the coil being wound. The jockey arm pivots on two bearings.

Frank

[FRANK.C]

More photos

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The take-up reel (for the want of a better word) on the old winder was purchased from China. It worked well but had a couple of bad points. It had no bearings and just ran steel on steel which needed constant oiling to keep it running smoothly the gears needed oiling or greasing as well and tended when running, to spray the oil or grease allover the place.

In my new Take-up the winding shaft is just a 10mm rod with a M10 tread cut into most of it. It has 4 gears, 2 x 24 teeth, a 60 tooth and a 80 tooth. This gives a ratio of 1 : 8.3. All the shafts are 10mm rod and run on bearings at each end. The whole lot is built into a mdf box which will prevent any spray. 5mm traded rod and 10mm tube was used to strengthened it. There is a small magnet mounted on the winding shaft it activates a reed switch which is mounted on the roof of the box. This pulse is sent to the control board for the turns to be counted and the transverse to be advanced.

[FRANK.C]

The transverse

The lead screw is M6 traded rod. it sits in bearings at each end. the bearings have a internal diameter of 10mm. Two M6 nuts soldered together one of them ground down to 10mm are traded onto the lead screw to hold the lead screw in the center of the bearings.
Trust bearings at each end of the lead screw prevent any lateral movement.

To couple the carriage to the lead screw, there is an arm on one side of the carriage that points towards the lead screw. The lead nut is a 20mm long M6, it has a short arm soldered to it at 90 degrees to the lead screw, this arm has a small piece of brass soldered to it which forms a "V" shape. The arm on the carriage fits into this V and is held in place by a spring. the action of the spring also keeps the lead nut pressed against the lead screw. This arrangement works very well there is no perceivable play between the lead screw and the carriage.

A 5mm coupling connects the lead screw to the stepper motor. I taped one end with a M6 tread, so the coupling would screw onto the lead screw.

There are no position switches as the controller counts the steps the motor takes to keep track of the carriage position.

I first tried running the carriage on two linear bearings but there was a little lateral movement at the top and bottom of the carriage it was pivoting around the coupling to the lead screw. I fitted two more linear bearings and that removed all unwanted movement.

The Transverse is not fastened directly to the base board. Instead there are two panels one each side of the transverse that is fastened to the base board. these panels has a slot cut in them, a traded rod goes through the transverse and the slots, wing nuts tightens the lot together. This allows the transverse to be positioned to suit different sized coils being wound.

The M6 traded lead screw has a 1mm pitch, the stepper motor that I am using has 100 steps, so each full step will move the carriage by 0.01mm. To get the carriage to move fast enough each step needs to be 2ms this will be approximately equal to 5mm per second movement of the carriage. To drive the stepper motor at 2ms per step and with good toque it needs a supply voltage of 18v, this is far too high a voltage to use as a holding voltage, the motor would overheat very quickly. I use a 5V holding voltage and the controller switches it up to 18V immediately before the motor takes a step.

[FRANK.C]

More photos

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The Auto Take-up

After coming across an old battery drill that the battery's no longer held charge, it occurred to me that it would be relatively easy to build a automatic coil winder with it.

I removed the gubbins from it. the chuck, gearbox and motor is all in one handy unit.
I mounted this in a box together with a unregulated power supply, a mosfet and its biasing resistors to drive it with.
There is a diode and a 33nF cap across the motor to tame the spikes it produces. It is driven directly from the controller with PWM.
This unit will be directly interchangeable with the hand cranked unit so I will have a choice of hand cranked or auto.

[FRANK.C]

The Controller

Is based around a PIC18F4520 micro controller.
It has a 4 line display. The first line is the number of turns that have been wound, the second displays the wire width, the third displays the winding speed and any errors and the fourth displays the coil width and the direction of travel of the carriage.

A 20 key keypad is used to input to the controller. The wire diameter is imputed in um, each time the take-up spindle revolves one turn the carriage moves one wire width. As the stepper motor moves the carriage in steps of 10um the carriage can only move distances of multiples of 10um. The controller will only move the carriage on in whole amounts of 10um if there is any amount leftover this is added onto the next movement.

E.G. if the wire with is 157um, the first movement of the carriage will be 150um with 7um leftover, this 7um is added onto the next movement to make it 164um of which the carriage will move 160um with 4um left over which will be added onto the next movement and so on.

The carriage will never be more than 9um from where it should be and at worse it will be exactly where it should every 10 turns. By using half steps and a little change to the code this could be brought down to no more than 3um out at any time, but I don't see any point in doing that as the mechanical tolerances are much higher than that anyways.

The controller monitors some switches etc and if everything isn't as it expects, it will either make a change to the wining speed or will stop winding. When it dose it displays an error code to indicate why it took action.

The user can change the speed of winding at any time but if the controller detects that the carriage is not able to keep up with the take-up (this will only happen while trying to wind larger diameter wire at higher speeds) the controller will take over control of the speed and reduce it to a level where the carriage can keep up. The controller then sets this speed as the maximum. From then on the user can decrease the speed below this set maximum but can not increase it above it. Error "1" will be displayed to indicate why the speed was reduced. The maximum speed can be reset via the menu.

At switch off or when power is lost all relevant variables are saved so that at switch on or when power is restored it starts exactly where it left off. If the take-up is active when power is lost, when power is then restored it starts up exactly where it stopped at, except the take-up is stopped and the start button has to be pressed to restart it. When power is restored after power been lost while the take-up is active, error "2" is displayed, otherwise it may not be obvious why the winder stopped.

If the main brake switch is activated while the take-up is active, the take-up is stopped and error "3" is displayed.

If the over tension switch is activated while the take-up is active, the take-up is stopped and error "4" is displayed

If no pulses are received from the reed switch while the take-up is active, the take-up is stopped and error "5" is displayed

As it stands now if winding using the hand cranked take-up, errors 1,3,4 and 5 will be displayed but obviously have no effect. I may yet include a "Manual" setting in the menu to stop these errors from being displayed. The "Ready" led on the control panel is off while the carriage is moving. While winding manually this led should be flashing, if it is off all the time this indicates that the user is winding too fast and the carriage cant keep up.

The control board, the LCD and key pad sits in an enclosure on the right hand side of the Transverse. There wasn't enough room to house the power supply so it is in an enclosure for itself to the rear of the winder.

Frank

[FRANK.C]

I have uploaded two clips of it working.

The first is here. In it I used a 19mm spade bit. I used the bit because it would draw the wire at an irregular speed so to test the function of the jockey pulley. I am winding 200 turns of 0.125mm wire with a coil width of 10.1mm.
The winder slows down at about 50 turns from the end of the coil.

The second one is here, this time 200 turns of 0.05mm wire is been wound, that is the thinnest that I have.
I have narrowed the coil width to almost 5mm (the coil width is calculated as the distance the carriage travels plus one wire width). The back tension and jockey arm tension have been adjusted to suit the 0.05mm wire. The wire diameter is set to 64um to allow for the insulation.

Frank

[McMurdo]

that's seriously sophisticated Frank! Very impressive. Beats my winding attempts by putting the bobbin in a model making lathe and holding the wire with cotton gloves!

[FRANK.C]

Hi Kevin
Thanks for your comments.
If I had access to a lathe I might not have bothered building a coil winder, a lathe can do a pretty good job.

Frank

[Mike Phelan]

Wow! That sure is impressive, Frank.

Lathe? You could probably make one if needed!

[FRANK.C]

Thanks Mike
In certain situations (this being one) PIC's make it easy.

Frank

[Colin Ames]

Wow, that is a serious piece of equipment. Very well done!

Colin

[kellys_eye]

Brilliant device, beautifully executed and wonderfully documented! Thanks for sharing.

[FRANK.C]

Hi Chaps
Thanks for your kind comments.

Frank