Taperred Capstan

Recently I was involved in discussion about the ½ - 1 degree taper you find on nearly all wet tandem drawing machines. However, nobody could come up with a real technical or engineering answer on why the capstans are tapered towards the front of the machine.
Does anybody have any idea what the reason for the taper and has a good engineering explanation for it. Thanks!

RWW

Hello RWW,

Would you please be more precise in what you mean by "tapered towards the front of the machine" so that there is no confusion in anyone's mind?

Do you mean:

a) Slight tapering on a few of the capstans starting at the wire or rod entry end of the drawing machine.

b) Slight tapering on a few of the capstans starting somewhere towards the wire exit end of the drawing machine.

c) Slight tapering of all the capstans towards (or away from) the operator's side of the drawing machine.

Thank you.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Dear Peter:

My background is non-ferrous, Cu & Al, wire drawing. What I refer to tapered capstan is the surface where you wrap the wire around after you pull it through a die inside a wet drawer. The tapered capstan surface is somehow related to slip what I was told. Also when you stop the machine you mostly find the wire wraps at the front edge (smaller diameter) of the capstans. As soon as you start drawing and pulling wire out of the machine the wire walks “up” towards the larger diameter of the capstan; if you stay idle, i.e. you do not pull wire out of the drawer, then the wraps are staying on the smaller diameter side of the capstan, what is always towards the front of the machine.
Hope my explanation could clarify my previous questions. Thanks!

Rgrds,
Rolf

Hello again RWW,

OK your second description is enough for me to decipher that you mean all of the capstans are slightly tapered towards the operators side of the machine.

I always thought this was to allow the wire wraps to fleet (slip sideways) easier across the surface of any one capstan before the wire went on to the next drawing die.

Keep in mind however that the conventional slip in a drawing machine that you are used to is not this fleeting slip.

Conventional capstan slip inside the drawing machine is in the direction of capstan motion as the capstan surface speed is faster than that of the wire.

The only capstan with no slip is the dry capstan outside the actual drawing section of the machine.

If you want to learn a little more about conventional capstan slip, (not fleeting slip) you can find it here. www.stewart-hay.com/pshslip.htm

Finally there is one more thing one has to be cautious in comparing.

Running and say jogging during stringing are really two different things because in my experience, drawing machine operators during jogging or very low speed running use the very least amount of lubricant they can get away with because they don't want to get splashed. I have even seen no lubricant used at all until a foreman or lead hand came by. If there is inadequate lubrication between the wire and the capstan surface during this time, the friction can indeed allow the wire to climb up the taper towards say the gear train side of the machine.

Clean and chemically well maintained, proper flows of drawing lubricant to all the dies and capstans are just as fundamental as the maintenance of the drawing dies, the maintenance of the capstans and of the quality of the non-ferrous metal you are drawing.

Too many people in the wire industry forget that drawing lubricants, spools and other peripherals are just as important as the production machines themselves.

In my experience, proper ongoing technical management of the production machines, well trained, well paid and properly motivated operators, quality materials, proper management of plant operations (JIT, 6 Sigma, MRP and so on) including plant cleanliness and organization results in high volume, low cost, highly competitive production with very little scrap.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Peter, how are you?

Some of what I learned or thought I learned.

Regarding the question about the taper being toward the operator. First off it does help the wire fleet on the capstan. Fleeting is important especially with copper (for magnet wire use ) because if the wire rubs on the other wraps it damages the wire and when you make wire the size. Tech 1, does that damage prevent you from drawing the wire that small? Any defect that occurs at say 8 awg is still there up until the point it causes the wire to break.

When stringing a machine, the wire comes on at the back side of the capstan and as you add wraps, the wire wraps get closer to the front of the machine. The taper allows the wire to fleet. If the capstan does not have a taper but is straight, the position of the next die will lead the wire off the capstan. On the typical non-step cone breakdown machine, the first die is closer to the back of the machine than the next die. Each die is positioned closer to the operator side than the previous.

If the capstan were tapered away from the operator side, it would be either challenging to string up or the wire would fall off the taper, slip on the capstan and perhaps crossover and break.

Does that make sense?

Hi Spectre,

Yes your comments certainly make perfect sense and thank you for your input.

As far as tapering is concerned and of course the machine design and die positions, the tapering could be towards the operator side (standard), towards the gearing side of the machine (unlikely) or they could be tapered in both directions (from the center of each capstan to the outside) so that the capstans can be turned once before refinishing.

I am well, thank you, but a little tired of this present heat/ humidity wave.

Best personal regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com