I have read several discussions that have related back twist to lay angle for a full planetary unit. My question is: Does the path that the cable takes from the cradle through the machine to the closing die have any effect on back twist.

In our situation we have a full planetary cabler (100%, non-adjustable) the material exits the cradle and over a guide sheave. It then follows a 15 degree path to a second guide sheave then into the lay plate and finally the closing die. I understand that the angle between the layplate and the closing die has an effect on backtwist, but does the angle and time that it takes to get from the cradle to the lay plate have any bearing on back twist.

Hello Eric,

It is a little difficult to answer your question without understanding what product you are closing and the exact design of your cabler however:

A planetary cabler in it's many forms is defined as having "back twist" because the back twist normally associated with rigid stranding is absent and therefore removed. There are however frictional forces that tend to twist the sub-components a little bit because these sub-components are rotating relative to the fixed mechanical items that are contributing to those frictional forces. (Eyelets, sheaves, closing dies, etc.)

In your case, I believe you have a classical planetary cabler with the cradles that hold the reels turning in opposite rotation relative to the rotation of the overall carousel which holds those individual cradles.

In my experience, I suggest that you set all your guides and the closing die so that the sub-components close naturally and are not forced to have any abnormal deflections. That should give you the best possible situation. I have also seen some companies place their closing die on freely rotating on bearings to try and eliminate the rotational friction but in my experience, that die will not rotate if indeed the cabler is "strung up" properly as above

The torsional stiffness (rigidity) of the sub-components also comes into play at start up but I assure you that algebraically the back twist is indeed removed.

You can test this for yourself by setting up an experiment using longitudinally striped sub-components and watching what happens to the individual stripes in the closed cable.

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

Peter,
Thanks for the response. This is, as you expected, a classic planetary cabler. One revolution of the machine=one reverse revolution of the cradle. In other words the cradles stay level the throughout the rotation. I am actually planning to run .375 dia stainless tubing with a 10" bend radius. I may need to modify the path that the material takes thru the cabler (change the angle from the cradle to the lay plate) to account for this material and guide sheaves. If I modify this angle will I see any change? For example if I change that angle from 15 degrees to 30 degrees will I introduce enough extra fricitonal forces to affect the material. Or even if I have to make the angle steeper. Again thanks for your help on this.

Hello again Eric,

I have cabled 0.375 inch OD copper coax on a classic planetary cabler such as yours many times and it would seem to me that 15 degrees from the exit eyelet or sheave straight down to the closing point is quite a gentle angle and should serve you well.

Don't force the sub-components into a larger angle like 30 degrees as you will introduce other normal forces at the deflection points because of the sharper angle. You might however find that 17.5 or 20 degrees serves you better. (Whatever angle that gives you the straight line right through the die entrance bell to the closing point.)

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

Thanks, we knew that is the way it should work. It helped being able to think it thru w/ someone.

Eric