Jump to content

Diameter of the coil


Guest StrongerthanArne

Recommended Posts

Guest StrongerthanArne

When you try to figure out the "corrected" IP for a #3 gripper, using a #2 as standard, remember to take into consideration the smaller diametre of the coil on a #2. Arne's 286 IP #2 has a 134.5 mm long non-dogleg and a coil diametre of 36.2 mm. My 396 IP #3 has a 136.2 mm long non-dogleg and a coil diametre of 37.5 mm. Using the #2 as standard, my #3 would get a "corrected" IP of 388, not taking the larger coil into consideration. Adjusting for the larger coil (which means subtracting half of 1.3 mm from the 1.7 mm difference in total length) the "corrected" IP is 391 IP (both calculations based on a 80 mm torque arm). I am sure there are several more things to take into consideration comparing grippers with different coil diametres but at least being aware of this reduces the margin of error.

Link to post
Share on other sites
Guest Luke Reimer

Mikael,

Why are you adjusting scores for coil diameter? To my thinking, as long as the spring-end reference point (i.e. the coil center) for the handle measurement remains the same, the diameter of the coil would not matter. Whatever the effect that the bigger circle of the coil might be upon the overall resistance, this would be detected also by the testing machine, and thus already reflected in the IP scores, I think. How am I misunderstanding this time (or what am I missing)?

Link to post
Share on other sites
Guest StrongerthanArne

Luke,

You wrote:Why are you adjusting scores for coil diameter?

The non-dogleg length on the #3 gripper is 1.7 mm longer than the non-dogleg on the #2 gripper in my example, but this is not the whole story. PDS's machine measure the torque arm from the centre of the coil to a fixed point a certain distance (which I have forgot) away from the centre of the coil. However, the distance from the centre of the coil to the end of the gripper (away from the handles) is not the same on a #3 and a #2 with the same total non-dogleg length. This also, of course, means that the distance from the centre of the larger coil on a #3 gripper to the end of the handle is less than the same distance on a #2 gripper of the same total length. In my example the difference was 0.65 mm. This means that the distance from the centre of the coil on the #3 gripper to the end of the non-dogleg handle is not 1.7mm more than on the #2 gripper but 1.05 mm as we have to subtract 0.65 mm (half the difference in coil diametre).

You wrote:To my thinking, as long as the spring-end reference point (i.e. the coil center) for the handle measurement remains the same, the diameter of the coil would not matter.

Well the problem is that this only works if we measure the length of the gripper from the centre of the coil to the end of the handle, which is very difficult to do by any degree of precision. It is much easier to measure the total length of the gripper but then we also have to measure the diametre of the coil if we compare grippers with different wire size. One additional potential source of error is that when compressed in PDA's torque machine, the inner edge of the coil on the side that is closest to the handles might be pushed against the bar that I would presume is holding the coil in place. This would further complicate the calculations.

Link to post
Share on other sites
Guest StrongerthanArne

Supersqueeze,

Outside diametre, since we are measuring the total length of the non-dogleg (and dogleg). The whole thing is easier to envisage if you think of a #2 with a 35 mm coil next to a #3 with a, lets say, giant 70 mm coil. If the two grippers have the same total length, and we placed them side by side, at a 90 degree angle to a straight line cutting through the centre of both grippers coils. Then quite a bit of the #3's coil woud extend beyond the end of the #2 gripper and likewise, quite a bit of the distal part of the two legs on the #2 gripper would extend beyond the end of the legs of the #3 gripper.

Cheers

Link to post
Share on other sites
John Szimanski

Mikael,

The SOSP retains the gripper from moving on the mandrel without binding it. It cannot shift. The torque arm is identical for every gripper. This is not obvious from the photos we release. PDA is an engineering company and our stock in trade is solving problems by building solutions. As such, key components of the SOSP were/are not displayed and important details are not highlighted. Likewise for the Nutcracker. Similarly, we don't discuss how our bars, for example, are assembled (most assume they are simply welded together).

John

Link to post
Share on other sites
Guest StrongerthanArne

John,

That is good news as it makes calculations easier for comparing two grippers with a given IP but with different "centre of the coil to the end of the non-dogleg lengths".

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use and Privacy Policy policies.