How to spec a hypotube-Important design considerations for catheter design

When considering laser cut hypotubes, there are some key considerations to keep in mind to make sure that you get exactly what you need for your catheter to meet it's required performance characteristics.

How to spec a hypotube

Let's first discuss generally how to spec a hypotube for laser cutting. Before we can cut your tube, we need to know what it is that we are going to cut. Hypotubes are specified by their outer diameter, wall thickness, and inner diameter. Naturally by defining any two of these parameters, the third can be inferred. If you have a 0.300" outer diameter with a 0.050" single wall thickness, then we know that the inner diameter must be 0.200". Depending on the design of your catheter, the critical dimensions of your hypotube (the two dimensions that you will explicitly define, while the third one will be a reference dimension) may be different, though typically, the outer diameter and the inner diameter are critical for hypotubes. Once the profile dimensions have been defined, the length of the part will also need to be specified. 

‍

Tolerance considerations for hypotubes

Each of these dimensions (besides the reference dimension because it is a driven value) will need to have a tolerance specified. The tolerance denotes the maximum amount that a dimension can vary from it's specified size while still being acceptable for your application. Tolerances are expressed using a plus and minus symbols. For example, a +0.0005"/-0.001" tolerance on the outer diameter means that a tube with a 0.300" outer diameter can be as large as 0.3005" and as small as 0.299". Keep in mind that if the wall thickness is a critical dimension, you will have to consider the tolerance twice when determining the reference dimension. For example if we have a tube with an outer diameter of 0.300" ± 0.001", and a wall thickness of 0.050"  ± 0.001" that means that the inner diameter could be as small as 0.197", or as big as 0.203". Tolerances on hypotubes are usually in the _ range. Keep in mind that tolerances can only be accurately controlled at certain dimensions, and extremely tight tolerances such as _ may be impossible to hold. Additionally, tighter tolerances usually correspond to increased costs due to additional processing parameters, strict inspection, and higher scrap rates. The tube's length dimension will also need a tolerance, which is usually between _ and _ for hypotubes. When considering the length spec of your part, it is important to think about how many parts one hypotube can yield. Maximizing the number of parts that can be cut from a single tube increases efficiency and cuts down on material costs. This is especially important for large scale manufacturing.

‍

Laser cutting tolerances

In addition to specifying tolerances on the hypotube's dimensions, one also has to consider acceptable tolerances for the laser cut pattern itself. Symmetry Laser holds a standard tolerance of ±0.0003" on all cuts, though custom tolerance options are available. (Is there more to cover here?)

‍

Standard hypotube sizing

Another consideration when designing you catheter system is whether or not you can use standard hypotube sizing. When designing a catheter system, it can be helpful to first look around for off-the-shelf hypotubes that are readily available from vendors. If you are able to incorporate sizing from an off-the-shelf component, you can eliminate the need for centerless grinding and potentially save time and money. Many times however, a catheter application requires an exact dimension that will require grinding to achieve the exact spec.

‍

Wall thickness considerations for hypotubes

Lastly, one of the most important parameters to consider for your application is wall thickness. Wall thickness is the major driving factor for the end tensile strength, pushability, column strength and more of your catheter. At Symmetry Laser we cut walls as low as 0.0007" and as thick as 0.050". Typically for catheter applications , minimizing overall wall thickness of the catheter shaft is critical. We generally recommend keeping wall thickness above _ for the best results. On the flip side, high wall thicknesses can significantly increase cutting time which drives the end price of the product.

‍