Shrinking and Distortion in Deep Slotting Parts

Parts after machining, cold rolling and welding usually generate internal residual stresses which may result in serious and unacceptable shrinking or distortion. Whatever the parts are made of metal or plastic. Recently, we are running a CNC machining project of rotor shaft for our Singapore client. At current, this project is still in First Article status. The rotor shaft is part of motor assembly which basically includes a rotor shaft and motor shaft. The motor shaft will be inserted into a deep, accurate, diameter Ø5 H7 (+0.012/-0mm) hole on the rotor shaft. There is a deep slotting cut for enlarging the hole when assembling. However, after deep slotting, the hole size will be slightly reduced and also out of tolerance which lead to a complaint happened. Our customer was using pin gauge 5mm to check the hole. When checking, the pin gauge must go all the way till depth 18.0mm, but failed.


CNC machining Rotor Shaft, shrinking may happen after deep slotting.
The rotor shaft shrinking after deep slotting


Root Cause for Shrinking Parts

In the meantime, after inner discussion, we believe that the downsize hole was caused by internal residual stresses. Prior to slotting, we had full inspection that the diameter 5mm pin gauge could go all the way as it is indicated in the drawing. In that way, we list two possible reasons for the situation below:

  1. The drawing says the internal hole is Ø5 H7 x 18mm, and we did machine the hole into 18mm in depth accordingly, even into 18.5mm.
  2. Besides, the internal stress would be very likely to lead the hole to slightly shrinking after slotting. Then, it will be unreasonable to meet the tolerance H7 standard after slotting. We suggest our customer to insert the pin gauge harder. So, it will not be a problem for the pin to go into the internal hole.


In conclusion, as the dimension was machined exactly based on the drawing, we think the situation is taken full control of by us.​Therefore, We recommend our customer to move forward to the mass production.​​


If you have similar design with deep slotting, send your 2D and 3D drawing files to our international team of engineers for a free quote. We look forward to cooperating with you. Please check our RFQ process and send us email.

4 Things That Will Impact Your Manufacturing Costs (Part 2)

A few days ago, we have talked about various factors which may affect your manufacturing costs in previous article. In short, material costs are directly relative to part quality and durability. And, surface treatment costs have significantly increased recently due to strictly environmental policy. No doubt, if you are working out a CNC machining project, APPORO can help you figuring out the manufacturing cost accordingly. Learn more about: How To Work With APPORO

Apart from the above two factors, there are still others which can affect your manufacturing costs:

3.) Manufacturing Process

Generally speaking, the slower the machining process is, the much higher precision is. For example, WEDM(Wire Electrical Discharge Machining) is one of the slowest metal machining process in the world. A series of rapidly recurring current discharges between two electrodes cut the profile of bulk material. Mostly used for stamping die cutting and prototyping which required high accuracy quality.

Furthermore, the complexity of design do play an important role in manufacturing costs. High challenge designs usually require cutting-edge machining facility for optimized quality. However, the investment in high-end machinery will also increase the cost of your project. Though, the advanced equipments can provide a great machining experience.

4.) Lead Time of Your Project

If you need a time effective production run, this can impact the cost depending on the project. To manufacture a project quickly is much more costly than a longer lead time. You may wonder what factors do have impact in a fast lead time project. Generally speaking, there are usually various necessary procedures prior to part manufacturing. For instance, to arrange CNC machines and engineers from mass production lines, to prepare customized jig and tooling. Urgent project results in much more impact from general mass production runs. In contrast, a longer turnaround can usually minimize capacity losses.

Customized Jigs and Tooling used in quickly manufacturing processes
Customized Jigs and Tooling

Get A Quote For Your Next Project

Via above various factors, a CNC machining services manufacturer can evaluate a quote your project. At APPORO, we can provide you with a competitive price. Pls send us your RFQ to get a free quote. Our production lines can offer a wide range of manufacturing processes to support your inquiry.