Modern Grip Wrench CNC Machining Case

Services: multiple CNC machining, light bead blast, hard anodized black, laser engraving, clear zinc passivation
Material: aluminum 6061, stainless steel 303, C45 steel, silicon, steel
Quantity: pre-production prototypes, 9 components per set

The Project

We received this project early this year and started to discuss material and feasibility for manufacture with our customer. After the test of some samples and the modification of design, we have come to the pre-production run recently and have already finished them. We are pleased to have the good feedback about the pre-production lot from our customer as follows.

“First of all we are extremely happy with the tools, you have done an excellent job with these. We only have a few very small suggestions for the main production run…Everything else is to a very high standard; the engraving is aligned correctly, the shaft looks nice and spins freely and tightening the sliding fit of the floating jaw has made a huge difference to its usability.”

We are glad that we can help our customers to turn the concept into product and meet their requirements.

The Product

This product is an adjustable grip wrench and a re-engineered and re-designed tool for the modern day. It can also be used comfortably like a fidget toy. This grip is made of nine different components and requires high-precision machining to control the correct play, make them not seize up and achieve smooth sliding fit.

Some Issues Discussed for Prototype and Pre-Production Run

#1 Seizing Up Issue of Prototype

A problem occurred when the prototype was completed. The tool seized up, even though every single part was done correctly. It might be the issue of friction and resistance. We analyzed this issue with the customer and found solutions together to solve the problem of seizing up. We added a spacer to the fix jaw, made a counterbore hole on both adjuster and floating jaw to reduce thread contact, removed sharp edges from the thread profile of shaft and sanded surface smooth. After the prototype, the design was modified and improved to avoid the seizing up issue and then all were ready for the pre-production run.

#2 Accuracy of Pressing Fit

To finalize the screw shaft length and prevent any clamping taking place, it is important that the final position of the end cap could be exact and the high accuracy could be achieved. We use an equipment to press the end cap onto the bent rod and control it within +/- 0.5 mm tolerance to make sure of the accurate position every time.

#3 Close Sliding Fit

Our customers want to get the sliding fit as close as possible. The larger the gap was, the worse the tool performed as the sliding jaw would be able to rock back and forth slightly and the effect would be exaggerated along the length of the jaw. They tightened the sliding fitting tolerance up on the floating jaws slightly, which relied on the ground bar of the bent rod being a consistent 7.92mm. We double checked this requirement. Considering the cost, we suggested that the holes on the jaws should accommodate the bent rod like before. If the rod was ground to 7.92mm, the cost would be double or even more than using standard 8mm rod. We can purchase raw material for the rod, measure consistency and then manufacture the sliding tolerances on the jaws to suit. If the fit is too close, it will also have the tool perform worse and make the bent rod deformed.

#4 Deforming Issue

There was a deforming issue with C45 steel shaft on the pre-production run. Some just deformed a little, but it affected the sliding of adjuster, while some were very worse and they broke directly during machining and the scrap rate was high. This deforming issue would not only increase the cost, cause a delay in delivery but also affect the use of the tool. There were two material options for this shaft, C45 steel and Stainless steel. Stainless steel was better, which would not have rust and deforming issues like C45 steel. But the cost of stainless steel was higher than C45 steel a lot and our customer was hard to afford this increase in cost. We discussed the deforming/break issue of C45 steel shaft again. The other solution was to harden C45 steel about HRC40 before machining, however, hardening would also increase some cost. Although our customer agreed on the hardening solution, we still tried to see if any better solutions and any possible machining improvements to settle this problem. After much effort, we found a perfect machining method to produce the unhardened C45 steel screw shaft without any deforming issues.

CNC Machining, Assembly and Inspection

Raw material is inspected, machines are adjusted, machining cautions, requirements and notes are attached to the board besides the machine, and then the production starts. The rod is turned from the standard material and bent. Because the rod has internal stress after being bent, the difficulty is to ensure that the rods can be paralleled, or the sliding will seize up. The shaft is CNC turned, has the sharp edges removed from the thread and the surface is sanded smoothly by sandpaper. Each step has a significant impact on the sliding of the adjuster and the free spin of the shaft. And tolerances must be controlled strictly during the entire production.

When all of the parts are finished, we assemble them together and add/remove the shim washers to make sure that the shaft has minimal play but still spins freely. After assembling them together and carrying out the final test of the tool, each is packed well to prevent damage during shipment.

Sandblasting, Hard Anodizing, Laser Engraving and Passivation

After the parts are machined, we sandblast both stainless steel parts and aluminum parts. Sandblasting can cover machining marks and give the parts a great look. Then the aluminum parts go to the next finish step – hard anodizing. Compared with normal anodizing, hard anodizing can let the parts wear-resistant. C45 steel shafts are coated with clear zinc passivation so it won’t get rust over time. Measurement markings are engraved exactly on the bent rod, which allows the users to measure with the grip precisely.