This thread is going to be a collection of all the shift knob information I have gathered over the past few years. I want others to add to it also, pics, dimensions, weight, reviews, etc.
THE TEST:
To test 2 types of threads on Polymer (Copolymer/Delrin) shift knobs. See which one is the strongest.
THE PROBLEM:
Simply put, metal shift knobs get hot in the summer, cold in the winter. Although I have many solutions for this, from knob protector booties to wrapped knobs, one good solution is to use a different material. I have been producing the Copolymer shift knobs for some 2 years now. Here is a brief description of the material:
ACETAL COPOLYMER is very similar to ACETAL HOMOPOLYMER (trade name: Delrin, by the DuPont company). Both of these materials have physical properties within 10% of eachother. For example, Copolymer has a compressive strength of 15K psi, while Delrin is 16K psi. Copolymer has a better chemical resistance than Delrin, and slightly less porosity, meaning it has a more consistent appearance. Overall, there is not much of a difference here, especially when considering the use of a shift knob, so we can consider the two materials equal.
The main problem with Polymers is that they are basically strong plastics. Plastic threads tend to get messed up easily compared to metal threads. Cross-threading during installation or stripping during hard use are two common issues myself and my early customers faced when I make copolymer knobs with threads cut directly into the polymer.
In my desire to produce the best all-around shift knob available, I decided to find the best solution to fix the weak polymer thread issue. I began using a brass thread insert that I custom-machined for each knob. I first tried using epoxy, superglue, and loctite to secure the inserts in. The inserts kept coming loose during regular use. I then tried making the hole smaller than the brass piece and pressing them together with glue. This did not help as the insert still came loose.
Over time, I developed the unique brass insert attachment method I call "WC-Lock". The specific technical details of this attachment method will not be discussed, but I will show proof that it is extremely strong compared to polymer threads with no metal threads.
THE TEST
This testing was conducted two outside sources:
I made 4 samples for this test.
Each sample was tested using an identical stainless steel M12x1.25 threaded rod with a pin hole. The samples were all threaded with the Subaru M12x1.25 internal thread into the polymer/brass.
The steel rods were screwed into each sample 0.250 (1/4) inch deep and the pin was attached to the head of an MTS Mini-Bionix servo-hydraulic closed-loop testing machine with data logging software. This machine is capable of pulling approximately 4500 pounds vertically via hydraulics.
The sample was then lowered so it contacted the table of the machine. Heavy-duty steel machining clamps were then used to hold the sample down at 4 locations.
The machine was then programmed to pull upwards at a slow rate. The results of the test showed that the polymer-thread sample (no metal insert) failed relatively early. The 1/4" of threads pulled right out of the knob as shown below:
In contrast, the sample with the WC-LOCK brass thread insert was tested under the same parameters and maxed-out the machine pulling force without failing. This force was 4 times the failure force of the first sample without failing. Here are the pictures:
Data image of the second test:
Here is the graph of the results:
This shows that using a brass thread insert with the WC-LOCK attachment yields a tensile strength MORE THAN four times that of solid polymer threads. You can see in the black line how the polymer thread first failed at about 50mm, and then the second thread failed around 65mm with the third thread breaking around 72mm. The brass continued to increase in load without a failure. An important note is that the brass threads were not damaged by the test and still worked smoothly.
I think it is impressive that they could not even break one of my shift knobs using the machine.
To convert the 17,800N load that the brass thread was subjected to, that is about 4,000 pounds!
You can hang a fully loaded Subaru off of one of my shift knobs without it breaking!
Sure, these values are more than you can inflict with your hand, but you can still easily cross-thread a polymer knob and damage the threads permanently. This test is a good example of the amount of force needed to really damage a good-quality knob, specifically with my WC-Lock insert.
THE TEST:
To test 2 types of threads on Polymer (Copolymer/Delrin) shift knobs. See which one is the strongest.
THE PROBLEM:
Simply put, metal shift knobs get hot in the summer, cold in the winter. Although I have many solutions for this, from knob protector booties to wrapped knobs, one good solution is to use a different material. I have been producing the Copolymer shift knobs for some 2 years now. Here is a brief description of the material:
ACETAL COPOLYMER is very similar to ACETAL HOMOPOLYMER (trade name: Delrin, by the DuPont company). Both of these materials have physical properties within 10% of eachother. For example, Copolymer has a compressive strength of 15K psi, while Delrin is 16K psi. Copolymer has a better chemical resistance than Delrin, and slightly less porosity, meaning it has a more consistent appearance. Overall, there is not much of a difference here, especially when considering the use of a shift knob, so we can consider the two materials equal.
The main problem with Polymers is that they are basically strong plastics. Plastic threads tend to get messed up easily compared to metal threads. Cross-threading during installation or stripping during hard use are two common issues myself and my early customers faced when I make copolymer knobs with threads cut directly into the polymer.
In my desire to produce the best all-around shift knob available, I decided to find the best solution to fix the weak polymer thread issue. I began using a brass thread insert that I custom-machined for each knob. I first tried using epoxy, superglue, and loctite to secure the inserts in. The inserts kept coming loose during regular use. I then tried making the hole smaller than the brass piece and pressing them together with glue. This did not help as the insert still came loose.
Over time, I developed the unique brass insert attachment method I call "WC-Lock". The specific technical details of this attachment method will not be discussed, but I will show proof that it is extremely strong compared to polymer threads with no metal threads.
THE TEST
This testing was conducted two outside sources:
- Dr. Clemow, PhD.
- Ms Roth, Mech.Engineer
I made 4 samples for this test.
- 2 samples - copolymer cylinders with standard polymer threads (no inserts)
- 2 samples - copolymer cylinders with "WC-LOCK" Brass Thread Inserts
Each sample was tested using an identical stainless steel M12x1.25 threaded rod with a pin hole. The samples were all threaded with the Subaru M12x1.25 internal thread into the polymer/brass.
The steel rods were screwed into each sample 0.250 (1/4) inch deep and the pin was attached to the head of an MTS Mini-Bionix servo-hydraulic closed-loop testing machine with data logging software. This machine is capable of pulling approximately 4500 pounds vertically via hydraulics.
The sample was then lowered so it contacted the table of the machine. Heavy-duty steel machining clamps were then used to hold the sample down at 4 locations.
The machine was then programmed to pull upwards at a slow rate. The results of the test showed that the polymer-thread sample (no metal insert) failed relatively early. The 1/4" of threads pulled right out of the knob as shown below:
In contrast, the sample with the WC-LOCK brass thread insert was tested under the same parameters and maxed-out the machine pulling force without failing. This force was 4 times the failure force of the first sample without failing. Here are the pictures:
Data image of the second test:
Here is the graph of the results:
This shows that using a brass thread insert with the WC-LOCK attachment yields a tensile strength MORE THAN four times that of solid polymer threads. You can see in the black line how the polymer thread first failed at about 50mm, and then the second thread failed around 65mm with the third thread breaking around 72mm. The brass continued to increase in load without a failure. An important note is that the brass threads were not damaged by the test and still worked smoothly.
I think it is impressive that they could not even break one of my shift knobs using the machine.
To convert the 17,800N load that the brass thread was subjected to, that is about 4,000 pounds!
You can hang a fully loaded Subaru off of one of my shift knobs without it breaking!
Sure, these values are more than you can inflict with your hand, but you can still easily cross-thread a polymer knob and damage the threads permanently. This test is a good example of the amount of force needed to really damage a good-quality knob, specifically with my WC-Lock insert.