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Delrin Acetal resin.

 

 This plastic is what I have chosen to use in making leather stamps. It is easy to machine and remains rigid.

 Here is what DuPont has to say about Delrin:

  Delrin, the world’s first Acetal resin, is a highly versatile engineering plastic with metal-like properties. It offers an excellent balance of desirable properties that bridge the gap between metals and ordinary plastics. Since its introduction in 1960, it has been widely used around the world in many applications, such as in the automotive, appliance, construction, hardware, electronic, and consumer goods industries.

 Delrin has gained widespread recognition for its reliability and performance in thousands of engineering components.

 Properties and Characteristics

 The chemical composition and highly crystalline structure of Delrin acetal homopolymers offer a unique combination of physical properties not available with metals or most other plastics. The outstanding characteristics of Delrin resins include: • High tensile strength, impact resistance, and  stiffness

• Outstanding fatigue endurance

• Excellent resistance to moisture, gasoline, solvents, and many other neutral chemicals

• Excellent dimensional stability

• Good electrical insulating characteristics

• Good resilience and resistance to creep

• Natural lubricity

• Wide end-use temperature range

 The main property limitations are repeated use in steam or hot water, and exposure to strong acids or bases outside the pH range of 4–9.

 Delrin® Design Guide—Module III - 230323c.pdf

 In testing Delrin as a leather stamp I have found that it holds up quite well.

 My first test was to take a cased (wet) piece of 8oz leather, lay it on a concrete floor set  one of my first stamps (grizzly tracks) on the leather and strike the stamp with a 1lb ball peen hammer multiple times.

 The grizzly track stamp has pin-like points that make a perforation of the leather surface to resemble a claw mark. If anything was going to damage the stamp I figured that would.

 But it didn’t. The hammer didn't even leave a mark on the strike face of the stamp.

 The next test was to place the same thing in my drill press and use the press as an arbor press.

 I put all the pressure I dared on the drill press, which is not designed as an arbor press, and failed to damage the stamp. How much pressure did I put on it with the drill press? I don’t know for sure because it exceeded the max load of my 350 lb. scale.

Now, I use a 1-ton arbor press and put all of my 240 pounds into testing each stamp. It is not a pretty sight, but I have never crushed a stamp.

 Let’s look at some data and do some calculations.

 According to the DuPont data sheet page 24 in the link above, Delrin will take a 10,000 lb. per sq. inch compression load and only deform 2%.

 But what does this mean?

 If you took a 1” sq. stamp blank and put 1000 lbs. pressure on it, that would be equal to 1000 lbs. per sq. in.

 However, the image milled into a 1” sq. stamp blank has a much smaller surface area that has to carry that 1000 lbs. The smaller the surface area that carries the 1000 lbs., the higher the Lbs./sq. in load the Delrin stamp face has to carry.

 Crunching a few numbers; if the milled stamp face has a surface area of  0.10 sq. inch and you put 1000 lbs. on the stamp block, the load on the face is 10,000 lbs. per sq. in.

 According to the graph on page 25 shown here, at that point you will have a deformation of 2%, which isn’t much. But it increases exponentially from there.

 If you put the same stamp in a 1 ton arbor press and take it to the max (2000 lbs.)  you will deform the stamp face dramatically.. Total collapse of the stamp face (not the block as it only has 2000 lbs. per sq. inch on it) is eminent under 2000 lbs. from the arbor press because the stamp face at 0.1 sq. inch is under 20,000 lbs. per sq. inch..

 Considering that using my drill press I have made quite nice impressions in 8-9 oz. cased leather putting less than 600 pounds* of pressure on it and pushing the stamp face 0.06-0.08” into the leather (60-80% of the depth of the stamp face which is 0.95”) I feel that Delrin is well suited to the job, unless you have Popeye forearms.

Conclusion:

Wither you choose to use my leather stamps or not is up to you. But under reasonable pressures or in using a mallet to make an impression into your leather project these stamps will serve you well.

 *600 lbs.: that s a SWAG – Scientific Wild Assed Guess.