Pitch Hardness Tester

[FraserClarke]

After a few trials and tribulations with making laps for polishing, I decided to build a Texereau style pitch hardness tester to test how my pitch is doing. It's a very simple principle -- see how far a weight sinks into pitch in a given time; the further it sinks, the softer the pitch. With some prior knowledge, you can see if your pitch is in the right range. The simple qualatitive version of this is the 'thumbnail test', but I like to have a more quantative measurement.

The design is quite simple, and similar to Mike Lockwoods; pitch_tester . There is a simple frame, which holds a vertical shaft and a dial indicator. The shaft has a 1kg brass weight attached (interchangable), and a tip in the bottom which presses on the pitch lap. The dial gauge rides on the top of the weight, and measures how far the tip falls into the pitch over five minutes. Attachment 1 shows it with a lap in place for testing. Attachment 2 shows it without a lap, but perhaps show the assembly more clearly.

My copy of Texereau is an early edition, and doesn't have the appendix on the hardness tester (if someone can confirm the specs for me, that would be fantastic!!). From the web, I gleaned the following;

Mass: 1kg

Point: 1mm2 tip with 14 degree bevel

Fall rate: 0.6mm (hard) to 6 mm (soft) in 5 minutes (Pitch Hardness Comparison: Acculap Synthetic vs Gugolz)

The tip is interchangable (attachment 3), so that I can also put in a ball tip as per this paper on pitch hardness measurements; http://www.zygo.com/library/papers/proc_3782_72.pdf [PDF paper]

If anyone is interested in making one, PM me and I can send you a set of drawings. I used a lathe, mill and drill press to make this, but I think you do it on only a drill press (plus files) if needed. Also, if anyone has a sample of pitch they'd like me to test, I'm happy to give it a go!

[Glasspusher]

Lovely piece of work Fraser. thanks for sharing. I will be starting mine soon.

John