Grantr - 1-12-2015 at 19:19
I tested 1 gram ETN hand pressed with all of my weight into a 3/8 inch diameter vinyl tube with .3 grams loose on top to set it off via spark gap.
Witness plate is a 1/4 inch steel finishing mower blade. To my surprise it did not dent or bend it. I am not sure if these are harden steel blades or
not.
I know it detonated as it was extremely loud and the blade was flipped over. There is a darken spot where the charge was placed. Is this typical for
a small charge? 40 grams of ammonal did bend the blade.
The blade goes to a king kutter 7 foot finishing mower. What type of metal and thickness is usually used as witness plates?
greenlight - 1-12-2015 at 20:29
I am sure a gram of ETN isn't going to dent a 1/4 inch steel plate.
Even though the ammonal is a less powerful explosive there is a big difference between 1 and 40 grams.
I don't know if there is a set thickness for witness plates. They are usually steel but I have heard of lead ones for detonator testing.
I use 3mm thick 15 × 15cm squares of steel. They are all exactly the same and I use a gram of explosive for each test with a detonator of the same
size to compare effects.
Grantr - 2-12-2015 at 05:00
Thanks that is good to know. I will find some thinner material to test on.
aga - 2-12-2015 at 15:22
If the 'witness plate' is not the same material each time, and common to each user, how do you EM guys compare results ?
greenlight - 2-12-2015 at 20:18
If you use the same material and thickness each time for your own tests you will get quite good results and you should be able to see noticeable
differences.
The plate test is good for the home EM experimenter but quite crude and only gives you a rough idea of the power of the explosive being tested.
There are much better test's out there but unfortunately most need a specialized setup or special equipment.
OneEyedPyro - 2-12-2015 at 22:41
In my experience hand pressed ETN really isn't too powerful at all compared to cast or machine pressed and with spark gap initiation I would have
doubts that you're getting full power dets, it might be worth a try to use a primary instead of spark gap and see what happens.