Hey Ali,
When we train Iron Palm, its similar to what you described.
We start by having the student already practise various sets of internal Qigong before they move on to the Iron Palm training.
The student has to be able to concentrate and move his/her Qi before they are able to start Iron Palm practise.
Then we start the student by hitting a normal sand bag by letting the hands or fist fall and hit the bag. Its important not to use muscle for these exercises.
The next step is to hit wooden benches or sand bags with mung beans.
Also a further note this practise has to be performed slow and will take long periods of time to develop the correct way.
The next step is for the student to hit steel shots or something equivalent in the sand bags, or hit concrete of some type after this is completed.
Also there are further exercises for Iron palm using the urn if you have one.
Our Iron shirt generally starts as most do, with the focus on the dan tien area. And moving Qi to the dan tien this is most important in Iron shirt.
So a basic exercise we start off with is having two people place a pole in the dan tien area of each other and let the dan tien push against the pole and then the partner does the same thing.
THis is just basics but has to be trained for long periods of time before the student moves on to more advanced training.
By the way Ali, you mentioned the type of Jau that you use.
How does it work for you?
take care,
Chang