As you might guess we are going to make these two consonants from their constituent sounds, thus /t/ + /ʃ/ = /ʧ/, and /d/ + /Ʒ/ = /ʤ/
But there are several ways to do this which draw in other learning along the way.
First the quick way:
1. Point to /t/, the class say it, then point to /ʃ/ and the class say it, then point to both /t/ + /ʃ/ in quick succession, and the class may join the two sounds in the way we want, or they may say the two sounds close together but separately. If the latter, then I take one sound in each hand, indicate one then the other while students say them separately, this continues as I gradually bring my hands together … until the two sounds fuse. When they say it well enough, point to the box /ʧ/ to indicate that is what they have said.
2. Now to make /ʤ/ you have a choice: you can either do the same thing again, this time starting from /d/ and /Ʒ/, or you can have students repeat the unvoiced sound /ʧ/, and use the voice button to create the voiced sound /ʤ/.
To remind yourself of the voice button, visit Episodes 8 and 9. To remind yourself of how /t/ and /d/ work, check Episode 3. To look again at how /ʃ/ works, visit Episodes 6, 7 and 9, and for /Ʒ/ see Episodes 7 and 9
A way that extends physical awareness. Try this yourself:
1. Say /t/ aloud. This will mean you say it followed by a voiced /ǝ/. Now whisper it so the schwa is no longer voiced, and you can sense more closely the movement of /t/. Notice you are stopping then releasing the airflow with the blade (not the tip) of your tongue pressing against the tooth ridge. Thus there is a stop of the airflow followed by a release of the airflow
2. Now say /ʃ/ and notice there is no stop of the airflow, just a single continuous friction as the air flows over the blade of your tongue against the edge between the tooth ridge and the palate. If you whisper /t/ and /ʃ/ alternately you will see that /ʃ/ has the tongue a little further back in the mouth.
3. Now bring the two together to make /ʧ/, noticing that the tongue starts by stopping the air as with /t/, and then moves to the friction position of /ʃ/
4. Finally say /ʧ/ several times, then /t/ several times, then /ʃ/ several times and see what the comparison tells you about the movement of tongue and breath. One thing you will notice is that the tongue moves each time you say /t/ or /ʧ/, but does not need to move when you repeat /ʃ/. Why?
And now do the same four steps for /ʤ/ starting from /d/ and /Ʒ/, and this time not whispering (because all three sounds are voiced).
If you can develop the discipline and attention to follow these small internal movements, you will learn all you need to know to be helpful to your learners, and to help yourself, and to feel the confidence that arises from that. When you work on sounds in this physical way, as if studying the positions and movements of a dance, you gradually develop your ability to make any sound at will.