First Proper Internal Kanban, then Involve Suppliers
Joe Marshall, Member
I had the good fortune to develop Kanban systems under the guidance of Akira Takenaka (who worked directly with Ohno and taught the systems on behalf of Shingijutsu) and his views were exactly as you describe.
My efforts at Kanban started inside the plant (and were laughed at initially by Takenaka San!) and became iterative as we refined the processes. Only when we had robust systems did we start to use them with our suppliers. The Kanban systems were the subject of many Kaizens and took a long time to develop. As with all aspects of Lean it is not easy but the journey was fun.
The original Kanbans in terms of design, calculation and data would have failed in a spectacular and embarrassing manner in the external supply chain.
When we focused our efforts on purchasing it was an immediate success and enabled both parties to benefit significantly.
Ohno was right!