The US actually initially supported the Sentinel as their own production was still ramping up. Once it became clear that the required machine tools, plant and equipment, needed to support Australian production was going to be more difficult to source than US build tanks themselves, they removed their support. By the end of 1942 the US had tanks to spare but still needed machine tools for other purposes.
Many of my relatives were tool makers by trade, its what boys with brains, but no money for a tertiary education, did up until education became more accessible in the 70s. They were not allowed to enlist in WWII as their skills were critical to munitions production. One grandfather who served in the RAAF in WWII, initially as a flight engineer, spent the later part of the war sourcing (sometimes even designing) jigs and fixtures required for aircraft maintenance and repairs, while the other alternated between the merchant marine and QA at a munitions plant depending on what had precedence the time (and how desperately he needed space and time away from my grandmother) and neither of them were indentured tradesmen, one was a bush mechanic and the other an ex RAN cook.
A number of their siblings and inlaws were however qualified toolmakers and even though each volunteered they were rejected because their skills were too critical to the war effort. A lot of the issue is that there were just so few of them, the industries that had stated to develop before WWI had withered and died between the wars because of economic pressure and short sighted stupidity. Cruisers had been built in Australia during WWI and destroyers assembled and built, submarines and aircraft were seen as the next step but then nothing. No work, no trained people and a steeper, more difficult leaning curve to get back to where your were, let alone to where you needed to be.