Excelsior

Tinkering is one of the easiest crafting skills to GM and usually the one I do first as it allows you to make tools and whatnot for other crafts to use

0 - 30 - Buy it (scissors or mortar and pestle)
30 - 40 - any small tool for 1 or 2 ingots (hammer, drawknife)
40 - 45 - Shovels, Sledge Hammers, Pickaxes
45 - 92 - Lockpicks
92 - 108 - spyglass, heating stands
108 - 120 - fancy chimes

Everything up to the end can be sold to either NPCs or players.
The only thing you can do with the spyglasses and heating stands is to junk them for tokens.
To get to 120 is a much harder and costs a lot more in ingots. Also you MUST have access to SE in order to get to 120 otherwise you will NOT be able to get past 108 or so as you need fancy chimes

If you are going to raise Tinkering, you should give consideration to whether you want to raise lockpicking also. The reason for this is that Carpentry, is the skill that creates the locked boxes you need to train the skill, but Tinker is the skill that determines the difficulty of the boxes to pick for training.

You could buy around 30 carpenter skill to start, and never add a point to it in order to train Lockpicking to GM. However, as you gain in Tinker skill you need to make lock boxes as you progress in Tinkering skill for workable levels of difficulty.

This is how I do it. Buy Carpenter and Tinker skill from NPC to start. This is around 30. Make a couple of boxes with this starting skill level now. If you don't make a couple of boxes at the starting levels, you may not be able to get started with the beginning level of Lockpicking if you raise you Tinkering before making these first couple of boxes.

You don't need anymore Carpentry so concentrate on Tinkering. You need to make boxes now at Tinkering skill levels of 40, 60, 80, GM. This is a basic step for levels of difficulty. However I make about 8 or 9 boxes at every 10 level of Tinker skill. This just makes it go quicker and saves you a bunch of broken lockpicks.

Some people will tell you, you only need to make one box at every level of 20 Tinker skill graduations. This is also true, but takes twice as long to raise lockpicking compared to making a dozen at each 10 level.

I guarantee you I would rather waste a few more boards on the extra boxes, to speed the process. And when you are done, remove the keys and sell the boxes. You can raise your Tinkering to be too high for your Lockpicking skil,l if you don't make boxes as you raise your Tinkering.

If this happens you can only start another Tinker or find some one else's boxes to use. Lockpicking requires few resources, but mostly only time to raise the skill. Yet the rewards can be great. Don't over look Lockpicking while you raise Tinkering.