If you would offer "parts" as been suggested before, and using a CNC plasma cutter, for the parts,
I would kind of think that basically cutting by order, would be the way to do it that way one has very little in stock and with the cut drawings saved in the computer, I would think one could pull up a unit and cut to order for the most part, I think I would only keep one or two stocked if that, on some items, when you start to sell, then adjust stock or amounts cut to the frequency of sales,
If you all ready have the tools and not making major investment in tooling,
I would think EBay and adds on forums like this one, and homestead type.self sufficiency types
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I think I would sell the plans and then the parts, keeping the plans in a affordable range,
I know before I built my back hoe, I bought and down loaded maybe 6 to 8 sets of plans, and many manuals and info on back hoes and basically made what I wanted out of all of those ideas,
some may want the plans, some may want the parts, and some may want to buy the completed machine,
what I am thing is if you do not bury your self in hundreds or thousands in stock, besides some time if things do not fly to your satisfaction you have not lost a lot.
years ago, (the reason I bought a computer), I had built and designed a band saw mill, and it worked well, I started to draw up plans, the plans were the main thing, I had a cad program and got so I could use it reasonable well, and then I started to write out the How to end of it, pictures were not even consideration as scanners and digital cameras were not consumer ready for a reasonable cost,
any way I could not find any one with language skills that under stood shop practice and (my wife very good with language) by the time my wife supposable corrected the grammar and wording to proper English, it no longer said what it needed to, and she did not under stand what was going on so she could not help so the project died, and I think if you can not explain what is needed to the non mechanical mind and the shop guru want be,
I was talking to my son a few night ago, and this forum is funny in some ways,
this example is not real.
but if some one asks how to attach a hydraulic hose on to a cylinder there are 30 reply's, and if some one asks a semi tectincal question, there will be a few hundred views and maybe 3 replies and 2 of the replies do not really relate,
there are some very smart people on this board and some that do not have a lot of mechanical skill,
those who have the skill most likely do not need your services and it is those who do not have a lot of skill but have the desire,
Or lack of money that will be drawn to your product,
(I got a old Forney buzz box and a pound of rod and ready to weld up the world), I was once there, mine was a Montgomery Wards buzz box, ever one has to start some where,
I think the assembly instructions will be the biggest asset on how o use the products you sell,
My two cents,