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ShapeOko is a dead simple Open-Source desktop CNC machine with an estimate build price of about $300. Get into CNC without going broke!
125 backers pledged $11,078 to help bring this project to life.

Adjusted BOM, lost sleep....

Posted by Edward Ford (Creator)

I've been losing sleep over how to present the costed BOM (Bill of Materials) for the ShapeOko mill.

The most straight forward method has been shown on the downloads page over at for the last couple of days. However, something just wasn't sitting right with me about the total.

When everything in the hardware category is listed with the cost of a *package* the "total" cost for that item isn't exactly transparent. 

Let's use for instance a 100 pack of .125" nylon spacers.
A 100 pack of .125" nylon spacers cost $7.04 from However, the shapeoko mill only requires 8 .125" nylon spacers. Not 100. So is the cost $7.04 for the nylon spacers OR is the cost $0.56 ($0.07 * 8)

So what's the cost?
I've spoken to several people who do this for a living: manufacturing engineers, engineering managers, and accountants. They all tell me the cost is $0.56. 

After thinking about it for quite a while, I've decided they know what they are talking about, and I trust their opinions on matters such as these and have changed the BOM to reflect that decision.

Now, it does makes the total "look" better. At $332.58, that's significantly lower than the previous $365.90. But, in reality your cost is going to be no different if you buy the 100 packs from McMaster.

There are two thigs that makes me feel a little better about the BOM change:
  • Most of you are Makers! And as a Maker, I know that I have no problem with extra spacers sitting in my "inventory" for use on a future project and hopefully you don't either.
  • You could buy them in single pieces if you have access to a hardware store. All of the nuts/bolts are pretty standard pieces and can be purchased at most home improvement stores individually. 

With all that said, what do you think?
Is the revised bill misleading? Should it be presented a different way? Are these blog posts explanation enough?


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    1. Edward Ford Creator on

      As you can see on sheet2 of that shared workbook, we would like to offer a "kit" that includes that hardware in question. The downside is that we can't exactly package up all those little parts for free. As there is some cost to purchase the bulk quantities in addition to the time it would take to pick and pack. Although I'd be happy doing it for a while, I'm sure that it would get old for fairly quickly.

      Our thought was that some of the stuff from the BOM you're probably going to get from us anyway (like the motor mounts). With combined shipping and even with a "premium" for the picking and packaging, it would still cost less to order the kit than it would be to order all of the 100 or 50 packs of hardware...

      But like I said in the original project text, we didn't really start this project to sell kits. We started it to produce a BOM that didn't require kitting to afford.... It's a tough spot.

    2. FurnLab on

      Edward, I think the current way to list it is the better one. BUT, perhaps you can include a simple explanation at the top so that people don't have to figure it out for themselves.

      You're thinking is right that most of us will be fine having leftover parts.

    3. Edward Ford Creator on

      I think this is what we're looking for:…

    4. Dale Hawkins on

      Hmmm... I can now see that this is indeed a Google Spreadsheet, but I can't see to get to the original. Can you add a link?

    5. Dale Hawkins on

      You could have the pack cost amount as a separate column. And FWIW, have you considered making this a Google Spreadsheet? Then people could copy the original and make their own lists, modifications, checklist, etc.

    6. Edward Ford Creator on

      Good point with the groups buys Pete. I hadn't even considered that from an individual standpoint. One thing we don't want is to be misleading., This is after all an "open" project. And how open can you be when you're hiding costs? Thanks Pete!

    7. Pete Prodoehl on

      I think the revised bill make sense, especially with this explanation.

      I've heard costs to build a RepRap, and often they don't include things like having to deal with minimum dollar amounts for orders, or shipping costs, etc.

      So as long as you're straightforward with any odd discrepancies in cost, I think it's fine.

      And as you said... the audience is makers. They know how to get things, hardware stores, makerspace surplus shelves, groups buys, etc.