Re: [CAD_CAM_EDM_DRO] milling circuit boards

Good analysis. Leaves out option of a combo assembly/pcb house and
that boards from them come with soldier mask and silkscreen. Beyond a
certain complexity, you'd want their pick/place machines to assemble.
And you can only make 2 layer boards, so it's difficult to do anything
with a microcontroller.

But it could pay back for small projects.

On 10/6/06, Jack Coats <jack@...> wrote:
> Dennis, (sorry this is so long)
>
> My take is,
> 1. environmentally friendly - a good tree-hugger answer
> 2. no chemicals - I don't like to keep things that others could get into
> around the house.
> 3. on-demand prototyping - it is hard to build a board 'yesterday', but
> at
> least you can have it 'today'.
> 4. incremental costs,
> 4a.for the home shop person, is minimal. In a hobby, part of the fun is
> in the process even more than the product.
> 4b.For business use (prototype or production) the purpose is the product,
> not the process of getting to the product.
>
> Incremental costs for a business are more, because time is the same as $$.
> Costs of preparation are close to the same. If the time value is worth
> more than the cost of production in small quantities, then it can be worth
> milling your own boards.
>
> If you have a tech that you pay $20/hr (fully burdened), and it takes
> 2 to 4 hours to mill the prototype board, you have paid for a service
> bureau to do the boards. The only really difference then is the
> turnaround time. What is that worth?
>
> Ok, you give the same circuit to a tech (paid the same), how long does
> it take to get a debugged breadboarded circuit back from the tech?
>
> If the $$ are the same or less then it makes no sense to do it with a
> machine.
> If you will be doing the layout and you would spend 2 hours using
> Eagle, and 0 or your hours using a tech, and your fully burdened
> expense is about $50/hour, then it could be cheaper to have a tech do
> it from schematics/drawings.
>
> A machine allows the flexability of a small production run, and
> 'easily' reproducable wiring, in case you need several of the same
> circuit. But the economics should guide a business decision.
>
> I like to think of things using tables for comparison.
>
> Scenario 1: you design, layout, service bureau used, tech builds
> Scenario 2: you design, layout, tech uses machine, tech builds
> Scenario 3: you design, tech breadboards from schematic
> Scenario 4: you design, tech does layout and uses machine and builds
>
> Scenario 1 2 3 4
>
> Your time $50/hr
> design time 4 hr=$200 4 hr=$200 4 hr=$200 4 hr=$200
> layout time 2 hr=$100 2 hr=$100 0 hr=$0 0 hr=$0
> wait time (non-billable - but lost opertunity cost)
> wait on tech 3 hr 3 hr 4 hr 5 hr
> wait on
> service 16hr (assume 48 wall clock hour delivery)
> bureau
>
> Service bureau cost
> guess? $60 $0 $0 $0
>
> Tech time @20/hr
> layout time 0 hr=$0 0 hr=$0 0=$0 2 hr=$40
> run cnc machine 0 hr=$0 1 hr=$20 0=$0 1 hr=$20
> build and check
> one board 2 hr=$40 2 hr=$40 4=$80 2 hr=$40
> -------------------------------------------------------------------
> Total $400 $360 $280 $300
> Wall clock time 25 hours 9 hours 8 hours 9 hours
>
> Second to N boards per board:
> $100/board $60/board $80/board $60/board
>
> 10 board total: $1300 $900 $1080 $840
>
> Scenario 2 and 4 the 'machine' is a small prototyping CNC mill.
> Now do you use it enough to have that payout?
> Is the convenience of a mill worth it?
> Do you have a 'lost opertunity cost' in the wait time?
>
> On the payout, assume you use it just for small runs, saving $40 per
> run, and it cost $4K, then you must go through 100 runs to break even.
> If you do 1 per week, this is a 2 year ROI (return on investment).
> Most companies would bite on that. One company I worked for required
> a 18 month ROI.
>
> If you find a 'magic bullet' answer, we would all like to know!
>
> ... Thanks, I enjoyed the mental gymnastics. ... Jack
>
>
>
>
> Quoting Dennis Schmitz <denschmitz@...>:
>
> > Sorry, this isn't an answer, but another question. I think I've read
> > posts from 2 or 3 people milling circuit boards, or trying to. What's
> > the cost breakdown? Is it really and truly cheaper to make these
> > boards after you factor in your time and amortize your equipment?
> >
> > You can get some pretty good prototype quantity boards from internet
> > outfits like PCB123 now for very cheap, and if you're running
> > production, there are plenty of board shops out there all undercutting
> > each other. Check out the back section of any of the EE mags for a
> > long list of them.
> >
> > Even 10 years ago "breadboard" meant giving a hand-drawn circuit to a
> > tech to solder together with perfboard. Today it means doing a quickie
> > in Eagle and sending it out to an overnight proto house. It's cheaper
> > than paying the tech.
> >
> > So where's the upside? Why bother building a machine for it? (serious
> > question, not sniping)
> >
> > This is probably off topic, so feel free to email me directly.
> >
> > TIP: you always pay for one panel, so lay-up several different ones in
> > the gerbers. If you have space, there are a bunch of free patterns for
> > proto-boards available to fill it in.
> >
> > On 10/5/06, wdavis364 <wdavis@...> wrote:
> >> Shopping around for a router, Some router have 1/4 collets and some
> >> have 1/4 collets and 1/8 collets. Not knowing much about this, what
> >> size collet will I would most likely to be using in milling circuit
> >> boards. Will 1/4 collets handle the very small size drill bits(1/32)?
> >> Thanks for any advice on this.
> >> bill
> >>
> >>
> >>
> >>
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> > http://groups.yahoo.com/group/jobshophomeshop I consider this to
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> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
> you have trouble.
> http://www.metalworking.com/news_servers.html
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for OT
> subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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