Re: [CAD_CAM_EDM_DRO] milling circuit boards

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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> 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
>
> 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........
> bill
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>
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