Hey Buffo! That's a really good point, but check this math out...
Actually we can make profit at those prices even after tapping all the holes,
we have rigid tapping capabilities on the mill, but we'd probably use our
dedicated air tapping machine... The reason the prices seem so low is that
the seller is using 1/4" plate which gives you a lot of area for the weight.
For example, for the plate you saw on ebay, if the seller bought premium
new aluminum at retail ($2.25/lb) then at 5lbs, you're looking at a bit
over $11 in material. Throw in $15 for labor and $10 (averaged) in spent
tooling, And you could make money even with one-off quantities.
For a 2' x 1' table 3/8", Here's how I'd compute it...Originally Posted by Buffo
24 x 12 x 0.375 = 108 cubic inches.
The density of aluminum is 0.0975 lbs/cu. in. but for rules of thumb we can
use 0.1 (aka divide cubic inches by 10) which also works out when sizing
material if the plate you bought has extra meat, etc.
So at 10.8 lbs... At $2.25/lb that's $24.30 of metal,
Add $15 labor and $10 tooling costs, it's $49.30 before shipping... If demand
is higher, we can amortize the tooling over larger quanitites so that can go
down later...
The tooling costs is the cost of "unusable" plates and broken taps, etc...
For example on a 24x12 plate you're looking at 253 holes... For really large
plates, labor (monkey + machine cycle time) goes up because of the
problems with workholding...
If you bump up to 1/2" plate, I get 14.4 lbs or $32.40 in metal...
Add $25 labor + tooling we get $57.40
Now one caveat is that if you want really funky sizes, we'd have to charge by
the largest full inch dimension because of how we get our metal, so asking
for 11.25 x 23.25 is the same as asking 12x24...
I'm hoping to get some standard sizes so we can bring tooling costs down.
For example if we just had a line of 3 or 4 standard sizes, then we could
make a work holding pallet and save some cycle time tooling for each unit.
I suppose we could make enclosures, but I really like the personalizationOriginally Posted by allthatwhichis
aspect of how everyone makes theirs differently right now. I haven't had
more than 1 or 2 people ever ask me about it...
We can do M5 holes with metric sizing, imperial is nice for table layoutOriginally Posted by QUAZAR
because you can divide by 2 quickly... Metric is more optimized for dividing
by 10...
I think you could start with a right angle extrusion for the main holder, theOriginally Posted by Laser Ben
other 2 main parts look like plate to me...
Actually optics holders is one of the things on my todo list to engineer and
build, the main reason is that most conventional systems are spring loaded,
and I've noticed that clamping the setscrew on the nicer units twist the point,
not a big deal for normal stuff, but most of my stuff is fiber launched and
that's a huge pain in the butt requiring 10-15 more minutes of alignment.
I was looking at the zero backlash ballscrew designs, maybe make a mini
one with integrated end bearing?
So anyways, enough rambling... your thoughts?
Now there is also another alternative I'm thinking of... If you don't mind "odds'n ends"
I've seen precision plate remnants go for very cheap, but the quantity and sizes
aren't assured... I might be able to swing a "odd sizes" category with super low prices.
For example if you get lucky, you can find good plate in the $1.69/lbs surplus bin, and
occasionally you see good plate in the $1.25/lbs remnants bin...