Sheet Metal Sticker Shock

I just got the following parts quoted (I asked for a ballpark quote, got a detailed one -- hmph). Here's a rough sketch, with unnecessary detail
_and_ things left out:
http://www.wescottdesign.com/Seminars/Control_Trainer_Frame.pdf
Over the phone we modified things such that I'd be responsible for the indicated holes, and the finish would be brushed & clear anodized. The quote came back at around $36 each in lots of 50.
Is this just what I can expect to pay for these things? Did I go to the wrong shop? What are the cost drivers here?
I'm trying to put together a training device that I can include in the cost of a seminar, $36 is more than 1/3 of the worst-case BOM cost that I was contemplating. I need to know if I can beat this down by being creative, if I need to bite the bullet and accept a higher BOM cost, or if I should yank my eldest out of school and put him to work in the garage bending metal!
The principal of this thing is that there's a counterweighted arm that swings on a shaft that's pivoted on bearings in the large holes in the frame. A microprocessor monitors the position of the shaft through a potentiometer and controls the voltage to a motor/propeller, with the goal of holding the arm at a commanded position. The hole locations are assumed to need tight tolerancing because of the apparent tolerance needs of the pot I'm planning to use, but I'll be re-thinking that decision here soon.
Thanks in advance.
Sorry this is off topic - would it help if I mention that I'm putting my vote behind Hillary McBama, with Ralph Paul as her running mate?
--
Tim Wescott
Control systems and communications consulting
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On Sat, 08 Mar 2008 00:15:56 -0600, Tim Wescott
<snip>

<snip> ==========Looks like an interesting project.
The first cost driver is the low volume.
I would take a walk through WalMart, a kitchen/restaurant supply with lots of pans, etc. and see what was close enough to modify. Possibly something plastic, unless you need metal. A plastic box with a snap on lid is good as you can pack everything inside.
These sites also looked interesting (stand on end?) http://www.radiodaze.com/catalog-306-page62-63.pdf http://www.hammondmfg.com/dwg20.htm http://www.hammondmfg.com/dwg11.htm (many other types on hammond site)
The brush/anodize finish looks nice but is extra handling and an avoidable cost. If possible get a prefinished container or chassis
It may be cheaper to drill oversize holes for the bearings and then use separate bearing pieces with sheet metal screws to allow adjustment/alignment rather than trying to hold close tolerances on position and size on a single fabricated/folded part.
I would consider plastic for the bearings also. You should be able to make quite serviceable bearings yourself from plastic strip, possibly reaming the bearing hole for a good finish if required.
You can also make a long reamer/alignment tool from a piece of drill-rod to insure that the holes are inline from side to side. Indeed, you might be able to use pop rivets here also eliminating the sheet metal screws and speeding assembly.
If you need it, as a box or pan with closed ends will be considerably more rigid, you may also be able to use off-the-shelf L brackets and pop-rivet to the sides.
A little value analysis and you should be able to knock these out at home with a drill press. For sheet metal a special drill is helpful. For examples click on http://www.castlewholesalers.com/GENERAL-34ST-Sheet-Metal-Drill-1-8-to-7-8-Capacity.html http://www.use-enco.com/CGI/INSRIT?PMAKA02-1109&PMPXNO”7556&PARTPG=INLMK3
Another possibility is a wood base with the "sides" made from commercial L brackets attached to the base with screws.
Good luck and let the group know how you make out.
Feel free to email if you think I help.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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On Sat, 08 Mar 2008 01:33:04 -0600, F. George McDuffee wrote:

to-7-8-Capacity.html
PMAKA02-1109&PMPXNO”7556&PARTPG=INLMK3
I'm planning on either using Rulon bearing inserts from McMaster, or just running the shaft against the aluminum.
Dunno about the adjustable bearing idea -- I've considered it, but if I'm paying to have it assembled it may be worth a bit of time on a milling machine to avoid having to find someone who's capable of doing the bearing adjustment right. The whole bearing adjustment issue is being driven by the sensor, so I'm going to look into that part independently.
It's important that it look reasonably professional, but bare aluminum may be good enough -- I may ask for another quote without the anodizing.
--
Tim Wescott
Control systems and communications consulting
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wrote:

$36 doesn't sound out of line based on my understanding of the sketch. What's the piece marked "bracket"? A welded-in gusset? Depending on the configuration and requirements, welding may be expensive.
Assuming the shop has a Timesaver belt sander, the brushed finish and anodize shouldn't add more than a couple dollars to the price.
You may be able pay for the finish by buying your bushings from Igus. http://www.igus.com/
--
Ned Simmons

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Tim, I believe there are several expensive areas in your design. First off, expecting .001" tolerance means it must be milled or wire EDM. Can you tell me why the tight tolerance? Does the mating part have the same tolerance? What size holes in the mating part?
Next, I don't understand the bracket. Is this a purchased item, or is it formed into the sheetmetal? Or, is it to be fab'd separately and attached, if so how?
Material thickness?
Anodize is not a big cost. Here, it's about $50 run charge, plus $1/ part. IIRC. Dave
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On Sat, 08 Mar 2008 08:12:03 -0800, Mechanical Magic wrote:

I knew I should have erased parts of that damn drawing and re-scanned it.
At this point I'm just trying to understand the cost drivers for the part without the holes -- I'll either have the cost to have the holes put in at a machine shop as a second operation, or I'll see if I can eliminate the need for such accuracy altogether.

Fabbed separately, screwed on.

The bearings I'm contemplating require moderately thick material -- it works out to 14 gauge, but I'm damned if I can remember exactly what the bearing spec is at the moment.

That's good to know, and a reasonable price.
--
Tim Wescott
Control systems and communications consulting
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Tim, I'm a very poor estimater, but::
Initial shearing of the parts is cheap, IF you don't have tight tolerances. If you are OK with +- 1/8" then things are cheaper than +- .010". 1/8" can be done on a cheap shear, .010" has to be done on a laser machine costing $300,000+
Bending tolerance, same issue, looser is cheaper.
A sheetmetal shop cannot hold .001" tolerance on hole position, unless they have CNC controlled equipment. You are asking for the equivalent of .05% resistors. Yes, they exist but is it required? A qualified machine shop will be required if you insist on that tolerance. BTW, how are you going to inspect the part to verify the tolerances have been met?
Dave
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Tim Wescott wrote:

I'm going to jump up and guess that you do not yet have a working prototype.
That might be a better place to start.
Richard
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On Sat, 08 Mar 2008 01:40:02 -0600, cavelamb himself wrote:

A student of mine built the prototype, which worked admirably well. Cost- wise, it made oodles of sense as a one-off, but not in any volume over onesie-twosie.
I'm trying to figure out how to achieve the desired behavior, but at a reasonably low cost.
--
Tim Wescott
Control systems and communications consulting
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Tim Wescott wrote:

Shoot!
Welcome to engineering 101...
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On Sat, 08 Mar 2008 02:01:42 -0600, cavelamb himself wrote:

Well, yes. My frustration is compounded by the fact that I'm accomplished at other aspects of engineering. Ask me how to make a low- cost circuit, or how to write software to allow for a processor that costs 1/2 as much, or to design a control system that maintains performance with a cheaper sensor or actuator -- I can do any of those.
But a feel for how much it costs to put a bend in a sheet of metal, or a hole, or what features of a mechanical design may drive the cost up or down? Not there.
--
Tim Wescott
Control systems and communications consulting
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You would be cheaper to make it 3 pcs and use the bracket for afixing the 3. The reason is that the parts can then be cut on a waterjet or laser, at very low cost, including tight location holes. When you get into bending, you cannot put the tight tolerance holes in prior to bending, because of tolerance stack-up. This makes fixturing for the holes to be put in later a difficult task. The savings would more than pay for a snap-in plastic corner strip to cover the sharp edges. I would re-think it along these lines Tim.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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On Sat, 08 Mar 2008 12:43:26 GMT, with neither quill nor qualm,

I picked up a 20' stick of 3/4" x 3/4" angle iron a few days ago and it cost a bleeding $14.90! He told me it had gone up 30% two weeks ago and was going up another 10% today. Steel plate is being rationed!
Hayseuss Crisco, it's getting expensive out there...
-- The best and safest thing is to keep a balance in your life, acknowledge the great powers around us and in us. If you can do that, and live that way, you are really a wise man. -- Euripides
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On Sat, 8 Mar 2008 14:06:26 -0500, with neither quill nor qualm, "Ed

I asked the steelmonger about that. He said that they were buying mostly scrap, but some fresh arn, too.

Ethanol is a losing proposition. I hope we don't waste any more money on it. I get 10-15% lower mileage with our newly mandated oxygenated fuels now. That's 10% ethanol here.

1000:1 that ain't gonna be DEEtroit stock, either.
-- The best and safest thing is to keep a balance in your life, acknowledge the great powers around us and in us. If you can do that, and live that way, you are really a wise man. -- Euripides
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On Sat, 08 Mar 2008 10:03:36 -0800, Larry Jaques
<snip>

<snip> =========When you no longer domestically produce "stuff" and your currency tanks compared to that of your supplier, and you gotta' have "stuff," you are *SCREWED,* be it oil or angle iron.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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On Sat, 8 Mar 2008 14:06:26 -0500, "Ed Huntress"

=========check the price of hops.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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This is an era of technical break throughs. They have finally discovered how to turn lead into gold. I bought a 12"X12"X1/8" sheet of lead from Aircraft Spruce. $63.!! Invest in precious metals now includes lead.
Stu
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Maybe aircraft lead is lighter. d8-)
-- Ed Huntress
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Tim Wescott wrote:

I will venture another opinion. It's your drawing. You are asking a guy to quote on a print with words like "about" and "3-4" with tolerances of .001". From where? Center to center? You didn't say that. The sheet metal guy sees trouble, and he will quote a premium price to compensate for the potential trouble. He or she is not in the engineering prototype business.
You might want to look at extruded C channel, in aluminum or plastic. In plastic you wouldn't have to worry about a bearing material. McMaster has some.
Kevin Gallimore
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On Sat, 08 Mar 2008 10:47:45 -0500, axolotl wrote:

My plan was to get budgetary pricing so I knew if I should even start the business, or use that approach, then to pay a mechanical engineer to finish the design with a nicely detailed and toleranced drawing.
Clearly this shop doesn't understand the notion of budgetary pricing -- I was getting back an honest-to-god quote with four significant digits; a "budgetary price" with more than 1-1/2 significant digits is either a lie of a wildly premature quote.
--
Tim Wescott
Control systems and communications consulting
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