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Old Aug 06, 2008, 08:58 AM
7000mw of raw power!
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poor mans mg scale

Hi,

I've been browsing the site for years and finally decided might have something to contribute. Here's a trick to enhance the $10 harbor freight digital scale so it can weigh millgrams. Only takes a few cents worth of materials: couple pieces of bamboo skewer and 4" piano wire. Cross piece is 1" from end of 11" lever. "Tray" is 3/4" square from tongue depressor but could also be made from balsa. 5-min epoxy. Hope pics look ok. Seems accurate +-10mg. Good for those bitty palnes, motors, actuators, etc..

Still working on sub-g bl plane inspired by Brian, Helmut, Martin, and the others. Got act and motor running on Tiny13 w/IR now trying to deal with that microfilm stuff. Thanks guys.

-Rich



Edit:

Chucks not the only one wondering how this works. I got 2 emails asking same thing. Apparently some do not believe in reading beyond the first post so I hope Pmackenzie don't mind if I move his drawing up here.
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Last edited by rich smith; Nov 27, 2009 at 04:27 PM. Reason: Pats drawing
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Old Aug 06, 2008, 12:13 PM
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simple and effective, the only issue I can see is that whenever the arm is off the horizontal some error might be introduced in the reading, not to mention friction on the pivot points. On the older mechanical scales for quantitative chemistry the pivots were usually carved from a hard stone to reduce the contact surface to the minimum. Perhaps something similar could be achieved with a grooved glass and a razor blade?
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Old Aug 06, 2008, 01:09 PM
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Very clever setup. A scale reading milligrams should not be expensive in todays computer age, at least I don't think so. I remember using a triple beam years ago, and when I went to look for an electronic scale it was priced at 600.00 to 800.00. I bought one two years ago for 50.00 and I know I payed to much for it. When I saw some of the prices on the net, I nearly fell off my chair. I also own a bigger scale and used it once, now it doesn't work on all settings. I have not shook it or abused it period, it just stopped working. The other smaller scale I currently use was tossed in a drawer and it stopped working so I had to get another one. There great for weighing but are really fragile. And if you drop it or it gets smacked around forget it, you will be buying a new one. Thats been my experiance. Jimmi
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Old Aug 08, 2008, 06:06 AM
56S
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Balance beam scale

Last night I dug out my reloading scale. These are graduated in grains so some math must be used to convert to grams. 1 grains = 0.06479891 grams. Type grains to grams on google and a caculator will come up. A UH 3.7 gr servo weighs 69 grains. 0.06479891 x 69 = 4.47112479 grams. So much for the 3.7 gram servo.
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Old Aug 08, 2008, 10:11 AM
Mc-Fly
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Melbourne-Australia
Joined Mar 2008
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Deal Extreme have a 0.01g Resolution scale for $16.74 Free Shipping on all their products. http://www.dealextreme.com/details.dx/sku.14386


They also have 0.001g Resolution scales for a mere $24
Although cheap the got a reasonably good review

I will be getting the 0.01g Resolution scales from DX next week.

Veteran
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Old Aug 08, 2008, 11:19 AM
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Houston, TX
Joined Dec 2007
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Jennings scales are very good quality and are relatively cheap. I got mone for $30 shipped. You can find them online (Google Jennings scale) and on eBay, though the online stores are actually cheaper a lot of the time. They are available with various resolutions and max weight. They are nice because they auto-zero when you turn them on and don't require re-zeroing between measurements like some of the cheaper scales. There are other good brands out there, but Jennings seemed to give the best value.

One of the many stores that carry Jennings Scales:
http://www.oldwillknottscales.com
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Old Aug 10, 2008, 12:24 PM
7000mw of raw power!
rich smith's Avatar
New Hampshire (not the old one)
Joined Dec 2006
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Thanks for the comments guys.

I really appreciated that link Veteran, a couple are on the way. I haunt DX almost daily but missed this because it was in the wrong area. Maybe my "Archimedes special" will boost it to 1 mg!

Don't know about grooved glass and stone though. We're talking mg not micrograms here. Vibration and air currents are big enough problem now. Also doubt friction is an issue. Do the math. Unless of course you decide to glue the fulcrum like that guy in Kiwis thread! And position not a problem either because that's what's used to fine tune. More practical upgrade might be CF tubes instead of bamboo to increase stiffness. But it would mean spending more than $1. Oh, No!

I remember 30yrs ago working in biomed lab if somebody left the glass door open overnight we had to send out for re-certification. I stuff the HF unit in my pocket all the time and it always come up 25.0 on the dime (haha, very punny). Thought maybe try the $24 one but closing the door to weigh is a pain and who makes 0.1mg motors or lipos anyway. Probably very fragile too.

-Rich







Quote:
Originally Posted by Veteran
Deal Extreme have a 0.01g Resolution scale for $16.74 Free Shipping on all their products. http://www.dealextreme.com/details.dx/sku.14386


They also have 0.001g Resolution scales for a mere $24
Although cheap the got a reasonably good review

I will be getting the 0.01g Resolution scales from DX next week.

Veteran
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Old May 31, 2009, 06:14 PM
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Ok, I must be a complete moron, because the more I look at those two pics of your scale, the more confused I am about how the thing works.

I take it the piano wire is used to hold the short end of the long stick down by securing it to the scale?

So, now we have a fulcrum stick laying on the scale, the short end of the arm hooked under the piano wire, and a dime sitting on the long end of the arm.

Ummmm.... how does it measure anything????

Chuck
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Old May 31, 2009, 06:26 PM
7000mw of raw power!
rich smith's Avatar
New Hampshire (not the old one)
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Chuck, I know you are not a complete moron. There are definitely some parts missing! (JOKE! JOKE! )

Wow, I forgot about this. It was my 1st thread ever on RCG.

It's not a see-saw type lever but more like a force magnifier. Could not have built my micro gram models w/o it. Try one and you'll see. Only takes a few minutes and works with any scale.

Quote:
Originally Posted by NoFlyZone
Ok, I must be a complete moron, because the more I look at those two pics of your scale, the more confused I am about how the thing works.

I take it the piano wire is used to hold the short end of the long stick down by securing it to the scale?

So, now we have a fulcrum stick laying on the scale, the short end of the arm hooked under the piano wire, and a dime sitting on the long end of the arm.

Ummmm.... how does it measure anything????

Chuck
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Old May 31, 2009, 06:36 PM
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Idaho
Joined Sep 2001
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Spring scale

I've posted this before but for those who haven't seen it, this is the smplest, most accurate and functional weighing system for .01 gm accuracy I have seen. It is made by Ray Harlan at Indoorspecialties. Mine hasn't left my workbench for 20 years. For over 10 grams I use an OHaus triple-beam.
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Old May 31, 2009, 06:40 PM
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Toronto (Don Mills), Canada
Joined Dec 2002
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Quote:
Originally Posted by NoFlyZone
Ok, I must be a complete moron, because the more I look at those two pics of your scale, the more confused I am about how the thing works.

I take it the piano wire is used to hold the short end of the long stick down by securing it to the scale?

So, now we have a fulcrum stick laying on the scale, the short end of the arm hooked under the piano wire, and a dime sitting on the long end of the arm.

Ummmm.... how does it measure anything????

Chuck
The wire is attached to the scales base, not the part that weighs things.
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Old May 31, 2009, 06:56 PM
7000mw of raw power!
rich smith's Avatar
New Hampshire (not the old one)
Joined Dec 2006
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Quote:
Originally Posted by pmackenzie
The wire is attached to the scales base, not the part that weighs things.
Oh man, wish I had thought of doing a drawing like that! Thanks.
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Old May 31, 2009, 06:58 PM
7000mw of raw power!
rich smith's Avatar
New Hampshire (not the old one)
Joined Dec 2006
5,986 Posts
Quote:
Originally Posted by cmartin
I've posted this before but for those who haven't seen it, this is the smplest, most accurate and functional weighing system for .01 gm accuracy I have seen. It is made by Ray Harlan at Indoorspecialties. Mine hasn't left my workbench for 20 years. For over 10 grams I use an OHaus triple-beam.
Wow! that can be built even cheaper. And no BATTERIES! I really like that design.
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Old May 31, 2009, 07:36 PM
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Quote:
Originally Posted by cmartin
I've posted this before but for those who haven't seen it, this is the smplest, most accurate and functional weighing system for .01 gm accuracy I have seen. It is made by Ray Harlan at Indoorspecialties. Mine hasn't left my workbench for 20 years. For over 10 grams I use an OHaus triple-beam.
Cmartin,
Very interesting, but tiny picture.
If it's on your work bench it would be helpful to see several views.
The other side seems to be a different range.
While you're at it please make them at least 800 pixels or more wide.
Should cost the same.
Thanks.
John255
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Old May 31, 2009, 09:06 PM
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Idaho
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Spring scale

Sorry, I took the easy way out and just copied over a pic from Ray Harlan's site. Since there's appears to be some interest, I'll take a couple more close ups and post them. It has a 0-1 gm scale on one side and a 0-10 gm on the other. Ray Harlan is an indoor model supplier/competitor so his little spring scale kit has some features that allows the user to adjust and optimize the accuracy of the scale read-out.
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