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-   -   Gram Scale Suggestions for weight matching pistons (http://www.hotrodders.com/forum/gram-scale-suggestions-weight-matching-pistons-226150.html)

zildjian4life218 11-16-2012 09:25 AM

Gram Scale Suggestions for weight matching pistons
 
I am looking at buying a gram scale to start weight matching pistons, rods, etc. Im building a fixture like the one used in this video. Any suggestions?

Thanks everyone!
Shane

69 widetrack 11-16-2012 09:32 AM

I have used the same gram scale that I use for mixing paint...They can be expensive but, if you shop around Auto Body supply stores they may have a used one that would take some cleaning (getting old dried up paint off). they are accurate and easy to calibrate.

Ray

69 widetrack 11-16-2012 09:48 AM

I just watched the video and a paint mixing gram scale would be ideal for this set up. Oh, by the way, the paint that has collected on a used paint mixing machine comes off with a razor blade and lacquer thinner. Both of mine have the scales read out on top and I had to remove the read out pedstol and mount it on my bench...works very well.

Ray

1Gary 11-16-2012 10:09 AM

Yeah,there isn't anyone in Roch to balance.Got to go to Batavia.

zildjian4life218 11-16-2012 12:12 PM

Quote:

Originally Posted by 1Gary (Post 1611916)
Yeah,there isn't anyone in Roch to balance.Got to go to Batavia.

My machinist down in Honeoye that takes care of my balancing now doesn't have a machine but he does the weight matching and rod balancing then sends the crank and bob weight measurements to who ever he has doing them. I just want to get more involved in some of the actual machining and blueprinting aspects of engine building not just the assembly.

cobalt327 11-16-2012 01:09 PM

Quote:

Originally Posted by zildjian4life218 (Post 1611904)
I am looking at buying a gram scale to start weight matching pistons, rods, etc. Im building a fixture like the one used in this video. Connecting Rod Balancing - YouTube
Any suggestions?

Thanks everyone!
Shane

I have three gram weight scales I use for fireworks making, so I can give you a couple tips.

Be sure the platform that will receive the objects to be weighed is large enough that the weighed item doesn't obstruct the display.

Be sure the accuracy is within your needs. I would think +/- 0.1 gram would be about right. My smallest scale is accurate to 0.01g (10mg), but the total capacity is too small for what you're doing. I use it mostly for test batches of fireworks compositions and reloading.

They all seem to have an auto-off feature. I find that frustrating; on one of my scales every time I turn around it seems, the damn thing has shut down.:smash: The length of time until auto off is not usually published, either. So keep a pencil and pad handy and write things down.

I have Ohaus and chinese scales and the accuracy is within the published range for them all. One chinese scale has been used for about 8 years now on a fairly regular basis (came from HF), no probs. So depending on your budget, buying a cheaper scale isn't necessarily sacrificing accuracy.

Get a set of calibration weights and use them.

The smallest scales do not have the option to use an AC adapter. In your case you might want to go w/one that has that option. An adapter or batteries can be used on most all of the larger capacity scales like the one below (I own one of these, BTW):

Digital ScaleThe resolution is 1g on this scale, has a 40 second idle time before auto off. I use it for bulk chemicals. You might want better resolution. Generally better resolution means less capacity or more money.

zildjian4life218 11-16-2012 03:05 PM

Quote:

Originally Posted by cobalt327 (Post 1611996)
I have three gram weight scales I use for fireworks making, so I can give you a couple tips.

Be sure the platform that will receive the objects to be weighed is large enough that the weighed item doesn't obstruct the display.

Be sure the accuracy is within your needs. I would think +/- 0.1 gram would be about right. My smallest scale is accurate to 0.01g (10mg), but the total capacity is too small for what you're doing. I use it mostly for test batches of fireworks compositions and reloading.

They all seem to have an auto-off feature. I find that frustrating; on one of my scales every time I turn around it seems, the damn thing has shut down.:smash: The length of time until auto off is not usually published, either. So keep a pencil and pad handy and write things down.

I have Ohaus and chinese scales and the accuracy is within the published range for them all. One chinese scale has been used for about 8 years now on a fairly regular basis (came from HF), no probs. So depending on your budget, buying a cheaper scale isn't necessarily sacrificing accuracy.

Get a set of calibration weights and use them.

The smallest scales do not have the option to use an AC adapter. In your case you might want to go w/one that has that option. An adapter or batteries can be used on most all of the larger capacity scales like the one below (I own one of these, BTW):

Digital ScaleThe resolution is 1g on this scale, has a 40 second idle time before auto off. I use it for bulk chemicals. You might want better resolution. Generally better resolution means less capacity or more money.

Really homemade fireworks? That's fricken awesome lol. I live around the corner from a harbor freight so maybe I will stop in later and check out the scale. How critical is it to have the hanging point of the small end and big end to be parallel? I noticed that in the video the scale and rod hanger are all on the same piece of metal. I imagine this is critical as well

cobalt327 11-16-2012 03:37 PM

That is correct, you want to weigh them on the same plane, so to speak. So the rod beam is parallel in other words. Hopefully a machinist who does this for a living will chime in.

I made a fixture once to weigh rods, but I could not get repeatable results. Years later I found it was because the fixture was magnetized from me having used heavy magnets to hold parts of it together during the mock up phase!

OT- the fireworks thing got its start from me making black powder to shoot with. I tamped a trouser hangar tube (you know the cardboard tubes that are on the hangars that come from the dry cleaners to keep from creasing your pants) full of BP, taped the tube to a BBQ skewer and lit it off, and darned if it didn't fly! Was hooked ever since.:D

1914 Popular Mechanics illustration:

http://www.hotrodders.com/gallery/da...d_balancer.jpg

cobalt327 11-17-2012 06:03 AM

I should have mentioned above to be sure to include the weight of the rod fixture that sits on the scale AND the weight of the piston when choosing a scale's capacity. Just the approximate weight of the piston is not enough capacity, in other words.

It's best to choose the scale capacity so that w/everything on it you will be right in the middle of the capacity. This means buying a scale w/quite a bit more capacity than you might think is needed.

BTW the BBQ skewer above is a bamboo shish kabob skewer, not steel.

MARTINSR 11-18-2012 09:13 AM

Quote:

Originally Posted by cobalt327 (Post 1612047)
I made a fixture once to weigh rods, but I could not get repeatable results. Years later I found it was because the fixture was magnetized from me having used heavy magnets to hold parts of it together during the mock up phase!

VERY interesting! You just can't make this stuff up, how bizzare! How many of us would have thought of that, not many is my guess. That is a trip, thanks for that bit of knowledge it's just interesting enough to stay in my gray haired old head. :thumbup:

Brian

ramzoom 11-24-2012 03:21 PM

I am a licensed scale tech and we've had a shop for over 40+years.. Feel free to PM me if you have any questions about scales or weights.

zildjian4life218 11-24-2012 09:48 PM

Any other suggestions besides the HF one from cobalt. This maybe.......

ramzoom 12-08-2012 05:02 PM

$1000+ Sartorius scale in that video and they should center the load and not load the rear of the scale..That scale has 4 load points..1 at each corner..they are loading the rear 2 mostly..A scale that good will have adjustments to make sure each corner is accurate and matched to the other 3. On the cheap scales you will most likely have an error if you apply weight to each corner individually..this is a shift test. Cheap scales usually fail horribly..so you could have a gram or more of error depending on where you load the scale..Better scales have better load cells..most inexpensive scales have no provisions to adjust corners..they are a center mount load cell and it is entirely up to the load cell to maintain accurate readings as the weight is moved from center load towards the outer portions of the scale platform..again cheap scales tend to fail in this test..not all but most and certainly over time and use. If you really want to be within a tenth of a gram you need a good scale ( and yes there are some offshore scales that will perform well) and I recommend a good test weight. The weights that come with the cheap scales are usually out of tolerance (made in China)..So it comes down to just how accurate do you want to be? Also there is the problem of linearity..cheap scales often fail. you can load your scale with the provided test weight and perform a calibration but if you check 3 points across the range of the scale you will most likely find errors with the exception of the test weight value you used. My advice..get the best scale you can afford for what you really need. Dont say you want to go 200 mph on the autobahn and then go to Yugo and buy a car..and vice versa..dont buy a Lambo if all you do is drive to the store down the street...of course figuratively speaking..lol..I'd love a Lambo to drive to the store! lol..


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