# DIY Epoxy Weight/Balance Scale

Discussion in 'Workshop Tips and Secrets / Tools' started by Aerowerx, May 28, 2016.

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1. May 28, 2016

### Aerowerx

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Introducing the new improved fat free high fiber Aerowerx Epox-O-Lator v3.0 balance scale!

You can make your own, too! The basic idea came from here and here.

One important factor is the length of the balance arm and the height of the pivot point above the balance arm. The larger these are the more sensitive it will be. Also, the pivot point should be as low friction as possible. I suppose you could use use a bearing, but I don't think that is necessary, as this one is quite sensitive---the air from my fan was making it move from 8 feet away.

In this one the pivot is a finish nail through two pieces of aluminum angle:

The beam on mine is about 26 inches long. Probably that is more than is needed, so you can make yours as long as you want. Just remember, the longer it is the more accurate it will be. The thing is put together with hobby store epoxy and wood scraps, so is quite cheap to make.

So, how do you calibrate it?

One one end of the balance beam draw a line an inch or two in from the end. This will be where you put your mixing cup:

Carefully measure the distance from this line to the exact center of the balance beam, which should be directly under the pivot point. On mine it is 12.0 inches. At the other end of the balance beam, draw a line the same distance from the center:

Label it 'H' for hardener. I also like to label it with the type of epoxy, in this case T-88.

Now the tricky part...

You carefully measured the distance from the center to each of the marks, didn't you? The mark labeled 'H' represents the total weight of resin and hardener (I'll explain why it is labeled only 'H' later).

From the thread on weight vs volume, I will be using a ratio of 1.00 to 0.86. This is the same as 100:86, or 100 parts of resin and 86 parts of hardener by weight, making the total weight of epoxy 186 parts. The amount of resin is only 100 parts, or 100/186 times the total weight. So make a mark 100/186 times the length measured (6.45 inches on mine), on the same side of the balance beam as the mark labeled "H". Label this mark as 'R' for resin.

Now you are ready to go.

Place a cup on the first mark (on the right on mine). Take a small weight and put it on the left side. Move it around until the beam balances with an empty cup.

Take some convenient weight, that represents how much epoxy you want to end up with. Place it on the mark labeled 'R'. I use socket wrenches, since they are convenient and come in different sizes.

Put resin in the cup until the beam balances.

Move the same weight to the mark labeled 'H'. Now add hardener to the cup until the beam balances.

Mix and enjoy!

One thing you may have to do, which I haven't done yet. You may have to put a small weight on the balance beam so it will balance by itself. When you find the correct spot, epoxy it in place. After applying the epoxy, verify the position of this weight while the epoxy is still wet, then let dry.

2. May 28, 2016

### BBerson

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This explanation is good until the sentence: " Place the cup on the first mark ( on the right)"

That instruction appears reversed from photo, and makes everything confused.

My first thought after review of method is that this may be difficult to remember if not used almost daily.
An almost fool proof method would be better. Just my opinion.

3. May 28, 2016

### Vision_2012

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You can calibrate with nails or pennies. If you use two cups, like adding the hardener to the resin, fill the hardener cup 1/2 way and pour it back into the storage container, so it will be as wet and as heavy as it would be after you balance the hardener to the resin. This ensures that when you mix, you won't be starving the mix of the hardener that is left in the cup.

Or you can use a digital cooking scale (no building anything) and only use one cup. The one I bought for under $20, has both grams or ounces. You put your mixing cup on the scale, zero the weight, add the resin, measure, look up in a chart how much hardener to add, add it and mix. I like to have my chart in grams as the ratio's are easier to calculate. Most epoxies clean up with white vinegar, no acetone or MEK needed to have clean mixing sticks, scale, brushes and hands. 4. May 28, 2016 ### kent Ashton ### kent Ashton #### Well-Known Member Joined: Aug 15, 2008 Messages: 723 Likes Received: 214 Location: Concord, NC Yep, and smelt your aluminum out of old beer cans. It is a whole lot easier to buy a postal scale at Walmart for$23. Then make a spreadsheet that shows for various amounts of resin, how much hardener to add to bring up to a total figure. Come into the digital age, my friend.

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5. May 28, 2016

### TFF

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6. May 28, 2016

### Aerowerx

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OOPS! Err, the mark on the left.

I don't see how you can get any more foolproof than this. It is a lot easier to actually do than explain.

7. May 28, 2016

### Aerowerx

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No calibration needed. The only "calibration" is the careful measurement of the marks on the balance beam.

Huh? Why? Just use one cup. If you are worried about the mixing, after measuring just pour the stuff into another cup and mix a second time.

Yes, but every time you want to mix a different size batch you have to calculate the weight and then carefully measure. With the balance beam it is based on the ratio of the two weights. No calculating or measuring---just pour until the beam balances.

8. May 28, 2016

### Aerowerx

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Its a whole lot easier to just go to the airport and buy a ticket if you want to fly. So why build your own plane?

9. May 28, 2016

### Vision_2012

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No calibration needed. The only "calibration" is the careful measurement of the marks on the balance beam.

Aerowerx, the calibration is a check, a second measurement if you will. Of course if "measure twice, cut once" is not your mantra, you can disregard. This comes from Rutan's 'Moldless Composite Homebuilt Sandwich Aircraft Construction' circa 1983.

I missed your double balancing with sockets, but of course you know that introduces a variable and a possibility for mistakes. I wonder if you will like your system when mixing epoxy to support a big layup where pints of epoxy will be used quickly. Waiting for a scale to balance is slow and delicate, not supportive of working quickly. I dislike balancing cups on lines on top of beams--too easy for it to fall off or be off. It also limits the size of the cups. And I hope you like building a new scale for each epoxy system you use.

You know with excel, a list of incremental ratio weights is calculated in microseconds, printed and never a new calculation is made again.
And since I built two composite aircraft, you can disregard my suggestions entirely. To each his own.

Another tip, go to your local Goodwill Industries store and buy a big mixing bowl, usually about a buck. When mixing microballoons into epoxy, do it inside the bowl. The 'balloons falling out of the cup remain in the mixing bowl--not all over the shop--and can be poured back into the mixing cup for more mixing. Now, if you can invent a self mixing epoxy bowl, you will have my attention.

my list for aeropoxy:
Hard. Resin Hard. Resin
2.7 10 27 100
4.1 15 31.1 115
5.4 20 32.4 120
6.8 25 33.8 125
8.1 30 35.1 130
9.5 35 36.5 135
10.8 40 37.8 140
12.2 45 39.2 145
13.5 50 40.5 150
14.9 55 41.9 155
16.2 60 43.2 160
17.6 65 44.6 165
18.9 70 45.9 170
20.3 75 47.3 175
21.6 80 48.6 180
23.0 85 50.0 185
24.3 90 51.3 190
25.7 95 52.7 195
27.0 100 54.0 200
spacing failed in copying to entry

10. May 28, 2016

### kent Ashton

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If you like things to be difficult, you're on the right track. Nobody building composite airplanes uses a beam scale these days. Rutan had one in the plans because they didn't have postal scales in those days.

No you don't. You put the cup on the scale, zero the scale, put in as much resin as you want, add hardener to bring the total weight up to what is precalculated on the spreadsheet. That takes, what, 12.5 seconds? If you you use different epoxies, you use two spreadsheets.

PM me your epoxy and I will email you a spreadsheet.

11. May 29, 2016

### Aerowerx

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How do you calibrate a ratio?

Huh? The socket wrenches are just dead weights. I could just as well use a stack of quarters, or dollar coins, or old tire weights. The important thing is the ratio between the moment arms at the 'R' and 'H' marks.

Layup??? Are you talking about a cloth/resin composite? T-88 is a structural adhesive, not suitable for 'layups'. And the recommendation from System 3 is that it is better to do several small batches instead of one large one.

So is pouring resin and hardener to the right amount. Besides, the balance scale would slowly come to balance as the resin and hardener are poured into the cup.

Then put a small curb or ridge around it so it stays in place. Or use some sticky stuff.

The cups I use are 266 milliliters (6 ounces volume). That comes out to about 275 grams of T-88. I can't think of any case where you would need that much all at once.

Why? Just put some more marks on the beam for the new resin:hardener ratio.

But I am building in wood, not composites.

12. May 29, 2016

### Aerowerx

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I am not building a composite airplane. Where did you get that idea?

13. May 29, 2016

### Lendo

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Aeroworx, I too tried that home made scale, learnt the hard way and bought a set of electric scales- never looked back. A small trick, use some glad wrap over the scale to catch spills and drips, keeps it looking nicer and easier to read.
George ( down under)

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14. May 29, 2016

### Vision_2012

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'But I am building in wood, not composites. '

Like we can read your mind. Thanks. Build in good health.

15. May 29, 2016

### Rockiedog2

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I been trying but I just don't get it...
not only this balance beam apparatus but the huge ratio thread as well
I've never seen so much ado about nothing
T88 is so well proven over decades to be tolerant to us amateurs
instead of this eternal fretting over pointless details...

why not just mix it one to one and build the **** plane?

put stick in can
pour to line
stir
glue the part

Last edited: May 29, 2016
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16. May 29, 2016

### Aerowerx

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Because...

It is easier to measure small batches by weight, and System 3 recommends it.

There is a discrepancy in the T-88 data sheet that I was trying to resolve. If you see something that doesn't look right, don't you want to figure it out?

The detail is not "pointless". If you are going to allow sloppy practices in your build, then how much "slop" is too much? I want to know that I am starting out with good numbers.

To all you guys... This is the Workshop Tips and Secrets forum. That is what I did---post a workshop tip. You don't have to build a balance scale. You didn't even have to read my post, or answer it. But maybe someone else might be looking for an easy and inexpensive way to get accurate epoxy mixes. There are many ways to "skin a cat", as the saying goes. This is just one of them, so what is wrong with wanting to share my ideas? Isn't that what HBA is for?

17. May 29, 2016

### Rockiedog2

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measuring T88 by volume with reasonable care is not "sloppy practices". It doesn't have to be perfect. There is no science involved in building with T88. It's not necessary at all; proven countless times by average guys in home workshops that successfully built a plane...measuring by volume. There is no balance beam required. This discrepancy(it was in thousandths wasn't it; or maybe hundreths...whatever; it doesn't matter) isn't important to me at all. The decades old service record of T88 has shown that it has no practical application(that seemed to me what the S3 tech guys were telling you when they indicated that it's your problem). You have proven it isn't easier to measure by weight (no matter what System 3 says). So I have to disagree that the "detail" isn't pointless...it is; if you're interested in actually building a plane. If we're into just academic exercises or stuff to put on the Net well that's different...sure fire away.

Sure I can "not read the thread" that's no problem. But there are many new guys here trying to learn that will think all the stuff in the balance beam and ratio thread is of great concern and be led to think that it's necessary. It isn't. Reasonable care mixing by volume is all one needs to know about T88 ratio. That's it. That's not from me...that's the field record. Decades, man...

You guys carry on...I spoke my piece; I'm outa here.

Spencer
Common Sense Rules

Last edited: May 29, 2016
18. Feb 4, 2017

### lr27

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This technique will also work just fine for epoxies that are more finicky or have weird ratios. T88 may be tolerant to amateurs, but there may be situations where you need the best properties possible. In that case, an exact mix will be better by some amount than a less exact mix.
---------
I have a triple beam balance, and I've worked in a couple of situations where we measured glop with a digital scale. However, I prefer balancing a stick. I take a stick and mark it up as mentioned. Instead of a formal pivot, I just glue something round on the bottom of the stick. For instance, a short length of a relatively small dowel. You only really need enough so that, when loaded, the stick doesn't sag down to the table on both ends at once. I glue a cup at each end, in the appropriate places. The glued down cups are just to hold the actual cups I will use. You could also screw them down, I guess. This way the cups will be much less likely to fall over, and they will always be in the right place. I place a fresh cup in each fixed cup, and use clay or stray bits of anything to balance the stick. Best to use something that stays put, and to check to see that the gadget continues to balance at the beginning of each mixing section. Always balance with cups inside the fixed cups, or it will come out wrong. (Unless the mix is 50-50) I put some of one part of the epoxy in one cup. Then I fill in the other until, when I hold it down, it won't always come up. That is, nearly balanced. If I can hold down each end, and it stays, the mix is just right. However, if it bounces back and forth a few times before settling down, that's close enough.

I admit this gives a cup of part a and a cup of part b. So I might pour almost all of the a into the b. I'll mix for a little while, and then pour it back into the remaining a, scraping the inside surfaces of the cup to get as much as possible out. Then I mix in that cup a while. Pouring back and forth, scraping, and stirring in this manner a couple of minutes gives a pretty good mix. Besides the convenience, I like this method because I don't have much to lose if it gets epoxy on it, get's stepped on, etc. If the stick and cups are light, and the cups are a consistent weight, you can mix very small batches accurately this way. I don't recall just what I was gluing, but I had some fairly expensive epoxy for an electronics application, but I was able to get accurate, very small batches. Several grams at most, I think, and maybe it was less. For that, I used some very small mixing dish/cup things from McMaster Carr, but that was a few years back and I don't remember just what they looked like. I think I also dispensed the epoxy with a small syringe for better control. Obviously, you can use larger cups and sticks if you need a lot of epoxy at once. Possibly a better way to dispense very small amounts of epoxy resin and hardener is from luhr lock squeeze bottles with luhr lock tapered plastic pipette tips on them. The taper means viscosity is less of an obstacle, and the squeeze bottle will pull back as soon as you stop squeezing it, unlike syringes I've used. For batches not quite as small, I usually use 1 oz. specimen cups from the drugstore, though these have the drawback of molded marks on the inside. Quite inexpensive. When building a boat, I used to use some marked cups which I think I got from Glen-L, but I guess with the balance beam that's unnecessary.

When mixing bigger batches, say a few ounces at a time, make sure you can take them outside in a hurry. Especially if the ambient temperature is high. You don't want that stink and smoke inside with you if it goes off too soon. Some people spread the epoxy in a shallow dish so that it takes longer to go off.

BTW, anyone know how to keep microballoons or fumed silica out of the air when adding it to epoxy? (Make sure not to add until the epoxy is well mixed. I know that much.)

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19. Feb 4, 2017

### lr27

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Oops, looks like the computer ate my homework again.

I'm willing to bet that, if the ratio with T-88 is off a little, the properties will be too. In some applications that may be ok.

I find my variation of the cup trick more convenient than mixing by volume, unless you trust those pumps more than I do. My pumps let a bubble through once in a while. My variation probably isn't my variation, I just don't remember where I picked up the idea.

Anyway, I use a stick like Aerowerx does, but I fasten empty cups on the ends of the stick, and I use something round glued on the bottom, like a short length of dowel, instead of a separate pivot. I know the ratio is just right if it I can push either end down and it stays there, though realistically if it bounces back and forth a few times before settling down, that's good enough. The empty cups never get epoxy in them, they're just to hold the cups you're using in a consistent position. It's probably best to fill the cup furthest from the pivot first, then add to the other until it's balanced. Then remove the cups and pour one's contents into the other, scraping the sides and bottom with the mixing stick. Stir a bit and pour back in the other cup. Repeat two or three times. By then, you ought to have a good mix.

For the really picky, putting the mixed epoxy in a bell jar will get the bubbles out. Just do it slowly, and in a plastic dish, so that it doesn't froth over and gum up the works. On a job I had, we used to do this with two part polyurethane rubbery goo. Fun to watch. That stuff was really sensitive. You could stir for several minutes, thoroughly, and there would be some spot that didn't cure. Ended up using pneumatically powered splitter guns instead. Like this if you haven't seen the nozzle on one:

Two streams go in and one very well mixed stream comes out. Pricey because you have to get the cartridges loaded ahead of time.

20. Feb 4, 2017

### Little Scrapper

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I buy T88 in caulk tube size. It has both parts in the same tube and dispenses both parts equally. I don't use a mixing tip because I'd need so many of those it's cost prohibited. Regardless, give it a squirt and mix with a stick. I'd never use a different system or method because it's a about as simplementation as it gets.