Epoxy weight and/or density? Buoyancy spreadsheet questions

[exx1976]

Ok, I'm doing things correctly this time.

I got a block of the wood I'm using, a square block, and measured it in mm using a digital caliper.  240.19 cubic cm.  It weighed 104 grams.  That says my density is .4330, which is pretty much spot-on with what I've read online for this type of wood (.43).

My carved & shaped blank weighs 24 grams.

The weight of internal hardware is 4 grams.

The weight of external hardware is 12 grams.

This says 15 grams of ballast (lead, in my case) should get me 105.1% buoyancy, which means it floats.  This is the desired result (though I don't know how fast that will rise, or anything else about it - just that it should float).

15 grams of lead equals a 1/4" hole 1.6 inches in depth, or three 1/4" holes that are 1/2" deep each.

Ok, this all makes sense to me so far.

What I'm trying to do now is to determine the weight and/or the density of the epoxy I'm using - eTex Lite.  Certainly that is going to add some weight to the finished lure, though it will also add volume, so it will affect all these calculations somehow.

 

How do I go about accounting for this?  I'm thinking that I can take the carved blank, and epoxy it with no hardware or weight in it.  Add the desired number of coats of epoxy, and then weigh it and do the archimedes test to get the volume of it.  That would give me the density of the "lure", not accounting for hooks and the like.  I would then use *that* density in place of the actual wood density to figure out how much ballast can then be added.  Would that be correct?  Or does someone already know the approximate density of eTex?  Am I overthinking this? Certainly I'm not the first person to try to solve this problem.

 

Thanks!!   (and special thanks to Vodkaman for the spreadsheet!)

Edited December 5, 2020 by exx1976

[exx1976]

I found an old post on here from 2014 that said that the density of 2-part epoxy is ~1.1.

So, figuring that I use approximately 2.5ccs of epoxy for each coat, and I apply 3 coats, that's 7.5ccs of epoxy.  Times 1.1 gives me 8.25 grams.  So I used 32.25 grams as the weight of my block, and then I used 62.9278 as the volume (added 7.5 to my previous volume (to account for the growth of the overall size of the lure by adding the epoxy - was easy to figure since the cups I use to measure and mix epoxy are graduated in cc), which was provided by the spreadsheet using the .4330 density), and I have a new density for the wood and the epoxy combined of .5125 grams per cubic centimeter.

 

Does this sound like the correct way to go about it?

I also added 1 more gram of internal hardware, just to be sure on that front, for a total of 5, and also added another gram of external hardware, for a total of 13.  With 10g of ballast, which is two 1/4" diameter holes approximately 1/2" deep each, my buoyancy is at 108.6%.

 

Does all this seem correct, or have I gone off the deep end?

Edited December 6, 2020 by exx1976

[Vodkaman]

Your numbers are spot on in the 1st post; 105.1% float. Good job.

Also, the numbers are correct on the 2nd post, once I got my head around them, again, good job.

if you are going for a slight floater then 105% should give you enough wiggle room for Etex and still have a floater.

Top-coat was always going to be the problem. I didn't add a top-coat section for fear of scaring everyone away, as it involved more numbers to be entered. But clearly (excuse the pun) a top-coat section is required. But now that you have scared everyone for me, I might as well build it in. 'Off the deep end', probably yes, but it was necessary. I will solve that problem for you.

The problem of top-coats in my perfect world of 2 decimal place density calculations; is repeatability, any numbers are reliant on how good you are at applying top-coat. Having said that, an extra dab or three of epoxy is not going to spoil things that much.

The work that you have done helps me a lot. I can see that I only need to add three boxes:

'Weight before top-coat' : 'Weight after top-coat' : 'Top-coat Density'.

I have modified the spreadsheet accordingly and your numbers come in at 108.4% float. Email me again to remind me who to send the new file to, then let me know what you think.

Dave

[Travis]

2 hours ago, exx1976 said:

Does all this seem correct, or have I gone off the deep end?

Are both parts of the question correct. 

 

Edited December 6, 2020 by Travis

[exx1976]

In looking at your spreadsheet, I think the field labeling is likely going to prove challenging for the intended purpose, which is (as I understand it) to determine the amount of ballast to add to an individual bait prior to epoxy. I mean, once epoxy is on, it's a bit too late to be trying to add internal ballast. The fields as shown require a "sacrificial lure", which sort of defeats that purpose, no?

 

Further, this is all predicated on the fact that a 6 year old post was correct in that the density is actually 1.1.  I went with it since it was all I could find, but I intend on weighing some resin and hardener. I do have a laboratory-grade scale availailable (a&d fx120i), so I'll do my best to eyeball the miniscus on 2.5cc of resin and 2.5cc of hardener and let you know what I come up with - for etex, anyway. That should provide the density, and then it'll be a simple matter I would think of adding a single field for "volume of epoxy applied", which could then be used to both increase the volume of the wood blank, as well as increase the mass of the finished lure. Once you've measured some epoxy and applied a coat to a few lures, you get a pretty good idea of how much epoxy is required per lure. My recollection is that I end up tossing about half of a mixing to do a coat on a single lure, but 5cc is the smallest amount I can make since the smallest graduation I have is 2.5cc.  I'll need to pay closer attention to this to fine-tune this. 

 

Also, one other thing I noticed on the spreadsheet is that it only calculates the sink rate, not the "float rate". Meaning, for a crank bait, if I stop cranking, how quickly should I expect to see it back on the surface again? When I entered the numbers for my floating lure, I got a #NUM error in the spreadsheet. I didn't dig into it to figure out what that error was exactly, but I suspect that the rise rate may also be affected somewhat by the shape of the lure, and the drag of the line/leader, so perhaps this isn't something that can be calculated. I just though it would be nice to know what that 105.1% equated to since I had no frame of reference. 

Edited December 6, 2020 by exx1976

[exx1976]

I also noticed that (at least in the pic you posted) you have "weight of body minus holes", which is presumably calculated using the volume of body to be removed to add the ballast. Interesting. Either that's new, or I missed it previously. The 24g I was using was after my approximated ballast holes had been drilled.

I did measure the holes, and calculated the volume, and the holes I drilled to get a weight of 24g with holes already made would provide enough volume for approximately 7.5g of lead.

 

The way you have it in the spreadsheet is much better, since I should definitely be calculating the ballast BEFORE drilling the holes. I got lucky. Lol  we'll call that one an inexpensive lesson.

Edited December 6, 2020 by exx1976

[Vodkaman]

Yes, I can go with those suggestions, after all, the spreadsheet only requires the volume and density of the topcoat. Obviously if you can measure your own density for the resin would be the best, but published numbers will do for most (MSDS sheet).

I have just been looking at the float rate thing myself. I will address and fix it. Float rate is just as important.

The "weight of body minus holes" box is a part of the calculation section that you need not concern yourself about. It calculates the volumes of ballast and internal hardware, subtracts it from the body volume and then re-calculates the the body weight.

I have done the changes, here is a new pic.

Dave

[Vodkaman]

I have fixed the 'sink / float rate calculator'. Float will give negative number.

Added inches to the 'Ballast Hole Calculator'.

Added a 'Wood Block density calculator'.

The manufacturer specific gravity (density) for Etex lite is 1.15.

Dave

Edited December 6, 2020 by Vodkaman

[DGagner]

Is it me but if the density of epoxy is about 1.1 g/cm3 then it seems to have almost neutral buoyancy in water? So one or two or three coats would affect buoyancy a little but it can almost be ignored. Or at least held in the mind as making a slight difference.

 

[Vodkaman]

Dgagner - true. If you were building a definite floater or sinker then the effect of the top-coat would not have much affect on the result. However, if you are skirting around neutral buoyancy, then the top-coat would play a significant role.

The spreadsheet is designed such that if you do not want to enter topcoat data then you can enter a zero.

The aim is to avoid the situation that Exx1976 had in another recent post were he 'winged' it and ended up with a bunch of sinking cranks. The system is designed to keep it simple and allow you to calculate how much ballast you will require before you start drilling holes.

Another thing that is missing is lip data. Dang! I will have to enter a few more boxes now!

Dave

[exx1976]

1 hour ago, DGagner said:

Is it me but if the density of epoxy is about 1.1 g/cm3 then it seems to have almost neutral buoyancy in water? So one or two or three coats would affect buoyancy a little but it can almost be ignored. Or at least held in the mind as making a slight difference.

 

It must just be you.  1.1 > 1, therefore it sinks.

Especially if one takes into consideration that water actually only has a density of 1 when it's a 4 degrees celsuis.  Literally EVERY other possible temperature, it has lower density.  I actually changed the value in the spreadsheet to .996 instead of 1, just to make sure it floats when the water is very warm or very cold.

[exx1976]

23 minutes ago, Vodkaman said:

 

Another thing that is missing is lip data. Dang! I will have to enter a few more boxes now!

Dave

I just threw the lip on the scale with the hooks and whatnot and added it under "external hardware".  My lure body was already drilled for hook hangers and cut for a lip when I weighed it.  For that matter, as I said, it already had two holes drilled to accept ~.02 ci of lead each, as well.  (.254" x ~.425").

 

Like anything else, the data you get out of the formulas is only as good as the data you enter.  But it makes sense to me that I should weigh it BEFORE drilling the holes for the ballast - otherwise, how do I know how much ballast to add??  LOL

[Vodkaman]

EXX1975 - I have now added a lip section. The idea is that you don't need to mess about doing side calculations. This is something that you are good at as you totally understand what is going on, but not everyone will.

As with other boxes, a zero can be entered if no lip is required.

Dave

Edited December 6, 2020 by Vodkaman

[exx1976]

oh boy...  Now because it's on there, I'm gonna have to use it.  That means I need to find the density for G10.  Ugh.

 

LOL

[exx1976]

Also, for anyone wondering, I did manage to find the density of eTex Lite..

 

It's 1.06.  Vodkaman - you were halfway there.  The resin is 1.15, but the hardener is only .97.  Here's the link to the MSDS for both components.

https://www.eplastics.com/pdf/envirotex-lite-resin.pdf

Edited December 6, 2020 by exx1976

[Vodkaman]

Thanks. I misread the file. I did this once before not too long ago.

G10 has a density of 1.8g/cm³ here is a link.

Later in the future, I will add drop-down menus that will allow you to choose a material and the density will be entered automatically.

Dave

Edited December 6, 2020 by Vodkaman

[DGagner]

19 hours ago, exx1976 said:

It must just be you.  1.1 > 1, therefore it sinks.

Especially if one takes into consideration that water actually only has a density of 1 when it's a 4 degrees celsuis.  Literally EVERY other possible temperature, it has lower density.  I actually changed the value in the spreadsheet to .996 instead of 1, just to make sure it floats when the water is very warm or very cold.

Gee, a wisecrack just because I pointed out that 0.1 g/cm3 might affect the result very little and you point out  you fudged the formula to take into account if the water is cold or warm. That means that with the formula, when the lure is built, you can be confident that it might float, be neutral, or sink when it's made depending on the time of year you fish it.

There are variables that affect the lure, sure. The 0.1 is one of them. But not much more than other things like the temperature or a fudge factor in a calculation.

[Vodkaman]

The purpose of this set of tools is to give the builder some indication of what they are going to end up with before cutting the shaped blank. It allows you a realistic look at the amount of ballast and prevents catastrophic errors of judgement.

I have been thorough, but there is still enough fudge to make an actual suspending lure fairly unlikely, but it should get you close. Paint, hole sizes, glues, fillers, etc. all have an effect on the final result. Experience builders will likely frill the holes before carving, this too will have an effect. Even so, a slow sinker prediction is still very possible.

It is amazing that even though some numbers look insignificant but they have a profound effect. The 0.1 density change is the difference between neutral and sinking at 10" per second. This is another useful aspect of the tool, it can teach the used the significance of certain parameters, it is a learning tool, you can gain experience without the pain.

I have added a few more features:

water density, useful for those that do sea fishing.

Drop-down for selecting standard material densities. These can also be added to buy the user.

Dave

Edited December 7, 2020 by Vodkaman

[exx1976]

12 hours ago, DGagner said:

Gee, a wisecrack just because I pointed out that 0.1 g/cm3 might affect the result very little and you point out  you fudged the formula to take into account if the water is cold or warm. That means that with the formula, when the lure is built, you can be confident that it might float, be neutral, or sink when it's made depending on the time of year you fish it.

There are variables that affect the lure, sure. The 0.1 is one of them. But not much more than other things like the temperature or a fudge factor in a calculation.

I had a big response typed up, but decided not to waste my time.  It's fairly clear to me that you don't understand the purpose of any of this, so it's just not worth it.

[DGagner]

3 hours ago, exx1976 said:

I had a big response typed up, but decided not to waste my time.  It's fairly clear to me that you don't understand the purpose of any of this, so it's just not worth it.

That's okay I understand. You're probably right. It must just be me. Sorry you wasted your time by typing up a big response. But I'm gllad you didn't sent it. I'll bet it was really good though. Sometimes just writing a letter and not sending it, but telling the person you gave them a piece of your mind without actually doing it can make you feel better. 

[lunkerhunter204]

Nice thread!

I'm brand new to lure making thanks to Covid.  I'm jumping right in making about 10 shallowraiders for musky. I've carved and sanded them, now cutting the bills, and getting ready to weigh the ballast. I'm curious as to where I can find this spreadsheet. I just signed up for this site and see I've got lots to learn! I've done the density part on my own already,  but this chart has so much more to offer in accuracy!

TIA

[exx1976]

29 minutes ago, lunkerhunter204 said:

Nice thread!

I'm brand new to lure making thanks to Covid.  I'm jumping right in making about 10 shallowraiders for musky. I've carved and sanded them, now cutting the bills, and getting ready to weigh the ballast. I'm curious as to where I can find this spreadsheet. I just signed up for this site and see I've got lots to learn! I've done the density part on my own already,  but this chart has so much more to offer in accuracy!

TIA

Before you go making 10 baits, you may want to spend a moment and review one of my recent threads, entitled "I'm an idiot".  Learn from my mistakes.  LOL

[lunkerhunter204]

5 minutes ago, exx1976 said:

Before you go making 10 baits, you may want to spend a moment and review one of my recent threads, entitled "I'm an idiot".  Learn from my mistakes.  LOL

Too late... lol.

And there's more than 10. We'll see how it goes!

Edited December 7, 2020 by lunkerhunter204

[Vodkaman]

30 minutes ago, lunkerhunter204 said:

Nice thread!

I'm brand new to lure making thanks to Covid.  I'm jumping right in making about 10 shallowraiders for musky. I've carved and sanded them, now cutting the bills, and getting ready to weigh the ballast. I'm curious as to where I can find this spreadsheet. I just signed up for this site and see I've got lots to learn! I've done the density part on my own already,  but this chart has so much more to offer in accuracy!

TIA

PM me your email address and I will send you a copy.

Dave

[exx1976]

4 minutes ago, lunkerhunter204 said:

Too late... lol

Not at all.  If you'd not read the thread, I'd encourage you to do so.  LOL  I went ALL the way - ballast, paint, epoxy, THE WORKS.

 

You've still got bare wood.  There's time to save yourself.