Heat curing epoxy...

[Shredd]

  Something I ran across to add to your knowledge of heat curing epoxy...

https://multimedia.3m.com/mws/media/1081388O/heat-curing-article.pdf?fn=Heat%20Curing%20Article.pdf

[Mad Max]

I'm going to shoot you down Shredd Good info too
Always use Manufactures recommendations.

Page 2
WOOD LAMINATING / BOWMAKING
https://www.smooth-on.com/tb/files/EA40.pdf

[Shredd]

  Sorry... I am not comprehending your post... I am not sure how you are consuming the info my post has to offer... To me it is general information... I did not see this as an exact guide or directions as to what temp you should cure your specific epoxy at... And they even talked about room temp curing... Of course all epoxies are different and I assume everyone knows that... To me it sounds like they got C and F mixed up... 200*C sounds way too high to me...

 I personally cure my bows at 110 to 120* under the gentle, even heat of an electric blanket... I feel it is easy on the forms and adequate enough for a full solid cure...  Reason forms warp is extreme and uneven heat on the form...

[Mad Max]

Page 2
WOOD LAMINATING / BOWMAKING??

[Kirkll]

The best part about using EA 40 is that it is pretty user friendly. When I first stared building bows I was pretty anal about exact mix proportions to the point of actually mixing by weight vs volume. There is a formula somewhere showing the weight ratio vs volume. It might be right on the can….

After building a lot of bows and going to using heat strips rather than a hot box, I started using a wee bit more part A to part B to increase the heat resistance of the finished product. Say about 5 parts A to 4 parts B seem to be perfect for me.

After mixing this stuff almost daily for years I got to the point where I can just eye ball the two amounts scooping it out of the can and into a mixing cup. Then I heat the epoxy for 15 seconds in a microwave it before mixing it…. Warming the epoxy makes mixing it thoroughly a lot easier…I do this with a paddle bit in a drill motor.

  As I’m mixing it I watch the color of the epoxy closely. It should be completely white after mixing for the best ratio of A to B and have a nice creamy texture.  If you have too much part B , it has a yellow tone to the color and the viscosity is different. It’s runny and It has a more translucent look to it too.   When that happens, I add a bit more of the part A.  If I get too much part A it gets sticky and the viscosity is much thicker.

I know all this doesn’t sound very scientific, but think of a good cook in the kitchen. After many many years your wife, or mom, or your grandma rarely measures anything while cooking, and their recipes are in their heads. Their cooking is excellent too….. their consistency comes with experience.

The other day I was mixing up a cup of smooth on for a limb lay up, and just went through the motions like I always do…. But something was off…. Looked like I had way too much part B and it had a yellow clear look to it. So I added more Part A without reheating it….. but something still looked off to it. It had a  Weird consistency and it just wasn’t the same…… So rather than take a chance, I just tossed the cup in the garbage and started again…. I didn’t trust it.   Next cup came out fine, so I proceeded.

This stuff is pretty user friendly guys…. But I’d highly recommend a bit more part A than part B on ratio for better heat resistance in the finish product and. Best strength.

Kirk

[kennym]

I do like Kirk (but not as often) , do not use too much hardener!!  Had a guy call once while I was at other job and say glue was no good.  When I got home I called him back and he said he had it figured out. He called Smoothon and had mixed extra hardener in to hurry it up. They told him it wouldn't set up properly that way. 

[Shredd]

Hmmm...  I wonder how many people mistakingly used more of the B instead of more of the A...    

I am sure it has happened...

  I use a hair more A also...

[kennym]

Doesn't sound reasonable to me, but they make the stuff, so I believe them...

[Kirkll]

Building bows successfully is all about consistency. Whether you use a hot box, or heat strips... Or cure out your bows with a different heat source, or just go 24 hours at room temp. As long as you do them all the same you will have consistent results.

The manufacturer states that you get better heat resistance and strength using a bit more resin to hardener rates on EA 40. But using 2:1  is just too much in my opinion. It's a nightmare to spread before it kicks off and gets too sticky. the 5:4 ratio works perfect for me. Smoooooooooth On. .... And.... heating the product while its cured also helps heat resistance.

I've used a lot of different types of epoxy for different projects. I worked with a LOT of west systems epoxy systems building boats, and some of that stuff is seriously hot stuff. I mean you mix up a cup and let it set in the cup and it will literally start smoking. You can feel the heat as it starts kicking off. That type of epoxy wouldn't work well with bow building at all just for the pot life alone.....

No sense reinventing the wheel here. EA 40 has been an industry standard  for quite a few years now. I for one don't plan on experimenting with different stuff when we already have a tried and true product.      Kirk

[Jeff tech]

The best part about using EA 40 is that it is pretty user friendly. When I first stared building bows I was pretty anal about exact mix proportions to the point of actually mixing by weight vs volume. There is a formula somewhere showing the weight ratio vs volume. It might be right on the can….

After building a lot of bows and going to using heat strips rather than a hot box, I started using a wee bit more part A to part B to increase the heat resistance of the finished product. Say about 5 parts A to 4 parts B seem to be perfect for me.

After mixing this stuff almost daily for years I got to the point where I can just eye ball the two amounts scooping it out of the can and into a mixing cup. Then I heat the epoxy for 15 seconds in a microwave it before mixing it…. Warming the epoxy makes mixing it thoroughly a lot easier…I do this with a paddle bit in a drill motor.

  As I’m mixing it I watch the color of the epoxy closely. It should be completely white after mixing for the best ratio of A to B and have a nice creamy texture.  If you have too much part B , it has a yellow tone to the color and the viscosity is different. It’s runny and It has a more translucent look to it too.   When that happens, I add a bit more of the part A.  If I get too much part A it gets sticky and the viscosity is much thicker.

I know all this doesn’t sound very scientific, but think of a good cook in the kitchen. After many many years your wife, or mom, or your grandma rarely measures anything while cooking, and their recipes are in their heads. Their cooking is excellent too….. their consistency comes with experience.

The other day I was mixing up a cup of smooth on for a limb lay up, and just went through the motions like I always do…. But something was off…. Looked like I had way too much part B and it had a yellow clear look to it. So I added more Part A without reheating it….. but something still looked off to it. It had a  Weird consistency and it just wasn’t the same…… So rather than take a chance, I just tossed the cup in the garbage and started again…. I didn’t trust it.   Next cup came out fine, so I proceeded.

This stuff is pretty user friendly guys…. But I’d highly recommend a bit more part A than part B on ratio for better heat resistance in the finish product and. Best strength.

Kirk

I always mix a little bit more part a than b never had a problem.

[Longcruise]

"I always mix a little bit more part a than b never had a problem."

That's exactly my strategy.  Guarantees there won't be too much hardener.  I just eyeball it but really should measure it.  Like Kirk says,  "consistency".

"I mean you mix up a cup and let it set in the cup and it will literally start smoking."

Talk about dejavu!

Quite a few years ago a guy in New York asked me to build a bow for him with some glue that he wanted to market to bowyers under license.   So I says yes and he sent me the glue.

It was West Systems but I don’t recall the designation.   I  was close to being finished with the layup and notice that the glue, in a red solo cup, was smoking.  I was done spreading on the lams and the glue that was spread wasn’t hot (mass??). 

So it  all went together.  By the time it was ready for the oven the cup had been melted down flat.    I put it in the oven even though it didn't seem to need any help with heat.

So I sent the bow off to the guy along with the advice that it wasn't suitable for bows.  About a month later it broke while his brother was stringing it.  He never responded to my inquiries about HOW he was stringing it. 😀

[Kirkll]

Great story bro!   

I had a potential customer ask me if i would do the same thing one time and use west system epoxy because he thought it was a superior product.... I said  , "No thank you, i'll pass on that one. I use EA 40 smooth on and have good results."   He was ok with that..... then he proceeded to tell me exactly how he wanted the limbs laid up, type of lam materials, taper rate, and the whole 9 yards..... I listened to him go on for a few minutes, then finally got a word in edge wise...... I  told him that i think the best plan is for him to build it himself, That he had some great ideas for a prototype, and politely declined to take his bow order.

I build custom bows, but i do not alter my limb designs and taper rates, or experiment with different core stock. Riser wood choice, veneers, overlay choices, and other bells and whistles lited on my website are fine. I've even done some custom wood carving and art work on some bows....But ya gotta draw a line somewhere....   There are some customers out there that you just cannot please no matter how good the product is... Thankfully i haven't ran into one of those in quite awhile, but they are out there...    Kirk

[OldRawhide42]

That is the fun part of doing this for a hoppy and not selling them. The only person I have got to keep happy is me .

[Kirkll]

I had to give up the hoppies years ago brother..... Oh wait... Those were poppies

[BigJim]

We weigh out the epoxy each and every time.. It's quick and easy to do so. We also mix right at 2 parts A to one part B.. We use gallons so buying extra gallons of the A is not an issue and thus doesn't cost us anymore to mix this way.
EA 40 is what I am speaking of here..
We also warm our epoxy before mixing. When weighing the glue proportions, that only leaves two possible mistakes.. Not mixing well enough, or not putting enough glue down.. I tell my guys "Mix until you think it is mixed well enough.. then mix longer!"
The EA40 does a fantastic job and is more than strong enough even without heat curing. Like in life, when someone experiences a failure in a glue up, they are eager to throw blame around and too often it is at the glue.. Heat curing or not, the glue will only hold to items if it has enough grip!
I have always maintained that the vast majority of the failures come from using wood that is too wet. Moisture content is the most confusing and least know part of what we do as bowyers. Epoxy does not like moisture and most delams blamed on oily woods is almost certainly moisture related instead. This can't be fixed by more or less hardener or cure temp!
BigJim

[Shredd]

  Jim... What kind of moisture content are you talking about to cause failure??

[BigJim]

I don't have those answers.. and its not all cookie cutter.. although 10% is considered standard for gluing, but then that is generic and doesn't consider the adhesive type. Lots of ways that a bond can fail. A bow being sent to a desert state would need to be dryer than max mc to start.
I think I understand how to estimate mc as well as most anyone yet am still often left scratching my head! 
BigJim

I

[Kirkll]

What is the formula for mixing by weight Jim?  It’s been so long that I’ve done it that way I can’t remember…. I do remember trashing out several food scales though.

I have used the gallon containers in the past. It was more cost effective to buy it that way when I was building more bows ….. but ….I had still had issues with contamination before I got through the stuff.  it seemed like I was wasting too much due to air exposure and saw dust contamination as I got to the bottom of the containers.

I’m curious how you dispense your smooth on without too much air exposure and waste?

It’s too bad that stuff isn’t packaged in grease gun cartridges. That would make pumping it possible with no air exposure until mixing time. I gotta admit the west systems epoxy is much easier to mix with a pump dispenser.

Kirk

[BigJim]

We mix 2 to one by weight... yes, it isn't a true two to one, but it's close. We go through a gallon of A every 3 weeks+-.
Bigjm

[mmattockx]

What is the formula for mixing by weight Jim? 

I have two of the pint cans sitting in front of me. Since the volume should be the same, the weight difference should be the weight ratio for a 1:1 mix. Part A has a weight of 1.12lb (0.51kg) and Part B has a weight of 0.94lb (0.43kg). That gives a weight ratio of roughly 5:4 to equal the 1:1 volume ratio. Jim mixing his at 2:1 by weight is getting the equivalent of a 1.6:1 volume mix.

It’s too bad that stuff isn’t packaged in grease gun cartridges.

Or a caulking gun cartridge. That would be really helpful for shelf life and easy dispensing, too bad they don't do one of those.


Mark