It seems like everything I’ve read recommends to tape on the outside and then pull it off after it’s vacuumed. What would be the cons of taping on the inside? With the right tape it shouldn’t add much weight nor sacrifice bond strength. Why bother with pulling the tape and having to sand off what you couldn’t get with your fingers?
As I understand it Cmphawaii, Oneula, and Benny tape the inside. Bert raised some concern about the adhessive in the tape failing down the road. Only time will tell if this is an issue or not. If you look in Benny’s vac bagging system thread at the bottom. There’s a tape that looks like it would hold a lot of promise. I bet it would work on the inside, but it is designed to be used on the outside and sanded off.
If the only problem would be the tape losing its grip on the balsa over time, couldn’t that be solved by using tape that allowed the resin to saturate it? That way the tape is only working to hold the pieces together while placing everything in the bag. Once the resin is in there and the tape is saturated, the resin would be doing all the work. Right?
I think I found the post you were referring to, for others that are interested: http://swaylocks.com/forum/gforum.cgi?post=193953
cmphawaii - “After reading the Bert Berger posts and talking to oneula, I have now started to inside tape(down side not out side) the pieces of with general purpose 1 inch masking tape(the cheapest you can find). This has shaved off probably 3 hours of total sanding time trying to get the expensive blue tape completely off.”
bert - "cmp , you just brought back horrible memories of detaping …
it was the worst job that no one wanted to do , especially if the tape got really resin soaked …
youd get blisters from trying to roll the tape off , and if you used a blade , could easily damage the wood …
so glad i found an easier way …
ive often thought about doing the method you mentioned in the past , but i noticed when the adhesive gets hot it lets go , so unless you had perforated tape or adhesive fibreglass tape , i felt uncomfortable with doing it that way …
even tho i never did try it just out of paranoia about something going wrong …
so id be curious to see how that technique worked out longterm …"
Any ideas on bert’s new technique? I’m thinking he’s laying out the skins w/ out tape, saturating the glass on a wet-out table, laying the glass on the skins, and then partially curing it (maybe in an autoclave?) before even attempting to put it on the core. But then again, I could be way off…
Thats the thread where the inside taping was brought up. To see the tape I’m talking about check out here http://www.swaylocks.com/forum/gforum.cgi?post=202703#202703 (by the way, it was waahoo who found the tape). I’m going to order some and give it a try.
Yeah, I actually saw that tape on veneersupplies.com a few weeks ago as I was looking at their wood stains. Looks like good stuff, though I’m not sure how absorbant it is.
You guys don’t understand…
The resin bleeds through the cheap tape and ends up on the surface of the balsa, just not as much as putting the tape on the outside.
If you want to learn the hard way just go ahead and put the tape on the outside ofthe balsa then you’ll have to sand through the epoxy just to get to the tape. Berts knows, CMP knows, beny knows and so do I… There’s a hell of a difference in time and effort spent cleaning up your lam with the cheap tape on the inside…
Sanding epoxy on soft wood is not a pleasant task if you don’t want to sand through the wood into the foam…
But you can learn for yourself we all did too.
Education by try-all and error is sometimes the best experience in the end-run…
That other tape waahoo found looks interesting but the idea is cheap tape… not veneer tape that’s more expensive than the blue tape we were using in the first place…
You option though…
What don’t we understand oneula? Your post seems to suggest
taping the inside, and that’s what we are suggesting in the posts
above. Sure the resin will bleed through the tape and onto the
surface of the balsa, but since you’re vac bagging it you won’t have
any major bumps to sand down (just a bunch of little ones if you’re
following bert’s advice – "have you seen that material that looks like
cling wrap with tiny holes
in it, that wont stick , then all youll have to sand off is small
nodes of excess resin …")
Losos
I have just vacuumed the 3mm balsa skins onto my latest board, having read all the posts on this subject, and done a test on taping on the inside, and having the edges peel up slightly before lamming the outside skin, I tried the following with much success:
1 Lay out your balsa planks (mine were 1000mm x 100mm x 3mm) with the joints nicely staggered, use a melamine board or plastic sheet on a table.
2 Glue your end grain butt joints with 5 minute polyeurethane glue (gorilla glue or titebond), using blue tape to keep joins compressed and weights where needed, make sure plank runs are as straight as possible.
3 Clean up edges, remove tape (easy) then glue up plank edge joins in same way, do make sure edges are nice and straight, slight wavers can be pulled together with tape.
You now have a complete panel of balsa that will vac down nicely, no tape to clean up, will conform to your deck or bottom shape and the major plus is that epoxy leakage to the outside of the balsa is kept to a minimum and the polyeurethane id soft and very easy to clean up.
Do give this a go, you will not regret it.
Good luck
Mark
Losos
Pretty simple, but thought these photos may help
Mark
hm , collective knowledge …
still plenty more problems to come , but so far so good …
regards
BERT
My first one, I used blue tape on the outside. Most of it peeled off, but for the bits that didn’t, sanding was a headache.
My second one, I used white cotton athletic tape on the inside. I am certain the epoxy can saturate that tape.
The map with tape (which will go onto the foam side):
And a break test of a trial piece. Notice how the balsa with 4oz glass & epoxy will bend without breaking even well after the EPS has failed. That bend has taped joints going parallel to the bend. The only way to even get the foam to fail was to bridge it between bricks and lean on it with my elbow. I thought it was interesting that it did not fail at a taped joint, but between 2 of them. This test was with glass under 1/8" balsa only, none on top. The strength of the sandwich construction is really amazing.
I was originally thinking about trying it your but I though it would fall apart under vacuum. I’m really glad that I’m wrong. I think that this is the way I’ll go. Maybe I’ll try the vener tape with the gorilla glue. Thanks!
They also sell a 3/4 inch tape without holes that can definately be used under the laminant. Maybe using the gorilla glue then the tape would stop almost all of the leakage.
You’re right Losos
didn’t mean to insinuate anything negative…
But all these pieces do add to the cost and time of production though.
the veneer tape, the bleed through wrap, the gorilla glue are all extra necessary/un-necessary costs
CMP just uses a razor and a sheet of of sand paper to clean up his butt-ends and his cheap white paper masking tape is about half the cost of the 14 day blue stuff. I think he can cut and tape togethor an uncomplicated lam in about 15-20 minutes prepare and brush on his resin in another 5-10 minutes and put it all togethor in another 15 minutes using tape, a taped release bag and sealing it in his vacuum bag with breather cloth.
My thought as to what Bert is warning us about here, is that by not allowing the extra resin to bleed thru to the surface, you’re going to get resin pooling underneath the lam which will make the board weaker in the long run. And in some cases like what happened to CMP once before is you can actually build up enough heat from the resin curing process to actually melt the foam underneath if the pooling gets too thick under the wood lam. If your putting glass under the wood you definitely do not want any kind of pooling of resin between the foam, glass and wood. So somehow supporting bleed thru seems to be to be the best option unless you have your resin calculations and measurements down to a science like Bert’s suggested. The perforated bleed wrap is a good idea but an expensive onetime use option unless you can find a cheap source. Last I saw it was $6/yd at ACP.
The vacumming pro’s probably use the bleed thru peel ply wrap to keep the surface clean like Losos indicated.
I be interested to hear more on the bleed thru versus no bleed thru methods as I have some cheap 4’x8’ sheets of 1/8 luan door ply i’d like to it give a go with instead of the expensive balsa sheets. CMP just did one on a tow-in board with glass underneath and didn’t like the look of it…
Oneula basically nailed it on all the benefits of taping inside. On the bottom wood lams you essentially eliminate all outside taping. The top side I still tape some outside critical areas and put full horizontal tape outside about every foot of lam to ensure tight seams on rail wrap. The tape after vacuum pull comes off very easy now.
Time savings…you say big deal, I am only making 1 board this year. The big deal is you can now go super thin veneer because the fear of sanding thourgh your pride and joy is elemenated. Since Jan 05, I have been using 1/16" versus 3/32" sheets.
Thinner is easier to bend, cut, wrap and be sealed with the expoxy from the inside out.
Concerns of tape failing and becoming a delam? I haven’t experienced it yet but we only have 60+ pulls with this tecnique. But this concern was thought through. Using 1"(not 1 1/2" or 2" or 3") wide cheapo paper thin crappy brand tape. Worse case senario with properly laid out wood, you have a 75-85% wood to foam only adhesion.
If you add a layer of 2oz cloth betweeen the foam and wood…case closed. No delams.
Seams coming apart during vacuum. Happens less than before because we are using thinner, eaisier to bend wood. The problem areas were reduced with thinner wood.
So compared to my frist laminated wood board in 1985. 1-3 blanks at a time of 3’32" thick 4"x48" balsa sheet to foam using elmers wood glue, books to keep down. 1 board every 3-4 weeks if I didn’t need to use the books for college. Things are better.
Vacuum tables versus vacuum racks. We use vacuum racks. It is an ajustable shaping rack with a vacuum set up below. In ways, this is a limiting factor, because I would imagine with tables and rocker forms you could acheive what we do with inside taping and other adjustments of our racks. Advantage for me is better use of space.
Using door skins. They are too heavy for surfboards but tow boards they will work.
I put the top on it yesterday with straight up thick balsa and it’s looking good and getting heavy. My only problem is that I can’t figure out where to put the door bell on this thing.
Thanks, cheap 1" it is.
What are the vacuum racks used for exactly? Any chance of some pics? This is the first time I’ve heard them mentioned.
I’m just wondering why everyone uses butt joints for joining the individual planks in a balsa skin.
i realize it’s easier, but…
OK,
Maybe I haven’t completely thought this through.
But, I am willing to accept that balsa is a good choice as a skin material.
Compared to divinicell, it has better strength, modulus and allowable strain.
Which must be a good (i.e. mandatory) consideration.
Maybe, I’m overstating this, but if the deck and bottom skins are truly part of a sandwich construction they must be allowed to “talk” to each other through the core and rails or stringers. That said, the sandwich skins will be see virtually no sheer stress as that component will be a maximum along the neutral axis. So…. My point should be coming shortly.
So the EPS core and balsa rails must be dealing with the bulk of the sheer and I’m pretty sure the EPS isn’t contributing a whole lot (yes/no?).
And the skins are now dedicated Tension/Compresion elements.
Additionally, if the balsa skins are such an asset (lots of spring and pop) it would make sense to try and maximize all of the properties that make it so appealing.
Even though the modulus of the Balsa is much less than the glass, the extra volume of balsa means that it is certainly carrying a significant percentage of the skin loads.
Finally, a question…
What is the net modulus and strength of balsa planks assembled with butt joints?
You folks must think they are weaker, ‘cause you stagger the joints.
Staggered makes sense to better distribute the loads. But if the joints are weaker (or have lower modulus) it would appear that you may be sacrificing a lot of potentially useful cross-section. (especially right below your big butt, where your feet are dancing on your favorite board) Just because the joints don’t break, I’m not so sure we aren’t sacrificing something that may make a good thing better.
Just a thought.
-bill
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Quote:
skins are now dedicated Tension/Compresion elements
This is kind of how I’m starting to view them. However, I don’t know if I’m correct or not . Are you suggesting that uninterupted skins would be better? I don’t know but Ben(Benny) tested his core/skins and they didn’t break along the seam.
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One,
If I was tapeing on the inside I think I might try the cheap fiber mesh tape that drywallers use for joints and cracks.