Vacuum molding

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Vacuum molding

Post by simso » Sat Sep 02, 2017 2:11 pm

After Rods recent build thread start, I decided I would start a new topic rather than destroy his one with constant questions.

Does anyone know the art of vacuum forming shapes with wood.

Specifically archtops, I want to do a Benedetto archtop, I currently do my own laminations but have never done a moulded lamination.

To date all archtops I have done have been carved.

After any links or advice

Here is my vacuum clamping machine, I have two of these units, one is permanently setup to sublimate, this one was purely for guitar and brace work.

It has two work plates, each with their own vacuum source and clamping, there is also provision for adding a heat source, not that I have needed one yet.


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Re: Vacuum molding

Post by kiwigeo » Sat Sep 02, 2017 2:17 pm

Can you do toasties on that thing?
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Re: Vacuum molding

Post by blackalex1952 » Sat Sep 02, 2017 4:25 pm

Can you do toasties on that thing?

Only if you edge seal the sandwich with a strong easily removed sandwich masking tape and a a rapid cure catalyst in the cheese.
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Re: Vacuum molding

Post by Mike Thomas » Sat Sep 02, 2017 5:59 pm

Laminated Back.JPG
Vacuum Bagging Back.JPG
Fibreglass Back Mould.JPG
The photos show how I laminated a Selmer/ Maccaferri back. I made an internal fibreglass mould on an MDF backing. Three plies of .8mm veneer (Blackwood/Poplar/Mahogany) were glued together using West Systems Epoxy in a vacuum press. Worked well, but may be a bit more work with a typical archtop's more complex geometry.
Last edited by Mike Thomas on Sat Sep 02, 2017 6:14 pm, edited 1 time in total.
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Re: Vacuum molding

Post by rocket » Sat Sep 02, 2017 6:03 pm

How does it go with no vacuum reservoir tank?

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Re: Vacuum molding

Post by simso » Sat Sep 02, 2017 6:06 pm

That is pretty good, did you need to heat or soak the wood prior to layering the sheets up to make it conform to the mold, that's where I am overthinking it at the momment.

I'm thinking and it's likely wrong, soaking a .8mm sheet in warm water, layering it onto the mold, vacuum clamping it, and putting a heat lamp above to help set it to that shape, then make a seperate one, do that five or six times and then glue all of them together and pull them down

As per rods comment, i find reservoirs great for keeping vac pump noise down, reservoirs are five bucks from the local tip, just grab a small dead air compressor and take the tank off, works fantastic.

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Last edited by simso on Sat Sep 02, 2017 6:11 pm, edited 1 time in total.
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Re: Vacuum molding

Post by simso » Sat Sep 02, 2017 6:11 pm

kiwigeo wrote:
Sat Sep 02, 2017 2:17 pm
Can you do toasties on that thing?
The one with the heat lamps still fitted, you betcha, that thing gets so hot you cannot touch the vacuum sheets when it come out from under the lamps, you have to wear gloves otherwise you will burn yourself

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Re: Vacuum molding

Post by blackalex1952 » Sat Sep 02, 2017 7:23 pm

There are issues with vacuum laminating that I have been faced with.
The first issue is getting a good seal, depends on your set up. My set up is home built.
Then there is the issue of pump cycling. A vacuum reservoir is important. The time taken for glue to set is directly proportional to the cost of running the pump, ie power consumption and wear and tear on a pump. If the system is not well sealed, the pump motor has to cycle on and off which means that, for an electric motor, the start cycle is heavy on current. Also a pump which is running continuously may get hot so a pump which will handle mishaps with the forming of the vacuum might be important, given that for long glue cure times the set up may be left unsupervised.
Water based glue and glues which need air to cure can be a problem in a vacuum eg hide glue or Titebond. There is also the issue of gel time relative to getting the laminates bagged up with HHG, but a heat press system rather than a bagging system might make this feasible.I've not experimented with vacuum pressing Titebond on guitars but have had moderate success with HHG using lots of absorbent paper included in the vacuum bag or press. In a high vacuum, water will boil at room temperature. I first used a vacuum press when picture framing. I used PVA glue rolled on to MDF to mount prints- the prints were vacuumed then immediately removed from the vacuum press and dried normally in the air. I suspect that for hide glue, as it won't set very well in a vacuum, removing the laminated timber veneers from the vacuum for air drying is a possibility I haven't tried. At the gell stage there might be enough of a bond to deal with the tension in the laminates which might cause them to debond before the glue fully sets. This has worked for laminated timber scratch plates that I have made with HHG.
As for laminating resins, temperature effects how fast they will cure, so in cold weather some heat helps. I use bathroom heat lamps to speed the resin cure (more electricity expense). Simso's press can apply heat, I assume variable temperature control so cure times should be reduced. Worth understanding the manufacturers data for ideal temperatures. Decorative birds eye veneers and porous veneers can be laminated with epoxy using the breather fabric on the back of the laminate and plastic sheet that the glue won't adhere to on the birds eye face. If successful, grain filling is unnecessary.
The information on bagging film, bleeder fabric and release fabrics etc are available on the internet. I have successfully used shade cloth as a breather.
I don't have enough experience with vacuum laminating large plates and guitar sides using HHG as compared to laminating with epoxy as far as the difference tonally goes. Epoxy glues are toxic and environmentally not so good, I hope to eventually work out ways to laminate backs and sides with hide glue.
I have laminated both backs and sides for Selmer style builds, as Mike Thomas has done, and also Craig Bumgarner. Craig posted a shot of his set up with a laminated arched back, complete with recurve somewhere on this forum but I can't find it now.
There are several ways to form laminated shapes. One is by having the shape placed on a mold which is within the vacuum bag or whatever (eg an arched back plate). Another way is to place a laminate inside a vacuum bag, the vacuum formed, then the bag is clamped on to a mold which is not within the bag (eg. guitar sides)
Cheers! Ross
Last edited by blackalex1952 on Sat Sep 02, 2017 7:35 pm, edited 1 time in total.
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Re: Vacuum molding

Post by blackalex1952 » Sat Sep 02, 2017 7:27 pm

reservoirs are five bucks from the local tip, just grab a small dead air compressor and take the tank off, works fantastic.
Mine was free, same source. One also needs a non return valve.
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Re: Vacuum molding

Post by simso » Sat Sep 02, 2017 7:38 pm

All good info,

I might next week, machine myself up a top plate to muck around with, I will gel seal and cure it so water and so forth won't affect it, then start experimenting, it's like everything, have to start somewhere.

This commercial sublimation unit is pretty good, the vacuum when set will hold upwards of an hr before the pump re-cycles, heavy duty rubber sheets have been used, the border of the bottom plate is a type of plastic with ribs in it, I'm assuming the rubber conforming over this is what gives the good seal.

The base of the unit has stainless steel sheet with lots of holes to allow air draw. When I purchased the one for sublimating, I thought even back then what a great machine to convert into a vacuum jig.

We will see how it goes for forming.

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Re: Vacuum molding

Post by Mike Thomas » Sat Sep 02, 2017 8:22 pm

I had no problems laminating backs (and sides) using .8mm veneer, dry, without any preforming. The recurve on an archtop may present problems, however. If I were to try it, I would start with an inside mould which also modelled the recurve. In order to get the vacuum to press the veneer stack into the recurve, it may be worth trying a hard(ish) shallow rubber strip of the right profile along the recurve. The aim would be to have the bag under vacuum in contact with the wood and the rubber strip, with no gaps leaving an unsupported bag.

Yes, a pump with a tank would be much better . But the little Gast pump is what I had access to at the time, and it worked well. I did speed up the epoxy drying process by putting the bag under an electric blanket (cheap single bed one from K Mart). The right elevated drying temperature also has a positive effect on the epoxy's mechanical properties.
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Re: Vacuum molding

Post by Crafty Fox » Sat Sep 02, 2017 8:33 pm

My only experience with vacuum moulding was when I did furniture design at Leederville TAFE many years ago...... From memory I used a formaldehyde glue and the press was heated and left running overnight. Worked a treat on a compound chair back.

Graham Hawkes was using one recently, to form arched backs on his classical guitars. He lives over in Woodbridge, near Midland. He hosts the "Plucked Strings" programme on RTR Radio, late Sunday afternoons. Nice bloke and I'm sure he'd be happy to share his knowledge.
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Re: Vacuum molding

Post by Allen » Sun Sep 03, 2017 5:28 am

simso wrote:
Sat Sep 02, 2017 7:38 pm
This commercial sublimation unit is pretty good, the vacuum when set will hold upwards of an hr before the pump re-cycles, heavy duty rubber sheets have been used, the border of the bottom plate is a type of plastic with ribs in it, I'm assuming the rubber conforming over this is what gives the good seal.

The base of the unit has stainless steel sheet with lots of holes to allow air draw. When I purchased the one for sublimating, I thought even back then what a great machine to convert into a vacuum jig.
Would you post some more detail photo's of this Steve. I'm planning on building a press, and looking for ideas on getting a good seal. The home made one I built 10 years ago is only mediocre at best.
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Re: Vacuum molding

Post by routout » Sun Sep 03, 2017 10:03 am

My take on Vac molding these was there is very little room for error 0.8 leaves no real margin. If you have a slight bump ect you cant repair.
John ,of way too many things to do.

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Re: Vacuum molding

Post by simso » Sun Sep 03, 2017 12:01 pm

Would you post some more detail photo's of this Steve. I'm planning on building a press, and looking for ideas on getting a good seal. The home made one I built 10 years ago is only mediocre at best.
Will take some photos tomorrow for you

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Re: Vacuum molding

Post by blackalex1952 » Sun Sep 03, 2017 2:17 pm

I have had good results with a recurve using 0.6 mm veneers with a 1.2 mm mahogany core. The veneers were maple on the outside and pear wood on the inside. I have even done birds eye maple. On the birds eye plate I had a couple of blisters in the veneer, so I repaired them by pricking the blister with a fine needle and blasted some superglue into the void. The pin prick was hardly visible, but didn't end up using that back for other reasons. I used a convex hand carved mold for the recurve plate, but have decided down the track to make the recurve more prominent- I just have to find time to make a new mold. I also now take the precaution of cleaning the veneers with acetone prior to assembly. Initially I used urea formaldehyde, but the West epoxy is cheaper in the long run and the glue set time can be somewhat controlled with the different speed hardeners available. As I pointed out in my previous post, Craig Bumgarner has a nice photo he posted on this forum, I believe. His backs look fantastic, on some he has a rather prominent and attractive recurve modelled on an original Antoine Di Mauro "heart" shaped guitar. The heart shape refers to the shape of the soundhole. Many of the Gypsy jazz and European archtops had laminarted backs and sides with strong arching and deep recurves. Probably all pressed in heated plates using HHG. So the issues with the recurve don't seem to be of great consequence for vacuum forming in my opinion. Hopefully he will chime in. His Corazon model is worth checking out. Incidentally, in my limited interaction with Craig via this forum and via emails, I have found him to be a kind, generous, intelligent and creative person. He has not hesitated to share his thoughts and experience as a guitar maker with me. https://craigbumgarner.wordpress.com/ga ... uary-2-15/
Cheers! Ross
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Re: Vacuum molding

Post by simso » Mon Sep 04, 2017 2:09 pm

Up close
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Re: Vacuum molding

Post by Allen » Mon Sep 04, 2017 3:39 pm

So is it the silicon rubber membrane that is making contact and the seal on that big sausage, or is it the metal frame?
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Re: Vacuum molding

Post by simso » Mon Sep 04, 2017 5:15 pm

Yep, the rubber sucking down over the sausage shaped ribbed plastic is the seal, the steel is just a sheet they have mounted / glued the hard plastic onto, it can be lifted out, the vacuum hose is connected to the underside

You can also see that the base steel is painted with a rough surface, allows the vacuum to pull down nicely as per the first photo.

I also stand corrected re it runs for an hr without rebooting, I used it this morning, it powered on, and created the initial tank vacuum, 2 minutes, then I used it to suck down onto the spanner and it sat there for 9 minutes before the pump cycled on again, the cycle was literally 15 seconds.



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Re: Vacuum molding

Post by Craig Bumgarner » Wed Sep 06, 2017 12:54 am

As Ross says, I've been vacuum molding backs for my gypsy guitars, both spherical and violin back shaped (I have a hard time saying arch-top back :-) Made the violin back shaped molds by gluing medium density PVC foam sheet to a 3/4" MDF board and carved out the shape in the foam, tapered into the MDF on the edges to insure it is even and in plane all around.

The tricky part is the compound curves near the edges. If the recurve is dramatic, there is a tendency for the the veneers to bunch up along the edges and in extreme cases may stand the veneer up on edge and crack. I have two molds, one with more recurve than the other. With the one with more recurve, I mold all but the outer layer first. I mold it dry to see what might happen and cut darts in the edges and remove a little wood in the trouble areas. Even so, I might get some bumps in it, but no worries, these can be smoothed out and then the final layer molded on. Single layers are less trouble than multiple layers. As the vacuum is first being drawn, you can sometimes smooth out bumps along the edges if they start to form. On my mold with less recurve, I usually have little trouble and mold all the layers at once. Sometimes a small bump can be clamped down like in the picture below.

I use a vinyl, reusable vacuum bag, plastic bleeder sheet, a small vacuum pump with no reserve tank (see pic) and epoxy glue (WEST brand, standard). Much prefer epoxy in that it has a longer working time and cures well in a vacuum. All the water based glues I tried hydrated the wood too much and cause warping and then shrinkage after finishing.

Epoxy will bleed through the wood, but that is okay because I use epoxy to grain fill and it blends in nicely. I use 30 grams of mixed epoxy per interface, so a three layer lam would use about 60 grams glue. I use 1mm poplar for the internal layer(s) and .5mm for the inner and out. Usually mahogany for the inner and whatever is cosmetically pleasing for the outer. In spite of worries about how thin the outer layer is, i have never gone through it in 40 guitars.

If your mold is heated, I'd be tempted to try hide glue. The French builders in the mid 20th century all laminated backs and sides, some with recurve. I'm told they did this using hide glue and a large pile of hot sand as a press. When the sand cooled off, the glue would set up.
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Re: Vacuum molding

Post by Craig Bumgarner » Wed Sep 06, 2017 1:34 am

BTW, I typically get 23 inches of vacuum with my set up, far from perfect, but more than adequate. I get excellent glue penetration, not voids and good reproduction of the mold shape even in the recurves.
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Re: Vacuum molding

Post by rocket » Wed Sep 06, 2017 8:27 am

Any experience with Nomex Craig?

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Re: Vacuum molding

Post by simso » Wed Sep 06, 2017 9:56 am

Very generous of you Craig.

That will help a lot, I am currently ordering some veneer in, I have lots of flame maple veneer sheets, but it would be kind of a waste to cross laminate them.

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Re: Vacuum molding

Post by Craig Bumgarner » Thu Sep 07, 2017 1:33 am

No experience with Nomex to date, but have a piece big enough for a back I'd like to try some time.

I only use the fancy veneers on the outside. With the Selmer guitar types I build, poplar for the middle plies and mahogany for show piece on the inside is standard. Both are light weight, glue well and relatively inexpensive. I can get poplar in thicker veneer which is helpful in dialing in the number of laminates and stiffness. More layers makes a stiff laminate, but also heavy because of the extra glue. Keeping the layers to three and varying thickness with the poplar internal ply yields similar stiffness, less weight. Some builders use poplar on the inside show side, but mahogany is a bit more classy looking. I've been able to find sheets of both that are wide enough to make a whole layer without piecing it together. I sometimes use full width birdseye maple for the outside show layer, but for others woods, I bookmatch and join the veneers simulating a solid wood back. Edge gluing veneers is a little tricky, I use tape and Titebond. This usually holds the two halves together long enough to mold. Once molded, they are forever.
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Re: Vacuum molding

Post by Craig Bumgarner » Thu Sep 07, 2017 5:50 am

Oh, another thing. I've found short nap 3" foam rollers work best for applying epoxy to the veneers. i use Wooster R039 trim rollers or WEST brand foam roller cover cut in half. This applies a thin, but uniform layer of glue. I wet out both faces of an interface to insure against dry spots. I have used other means like disposable brushes and toothed squeegees but rollers are much better for even distribution in a thin layer and faster too. If you are not using epoxy, however, my foam rollers comments may not apply.
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