Correct hand tool for jointing?

[Mikey R]

Hi everyone,

Im sure this question has been covered many times here over the years, but a quick search didnt bring anything up.

I was always taught that you joint with a plane that is long enough for the board you are working on.

So I was chatting with a guy called Jon last night, a professional electric guitar builder, and we got onto the subject of jointing laminates of maple (~22mm) and dense exotics (~6mm) to make a guitar neck.

Anyway, Jon says that he uses machines to joint his neck laminates - which is fair enough, he needs to make a living and hand tools would be slow for this. But then he says that he uses a drum sander for the 6mm laminates.

He says that using sandpaper creates a better surface for gluing than a planer, as the tiny scratches increases the glue area, allows the glue to sink further into the wood and makes a surface similar to a 2d finger joint.

Now, this goes against everything Ive ever been taught - you joint with a hand plane and NEVER with sandpaper on a sanding caul. EVER. But Jon is an increadibly accomplished craftsman and makes truely amazing instruments with invisible glue lines.

So, the first question is, whats the modern wisdom when it comes to preparing a glue surface for both strength and appearance. The second is, does it matter?

 

[Calpol]

We always got told to plane it as well and that was the end of it.

Although you do get toothed blades for preparing surfaces for veneer and whatnot so you never know... :?

 

[bugbear]

So, the first question is, whats the modern wisdom when it comes to preparing a glue surface for both strength and appearance. The second is, does it matter?

To the best of my knowledge, a FRESHLY hand planed surface gives the best results.

However, modern glues are so extraordinary that you don't need the best results, or anything close.

BugBear

 

[Mikey R]

To the best of my knowledge, a FRESHLY hand planed surface gives the best results.

Cheers BugBear - Does the surface deteriorate then?

However, modern glues are so extraordinary that you don't need the best results, or anything close.

Im using Titebond yellow glue, which Ive found to be fairly strong even on some of my fairly sloppy joinery (not that I do any other kind )

So I guess if the bond is strong enough for the stress it will see in its working life, then cosmetics are the most important. What gives a better glue line? a fuzzy edge with sandpaper or a crisp edge with a plane?

Im still leaning towards using a plane but Im interested in other ideas.

 

[newt]

Bugbear's comments are spot on

 

[woodbloke]

Bugbear's comments are spot on

A freshly handplaned sufrace ought to give the best reslults - Rob

 

[dunbarhamlin]

I usually plane or scrape drum sanded components before glue up, though the surface straight off of the sander can be very good and almost as accurate as a plane, provided it is properly loaded, callibrated and maintained. (Though of course just like a thicknesser, it won't remove wind, and can introduce snipe.)

 

[wizer]

80 grit freehand will do it

 

[Mikey R]

...though the surface straight off of the sander can be very good and almost as accurate as a plane, provided it is properly loaded, callibrated and maintained...

80 grit freehand will do it

Since Im using hand tools and not machines, I suppose my question should be - should I continue with my friendly no 7 jointer or should I make myself a 22" x 2 3/8" sanding caul from MDF with velcro and totes?

Hmm, planes are fun, dust isnt!

 

[bugbear]

People may be wondering where my confident claims come from.

The people who are most interested in wood bond strength (apart from wood scientists) are people making laminated bows. The information I present is from them, derived from careful experiment.

The wood scientists found the same thing. IIRC Jeff Gorman's site used to have this information before h took it down for copyright and re-use reasons.

This is one of the rare, semi-famous cases where the established wisdom of "the old guys" was found to be (simply) wrong.

BugBear

 

[Mikey R]

The people who are most interested in wood bond strength (apart from wood scientists) are people making laminated bows. The information I present is from them, derived from careful experiment.

Hi BugBear,

What kind of glue where they using? Epoxy or PVA types?

 

[wizer]

80 grit freehand will do it

Since Im using hand tools and not machines, I suppose my question should be - should I continue with my friendly no 7 jointer or should I make myself a 22" x 2 3/8" sanding caul from MDF with velcro and totes?

Hmm, planes are fun, dust isnt!

Sorry Mikey, my poor attempt at sarcasm....

 

[BradNaylor]

But then he says that he uses a drum sander for the 6mm laminates.

He says that using sandpaper creates a better surface for gluing than a planer, as the tiny scratches increases the glue area, allows the glue to sink further into the wood and makes a surface similar to a 2d finger joint.

There are a couple of issues here.

A 6mm strip of wood is basically a veneer, and hand planing it to an accurate and even thickness presents serious difficulties. A drum sander with say a 120 grit belt on it will produce nigh-on perfect results time after time.

I finish all my lippings for furniture on my drum sander; I normally make them 10mm thick and simlpy glue them with PVA onto the sawn edges of veneered MDF. I do many of these every day of my working life and have yet to have a single joint fail or have an insightly glue line.

Hand planes have their place, even in my mechanised workshop, but there is simply no point in hand planing the glue face of a lipping or laminate.

If you guys were making laminated rails for curved doors would you hand plane each strip before putting them on a former?

A drum sander is a far better solution for this application.

The thing about the scratched surface making for a better bond is a red herring, however. Smooth surfaces are better with PVA. The surface left by 120 grit on a dum sander is plenty smooth enough though.

Cheers
Brad

 

[Karl]

there is simply no point in hand planing the glue face of a lipping or laminate.

Brad - but what do you do if you don't have a drum sander????

Cheers

Karl (who is secretly saving up for a drum sander :lol: )

 

[newt]

No drum sander only option is to use a plane. I can understand for production work planing would be a non starter.

 

[Night Train]

Adhesives are supposed to be a chemical bond and not a mechanical one so a smooth surface would provide the better bond. This happens because the two surfaces of the wood are closer together and the adhesive is down to molecular or atomic thickness bonding the two wood surfaces together. If this joint is tested to distruction the joint should fail in the body of the wood.
An indication of the strength of a 'bond' with a smooth surface is a drop of water between two plates of glass. The air pressure will squeeze out the water onto a thin film and hold the glass together but then, at the atomic level, the water atoms are cohesively bonding with the glass atoms to make the joint hold tighter still.
This is what happens in a very well prepaired and planed wood joint as the adhesive atoms produce a cohesive bond at the atomic level with the surface of the wood on both sides of the adhesive.

If the surface is rough then the bond becomes weak due to a cohesive bond between the adhesive and the wood, then a thickness of adhesive which is in itself weak, followed by another cohesive bond between adhesive and wood. If this joint was tested to distruction then the joint is more likely to fail in the adhesive thickness.

This, of course does depend on correct cramping pressure during curing and the relative physical strengths of the wood and the adhesive.

Modern adhesive are very strong though, even with gaps.


My personal preference is to avoid modern gap filling adhesives and to have a planed mirror surface for jointing where ever it is practical and worthwhile. Some of my students use gap fillers as 'they fill gaps'. I encourage then not to have gaps in the first place.
I have also found that sometimes if there is uneven or insufficient cramping then a gap filling adhesive can sometimes expand in the gap causing a rippling surface especially when laying up laminations.

 

[newt]

Night train, very useful description why smooth is better than rough

 

[Night Train]

It's what we teach at college in the HND tools and technology module. I'm surprised I remembered it after all this time. I may well be teaching it next term. :lol:

 

[Setch]

I agree with everything above. In addition,the reason a freshly planed or scraped surface is best is that it exposes fresh, uncontaminated timber, which is most receptive to gluing. The longer you leave between jint prep and glue up, the more time there is for oxidisation and other contamination of the surfaces to occour.

 

[bugbear]

The people who are most interested in wood bond strength (apart from wood scientists) are people making laminated bows. The information I present is from them, derived from careful experiment.

Hi BugBear,

What kind of glue where they using? Epoxy or PVA types?

Multiple types, including hide glue. Surface prep is the same in all cases.

The surface needs to be fresh because it oxidises (quite quickly IIRC).

BugBear