Too smooth for gluing?

[JonathanJung]

Is it possible for a cut to be too polished to accept glue?

This is in relation to my other thread, about blades for precise crosscuts.

My Tenryu blade on the miter saw cuts so smooth it is shiny. I've always wondered, since glues need to absorb into the wood fibres, can a surface be cut too well?

(Yes I know there's gobs of tearout...not every blade does everything perfectly...that is a separate dilemma)

[attachimg=1]

 

[ChuckM]

My handplanes including the shooting plane give very fine edges and surfaces. Glue works well on them.

 

[chrisrosenb]

If you are asking about gluing end grain. End grain does not glue well, rough or smooth.

 

[Svar]

No. As already mentioned when gluing panels you use plane or jointer to get the surface perfectly smooth.
For end grain I'd also prefer perfectly clean cut to open vessels for glue to go in.
Perhaps if you burnish the surface with very fine sanding, you might decrease adhesion because pores will be packed with dust.

 

[Birdhunter]

Looking at the blowout and the cut surface, I’d say the blade is burnishing the surface. If the surface is burnished, it will not glue well.

I’ve never gotten that much blowout from any saw blade. Something is not right.

 

[usernumber1]

that looks horrible.

 

[kevinculle]

End grain surfaces are irrelevant in a glue up and the surface finish on them is immaterial.  No reliable joint design will use end grain as a loaded member in a joint.  Long grain to long grain surfaces as are created in mortise and tenon, dovetail and other joint styles are where attachment strength is created.  Since plywood plies alternate the direction of grain orientation the "end grain" of a plywood piece is roughly 50% long grain and can provide a useful attachment surface.  The best preparation of long grain to long grain surfaces provides a close mating of pieces to be glued together with minimal gaps and this is best achieved with smooth surfaces.

 

[Packard]

When I was a picture framer I had a Lion Miter Trimmer (they are out of business now).  The trimmer used a razor sharp knife to slice slivers of the miter off after sawing.  It was a corrective device, if a miter was not tight or if the length of the piece was off by a few thousandths. 

The slices were so thin that you could see light through them and the surface was smooth as glass. Because of the smoothness, the joint would hold less glue. The key to this was to make sure that there was adequate squeezeout of glue at the joint.

I still have the miter trimmer (and the sliding table miter saw).  I will try to find time to make sample joints this weekend and compare the strength of a standard sawn miter and a miter with mirror-smooth joining surfaces. 

I've done tests like this in the past so I know how to do this.  I can test in increments of 5 pounds.  The results should be interesting.

 

[ChuckM]

If we're talking about endgrain to endgrain joints, no glue alone will hold a joint together that's subject to a lot of stress. Glue sizing will help, but for a structurally strong joint, some kind of physical fasteners must be used be it dominoes, dowels, brads, etc.

 

[JonathanJung]

Why is everyone going on about the blowout? I clearly said that I was aware of it, and my post clearly says that the info I'm after has nothing to do with blowout. But since ya'll are bringing it up, perhaps you can be helpful and provide suggestions for a  different blade, around 100t, that has negative hook angle, mid to full kerf, without blowout under or behind the miter cut?

Also, yes, my picture shows endgrain, but if you read my post, I never specified the type of cut. I was asking about the smoothness of any cuts in general affecting gluing. The picture was only for reference for the smoothness of cuts I'm getting, as an example.

When I was a picture framer I had a Lion Miter Trimmer (they are out of business now).  The trimmer used a razor sharp knife to slice slivers of the miter off after sawing.  It was a corrective device, if a miter was not tight or if the length of the piece was off by a few thousandths. 

The slices were so thin that you could see light through them and the surface was smooth as glass. Because of the smoothness, the joint would hold less glue. The key to this was to make sure that there was adequate squeezeout of glue at the joint.

I still have the miter trimmer (and the sliding table miter saw).  I will try to find time to make sample joints this weekend and compare the strength of a standard sawn miter and a miter with mirror-smooth joining surfaces. 

I've done tests like this in the past so I know how to do this.  I can test in increments of 5 pounds.  The results should be interesting.

This is the type of answer I'm after, thank you! Looking forward to the results.

No. As already mentioned when gluing panels you use plane or jointer to get the surface perfectly smooth.
For end grain I'd also prefer perfectly clean cut to open vessels for glue to go in.
Perhaps if you burnish the surface with very fine sanding, you might decrease adhesion because pores will be packed with dust.

My question is, if the vessels are burnished, or finished too smoothly, doesn't that in essence close them, not open them up?

My handplanes including the shooting plane give very fine edges and surfaces. Glue works well on them.

This is a very good point. Would you say that planes burnish the surface at all?

 

[ChuckM]

Snip.
But since ya'll are bringing it up, perhaps you can be helpful and provide suggestions for a  different blade, around 100t, that has negative hook angle, mid to full kerf, without blowout under or behind the miter cut?

My handplanes including the shooting plane give very fine edges and surfaces. Glue works well on them.

This is a very good point. Would you say that planes burnish the surface at all?

On preventing blowouts, ZCI and ZC fence (providing support on the exit side) are the key. Judging from your photo, you might not be not cutting it with a ZCI.

On plane blade or chisel burnishing, I doubt it if the blade is really sharp. But I'll take a closer look next time I shave endgrain.

 

[Birdhunter]

Looking at the blowout pattern, is it possible the sawblade is skewed. Toe in or toe out?

 

[Packard]

Why is everyone going on about the blowout? I clearly said that I was aware of it, and my post clearly says that the info I'm after has nothing to do with blowout. But since ya'll are bringing it up, perhaps you can be helpful and provide suggestions for a  different blade, around 100t, that has negative hook angle, mid to full kerf, without blowout under or behind the miter cut?

Also, yes, my picture shows endgrain, but if you read my post, I never specified the type of cut. I was asking about the smoothness of any cuts in general affecting gluing. The picture was only for reference for the smoothness of cuts I'm getting, as an example.

When I was a picture framer I had a Lion Miter Trimmer (they are out of business now).  The trimmer used a razor sharp knife to slice slivers of the miter off after sawing.  It was a corrective device, if a miter was not tight or if the length of the piece was off by a few thousandths. 

The slices were so thin that you could see light through them and the surface was smooth as glass. Because of the smoothness, the joint would hold less glue. The key to this was to make sure that there was adequate squeezeout of glue at the joint.

I still have the miter trimmer (and the sliding table miter saw).  I will try to find time to make sample joints this weekend and compare the strength of a standard sawn miter and a miter with mirror-smooth joining surfaces. 

I've done tests like this in the past so I know how to do this.  I can test in increments of 5 pounds.  The results should be interesting.

This is the type of answer I'm after, thank you! Looking forward to the results.

No. As already mentioned when gluing panels you use plane or jointer to get the surface perfectly smooth.
For end grain I'd also prefer perfectly clean cut to open vessels for glue to go in.
Perhaps if you burnish the surface with very fine sanding, you might decrease adhesion because pores will be packed with dust.

My question is, if the vessels are burnished, or finished too smoothly, doesn't that in essence close them, not open them up?

My handplanes including the shooting plane give very fine edges and surfaces. Glue works well on them.

This is a very good point. Would you say that planes burnish the surface at all?

This article, which is about staining, states that sanding to a very fine finish inhibits the absorption of stain (and I would presume glue), but sanding and slicing are different  processes and I  am not sure you can make an assumption based on sanding and apply it to a fine, sawn surface.
https://www.popularwoodworking.com/techniques/rules_for_sanding_wood/

Fine sanding. Sanding finer than #180 or #220 is wasted effort in most cases, as explained in the text. In fact, the finer the grit the wood is sanded to, the less color a stain leaves when the excess is wiped off. In this case, the top half was sanded to #180 grit and the bottom half to #600 grit. Then a stain was applied and the excess wiped off.

 

[ChuckM]

Snip.
This article, which is about staining, states that sanding to a very fine finish inhibits the absorption of stain (and I would presume glue), but sanding and slicing are different  processes and I  am not sure you can make an assumption based on sanding and apply it to a fine, sawn surface.
https://www.popularwoodworking.com/techniques/rules_for_sanding_wood/

Fine sanding. Sanding finer than #180 or #220 is wasted effort in most cases, as explained in the text. In fact, the finer the grit the wood is sanded to, the less color a stain leaves when the excess is wiped off. In this case, the top half was sanded to #180 grit and the bottom half to #600 grit. Then a stain was applied and the excess wiped off.

I'm certain sanding is different from planing in their effect though the surface feels smooth in both cases. Sanding clogs or fills up the surface pores (hence wet sanding) while plane blades or chisels don't. I deliberately sand endgrain edges to 600X or higher so they absorb less oil or stain, reducing the contrast between the surface and edges in a furniture piece. That's also the main reason that I bought the Festool new positioning aid for my Pro5.

 

[usernumber1]

here you go straight from the manufacturer [of our favorite glues]
https://www.popularwoodworking.com/techniques/best-wood-glue-surface-smooth-or-rough/

 

[ChuckM]

Does that article cover endgrain too: "... to get flat or tight-fitting joints works well."? I know glue sizing does help the end-grain bonding. I expect high-grit sanding (600x, for example) on the endgrain to weaken the adhesive bonding. No? 

 

[mkasdin]

Is it possible for a cut to be too polished to accept glue?

This is in relation to my other thread, about blades for precise crosscuts.

My Tenryu blade on the miter saw cuts so smooth it is shiny. I've always wondered, since glues need to absorb into the wood fibres, can a surface be cut too well?

(Yes I know there's gobs of tearout...not every blade does everything perfectly...that is a separate dilemma)

[attachimg=1]

the tearout is pronounce. Cut an a SCMS? Deristi used painters tape to make a zero clearance fence on the base (kerf). Not sure of your setup.

 

[usernumber1]

Does that article cover endgrain too: "... to get flat or tight-fitting joints works well."? I know glue sizing does help the end-grain bonding. I expect high-grit sanding (600x, for example) on the endgrain to weaken the adhesive bonding. No?

in my opinion with endgrain it's a misnomer to call it a joint unless you create an actual joint : add a domino, dowel, dovetail whatever.
it's not gonna hold anything even if you epoxy it, relatively speaking.
sanding is the least of it's worries

 

[Packard]

Picture framers use miter joints with (usually) V-nails to hold the miter in position while the glue is drying.  Its only reason for existing it to eliminate the need to clamp.  While clamps work well, 20 picture frames would require a lot of space if you had to clamp them.

Also with the fast setting Corner Weld glue and the v-nails you could handle the frame in 5 minutes and continue to assemble the work. 

But remember this is a "non-load" joint.  Only seasonal movement is an issue with picture frames and usually only if the frame is more than 2" wide.  I only had season movement issues on 3-1/2" wide molding, and that was after several years.

As a trim, I think we can call it a "joint".  And with good gluing protocols, it is surprisingly strong.

 

[JimD]

I don't think a surface can be too smooth for gluing but Matthias Wandel tested joint gap versus strength for mortise and tenon joints.  Tight fitting joints failed at lower loads than joints with small gaps - loose fit.  It is apparently possible to force the glue out of a joint resulting in lower strength.  That might be easier to do on a smooth surface.  Maybe.  But I think the key thing is not to try and get joints too tight, either through fit, or by too much clamping pressure.