Sanding off laser burn from bulkheads?

[Bill Hime]

I searched this subject multiple ways but found nothing. Perhaps I didn't use correct search tags... So the question is;

 

Does it make a difference in how well glue adheres to bulkheads during planking if the laser burns are not removed? I know in the fairing process some will be removed by default. Do wood parts in general adhere better or worse to laser burned wood?

 

Warm Regards,

 

Bill

[JeffT]

Bill, you will need to clean it up as best you can. As you mentioned, fairing will take care of most of the hull. It does leave kind of a residue on the surface of the wood that may affect gluing.

[augie]

Jeff is correct.  It usually just takes a light sanding to get the burn off but it always improves glue adhesion.  Your model needs to last 200 years !!

[Bill Hime]

Jeff & Augie,

Thank you guys! That was the answer I needed. MY OCD inclines me to remove all or as much as possible. Wanted to make sure I wasn't spinning my wheels, lol !

 

Warm Regards,

 

Bill

[Q A's Revenge]

I would expect that it would be best to remove the burnt residue. Is there a good solvent that can be used instead of sanding on bulkheads that are to be left unfaired?

[augie]

No solvent that I know of QA.  Good question though.

[WackoWolf]

I also never heard of any solvent that removers that. Just take you time and sand nice an easy, it will be up to you as to how much sanding that you need to do, but it will help with the glue. When in doubt just ask.

[Modeler12]

Does it make a difference in how well glue adheres to bulkheads during planking if the laser burns are not removed? I know in the fairing process some will be removed by default. Do wood parts in general adhere better or worse to laser burned wood?

Bill

At first I agreed with Jeff. After all, wood that is 'burnt' should not have the fibers to grab and adhere to with glue. But I decided to run a little test.

I took a few pieces (shown below) and used 'carpenters glue" (PVA) to bond three of them together. You can see burnt to burnt, blank to blank, and for good measure blank to burnt.

The clamps apply about the same amount of pressure during this glue-up.

 

I don't have a testing machine, but tomorrow morning I will put each one in a vise and hit with a hammer sideways.

I will let you know how it goes tomorrow. You know, glue should be given some time to cure!!!

 

BTW 'Burnt to burnt' is to the right and 'blank to blank' is in the background.

[augie]

Don't forget to calibrate the hammer .  

[Per]

Interested to see the result.

I think that the only solvent that works on laser burns is elbow grease. Works every time. 

 

Per

[augie]

Afraid I have to agree, Per.  One of the few times where 'Better Living Through Chemistry' comes up short. 

[jud]

Good experiment for the wood you are using, thin and cutting quickly should result in light charring. From what I have seen on this board, bulkheads appear to be charred much more, probably because of the increased thickness and more durable woods or as some shown in build logs are made from plywood. Charcoal would make a poor joint, If just discolored by heat but not charred, might be fine as is, a light sanding to remove any loose material would be good insurance.

jud

Edited November 17, 2013 by jud

[Modeler12]

OK, here is what I did and the results.

 

I clamped the glued up piece (started with the 'burnt to bare') in a wood vise. I used another piece of wood leaning against the top part and hit it with my calibrated hammer. I did the same thing with the other two, hitting it with about the same force.

 

All three pieces sheared where I had clamped it and none broke at the glue joint.

 

I then tried to break the remaining parts with pliers. Indeed the 'bare to bare' splintered some more but not at the glue line (top left). The 'burnt to burnt' (right) broke a sliver at the glue line, and the third one ('burnt to bare') did break through the burnt joint leaving burn marks on the bare side.

It felt like it took about the same amount of force to break each one.

 

My conclusion is that it makes very little difference if you sand the burnt edge or not. Al least with the glue I used. I suggest that others might try something like this with other adhesives.

[augie]

After careful analysis of the data presented, it would appear that an alternative conclusion may also prove viable.  Specifically, the glue joints in each case are stronger than the wood itself.  It is suggested that further experimentation be conducted to determine the strength of the joints in the tension, rather than in the shear,  mode.  This might best be accomplished with the use of either an 'Instron' device or the application of opposing forces using two identical teams of draught horses

 

Pending the publication of the results of the modified experimental design, I shall continue to get the 'brown stuff' off prior to gluing   

[mtaylor]

Draught horses???   Belgian or Clydesdale?   (apologies to Monty Python but this isn't about sparrows).

[NMBROOK]

I thought they would be just as strong,but didn't post anything for fear of walking into a hornets nest   The ash produced by laser cutting is on the floor under the machine.The black  is purely discolouration unless it was 4pm on a friday when they were cut .You still end up cleaning the edges though because the laser cutting pattern is tapered just like waterjet,This means all cut edges aren't square anyway unless of course you buy a kit that is cnc routed.

Kind Regards Nigel

[Nirvana]

Thank you Bill for the test,

[Bill Hime]

Sound point made; Tension separation would represent plank/bulkhead adhesive failure more clearly. I must also concur that draft horse teams, specifically cloned to rule out any deviation in the baseline designed of the testing guidelines. While this is continued to be reviewed by executive committee, I too will continue to remove all charring that remains in question here above.

 

 

 

Bill

[dvm27]

I read somewhere that you can just wash the residue off but I'm sure someone has tried that. Perhaps the implication was just wash off as much residue as possible before gluing.

 

The other problem with laser cutting is that the cut is not always perpendicular. The thicker the piece, the more exagerated this is. Did you note a larger gap on one side vs the other Jay?

 

Dave Stevens, of the LumberYard, addresses these issues on his website http://www.dlumberyard.com/oneida-laser.html

Edited November 18, 2013 by dvm27

[Modeler12]

The original question did not imply that bulkhead parts were to be bonded with 'burnt to burnt', but I just included that because I was curious. To do that, however, I flipped the two pieces so the edges mated and did not have any or much of a gap. Yes, the 'burnt to bare' did have a small gap and that is why it probably broke the way it did with the pliers. But even that one did not break at the glue joint when hit with a hammer. The PVA is known for a limited amount of 'gap filling', unfilled CA glue does not, and epozy is very good in that regards.

 

When you plank a hull with bulkheads, I think it is more important to minimize the gaps than whether or not the edge had a dark residue from the laser cutting. In other words, bevel the edge as necessary towards the bow and stern and don't worry about some dark smudges towards the center. That is my opinion. If you want to spent the extra time to make it look bare, go at it.

 

I am sure we all have to agree that planking will come loose more easily in the curves sections, but even where I spliced two planks on a bulkhead, I had very little problems bonding the two to make a joint.

[Modeler12]

Bill Hime, I have a suggestion for you. Since you live in Madison, you should go to the Forest Products Lab there and ask one of the engineers if they could run a similar set of experiments. Perhaps they already can provide you with a better opinion than mine.

FPL is well known for the work they have done in testing all kinds of wood structures.

 

BTW Rather than tension, I think a cleavage or peel test would be more meaningful. Planks bonded to bulkheads will want to 'peel' loose. I don't foresee much 'tension' nor 'shear' in those joints.

Edited November 18, 2013 by Modeler12

[augie]

Draught horses???   Belgian or Clydesdale?   (apologies to Monty Python but this isn't about sparrows).

Not to ignore our French colleagues, don't forget the Percherons.

[Sonofagun]

When faced with this problem previously, someone mentioned that scraping the char away with a single edge razor works well and removes very little wood.

Tried it. It is a very good and efficient method. May seem a little daunting at first, but really, it is easy and takes almost no time at all. I did not, however, try gluing the charred parts together. I will be interested to hear the results of the tests.