Laser cutting questions

[SardonicMeow]

I'm working on a laser cut plank-on-bulkhead project and could use some advice from anyone who has done the same.  My design is complete and I have been trained on the use of the laser cutter at my local Makerspace.  So, I'm almost ready to proceed to the cutting.

 

My first question is what wood to use.  I know I don't want to use plywood, because I had issues with the plywood layers coming apart when I built the Virginia 1819 kit.  Is basswood definitely out?  My design has some delicate parts, so I guess basswood would be too easy to break?  So what about cherry?  Maple?  Alaskan cedar from a certain someone?  I really don't know how the different hardwoods compare.  My design assumes sheets will be 1/8" thick.

 

To what extent should I consider the grain direction when aligning parts?  It seems obvious that long, skinny pieces should be aligned with the grain, but are there any other gotchas?

 

How narrow can I safely cut parts?  I have a few parts with sections that narrow to less than 2mm.  Is that doable or will cuts that close together get burned through?

 

Thanks in advance for your help.

 

[mtaylor]

Here's my take.... 

 

Question 1:  Use whatever wood works for you.  Ebony and plywood do have issues from my experience so I don't cut those on a laser.  

 

Question 2:  2mm separation is doable depending on the thickness and the type of wood. There is a kerf that gets bigger depending on power and cutting speed.   Just make sure that your cut line for the laser is outside the piece such that you end up with the 2mm piece.  It'll take some trial and error.  Note that if the wood is too thick to cut in one pass, the kerf gets larger and more angled with the second cut.

 

As for cutting in general, spend some time cutting and dialing in the power and speed on the types of wood and the thicknesses as everything will be different.   With a shared unit, always do a test cut first since power levels may fluctuate and users may fiddle with things like focus.   So you want the machine at a known point.  Even if the lens is locked down, do run a test cut first.

[Gregory]

Don't shy away from good quality plywood for your frame parts.

 

A good example is Chuck's Cheerful project.  Click through the log to see the plywood framing..

 

Of course, you don't want plywood showing on the outside of your model, so the " finish " parts should be  woods like boxwood, pear and the Alaskan yellow cedar that is showing up lately.   There are many other choices, but those are a few.

 

How precise your cutting is, will depend on the machine itself, and you will have to experiment.

 

The best examples I know of is our own, Chuck Passaro's  Syren Ship Model Company

 

He turns out parts in boxwood that are 1/32" thick, and having dimensions in that range, if not smaller, also.

Stern Lantern Kit

 

 

For what it's worth, I have a low power laser engraver that needs several passes to cut through anything thicker than card stock.  However, it is great for making precise patterns that I can then cut out with my jig saw, and follow up with detailed finishing.

 

 

 

 

 

 

 

 

Edited March 5, 2019 by Gregory

[SardonicMeow]

Interesting.  I didn't know that not all plywood is created equal.  Where would I get quality plywood and how would I know it's good?

 

I should have mentioned in my original post that all the laser cut pieces will be planked over and/or painted over, so the appearance of the wood doesn't matter to me.

 

[Jaager]

Wood Craft has Baltic Birch plywood in a variety of sizes and thicknesses.  Hobby locations have aircraft plywood, but the really thin stock is kinda the opposite of what you need as planking support.

there is the option of getting 1/16" or 1/8"  Hard Maple or Basswood, etc- cutting 3 copies of each mold/ bulkhead - one with the grain 90 degrees rotated - and glue up the layers as your own homemade plywood.  All that is needed is a strong press. 

[russ]

Aircraft grade plywood like Baltic Birch would be good. Even at 1/8" it has many plys and there are hardly any voids. It is generally stable and good for this sort of work. 

 

That said, basswood would work as well. It will be easier to sand when it comes time to fair up the hull before planking. The plywood will be more difficult to sand. 

 

Russ

[Gregory]

17 hours ago, SardonicMeow said:

Interesting.  I didn't know that not all plywood is created equal.  Where would I get quality plywood and how would I know it's good?

 

I should have mentioned in my original post that all the laser cut pieces will be planked over and/or painted over, so the appearance of the wood doesn't matter to me.

 

 I have used this 1/8 plywood from Amazon.

 

3 mm 1/8" x 8" x 8" Premium Baltic Birch Plywood

 

P.S.

You can shop around on Amazon for various dimensions..

 

This is more versatile at 12" x 24" ..

3 mm 1/8"x 12"x 24"Premium Baltic Birch Plywood

Edited March 5, 2019 by Gregory

[reklein]

There are some types of MDF and resin impregnated materials designed for laser cutting. I see there use in kits from time to time. It might involve different building techniques but the pieces seem sturdy and accurate. You'll have to google the sources,I'd probably start with materials suitible for laser cutting.

[SardonicMeow]

Thanks for all the responses.  Lots of options to consider.

 

[Erebus and Terror]

This might seem blasphemous, I have had good results with MDF for bulkheads. With care, it can be faired as easily as plywood. It is often much straighter and less prone to warping than traditional ply. 

[Charter33]

Just a quick note - there are grades of ply that are produced specifically for laser cutting - we use them with the students at school. They char much less than birch ply of similar thickness. 

Another tip - when cutting wood with the laser cutter I often set the machine up to run at a lower power / faster speed setting and repeat the cut several times until full penetration is achieved. I developed this technique when teaching myself how to use the machine and software by drawing and cutting components for an R/C model aircraft from balsa wood. This reduces burning and is very useful for those small or delicate parts. I have successfully used this on lime (basswood), mahogany, yew and cherry - although not necessarily all for model ship building. I also fully agree with the previous post about using MDF...

Best way to learn is to dive in and 'play'.

Good luck!

Graham.

[Nirvana]

Plywood can be found made out of  various material such as basswood, cherry, pear and more.

Basswood ply of same thickness is more flexible than birch wood ply. 
I just did a quick search a got hits on each material.