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Old 6th September 2005, 07:29 PM   #1
morbo is offline morbo  Canada
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Default working with baltic birch plywood

I'm about to start using baltic birch plywood for the first time, and as someone who has only used MDF before, was just wondering if there is anything significantly differnet about working with/machining ply? Anything I need to do differently when routing circle cutouts, do screw pilot holes get stripped really easily like MDF, do I need to change the speed settings on my router/jigsaw, does BB ply sand differently than MDF? Any tips would be appreciated, as I don't have a lot of scrap to play with.
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Old 6th September 2005, 10:34 PM   #2
Sherman is offline Sherman  United States
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Here are a few things to keep in mind.

Birch plywood is much harder and denser than MDF. That usually means slower cutting. It also means screws do NOT strip as easily.

Birch plywood is of course made of layers. The outer layers are quite thin and it is possible to sand right through it before realizing it. If you intend to paint it or veneer it that might not be too much of a problem but if you want to finish the birch be very careful.

If you have a variable speed router you will probably find that slowing it down a bit and cutting more slowly causes fewer burn marks. If you can use a fine toothed blade in your table saw. Also tearout isn't a huge problem with birch ply but if you can put a piece of scrap under it while cutting on the table saw.

If finishing the birch itself you may find you like the look of having the edges rounded over.
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Old 7th September 2005, 12:56 AM   #3
morbo is offline morbo  Canada
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Thanks Sherman, I do have a variable speed router and will take all your advice into consideration.
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Old 7th September 2005, 01:49 AM   #4
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Quote:
Originally posted by Sherman
Birch plywood is much harder and denser than MDF. That usually means slower cutting. It also means screws do NOT strip as easily.
Birch plywood is about .7 g/cm^3, MDF is .7 g/cm^3 and higher. Of course some birch plywood might be denser than some MDF, but this is mostly not the case.

Yellow Birch hardness is 1260 Janka (lbs/in^2). MDF is about 1000-1200. Really depends on the type. Also with plywood. In general I would say MDF is denser than Birch plywood. And they are about the same hardness with Birch plywood slightly being harder, but hardness specs are hard to come by and often considered trivial.

This forum is often not the place for accurate information about wood products. I have not heard many say inaccurate things about wood products. People have even taken sides against me and sided with what they called an "expert" cause he worked at a plywood factory or something.
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Old 7th September 2005, 02:00 AM   #5
Mark Kravchenko --- www.kravchenko-audio.com
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Default Tips from the dark side

Pre drill your screws to the root diamter or there abouts. It makes it easier to drive them in.

BB is much more stiff than MDF so that is a plus when building boxes. As for cutting figure out the best feed rate by listening to your machine and watching the end product of the cut. You know what both of them should look like. And you know what an un laboured router sounds like.

Other than that there is not much to know about. The outer layer of the birch ply is about 1mm so don'r worry about sanding through to easily. Finishing can be tough as birch does not stain evenly. But with a coat of shellac it will take an even stain.

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Old 7th September 2005, 02:12 AM   #6
kmj is offline kmj  Sweden
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Quote:
Finishing can be tough as birch does not stain evenly. But with a coat of shellac it will take an even stain.
Could you (elaborate?) a bit?
I'm planning to bauild a pair of fullrange speakers and at the same time redo my old cabinets so it could be a good thing to start collecting facts.

Shellac, isn't that some kind of coating used with metals or something? In any case, shellac first, then stain?

OT
planning to use a ply called Lauan, some kind of red colored wood.
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Old 7th September 2005, 02:18 AM   #7
Mark Kravchenko --- www.kravchenko-audio.com
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Default Shellac=

It is a finishing product that is taken from the secretions of the lac bug. It usually comes as flakes and is thinned in alcohol. It is like a laquer. Only not as durable. It sticks to anything and it makes a good first coat on raw wood that is difficult to stain evenly. When coated and stained within about twenty minutes it will absorb the stain and allow an even coat colour.

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Old 7th September 2005, 02:31 AM   #8
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Default Re: Tips from the dark side

Quote:
Originally posted by mwmkravchenko
BB is much more stiff than MDF so that is a plus when building boxes. As for cutting figure out the best feed rate by listening to your machine and watching the end product of the cut. You know what both of them should look like. And you know what an un laboured router sounds like.
M.o.e of MDF is about 3950 N/mm^2

M.o.e of Birch 3700, 5000 N/mm^2 for a piece I found 18 mm in thickness and 13 plys. 3700 is perpendicular to facegrain, 5000 is parellel to facegrain (the less plys the greater the difference will be, I would imagine). So Birch has more so less the same stiffness as MDF; it is different depending on the orientation of the grain and the type of Birch plywood and MDF used (manufacturing process and what they're made of).

The MDF spec sheet I looked at is made of pine it's called Medite and plywood is wisa Birch plywood. The plywood is .63 g/cm^2. The MDF is probably less stiff and had less density than average piece of MDF I'm guessing.

I think baltic birch plywood would be more stiff than MDF generally. Much more I don't know though. You should check yourself, if you interested.
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Old 7th September 2005, 02:44 AM   #9
kmj is offline kmj  Sweden
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So, you apply shellac and later (approx 20min as you said) you stain the half-dry shellac, not the accual wood??
Then later when it has dried you start the accual polishing, or am i wrong?

I found this link when i googled for "french polishing".
How to apply Shellac

I think it's kinda good and since there's probably going to be more people than me looking for it i thought that i should post it.
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Old 7th September 2005, 03:17 AM   #10
doorman is offline doorman  Canada
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One thing you WILL like, using BB , is the dust generated is much less obnoxious than mdf. Mdf is somewhat easier to machine, but full sheets of the stuff are real heavy, and not easy to handle
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