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I'm designing wooden speakers with MDF using Sketchup.

How much space is taken up by the glue between two pieces? 1mm per side? Less?

I'm using biscuit joining and white wood glue.

Explanation with screenshot :

I have a back panel of 351x276 vertically, external size is 320 - 22 - 22 = 276mm, which is the ideal space to fit vertically the back panel. But, after assembly, it takes more space

How much space would you plan to account for the glue?

enter image description here

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  • Last time i had to remove some matter for a perfect fit, which was quite difficult Oct 27 '15 at 13:36
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    I'm afraid I don't understand the 2nd sentence. Where do you plan on putting the biscuts? I would include a picture of the plan you have,.
    – Matt
    Oct 27 '15 at 13:39
  • Please include a picture or diagram of what you're working on. As it stands, it's impossible to tell what exactly you're asking.
    – grfrazee
    Oct 27 '15 at 14:11
  • edit with an image Oct 27 '15 at 14:50
  • Are you saying that your design mesurements and actual box are not matching? Are you sure your MDF is the same height across its length
    – Matt
    Oct 27 '15 at 14:51
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How much space is taken up by the glue between two pieces? 1mm per side? Less?

Usually, this thickness of glue in a butt joint is negligible to the point of being zero, at least as far as woodworking tolerances go.

Yes, the glue does have some finite thickness, but it's probably on the order of 1/10mm in a properly-clamped joint. Trying to account for the glue line when you cut your pieces will be an exercise in frustration and futility since there's no way to make your cuts that accurate.

To answer your question, I would assume the glue thickness is zero. Clamp the pieces tightly and make sure your joints are all properly fitted, and this assumption should be pretty much accurate - at least, accurate enough for woodwork.

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    in fact, if you are using wood and white glue, the thickness SHOULD be essentially zero.
    – aaron
    Oct 28 '15 at 14:05
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I would say that you don't need to account for the space unless your angles will all be exactly, without fault, 90 degrees, and each cut will be accurate within 0.25mm.

In other words, woodworking is not the same as designing a car part from metal with very precise tolerances. If you do need that level of precision, I would venture to say that you will have to take measurements using your cut MDF, your glue, and your clamps because slight variations in any of those might affect the measurement (which will probably end up being less than 0.1mm).

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I agree with this answer that having a zero tolerance precision can make for a big headache in woodworking (This is more true for real wood as it expands and contracts but the point still applies).

I offer a design compromise for these inaccuracies. You should be able chamfer the edges of your box to hide and inconsistencies in your external dimensions. An extreme example to illustrate my point would be this picture I found

Chamfered box

Image from dhandanought

MDF is known for its dimensional stability but slightly less so for its strength. What I mean by that is it can dent easily and especially on the corners. Chamfers remove the corners. That should keep the overall appearance of the speaker box and possibly add some flair to it.

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