Cutting 25mm plywood

benwheeler

benwheeler

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Joined
Sep 29, 2014
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164
Good morning knowledgeable people,

I'm making a bookshelf for a client out of  25mm plywood. It will be varnished, and the edges left exposed.

I have a new 48T blade for my TS55 - should this be up to the task? If so, are there any recommended blade and travel speeds? And any other tricks to get the best result, ie scoring the top surface first before sawing all the way through?

Thanks for any help.
 
If you want to score the surface make sure you clamp the rail.

A clean sharp 48 tooth blade will cut through the plywood without any issues at all.

Tom
 
Great, thanks. Yes it's a $300 sheet of plywood so I'll be measuring 5 times before cutting, and clamping it to within an inch of its life!
 
If you are cutting with the surface grain direction the cut should be perfect. If crosscutting the grain, as long as the splinter guard on the rail is correctly set and you use the external splinter guard, both sides of your cut should be perfect.

If the offcut edge is not required as a finished cut then you don't even need the external splinter guard.

Travel speed is a matter of feel which comes from experience but try to not pause as this may leave a burn mark.

The cuts that you should get should only require a light sand before finishing.

What length will the shelves be and will they be supported by the back of the bookshelf?
 
Just wandering.  Thats pretty expensive ply.  I just bought some azek 4'x8'x3/4" for $180 and thought that was expensive.
 
Hi Ben,

There is a lot of good advice above.

I would also place the sheet on top of a brand new sheet of MDF for all of the cutting in order to reduce tear-out underneath.

When you sand the sawn edges use offcuts clamped on either side of the edges and flush with them to reduce dipping (going off square). You could also clamp up several pieces of your prepared stock to do the same. Use a square to line things up during clamping.

Use your vacuum hose with the brush attached to very carefully clean the edges in case of very fine pockets in the ply which get disguised by dust from cutting or sanding.

Now you have told us what you are doing you will have to post some pictures of the finished piece !

Peter
 
Thanks all for the great information.  I shall follow it to the letter!

This is the item in question - I still haven't quite decided how to make it!
Bookshelf.jpg


It doesn't have a back - I have to work out a concealed fixing.

Regarding the pricing, I've probably been shafted, but one gets used to that in Australia.  The material is Exterior B/B Hoop Pine Plywood, 25mm.  I'm pretty happy with the quality.  It has no voids:

Ply.jpg


I've found it really difficult trying to price plywood.  Almost no-one publishes pricelists, and when I've called for prices they seem to vary wildly.  I'm sure the quality would also vary a lot.  When I recently put together a Paulk-style bench, I decided to make it from 12mm hardwood ply.  Plyco quoted me something like $150-160/sheet!  I ended up buying some from Tile Importer for $54/sheet.  The quality wasn't out of this world, but good enough.
 
Interesting design. Is it going to carry books or just the occasional "object" because if its books I don't think it will have the structural integrity to support the weight on that top shelf.
 
The supports will be interesting. I had to hide the side supports for a bookcase I made but had the advantage of backs on the unit to give additional support along the back. My shelves were a stressed skin design (to stop bending under the weight of books) and were hollow which helped with the inserted side support.

This first picture shows the male supports on part of the unit before receiving the shelves.

[attachimg=1]

This is the finished item.

[attachimg=2]

Peter
 

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Birdhunter said:
It looks highly unstable. Is it attached to a wall?
Click to expand...

If that is my last post that you are referring to then yes - it is attached at the top of each vertical member and also fixed, from below, to the base unit which is itself fixed to the wall.

Peter
 
[member=15289]Birdhunter[/member] and [member=36526]Bohdan[/member] - thanks for your thoughts.  I'm afraid I hadn't really considered its strength, as the client's design is based on an existing design that would be structurally similar.  (Bear in mind that I am a lowly carpenter starting to do some weekend joinery / cabinet work.)  The maximum width of the shelves is 550mm, and being 25mm ply, it may not be too weak.  Perhaps I'll suggest having a thin back, painted to look like the wall.  Then I just have to conjure up a concealed fixing system!

Peter - that's a beautiful bookcase!  *Googling "stressed skin design"*

Incidentally, does anyone know how I would go about tagging "Peter Parfitt"?  If I type in "[member=41421]Peter[/member]", his name isn't in the list due to alphabetical reasons..
 
Hi Ben

I may be using the wrong term for the hollow shelf design as it was not pre-stressed - I suspect that Monocoque is more accurate but I am happy to be corrected by some knowledgeable FOGger.

I went to the workshop and hunted for any remnants of the piece - I usually keep something as a reference for the next time something like this needs to be made. I could only find a section of the prototype and it is pictured below. I have drawn on what would be the solid oak front. I can't remember whether I used solid wood spars (as in the picture below - looks like sapele) or MDF.

I cheated on these shelves and used plain MDF for the top and bottom faces which I sealed with several coats of shellac and finally treated with clear satin polyurethane. This helped to bring the price down which I seem to remember was an issue at the time.

Peter

[attachimg=1]
 

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Peter Parfitt said:
Hi Ben

I may be using the wrong term for the hollow shelf design as it was not pre-stressed - I suspect that Monocoque is more accurate but I am happy to be corrected by some knowledgeable FOGger.

I went to the workshop and hunted for any remnants of the piece - I usually keep something as a reference for the next time something like this needs to be made. I could only find a section of the prototype and it is pictured below. I have drawn on what would be the solid oak front. I can't remember whether I used solid wood spars (as in the picture below - looks like sapele) or MDF.

I cheated on these shelves and used plain MDF for the top and bottom faces which I sealed with several coats of shellac and finally treated with clear satin polyurethane. This helped to bring the price down which I seem to remember was an issue at the time.

Peter
Click to expand...

Thanks for taking the time to do that, Peter.  I've been having a look at Wikipedia articles on stressed skin, monocoque, semi-monocoque.. I'm almost none the wiser!  Time for bed, I think.

I'm interested that you used shellac on MDF.  I don't think MDF is always cheating - it can be used to good effect!  Here's an exhibition work which I had the opportunity to help build - I think it was quite simple and beautiful:

http://www.ngv.vic.gov.au/essay/celeste-boursier-mougenot-clinamen/#.UeJU1Y4rw5Q
 
I believe that by "stressed skin design", Peter is referring to a torsion box. Similar to a hollow core door.
 
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