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Sometimes I need to cut sheets (cca 50x80cm = 20x32") of soft 4mm (1/8") poplar plywood into smaller rectangular pieces and I find it surprisingly difficult to do with hand tools - it's too soft and thin for most saws, but it's too thick for a knife.

Currently, for most cuts I do:

  1. shallow line with a marking knife using ruler or a square
  2. follow the line "freehand" with chip carving knife to make it deeper
  3. repeat heavier cuts with chip carving knife until it's done (it usualy takes 3-5 cuts)

But it's very tedious process which also leads to heavy damage to cutting surface and I have to be very careful to stay in the marked line while applying quite a lot of pressure on the knife. Also the knife must be VERY sharp, otherwise I get jagged edge with chipped out pieces.

For smaller pieces needing more precise cuts I use small 24 tpi saw (Zona). Which is also slow and usable only for really short cuts (no more than 15cm / 6").

I can't use heavier saws because anything less than 24tpi destroys the edge badly.

Is there a better way/tool to do it? (I'm only interested in hand tools)

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  • Kudos for the well-asked Q with plenty of relevant detail! Do you have any experience with Japanese-style saws? Depending on the orientation of the surface veneers a rip or crosscut pull saw with a high tooth count (e.g. 17tpi or higher) would cut through this stuff like butter. But TBH with ~4mm soft plywood I would be sorely tempted to just cut it with a steel rule and a Stanley knife.
    – Graphus
    Nov 16 '21 at 18:31
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    I would use masking tape over the cut line and mark the cut on the tape. After cutting, peel the tape from the interior of the cut toward the edge. Nov 16 '21 at 22:23
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    Do you need good surface both sides or 1 side?
    – Volfram K
    Nov 17 '21 at 8:16
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    A pull saw will naturally tend to lift flakes on the up stroke, so you need to work from the back, i.e. with the show surface down. Or, cut first with a knife to sever the surface wood fibres. Cutting at a shallow angle is another good way to improve surface quality on the top, and this also allows a backed saw to make longer cuts (technically any length) although it does limit stroke so long cuts can be tedious. But remember as a crosscut saw a dozuki will cut better one way than the other — although all plywood cuts are a mix of rip and crosscut the veneer cut is one or the other.
    – Graphus
    Nov 17 '21 at 8:55
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    @Graphus well, you just described last 2 years of my life.. but last week I did cut more of this plywood than usual and I was a bit more frustrated than usual, and than I realized I just can ask here, which I did :) And I think best solution would be the mat cutter suggested by Caleb - and I think it could be useful for other things too
    – Jan Spurny
    Nov 17 '21 at 15:03
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I thought I remembered something from Colin Knecht (WoodWorkWeb) on this and here it is, Woodworking with Thin Plywood, like Baltic Birch Plywoods. The relevant portion is right at the beginning, with a tip not just on how to cut it with a knife1 but also on a good way to back the cut, although if you have a decent cutting mat that should be fine too. I've cut 3mm / 18" hardboard (much harder to cut than ply) on a cutting mat many times without causing undue damage, although there is inevitably some wear and tear.

An alternative method that may also work nicely with your material: scribe-and-snap2. See it in action here, Cut thin plywood without saw and chippings Be conscious of the orientation of your plies here. Note that Colin's tip about which way to orient the plywood cutting surface underneath isn't relevant here, since you don't cut right through.

Note: when cutting flat material with a knife it is the point that does almost all of the work. With a standard Stanley knife/utility knife you can greatly extend the useful cutting life of every blade by filing, grinding or honing the tip back a small amount each time it has become blunt. I've extended the life of single blades for more than a year using this simple trick. Here's approximately what they looked like after many months of 'resharpening':

enter image description here


1 He's using a standard utility knife but a boxcutter/Olfa knife should work as well, and more easily allows for a fresh cutting point to be available after the material inevitably blunts the tip.

2 If your thin plywood is more than 3-ply this method won't be quite as effective as shown, but could still work well enough that it's the method you'll end up using.

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    Thanks, the start of Colin Knecht video is pretty much how I do it. Except how he does it looks so easy. Maybe I'm doing something wrong. When I'm using straight edge and cutting hard, I have to clamp it down, because I push the knife against it so the knife doesn't wander off by following grain (cutting with the grain on top layer). But it looks like nobody else is clamping the straight edge or even pushing particulary hard on it. That's why I do first shallow cut with a marking knife (1 sided bevel) against straight edge (unclamped) and then freehand rather than clamping straight edge.
    – Jan Spurny
    Nov 17 '21 at 15:29
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    Also it looks that abandoning stanley knife was perhaps wrong.. I can see that thickness of my chip carving knife (cca 2mm - 1/16") may be a problem - the stanley knife is much thinner..
    – Jan Spurny
    Nov 17 '21 at 15:32
  • Interesting method of "resharpening" a utility knife blade. I've found that they're cheap enough that I don't bother. Also, for whatever reason, almost every time I've gone looking for my package of blades, it comes up missing. I go buy a new pack of 50 or 100 ($5/100 maybe?), and as soon as I get home, the old one has crawled out of its hiding place and is right where I'd expect it to be. I've got so many now that resharpening them is pointless. (Pun somewhat intended.)
    – FreeMan
    Nov 17 '21 at 19:13
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    Of course, mine aren't fine Sheffield steel, they're probably cheap Chinesium, so yours may be more worth the resharpening.
    – FreeMan
    Nov 17 '21 at 19:14
  • @FreeMan, hehe I nearly made a similar pun myself in my Answer ("Point to note:"). There is an easy argument to be made that this isn't worth doing.... except that it takes just seconds to do (even later, when the flat gets larger it can still be literally seconds). I have read many posts to the same effect about fully resharpening the edge of utility or craft knife blades, and that does take lots longer (at least manually, power strop not to much) and yeah for some people workshop time is precious, you must pick your battles etc. [contd]
    – Graphus
    Nov 18 '21 at 10:47
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Here are a couple ideas that might help:

  1. Get a mat cutter that makes vertical cuts, such as a Logan 350-1. These normally use razor blades or sometimes utility knife blades. 4 mm plywood is probably a little heavier than what they're meant for, but a half-decent one would still help you make a nice straight cut several times on exactly the same line. You'll probably go through a lot of blades, but that's OK, they're very inexpensive.

  2. It sounds like edge quality is very important to you, so consider cutting your pieces just a bit larger than you want and then sand the edges to get to the final size. You could make a long, narrow sanding block to help you keep the edges very straight. A roll of 1"-wide, 150-grit sanding cloth would be a good choice for this application: it'll leave a smooth edge but still cut quickly enough to get the job done in no time.

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    Thanks, mat cutter looks like a good idea...
    – Jan Spurny
    Nov 17 '21 at 0:42
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    @JanSpurny >$150!! + will not cut plywood: "Works with standard thickness mat board only (1.4-mm)"
    – Volfram K
    Nov 17 '21 at 8:18
  • @VolframK I understand its not supposed to do that, but a lot of things I use are not supposed to do things I do with them :) . What I like is that it provides me with a guide, so my cutting line won't wander off by following grain (which happens now quite often even with a straight edge) so if I'd still have to do 3-5 cuts, it would be much more comfortable and more importantly - it would be guaranteed to be straight. Anyway, I'm not buying one without trying it first :)
    – Jan Spurny
    Nov 17 '21 at 14:43
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    @JanSpurny Look for one at yard/garage sales, or on local sale sites like Craigs List. I bought one for about $5; you might not find the same deal, but I saw one recently on Craigs List for $65.
    – Caleb
    Nov 17 '21 at 14:57
  • amazon.com/Logan-701-1-Straight-Matboard-Foamboard/dp/… This one is just the cutter without the rail system and is much cheaper Nov 18 '21 at 22:49

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