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I have a metal bed frame. Its metal slats are 6" apart. I am buying a new foam mattress, but I don't want to buy new frame.

I think that the 6" spacing between slats is too wide for the foam mattress. I am thinking of placing hardboard panels over the frame and then putting the mattress on top of it. I am going to use mattress retainer bars to keep the mattress and hardboard panel from sliding.

Home depot has 8'x4' hardboard panel, the size of a king bed is 76" x 80" so I need to buy 2 panels and cut it as follows:

  • Panel 1: 6'8" x 4' (cross cut to reduce the length)
  • Panel 2: 6'8" x 2'4" (cross cut to reduce the length, rip cut to reduce the width)

I don't have power tools. I can ask Home Depot personnel to cross cut both panels to 6'8" long. But they won't be able to do rip cut the 2nd panel. They always say no.

My questions

  1. How can I rip cut 8' long, 1/8" thick hardboard panel? I only have utility knife.
  2. Is this the best solution to my problem?
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    They don't say no. They just charge you a small fee for additional cuts. If you don't want to own power tools, this is the cost.
    – isherwood
    Commented May 10, 2023 at 13:17
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    Even if you have power tools, Home Depot (or similar) small charge is often worth it, particularly on big pieces. Of course, a lot depends on how precise the cuts need to be. Commented May 10, 2023 at 14:06
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    If you live near a real lumberyard, try them. I suspect they could cut to exactly your dimensions. And you wouldn’t have the heartbreak of showing up to home derpo and discovering that the panel saw is out of service again. Commented May 10, 2023 at 15:15
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    Consider 1/4" plywood. I've used 1/8" hardboard for this purpose and it works nicely especially with a traditional mattress at least 6" thick. But with a foam mattress, if a heavier person sits down heavily on the bed or a child or anyone treats it roughly, the hardboard will break. And either way, if you don't own any tools just pay the 50 cents for the extra cut at the store! Half the time they are nice and don't bother charging you.
    – jay613
    Commented May 10, 2023 at 15:23
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    I have a foam mattress on my bed, the sort that comes compressed in a box. The slats are about 4" apart, though they shift over time and when I just went to check the spacing I found a pair that were over a foot apart, yet I had never noticed. Don't just assume your 6" spacing won't work. Put the mattress on the bed and see if it works for you. If the slats can be moved, you might space them more at the foot of the bed and narrow the gaps where your torso goes. You might be trying to solve a nonexistent problem.
    – Llaves
    Commented May 10, 2023 at 23:13

6 Answers 6

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You absolutely can cut 1/8" hardboard with a utility knife using good technique. I've done it without much trouble. It's basically like cutting 1/8" acrylic sheet. 1/4" would be too thick, however. I've also tried that. It's nearly impossible.

  1. Mark the cut line accurately on both faces.
  2. Using a new blade, make a light cut to act as a guide.
  3. Make additional, deeper cuts with the knife held fairly high. This increases pressure on the point, and therefore cut depth.
  4. Repeat steps 2 and 3 on the second side.
  5. Lay a board or pipe along the cut and bear your weight on it, then lift the sheet to snap it at the cut line.
  6. Clean up the resulting edge with the knife or a sanding block.

Use a straightedge when making the cuts if available. As Olivier suggests, you can use the factory edge of one panel as a straightedge to mark the other. You can also use the corner as a square.

Also, be very careful. Applying force to a knife opens the possibility of slips. Keep clear of the cut direction.


Regarding the viability of using 1/8" hardboard for this in the first place... I think it'll work fine. While this material is rather flexible, over that short span it won't sag much at all. It'll offer good support to a foam mattress.

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  • I don't doubt that you can cut 1/8" hardboard with a utility knife. I think the real issue here is that 1/8" is unlikely to work well here to bridge 6" gaps.
    – Huesmann
    Commented May 11, 2023 at 13:25
  • After making the initial cut(s), I have found that angling the blade a bit to create a V-shaped cut produces good results upon snapping.
    – JimmyJames
    Commented May 12, 2023 at 16:25
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You're not going to be able to do this with just a utility knife.

I would start by asking, nicely, at Home Depot. I have had similar cuts done before on plywood and as long as the machine is working (sometimes it isn't) they do these cuts without any problem. The only difference is that I am usually getting ordinary plywood. And I actually don't see a need for anything fancy here, as you are not using this as a visible, painted or stained, piece of furniture - it is going to be hidden away under the mattress. Plywood is quite common for exactly this purpose, at least 1/4" and even 1/2" would make sense, though plywood prices are still a good bit above pre-pandemic levels. Depending on the store, and the mood of the saw operator, you might get all 3 cuts for free or some or all might be $0.50 to $1 each.

If that fails, go over to the tool aisle and pick up a saw. Yes, power tools will do this much faster, but buying a power tool for 3 cuts is a bit much. Plenty of saws at Home Depot in the $10 - $15 range that will do the job, and then you can use it again for a future task. If you've got a Harbor Freight nearby then you can get some reasonable saws (can't guarantee the quality, but as long as it makes it through the 3 cuts...) for less than $10.

But a utility knife? Fuhgeddaboudit.

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    Yes, IIRC Home Depot (at least the one near me) gives you two cuts on a sheet of plywood "for free."
    – Huesmann
    Commented May 10, 2023 at 12:25
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    I disagree. Cuts from both sides would allow 1/8" hardboard to be snapped. 1/4", not so much.
    – isherwood
    Commented May 10, 2023 at 13:27
  • @isherwood Interesting. That would require pretty close cuts on the two sides across several feet. Commented May 10, 2023 at 14:03
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    Yeah, but "pretty close" isn't that hard to achieve. :)
    – isherwood
    Commented May 10, 2023 at 14:07
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    I agree that you can score and snap 1/8" hardboard but I wouldn't use 1/8" hardboard for this job! And my DIY philosophy is to always buy a tool if it costs less than a contractor would charge to do THIS job. So if you have no tools at all and for $10 you can get this job done ... don't take short cuts. Buy a saw. This is how you become better at DIY, one cheap tool at a time (and eventually not so cheap ones ... but you'll never improve if you try to do everything with what you have in the kitchen drawer).
    – jay613
    Commented May 10, 2023 at 15:27
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Instead you might also consider buying a set or two of "bunkie board" slats like those shown below. They are straight wooden boards attached to each other by flexible cloth straps, allowing you to position the boards anywhere from right next to each other (maximum support) to as far apart as the cloth straps allow (maximum coverage).

enter image description here

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  • Yes, I did find this in google search, but a bit expensive. I don't want to spend much. Commented May 10, 2023 at 2:53
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    @user2716454 Agreed. Aside from the hand saw route, you might also consider buying a used older corded circular saw at someplace like a pawn shop or garage sale. I bet you could find something decent for around 20 USD.
    – Armand
    Commented May 10, 2023 at 2:56
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    Even the cheapest bed-stiffening boards are surprisingly pricey given what you'd pay for a full set of close-spaced slats from Ikea. (w.r.t @Arnand's comment) A jigsaw would also work, and I'd prefer that to my circular saw on hardboard. A larger reciprocating saw would also be good (Sabre Saw, Sawzall etc); all of these (especially circular saws) need the workpiece to be securely fixed to something solid and get rather messy.
    – Chris H
    Commented May 10, 2023 at 15:20
  • @Armand: You can find something new for around $20-25 USD. Commented May 12, 2023 at 2:00
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Your answer might work from a "how do I get the wood to the right size" standpoint, but I'd strongly recommend against it from a health and safety standpoint. In my experience moisture collects under mattresses and if the entire mattress is sitting on top of wood, you will get mold/mildew/nastiness on the bottom of the mattress. A much better alternative is to cut many slats of wood with airspace between them to allow for ventilation!

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    Plywood under a mattress has been common for decades and really shouldn't cause a mold/mildew problem. Commented May 10, 2023 at 16:54
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    The picture in my mind is the slats or sheet of plywood or whatever sitting on top of an open support frame or platform bed, so plenty of airspace directly underneath for ventilation.
    – Armand
    Commented May 10, 2023 at 19:30
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    @MikeB Of course it's load bearing. The mattress literally goes on top of it and you lie on it. :) It's slightly thicker hardboard than the OP will use, but divan bases are normally constructed in two halves (for ease of transport) and (contrary to your assertion) there aren't normally struts across inside, so you have an unsupported 5'x2.5' area. The OP has at most a 4" gap (assuming 2" slats) between supporting slats, and those slats are the load bearing elements. The hardboard is just spreading the load a bit.
    – Graham
    Commented May 11, 2023 at 12:25
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    My new bedroom set has 1/2" hardboard panels as a support surface. I can't imagine why moisture would accumulate there. If there's that much there, there's enough to be a problem in the carpet and walls as well, and you have bigger problems.
    – isherwood
    Commented May 11, 2023 at 12:47
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    Anecdotally, we had hardboard under a mattress for ~10 years when I was growing up. When it was replaced I used most of it as construction material. It wasn't remotely affected by moisture (it was when standing on end and the garage flooded, though).
    – 2e0byo
    Commented May 11, 2023 at 13:20
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Cutting hardboard with a panel saw is perfectly possible. It's actually a technique I use quite a lot, since the stuff is very cheap, workable by hand, and fine for quick boxes which live in a cupboard anyhow.

Cutting thin stuff with a handsaw requires good technique. That saw needs to be absolutely true in the vertical plane, so get your shoulder and body in line with it (it can move in a curve inline with the cut, but if it wobbles side-to-side the board will snatch, bind and keep snapping). Angle the blade 30 degrees from horizontal or so so it acts like a fence: the width of a panel saw is supposed to keep the cut straight by riding in the cut you've already done, and you compound that effect by angling the blade, which is what keeps long cuts straight.

Cut on a flat surface: board this thin can't support itself. The edge of a table is fine. Let the saw do the work (if you try to rush you'll go off straight). For thin strips I'd use my other hand to support the material being cut: otherwise a clothes peg will do fine as a clamp to hold the far end of the board up.

With practice you can do this accurately enough to build boxes without truing up the sides, although hardboard actually planes fine if you use a sacrificial fence, or a very sharp plane and care. You can certainly cut accurately enough for this.

Get the finest (hardpoint) panel saw in the shop---22TPI is good. Here in the UK ~ £10.

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  • This may be a US/UK thing. "Panel saw" in this answer means a handsaw with no backing spine. I (and other US folks?) usually think of a panel saw as a big frame holding a circular saw, used for straight cuts in sheet goods. I agree that a hardpoint handsaw would do the job pretty well, and might be a reasonable tool acquisition for OP. Commented May 13, 2023 at 14:15
  • @MatthewBourque oh! I didn't know that. So you'd just call it a handsaw (and then differentiate other kinds, e.g. a tenon saw)?
    – 2e0byo
    Commented May 13, 2023 at 20:32
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Here is another approach: Buy ONE piece of 1/4 inch plywood. Or 1/4 inch anything, whatever is cheapest. One cut, at the store, to 6'8" (the width of your bed). Lay it across the bed in the shoulder-to-hips position. The head and legs do not need extra support.

If you don't have a footboard you could also get a couple of free scrap offcuts (including your own) to lay across the foot of the bed in case people sit down heavily there.

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