How to cut 4' foam (perfectly) for cushion??

texashottieMarch 25, 2008

I know this sounds funny but I'm hoping some of you upholsterers will chime in.

I bought outdoor foam (expensive!) that is 4" thick. My seat cushion that I'm making curves and flares. I need to cut my foam perfectly so that it holds it's shape on the sides for my fabric to lay over nicely. I mean, I'm afraid that if it has hacked edges or if I compress the foam to cut it, maybe the sides will bulge therefore making me cut too much out of the sides. Does that make sense? I just want the "planes" of the cushion to be at 90 degree angles of each other.

I feel like taking a huge steak knife or saw blade and chiseling out the shape---but what is the proper way to do it?

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paint_chips

"I know this sounds funny..."

Well, I know this sounds crazy! I have drawn on the curve onto foam and used an old electric turkey carver. It cut through it like butter.

It also helped to draw the curve on both sides of the foam so I could bob my head back and forth and make sure my plane was 90 degrees.

    Bookmark   March 25, 2008 at 3:25PM
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mlraff53

I've always seen it done with an electric knife. Personally I've never done it though.

    Bookmark   March 25, 2008 at 3:25PM
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maddielee

I've had good results using an electric carving knife.

    Bookmark   March 25, 2008 at 3:26PM
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budge1

If you don't have an electric carving knife, use a large serrated blade knife (bread knife).

    Bookmark   March 25, 2008 at 4:12PM
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magothyrivergirl

Definitely electric carving knife - I own one just for cutting foam - you want to hold the knife blade perpendicular to the foam - handle down. (The foam you are cutting needs to hang over the surface it is laying on top of.)
paint chips - good idea to draw on both sides - use a sharpie for the line.

    Bookmark   March 25, 2008 at 4:19PM
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texashottie

Oh, you guys are great!!!

I don't have an electric carving knife... if I used my good bread knife, will it ruin it?

    Bookmark   March 25, 2008 at 5:57PM
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chelone

Here's my opinion (I own a foam saw, but I do this stuff for a living, too):

Spend $15 and buy an electric knife. Scope out the Goodwill or Salvation Army store, but buy one. 4" foam is getting thick for an electric knife and I sure wouldn't want to tackle it with a bread knife! If you want to torture yourself, then go for it. ;)

You want to overcut your foam. The foam should be bigger than the finished size of cover. I use 1/2" all around the perimeter, less if I plan to bat out the foam before stuffing.

I cut foam while it's flat on the floor. I stand over it and make sure I hold the knife perpendicular to the floor. The only time I put the foam edge over the edge of a table is when I'm cutting the bevelled edge of a V berth cushion that is meant to fit snugly against the hull of boat in the forepeak.

    Bookmark   March 25, 2008 at 6:10PM
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greenmtn

I recently cut a 4" foam with an electric knife. I had a template out of brown paper and drew on the foam with a Sharpie. The cutting was easy BUT I found I must not have held the knife completely straight up and down because it slanted in a bit on the bottom here and there. (Perhaps the marking on the top & bottom would have been a good idea for me). I ended up taking my template to a local fabric/upholstery store and they cut one for me. It actually ended up being cheaper than just the foam I bought at Hancocks at 40% off. I was amazed.

    Bookmark   March 25, 2008 at 6:50PM
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lynninnewmexico

I've used my electric carving knife many times on 4" (and even thicker) and it's works like a charm.

    Bookmark   March 25, 2008 at 7:44PM
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chelone

I have cut a lot of foam over the years. I learned early on that if you're going to perform an operation regularly you ought to buy the proper tool to make it easy. THAT'S why I have a foam saw!

I cut foam for yacht interiors with a friggin' electric knife for YEARS before I was finally able to convince my boss to buy the proper machinery, lol. The TIME saved by purchasing a proper foam saw was shocking for her. My calculation is that she paid for it in 4-5 jobs... that's how much faster a saw is than a carving knife.

And that's how much faster an electric knife will be than a bread knife. An electric carving knife is going to make it A LOT easier.

    Bookmark   March 25, 2008 at 8:03PM
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oceanna

I wanna see pictures when you're done, Tex!

    Bookmark   March 25, 2008 at 11:45PM
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texashottie

Thank you! I really appreciate the feedback. Chelone, I was hoping you would respond. Thanks for the tip on adding the 1/2 inch around the perimeter.

Oceanna, I'll post! :)

    Bookmark   March 26, 2008 at 8:33AM
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magothyrivergirl

Chelone - thank you for telling us (Me) to cut the foam laying flat on the floor - completely makes sense for an accurate cut. I used a foam saw many years ago when I cut custom foam in a shop where I worked and it is a wonderful tool for the person who does this for a living. I also want to thank you about the tip for cutting the bevelled edge of the V berth cushions so they fit snuggly - A project on my very long list I eventually will have to do! Thanks again!!!
Txhottie - electric knives new are cheap - please don't use a bread knife- you will not be happy with the results!

    Bookmark   March 26, 2008 at 8:35AM
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kitchendetective

Uh oh, another soul has to do V berth cushions. DO post when you get started. DH just put that on my list.

    Bookmark   March 26, 2008 at 12:30PM
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susieq07

Try an electric kit. carving knife, it should cut like butter...

    Bookmark   March 26, 2008 at 12:41PM
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chelone

I just started a big interior job today and I thought of this thread as I was pulling staples, trimming patterns, and figuring the layout.

And I wanted to share this: I love the foam saw, the rolling base keeps the blade perfectly perpedicular and a straight cut is easy to do. And fast! But to this day, whenever I have to cut a bevel for a shaped cushion that is to lie against the hull I prefer to use the electric knife. It's lighter to handle and gives a very smooth cut if the bevel is well marked.

    Bookmark   March 26, 2008 at 3:27PM
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spanky_md

Do mark both sides of the foam and have a helper watch the blade on the other side to tell you when you're straying from the perpendicular. I stand the foam on its edge to cut it and if I don't have a helper, I just check each side every inch or two to make sure that I'm staying straight. It's very easy to get five degrees off!

Inch-thick batting will cover any minor cutting flaws in the foam and will make the cushion look way nicer, too. Fabric directly on foam tends to grip and wrinkle every time someone sits and then gets up. Batting prevents this. Be sure the get poly batting that is made for upholstery, though. Quilt batting is too lightweight and will come apart and end up in rolls at one end or the other of the cushion.

I use 3M Spray Adhesive to attach the foam to the batting but you can also just wrap it around and secure edge to edge with big hand stitches.

I'm waiting for a foam saw to show up at auction someday. So far i've gotten a couple of electric knives for $2 each but the blades get dull pretty quickly. I don't cut enough foam to warrant investing $100 in a foam saw.

    Bookmark   March 26, 2008 at 4:01PM
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chelone

A new foam saw costs considerably more than $100. The cheapest I've seen new is around $300... mine was more.

    Bookmark   March 26, 2008 at 4:42PM
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texashottie

spanky, do they make poly batting for outdoor use? I need to look...

    Bookmark   March 26, 2008 at 5:47PM
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chelone

We use the same poly. batting for indoor and outdoor work.

What's more important for outdoor use, I think, is the quality of the foam. If it's going to be outdoors ALL THE TIME, the best product is reticulated foam. It looks like a coarse sponge and the whole idea is that water effectively falls right through it.

Ordinary foam tends to hold water... like a sponge. Water gets into the foam via the stitch holes on the covers. If the cushion covers are densely woven (Sunbrella!) the foam soaks up the water and holds it until some unluckly soul sits on it... with predictable results.

Batting isn't the issue, the base foam IS.

    Bookmark   March 26, 2008 at 6:05PM
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texashottie

Okay. I am using two different fabrics, and Sunbrella is one of them.

These cushions will be on my back patio that is covered. So I guess I'm safe using a poly batting? You don't have to worry about mildew with it? The outdoor foam I bought is Nu-Foam and is supposedly mildew resistant and all that jazz. (Hancocks has a sale right now on foam/batting.)

Thanks, Chelone.

    Bookmark   March 26, 2008 at 6:54PM
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chelone

You ALWAYS have to worry about mildew, lol. It's the damnedest thing... no mater what you do to prevent it, it still shows up.

But keeping rain off the cushions is a giant step in the right direction.

The mortal enemy of mildew is SUNSHINE. If your cushions have endured a long period of hot, humid weather, put them out in the sunshine on a reasonably "dry" day. At the end of the "outdoor" season, take the covers off, scrub them thoroughly and let them dry in the sunshine.

A great product for mildew is Iosso. You can usually get it through suppliers for the marine market. It comes in a jar, crystal form. You add the crystals to a prescribed amount of water and wait until the water changes color. Scrub the fabric thoroughly and rinse well. Dry in the sunshine. Works great. (usually!)

    Bookmark   March 26, 2008 at 7:23PM
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kitchendetective

What kind of sewing machine and needle are you using? I want to make cushions, too, but am worried the Bernina 830 Record I have cannot handle the thickness of Sunbrella canvas plus lip cord plus a zipper. Any thoughts on this? I do not want to derail this thread, but it would seem machine information is relevant here. Thanks. If it cannot, what would be a good machine to get?

    Bookmark   March 27, 2008 at 1:33PM
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chelone

I have a Juki 562 (an older machine) with compound feed and a walking foot in my shop. I have a couple of sets of feet for it (to accomodate different welt sizes). I typically use an 18 or a 20 needle for cushion work. An 18 is generally fine for Sunbrella.

I have not used a "home machine" in nearly 30 yrs.. I'm rather a sewing machine junkie, frankly... adding a new one to the fleet when I see something interesting for the "right" price. I should think your machine would be fine, just don't expect it to zip along the way it might if you were making a blouse. You'll probably have to "help" it since it doesn't have compound or a true walking foot. Take your time and be patient.

    Bookmark   March 27, 2008 at 3:11PM
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ladyamity

I've used my Sears Harvest Gold electric knife.
I bought it on Ebay for $4.88 w/$5 shipping.

It's paid for itself 100 times over in the last 6 years.

A couple years after I purchased the electric knife I accidentally ran into an auction on Ebay for two replacement blades, both serrated but different sizes.

I've cut everything from foam to unwanted soft-wood stalks on my plants.

From a non-pro, DIYer I have to agree 110% on the batting.
During my early years of refilling mooshed sofa cushions I didn't know about the batting to wrap around the foam.
What a difference the batting with spray adhesive makes!!!

But now you all have me curious.
Are these the types of foam cutters you pros are talking about?

Here is a link that might be useful: Foam Cutters?

    Bookmark   March 27, 2008 at 3:19PM
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texashottie

Sweet! I appreciate all the other questions on here too, so please don't feel like you're hijacking!

I bought the batting today to wrap around and the spray adhesive. I also intend on getting that electric knife.

Chelone, I have another question. I am making a box pillow. I've made a template of the chair with brown paper. Do I cut the fabric to that size plus a 1/2" seam allowance? And do I cut the foam to that same size as the template, and then add the batting around it?

I'm asking in the interest of being certain the fabric is "tight" around the foam/batting.

Thanks.

    Bookmark   March 27, 2008 at 5:47PM
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kitchendetective

I appreciate all the generous feedback. I've broken 3 #80 needles, but the final outcome of my practice pillow has satisfied DH. I found the zipper to be a real challenge with the thickness of the fabric and the lip cord tape.

    Bookmark   March 27, 2008 at 7:53PM
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texashottie

KD, post pics for us! :)

    Bookmark   March 27, 2008 at 11:29PM
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spanky_md

Oops, sorry, I am not sure where I got $99 as a price for a foam saw. I just looked it up in the Tedco Industries catalog and theirs is a Bosch for $595.

    Bookmark   March 30, 2008 at 2:30PM
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markspencer

If you don't have an electric carving knife, use a large serrated blade knife (bread knife)

Here is a link that might be useful: foam cut to size

    Bookmark   March 30, 2011 at 2:25PM
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sewshop_hotmail_com

Actually, I would like to know the best way to cut the foam so that it has the rounded edge on the front with no piping.........like they have on couches and recliners. This is for lawn furniture but wanting to get away from piping......

    Bookmark   March 30, 2011 at 5:32PM
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