Expert: Mark H. Miller - 7/29/2010

Question
QUESTION: Hello, I asked you a question a few months ago.  Thank you again for your help.

Now I'm finally getting started on my project and have a couple of more questions.  I'm making a 3" welted box cushion for my bay window.  It measures 111" long on the front side an 67" long on the back side so I'll need to make a sharp triangular corner where the front joins the side.  I'm a little stumped at how to do this. I'm guessing that I'll need to cut the strip that forms the box edge and not fold it around the triangular corner? Should I first sew the front box edge and leave the last 5/8" open on each corner?  Next, sew the side box edge to the top?  Then sew the corner of the box edges together?  It seems like this will be very difficult, especially with the welting adding to the bulk in this tight space.  Do you have any suggestions to make it easier or another way to do it?

Thank you for your suggestion to make the cushion fit tightly by making the sides 1/2" shorter than the thickness of the foam.  Should I make the box sides 2 1/2" rather than 3"?  I'm a little afraid to do this because I'm adding a dacron wrap and wondered if 2 1/2" will be big enough since the dacron will make the cushion a little bigger than 3".  Should the cushion cover also be 1/2" smaller from front to back and side to side than the cushion or does the smaller measurement apply to the box edge strip only?  Thank you in advance for your help.

Sincerely,

Anita

ANSWER: Hello Anita,

You should begin by sewing the welting first,  make certain you sew the cording inside the welting slightly loose,  that way, when you sew the boxing you will hide the stitching for the welting.

When you sew the boxing you should start somewhere along the side and sew clockwise around the perimeter of the cushion,  under no circumstances should you join your boxing on those sharp corners or any corner.  

If you are using 3 inch foam your finished boxing should be 2 1/2.  if you add dacron batting you should compensate for that and the finished boxing should be 2 3/4.

I recommend that you cut your foam the exact size of the finished cushion,  add your dacron and make a muslin cover using a high quality heavy weight muslin.  Then place that as an inset into your finished cover - your cushion will look much better if you have a muslin inset rather than just your finished fabric only.  

A trick of the trade,  be certain to pin the boxing before sewing,  but you should not pin the welting when you sew that onto the cover.   Instead of pins if you have a good hand-stapler one of those that looks like a pair of pliers - they work best - by stapling you won't have to remove the pins as you go and could leave them on the cushion without removing them.

Also,  when you sew the sides you are sewing the fabric against a bias cut which will cause the fabric to stretch,  before sewing lay the fabric on a flat surface face down and put some kind of tape to help the fabric keep it's shape,  ordinary masking tape used by painters will do.

When you place the foam and dacron into the cover, before you close the cover make certain to run your hand around the perimeter on the inside of the cover and push the flap / selvage so that it lays flat against the front of the cushion and not on top.  

Also, for such a large cushion it may look much better if you eliminate the welting and just have a seam.

I hope this helps.

Have fun doing the job.

Mark Miller.

---------- FOLLOW-UP ----------

QUESTION: Hello Mark,
Wow, thank you for such a quick reply and for all of the helpful tips.  I really appreciate it.  If I understand correctly, you mean that I should sew the boxing in a continuous loop.  I will be interested to see if this can be done on the sharp corner.  It seems too tight so maybe I will have to stitch that part by hand.  Should I clip the corner in a few places before trying to sew around it?  
You said to pin the boxing but staple the welting.  Should the welting then be sewn on in a separate step before the boxing is added rather than sewing all of the layers in one step?  You also suggested eliminating the welting.  I really want to have the welting on the front edge.  Would it look better to eliminate it on the sides that will face the walls?  
To make the muslin cover, would I need to make another boxed cover exactly like the outside cover or could I just wrap the muslin around the Dacron and staple it in place?
Should the painter’s masking tape that you suggested adding to help the fabric keep its shape be placed on the seam allowance of the fabric?

Answer
you mean that I should sew the boxing in a continuous loop.
Yes, at least for the front part,  if you need to have seams they should be at least two inches away from any sharp corner.

It seems too tight so maybe I will have to stitch that part by hand.  Should I clip the corner in a few places before trying to sew around it?  
Sewing the corners by hand will certainly work,  you can also clip the boxing when you turn the corner but there should be only one clip - directly to the corner - not several.

You said to pin the boxing but staple the welting.
Woops, I did not make myself clear,  you should not pin the welting at all when you sew that to the cover and you should sew the welting first.   Then, instead of pinning the boxing you can either pin or staple the boxing,  stapling the boxing in place is easier.

If I di Should the welting then be sewn on in a separate step before the boxing is added rather than sewing all of the layers in one step?  
Yes, there should be two or three steps.  One sew the welting by itself first,  then sew the welting onto the cover and last sew the boxing to both the welting and the cover - that is the reason I advised you not to sew the first two steps too close to the welting but sew them a little loose, that way when you sew the boxing you will hide the first stitching lines.

You also suggested eliminating the welting.  I really want to have the welting on the front edge.  Would it look better to eliminate it on the sides that will face the walls?
No,  welting should ber all around or not at all.
 
To make the muslin cover, would I need to make another boxed cover exactly like the outside cover or could I just wrap the muslin around the Dacron and staple it in place?
The muslin cover should be made exactly the same way as the outer cover but slightly bigger to allow it expand inside the final cover,  and the muslin cover should not have welt but just a seam - when the cushion is up in muslin it should fit and look like the finished cushion - with the exception that it should be slightly larger so the cover of the finished cushion will be tight.

Should the painter’s masking tape that you suggested adding to help the fabric keep its shape be placed on the seam allowance of the fabric?
Yes,  after you sew you could remove the tape or just leave it in there,  if the tape is wider than the seam allowance and your machine strong enough the needle will sew right through the tape.  Some of the glue will stick to the needle but that can easily be removed with any solvent such as "goo-off".   There is no need to place the tape all around,  just on the sides to prevent the bial cut from stretching.

I hope this helps - have fun.

Mark Miller.