Thought I'd write this up with some pics in case anyone else ever needs to do this and wants some hints.

Working on a set of 70 442 buckets, ACI only offers buns with no channels or full channels... I prefer to get the no channel buns and modify them rather than try to fill the unused portion of the channels.

First step is to test install (no hogrings) the bun to the spring assembly...
Get it on and centered, then flip it over.
Use a sharpie and mark the spring side listing rods on the underside of the bun.
You may need to put a hand under it so it's tight to the springs when you mark it. Just be sure it stays centered to the spring assembly.

Take the seat frame off the bun and use a ruler to extend your marks.

Lower cushion channels are 11" longUpper cushion channels are 9" long*Measured from original buns
use an awl or thin wire to push straight up through the foam at the beginning and end of your line.

Flip the bun over and mark that spot.
Use a ruler to connect the lines.

Cut the channels...
The original channels are not just a single razor blade cut through the bun, rather a 1/2" groove that goes nearly all the way to the backer (but not through).

You can use a fresh sharp razor to cut two slits on either side of your marked line, then pull out the foam between them. Your razor blade will dull quickly, so have several and plan to swap them out regularly when cutting.

I did it that way for a long time, but always had trouble with keeping the cuts looking nice, and it was hard to cut the foam out w/o braking through or having a rough channel bottom.
The way I do it is to use this handy little 1/2" belt sander from harbor freight... Makes it super easy to control and make a really nice uniform channel w/o cutting through the backing....
A friend turned me into this way a couple years ago and now it's the only way I do it. So much easier!

Anyway... As with everything, there are many ways to do this, but thought I'd show how I do it.

 

More pics, upper cushion.
be sure the top corners of the spring assembly are all the way into the top corners of the bun.
The bottom corners should pretty much line up with the bottom of the side kickups of the bun as shown. (Have to trim the attaching cloths back to see it like this)

I mark the bottom of the spring assembly for the upper cushion, because the bottom few inches wrap around, no need to cut the channels down there.

Rest of the steps are repeated from the bottom cushions, mark the listing rod locations on the bottom of the bun, transfer to the top side using an awl to poke through, and connect the dots.

 

Last batch... Cutting the channels
I always extend and angle the ends so that they gradually drop down.

The belt sander throws up a ton of foam particles so wear a mask, and if you can have someone next to you running a shop vac it helps keep the mess down.

Whole process, marking and cutting the channels took me about an hour.

 

Thanks for sharing, Ben. Do you have any pics of the belt sander actually in use? I'm having difficulty "seeing" it.

 

I'll see if I can get one of my kids to take a video clip of it in action on a piece of scrap foam tomorrow.
THe sander is made from an angle grinder motor (I think) so you just hold the handle like an angle grinder and press the belt tip against the foam and it just digs in.

 

Thanks; I think I get it now. I envision it as a repeated "stabbing" motion, to begin with, going straight into the material, then going back and cleaning up any rough edges along the away, and adding the angled end "cuts" after completing the main "trench." Does this make sense?

 

I think the whole exercise is a little beyond my paygrade, but appreciate your showing how it's done just the same. Thanks for sharing!

 

Great post Ben! I highly recommend him for supplies and guidance if your tackling a seat project.

I was cutting my buns today and your guidance helped a lot. I didn’t have the cool little belt sander which was probably quicker than what I did, but I used a coarse grit sanding wheel on a dremel tool set about on 15 speed. Don’t get me wrong I always love an excuse to go buy a new tool but this worked well for me to cut the channel. If anyone else tries to use a dremel use two hands and use one hand as a solid base against the foam and draw the dremel slowly along your cut line. Kinda like your pin striping a car. The dremel tool is spinning sideways and will want to pull the foam until you get a bit of a channel going. Take small layers at a time off and it will work just fine. And yes it makes a mess so do it outside if possible!

 

Very nice work!!! Other than the mess, the channels look super neat and consistent! Like they were made that way!
As always, what I posted is only one way to do it, and this shows exactly that! Many ways to skin this particular cat!