Rulers - When the numbers/lines wear off
Cutting Mats - Every 5 or 6 years or so
Rotary cutters - When they break. I sew a LOT, so I'm hard on them
Rotary blades - When they start skipping more than a couple of times per WOF cut
Pins - When they're too bent to straighten back out, or when the "head" comes off
Needles - My machine makes a "whumping" sound when it needs a new needle. I don't hand-sew enough to wear regular needles out.
Chairs - Not often enough. My current chair is an office chair with a pillow on it. I wore the cushion out. :D
Sewing M achines - When it starts causing more frustrations than it's worth, or when I happen across a really good deal on one I like.
Sc issors - Every couple of years for "everyday" sc issors. I inherited my Granny's Ginghers, which I'll never replace. <3
Seam Rippers - When they get dull or when they sprout legs and walk off.

Rulers - haven't yet but I'm a novice quilter
Cutting Mats - when they get groves in them
Rotary cutters - haven't yet
Rotary blades - when the skipping gets bad and sharpening doesn't fix the problem
Pins - when bent
Needles - when broken
Chairs - I only wish I could
Sewing Machines - not yet
Scissors - when they get loose and don't cut cleanly
Seam Rippers - not yet

I only have had to replace blades. Everything else is still going strong. I do replace pins a lot. I like real fine pins that seem to get dull quickly. Would like to find some very fine long lasting ones. I keep looking! Sewing machines don't count for me.....I just love to upgrade!

I have the same Bernina I bought 10 years ago and will never ever get rid of that, in fact, I just bought another at a flea market. Needles, pins, mats, rotary cutters and rulers are the same ones I started with 10 years ago. I buy blades in bulk off ebay and when they skip, they go. I bought some used office chairs on wheels cheaply and have no clue when I will replace them. I use irons until they stop, which they haven't for almost 10 years. Seam rippers do need to be replaced as I have had some of mine for 10 years and they are difficult to use, sure wish I sewed so good I didn't need them !

I usually buy in bulk. I discard when items, rust, crack or break and are irreparable. I have a plastic peanut butter jar with the lid and I throw these items in then throw the whole shebang into the recycle bin. Every room in the house has it's own pair of scissors to only be used in that room. the only way any scissors designated for sewing make it out of the room is in a go/to bag/kit for handwork. Dh wanted to cut a large piece of tarp, I showed him the shears in his shed to be used for such work. they weren't rusty because I had them wrapped in an oil soaked cloth to keep them from rusting. They cut through that tarp like butter. I have 2 sewing machines both in great condition. Almost bought another the other day and decided not to since redoing the sewing room isn't completed.

Rulers -- I just purchased two for 50% off at JoAnns
Needles -- Keep new ones in stock
Chairs -- When needed
Sewing Machines mine are mostly vintage
Scissors -- Whenever I find a good deal
Seam Rippers -- need a new one now

I suppose it would be "fair" to fill in what I do - - -

Rulers - when I notice a curve on the side - or I break it - or I notice that the markings are inaccurate - or I want I different brand than the ones I already have - or need a specialty one for a particular project
Cutting Mats - when they get warped, gouged, or break
Rotary cutters - got a deal on e-bay so have several - they only one I actively dislike is my Gingher one
Rotary blades - also got deals on e-bay - probably not as soon as I could - about the time I realize that I have table knives that are sharper than the blade I'm trying to cut fabric with
Pins - when they get bent, broken, dull, or rusty
Needles - when I realize they are dull, bent, or broken
Chairs - mine are all from yard sales -
Sewing Machines - my "newest" to me one purchased used - was originally purchased in 1985.
Scissors - when I find one I like better than the ones I have
Seam Rippers - I swear these things are geniuses at disappearing - it finally dawned on me that these things also get dull - and I am not aware of any way to sharpen them - I have several - and almost always have trouble locating just ONE when I need one

I think part of my problem in keeping track of things is that I have machines in two locations - so I end up with three seam rippers at one machine and none at the other, and so forth.

I can keep track of the oil - because I put that back on the shelf because I've had it leak when i had it in a drawer.

The brushes to clean the lint from the bobbin areas - they have feet, too!

I think the truth of the matter is - I tend to add to, instead of replace!

If it ain't broke, don't fix, or in this case, replace it. Problem solved. Money saved, too.

I agree! I did without while raising 2 kids and putting them through college. They are married, have great jobs and are very independent now, so it is time for us to do the things we want to do. I don't regret giving up my hobbies while raising kids, but I'm very thankful to be able to buy the things I want, not just the things I need. I earned that privilege.

As necessary. I used my original mat 25 years maybe? then kids used it as a craft mat for school projects. I try to be attentive when it comes to my rotary blades and I will willingly pitch seam rippers when dull.