My friend was a set builder at Ikea. She said they glued everything. So as you build the frame, glue the dowels in, add a seam of glue as you put in the top, bose, and fixed shelf. Ive had great luck doing this, 15+ years of very sturdy Ikea furniture. Great ideas here, thanks!

I often overlooked the back board thinking it is only cosmetic, didn't know that is the most important bit. Thank you so much 🙏

I assemble IKEA and Steen furnisher as a side hustle and have always recommended to my customers that I glue all joints and backs. I do this for book cases, chest of drawers etc, plus I have invested in an electric staple gun to aid the process. Nice tip in bracing the back, I'll use that in future.

I can't imagine what my wife would say if she saw me with a bottle of glue near that beautiful carpet, to be fair to her though, I can't be trusted

Everything about this video is great - the way you explain WHY you’re doing every little step not just how, the camera work, the pace. Very easy watching. Thanks so much, I’ve subscribed!

Always refreshing to see someone on KZfaq who knows what he's talking about. Thank you!

When I did my first ikea kitchen, the store told me to buy one of their large plastic spatula's (the ones for turning fish) and use that for opening all the boxes. WHAT A REVELATION!! I still have that same spatula 7 years later for opening all flat paks. It is perfect for running down the glued seams and does manage to break the tape which is designed to tear length ways so you don't need a knife.

i usually screw some metal or plastic L-brackets at the 4 corners for all Ikea furniture, seal all exposed particle board edges with PVA glue and fix some rubber/plastic pads on the furniture legs/bottoms. My late father usually went overboard and painted the backboard as well. Usually he just use left over paint or varnish and sometimes just undercoat. And all my Ikea and other particle board furniture still good today when I bought it 10 years ago. These are some tricks from my late father who is a carpenter.

Perhaps glue TWO wooden strips at the back instead of just 1. This way you can cover both seams of the triple folding backboard (seams which tend to start wobbling over time, or even partly rip through), and also you can now use 2 screws per shelf to avoid sagging, each at 1/3 of the width.

I have three full height and full width Billys with full height glass doors. I bought them 27 years ago in 1995 and absolutely love them. I will shortly be moving them as I am having my living room altered and may very well take up the tip of the rear batton and drilling through. I have to say that nearly all the shelves are crowded with books and there is no sign at all of them bowing, even after all this time. Thanks for the video. 👍😀

Growing up when it came to preventing bowing in shelves, we always just flipped them as part of our spring cleaning. Empty everything off when dusting, flip, and put everything back. Despite heavily loading them up they stayed fine for decades. The only problem was the middle shelf on our DVD cabinet which was screwed in so couldn't be flipped. That bowed plenty. I still do this even with the solid wood shelves of the bookcase I have now as a precaution and so far no problems. I am definitely going to keep the gluing of the back in mind though as I've seen the backs come off too many when being moved about. Thank you very much for sharing!

Very interesting ideas. FYI: You can buy individual boards for the Billy, so you could use those for stiffening and would have perfectly matching material.

I’ve put together/installed/moved 5 billy bookcases in the past year, and I have to say I really like the thin & tall version of the billy bookcase the best because it’s only about 40cm across and the shelves will probably never visibly bow. They look small but 3 of them together is more shelf space than a regular billy, and you have the flexibility of being able to set it up in a corner. I’ll definitely remember this the next time I put together another one!

Some 20 odd years ago we built a rank of standard Billy bookcases 3 wide + corner units each end + narrow units next to them to make a shallow U shape. To tart them up to go in our period house we stood them on several 4 inch fence posts, put ogee skirting board around the bookcase base & sides, picture rail around the tops, decorative timber mouldings down the fronts to hide the joins between units, & painted them pale cream. They look fabulous, haven't sagged, & I get admiring comments about my expensive bookcases. I dont always own up to them being Ikea....

A drop of wood glue on the dowels works really well as they usually remain fairly loose and don't give the furniture any additional strength.

One thing I've learnt from these - if you want them to sit flush to the wall, before building sit the side panels up against the skirting board, mark them up and then cut the profile out on the side panel of the billy (it's harder to do this when they are built). I usually keep the cardboard too when working on carpet and set the panels on it to stop any carpet dents until its in its position.

Fab video Stuart, i build & fit quite a lot of this type of furniture & also glue wherever i can, another tip i will share with your viewers is at the back of this unit (Around 9.20 mins) into your video you will see raw chip board, i usually paint some sort of wood sealer on to this, especially if it's an old house i'm working on just to prevent expansion in the board due to high humidity or damp in the house.

The timing of this was incredible; planned to rebuild a Billy today. Glad I watched this first, it now boasts a wooden spine for added strength! Thanks for the tips.

I have three, fully loaded with academic hardcover books, 3 feet wide, glass-doored Hemnes bookcases. Bought and assembled in July 2014 and not even a hint of sag. Real wood is much stronger than particle board.

I'll keep this in mind if I ever buy a Billy bookcase again. The ones I have are 40 years old and have been moved at least 10 times with no problem.

My Billy bookcases are now 30 years old. They have moved house with me SIX times over those years and are still in excellent condition. If I ever needed another bookcase, I'd head straight for Ikea and look for the Billy section 😎

The additional wood strip and screws into the shelves is a great tip. I've always glued mine together as well - great minds think alike! ;-) If you wanted to go the centre support route, as you demonstrated, Ikea sell additional shelves, so they'd be the same colour, and you could cut them to size. Cheers

YEAAA!!! Finally someone who knows what they are talking about... glue dosen't dry, it CURES!!!

Love the ideas here. Though I might go with countersunk screws for the vertical support into shelves, to avoid the risk of the domed screws scratching the wall

Great tips for strengthening a bookcase! Gluing a strip to the back and screwing shelves through it is brilliant!

I assembled 3 billies at around 1984, moved 4 times, they’re still fine and probably will outsmart me.

Chipboard is not inherently strong with screws in the width as shown here. In fact they can themselves be the cause of the shelf delaminating. However, if you predrill the screw holes completely, and use long screws, then fill the predrilled holes with wood glue, this will make a much stronger support, and the glue will help prevent delamination. I had a number of these shelf units which lasted very satisfactorily, but had to be left at he last house as I was moving internationally again.

If your going the glue route. Glue the dowels as well. I use 25-32mm gyproc screws instead of the pins for the back board and either side of the folds to prevent it splitting over time. This stops heavy handed people knocking the back out.

I bought the Bill bookcase back in the first half of the eighties. It STILL looks new!

Great idea for the back bone support! I agree glue the backboard before nailing it will make the structure a lot stronger. I also apply acrylic paint / water sealer to all bare "wood" sides of panels, as moisture will attack those areas more often. Especially important for those living in those hot and high humidity countries. For heavy books like those full of art and photography, solid wood is my first choice.

I have some some Billy Bookcases that were bought in 1995. They were moved from the UK to the US in 2000 and since then have been moved through five more moves and three states. Still going strong and have not sagged!

When I built my Billy cases, I glued every dowel and every fixed shelf jointing face, the lower stiffener as well as the backing as shown in this video (but I doubled the amount of Brad nails in it) Been rock solid for 10 years!

Just built the 1st of 2 Billys and slid it into place after watching your video several times. Felt like an expert, thanks. The Proper DIY videos are WONDERFUL, not only in the advice and clear directions, but in the excellent camera work and editing. And you're adorable. 😁

The content we didn't know we needed! This is DIY on a whole other level

I am a relatively new devotee Stuart but I love your videos. They speak to me as a 56 year old man who is relatively handy but still a DIY’er. The biggest thing is that most of your videos appeal to me as they are the sort of jobs I’m doing for me and my two grown up daughters

Last year we helped our son move into his new flat, including a couple of Billy Bookcases and some other Ikea stuff. It's 3rd floor with just stairs, no lift. Although they had to go up each in their box, if, as and when the time comes for him to move out and I'm still in a condition to help, I can guarantee that if it's anything to do with me, they're all coming out bit by bit rather than as complete units! 🤣

Glueing isn't necessary, it's quite messy and will run, but doubling the amount of tac nails is better. Also the adjustable shelves have very weak plastic inserts that will stretch and fail under a heavy load. Replacing them with all metal fittings is best. My local hardware store carried these for a dollar. You can't go wrong.

Nice video. tip: if you want extra shelves check the prices for those shelves separately compared to how much another billy costs. When i bought my Billies in 2001 the price of a Billy (which has 4 movable and 3 fixed shelves) was only 80% of the price of 5 extra shelves. So i bought 8 Billies and built up 5 of hem and added the shelves from the other 3 for very full bookcases (2000 pocketbooks); built 1 with only the middle shelf for board games. And when my friend moved and severely damaged one of her billies i gave her 2 sides as replacement. Still have 2 sides left to this day.

I am in my 70s and have put to a few pieces of ikea on my own and also used the glue idea years ago and put glue in the dowell holes

I went to a customers house, I'm a gardener, to sort out her Ikea cube thing. It was brand new, only just built, and it was falling apart. I couldn't work out how it was in such poor condition till I asked the question. Who assembled it and how did he do it? My son assembled it, and he he used a drill to really tighten everything up! Every screw a was stripped in the chipboard. I glued it all up and filled in the oversized holes with matchsticks and more glue. Seemed to be ok. And a few weeks later was still standing rock solid. I was the hero! And a few £s better off.

Another good tip with flat pack furniture is to put some wood glue in all the screw and dowel holes. It’s something my grandad always did. It helps stabilise the chipboard and stops the screws from pulling out as easily, as we all know wood glue is stronger than the actual wood.

Thank you, this is super useful. I have 5 BILLYs, which I put on floor-particle board and added wheels, for a pull-out archive. And while it works well, then after 5-7 years they have become a little unstable, and the back pieces keep popping out. I will definitely use your tricks for them.

That is a fantastic idea! I think that i will always add a screw to the shelf of a bookcase from this day forward! Thank you so very much!!

On another point, one trick I found for Ikea drawers was to use a bit of beading lengthwise underneath the hardboard base of each drawer. It then allowed me to put more than one pair of socks in before the base slowly warped downwards.

Great video! Good pacing, very clear instructions and nicely filmed. Wish I saw it before assembling my own shelf. I'd definitely use some of the techniques used here :) Looking forward to more of simillar content!

Wish I had watched this before I recently assembled 12 x 80cm full-height Billys and 5 x 40cm full-height Billys, all with Oxberg doors and extensions. Great video, thank you. The Billys, especially with Oxberg glass doors, are just great and make a fabulous library at a reasonable cost. As an engineer, I really appreciate the precision of their manufactured parts. Not once was any part or screw missing and everything fitted precisely. I found it best to assemble them on a big table, just to save my back and knees. I thought about gluing but decided not to as I wanted to keep the disassembly option open, but I agree with you that removal companies will just take it away whole. I can always retrospectively glue or silicon but don't really think it is worthwhile. With multiple bookcases, I joined them together using Hafele's cabinet screw-and-sleeve 36 cm connectors for added solidity. When each of these is connected to the wall (preferably via a stud, but this is not essential) the whole assembly is as solid as a rock. As you say, the shelf bending issue is the biggest issue with Billys as it is for all bookshelves, an issue I puzzled over for a long time. Not only is there simple bending that relates to the elasticity of the shelf, which the current thicker shelves largely solve, but more importantly is the issue of creep. Creep, or stretch, occurs over years and all wooden shelves, regardless of wooden material or manufacturer, are susceptible to. This is the major problem with any wooden shelf, solid hard wood or chipboard. I have very heavy books that are at the 30kg limit of each shelf, This is where I wish I had used your batten at the back. My solution was twofold: a) on the fixed shelves, hammer in a lot more more nails. The most recent Billy have a pretty solid backing (not as flexible as shown in your video, although I was using White Stained Oak as opposed to the white you used). These were more expensive so that may explain the difference. With a more solid backing and lots of nails, I am confident that this is equivalent to the rear batten in the video. b) I used an aluminum U-channel cut to precisely the width of and length of each shelf and just slotted this into each shelf, I had these cut by an aluminum company here in Melbourne Australia. They each cost about a third of the cost of a new shelf ($8). The bottom and top shelf don't need these. The middle shelf could use this but I used extra nails to strengthen it. All other shelves have this U-channel at the back. Yes, it creates a lip that prevents sliding books to the back, but I was willing to accept this tradeoff. The tradeoff is that these shelves will never bend!!

We got MFI kitchen and bedroom furniture years and years ago, my has and was a belt and braces type of chap. Years later when we were changing the kitchen he had to use an electric saw to it, everything that had been glued and screwed was all still intact, the bedroom units are still in use by my now 34yr old daughter.

Those were brilliant tips to help prolong the life of these bookcases but then I had a nightmare when I saw that 'A' level Physics textbook on the shelf !

It makes sense with flat pack furniture that they would orient the face side of the boards towards the cardboard because they would be least likely to get friction damage from rubbing against other parts during shipping. The hint of using a chisel is great.

One thing you forgot to mention was to ensure that the little arrow on the cam points in the right direction. Easy to forget and can cause issues when assembling large pieces. Also I use a dish or Tupper ware container for all the little fixings, you can be sure that you will nudge the cardboard box during assembly sending bits everywhere.

As the glueing and the piano soundtrack flowed in, fat warm tears arrived to my face in awe. Beautiful.

So many great ideas here. Will need to apply these the next time I put the shelves in

I put aluminum L profiles with epoxy clue on the back of heavy loaded shelves to prevent bending. Worked like a charme - they're almost invisible, don't change the look and are still movable.

We had a library room of these Billy bookcases with glass doors. The cut out for the skirting and fixing to the rear wall were essential.

Nice assembly review, but the ‘bottom stiffener’ is actually called a plinth. It’s to stop rubbish collecting under the shelves and as a finish. I also glue the bottom shelf to it. You may want to check diagonals before attaching the brads. Lloyd

Billy bookcases are a great starting point for other projects. The side of a Billy bookcase makes a great 6' shelf with two wall mount brackets at 24" intervals. I've used extra shelves to add storage to kitchen cabinets and custom built-ins for other rooms.

Another option for shelf stiffening is to glue a length of aluminium angle (say 16mmx16mm) along the back edge of each shelf. This helps enormously and is pretty subtle to look at against a white shelf.

I still have my 3 Billy bookcases from over 35 years ago; and have moved at least 8 times with them. These are the old school ones with the single piece backing hardboard that is thicker and does not bend or fold in any way. They came with all metal hardware (no plastic anything) and fairly big nails with large heads to fasten the backs with, not small pins. Maybe I'm the anomaly, but I'm relatively poor, so hiring a moving company would be totally out of the question. I have always needed to take them back down to flat pack and then reassembled. No issues or problems with degradation of fit or finish, no glue.

Thank you so much for this! I am about to use Billy cases to create a built-in-looking bookshelf wall and I want it to be cost effective, handsome, and sturdy. Your instructions are exactly what I needed!

My trick to keep it sturdy without glueing is to fix an Observator cross brace to the back. Works like a charm. All the other tips are sound too 👍

A fourth option is one that you kind of covered. Use a horizontal stiffener beneath the shelf, but rather than putting it at the front of the shelf, put it at the back. Not only does this eliminate the problems associated with matching the existing material, it also means that the shelves remain adjustable.

All good points presented. Been screwing and gluing this type of "furniture" for years, and it works.By the way, should have glued the wooden dowels. Also, glue will run so you should have left the cardboard on the carpet.

Fantastic tip to run a 1x2 up the back! It not only keeps the backboard from being pushed back, but the idea of using it to support the middles of the shelves is brilliant! Thanks!

Went in thinking this was going to be something that made it impossible to take apart, and was really happy to see this simple addition is college student friendly!

No glue. We bought our shelves in 89 in Holland, took them apart and moved to Switzerland where they put together. 22 years later, we took them apart to move them again and put together again. They are still good. Great product.

Most of these fixes can be mitigated by buying the appropriate model of Billy. If you're intending to fill it full of heavy books, get two 40cm wide versions instead of the 80cm wide. Yes it's a tad more expensive but they're designed to be tanks - there's nothing you can put on those 40cm shelves which is heavy enough to cause a sag that won't cause the fixing points to fail too. I can't say I've ever experienced re-assembling a Billy and it not going back together quite right. I've always found them to be rock solid and that's after 5 moves including extended periods of them being left disassembled in storage. One thing I would suggest doing if you're planning on putting bookshelves/wardrobes - anything floor-standing against the wall on a carpeted floor, is make accommodations for the thickness of the carpet/gripper rod - you can either cut a small section off the rear bottom of the uprights, or, as I do, add small feet at the front of the uprights. That way the shelves always 'want' to lean backwards into the wall rather than away from it which the gripper rod normally causes. This also, has the added benefit that when you come to move, you only leave behind two small dimples in the carpet, rather than the outline of the shelves.

I reinforced my Billy shelves by attaching some aluminum U-channel on the back edge. (My shelves are older, so they all fit nicely in the 3/4" U-channel I could get at Home Depot... the newer size might be harder to find U-channel for.) This adds *tons* of stiffness to the shelves. I've got lots of weight on them, and they haven't sagged yet. They're also still re-positionable, as my needs change. I also join multiple bookcases together by drilling through several of the shelf holes and inserting shelf-pins of the correct size though the holes to connect both bookcases; this ensures that their fronts always line up perfectly.

Great video Stuart. Was thinking at 2min58secs in that we might be seeing you glue the tip of your finger back on as well! Another idea is in old houses with carpet where the floorboards might not be so level is to put some small spacers underneath the bookcase frame to ensure its all level before you then load it up with books and fix to the wall. The spacers get hidden by the carpet pile.

Another good tip is to use small screws, instead of the nails, easier to take out if you want to dissmantle the case when you move.

We bought our first Billy bookcases in 1974! I have used them ever since. Some moved with me from the UK to France to the US.

I always use my drill, but I make keen use of the torque clutch settings. I start low, I think the sweet spot for most flat-pack furniture usually ends up around 7-10 on the dial. Just enough to get it flush but the clutch will engage as soon as it's set.

Thanks for the good ideas! I've built a bunch of these over the years and can definitely see the benefit of making it more sturdy. One slight issue to have in mind when it comes to screwing the shelves in place from behind is of course that it will leave visible holes in the back if the shelves would ever need rearranging.

The timing on this video is pretty extraordinary. I just assembled a Billy bookcase two months ago - before this video came out - and I came to the same conclusion that strengthening of the structure was desirable. I did this by doubling the number of nails going into the backs of each shelf, and also added wood glue to the backs of each shelf. This entailed pre-preparing a damp cloth to wipe up the trails of wood glue that I knew would squeeze out as I nailed through the cardboard backing.

I have an unassembled Billy just waiting for me to finish building out my office. Lots of great tips. Thank you!

Absolute genius tips and tricks by proper DIY…

Great video...certainly agree with the glue reinforcement and I've also used a staple gun to provide additional strength through the backboard/rear shelf edges with a run of staples there. Also, regarding your additional mid-point shelf supports, another way (similar to your first suggestion) is to simply glue in very thin vertical laser-type ply panels (3-4mm) that are not as deep as the shelf by about 20-30mm so they sit well back from the front shelf edges. Incredibly strong in compression, but so thin that in practice, and even unpainted, they are almost invisible between the vertical spine lines of your books..

Very brave using PVA directly over a carpet...if only you had something like a piece of cardboard to protect it from drips!

I've got one of the half height ones of these...it has had a lot of use and is still just as sturdy and strong as it was when I got it, about 20 years ago. It's already a really well made shelf unit.

It's a pleasure to watch you at work ♥️

I've had a bunch of these bookcases for almost 20 years now. The last time the back boards started coming out again I simply used plywood screws to drive them into place, and it has worked so far. Additional glue would definitely do an even better job.

You’re like me. I always pour all the small parts into a bowl (or, like you did, the small piece of cupped cardboard) to keep them together. It drives me bananas when folks pour them out onto the floor and they go everywhere!

I love IKEA. My Billy book case is now 15 years years old, with glass doors. I also have a dresser that I bought and built 1992 and has survived 4 house moves.

Another fantastic tip filled video Stuart, love the wooden batten on the back and the strengthening screws into the shelves...fab!!!

i have used the batten under the shelf before and its great. You just need to attach it at the back of the shelf though, not the front. Then minor colour changes/gaps etc don't show. It also means the shelf is adjustable in the future. Love the idea of the extra backing board, will use that in the future Also I always glue all fixings, both the dowel and the screws. I think although it doesn't bond to the screw it stiffens the chipboard, giving a firmer foundation to the screw

Some brilliant tips there stu. Another good video. Keep up the good work.

Good info. My only Suggestion if I may, "When adding timber to the back center, leave it long by 2cm or 3/4" so you can adhere to the wall. Also, using three timbers on the back can add more strength to the overall shelf especially against sagging and can allow 3 points of contact to the permanent wall." I appreciate this video and do have a job to do much like this. I will use some of your ideas to strengthen the shelf. Thank you.

My Billy bookcases are 20+ years old. I have 12 lined around my apartment with the ceiling toppers. Some have extra shelves, some have wooden doors and some glass doors and shelves. I have the old oak looking ones. I have some 30year old Abodio cabinet cases in redwood. I do something a little different for the backboard. I use wood glue or mod podge and decoupage the back with newspaper, wrapping paper, or brown craft paper. Let it thoroughly dry to one solid piece.

Personally, I prefer the first option you suggested as it is flexible, in that the vertical braces don't have to be in the centre, they can be moved to best accommodate the book widths or to create a nook for ornaments and they require no fixtures, a good snug fit is all that is required. As for the problem of matching the materials, no problems. Rather than trying to match them, make them a feature with a contrasting colour. Alternatively, be creative and make it look like a book by either painting a spline on raw timber or gluing an actual book spline onto the board.

Nice video. I have 8 Billy bookcases since 1996, which are filled with books and are still fine. Back then Ikea only added a few nails to secure the backboard and we added our own nails to secure it. This helped to keep the boards pretty secure. But if I could do it again I would definitely add a plank im the middle like you did. If you decide to follow the advice and add a board in the middle between the shelves to prevent sagging, you don't need to buy an extra Billy bookcase. Ikea sells extra shelves in the same colours as the Billy bookcases. So you could just buy a few extra shelves if you decide to do that.

I have always glued the backs, also the wooden dowels. This is contrary to what the Ikea CS has said though, they do not think you should be gluing them. Won't stop me doing it though, things last longer when better built.

IKEA have a very good ‘wastage’ system of putting odd, damaged or ex-display items out by their collection points for you to take for free. You can, with a view visits, usually find appropriate spare pieces of melamine.

A great idea to do IKEA build improvements, Stuart. As Davie says, the extra IKEA melamine shelves are very reasonably priced (last time I bought some they were £8 for 2) and so slicing them up for the vertical bookend idea is a cheap alternative. However, after watching you drill through the back into the shelves through the middle it does mean that you can never readjust the shelf heights and I have moved ALL the shelves in my 10+ Billy bookcases more than once even though I moved into my house only 4 years ago! So, as an alternative, you could mark the shelves as you did but instead of screwing from the back, use an IKEA bullet type peg which you can get very easily from the Returns Section spares bins and just drilling a suitable sized hole for it from the front, into the hardboard and vertical timber. so it props up the back of the shelf. Of course, you could use the Billy shelf clips but then you would need to countersink the underside of each shelf to accommodate the poky-uppy bits in the newer billy shelf clips. The vertical timber is a fantastic plus since instead of clambering up to fit the anti-tilt mechanism to the top, you could just take out a shelf and drill through the area that will be hidden behind the shelf and fit the bookcase to the wall that way. I am in a bit of a rush atm so haven't yet watched right through to the end - but I will - and I have to mention that the little scoop out of the bottom rear of the uprights is designed for continental european style skirting boards and I have often found it necessary to use a jigsaw to rake that scoop a bit further up so the bookcase fits level with the wall and avoids the higher UK skirting boards. This might also mean the vertical central timber may also interfere with the skirting board, so before I ever fully assemble a Billy bookcase, I always measure the height of the skirting board since modifying the back/bottom of the bookcase uprights is easier when it is not assembled. If of course the skirting board is less than the IKEA gifted 'scoop' you do not need to do any extra jigsaw work. One final tip on using 800mm wide Billy bookcases is that if you are filling an alcove and you want to have it look fitted right across the alcove, you can buy the narrower 400mm wide Billy bookcase and trim down the narrower shelves to span the extra width or if it is only about 240mm, you can buy the Gnedby CD/DVD bookcase that will fill that gap. That Gnedby n bookcase is not as deep as the Billy bookcases and so it is idea if you want to get a power extension or in my case, a load of computer cables up to the top of the bookcase. Keep up the good work, Stuart, you are one of a small number of my YT favourites.

Gets bookcase perfectly square, applies glue, moves bookcase (completely messing up the square), applies backing… 10/10

If you want to have the same types of color/material/etc you can look at the sale corner of the IKEA where they sell showmodels and returns that have gotten damaged (or atleast the IKEA in the Netherlands has got that. For us it’s near the checkout). BUT they also sell spare shelves/doors/table tops etc. That saves money and you will get the same look.

Well done. I've tried all three suggestions you've made in regards to preventing shelf sag and found them all lacking and honestly not worth it. I've learned to accept that they will sag, but not the sag. I merely flip the shelves twice a year and use the tendency to sag to straighten the sag.

For the metal screw pins, you can use a drill. Just set the clutch to the weakest setting to avoid over-tightening.

All the issues you mention and fix, are reasons why I always have bought the less wide Billies... 40 cms wide shelves tend to not sag, even when fully loaded, the backboard tends to stay in place without issues, and having narrower furniture means you can configure it with more ease, for instance placing one at an angle to "do a corner". yes, it probably costs a little more than buying fewer units, and you do lose a few cm of storage capability on account of having more side panels, but I think the tradeoff is worth it.

I used to replace the hardboard with thin ply and glue/pin it in place - made it truly bomb proof

Be sure to drill pilot holes from the back into the shelves before putting a screw in. This will prevent the shelves from splitting.

You can often find extra shelves at a very low price in their circular hub (what used to be bargain corner) 😊