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Advice on approach to take to this chunky bookcase/dresser.

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Jeffo

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Hello,

I'm about to embark on a large bookcase project, but it is a step above the basic 18mm MDF with Domino construction I've used in the past. It is putting me well out of my comfort zone, so would really appreciate any advice. I'll probably end up planning a lot of it out in SketchUp, but I'm also something of a novice, so I'm keen to get things straight in my head as much as I can before I spend time getting it millimetre perfect.

I want to build a version of the bookcase/unit as per the attachments. It will be similar colour, finished with an airless paint sprayer, with a slightly sheeny paint. A bit flexible on the details (not desperate for a 'copy'), but I do want to maintain the chunky style and seamless finish between the shelves/verticals and frames around the cupboard doors.

There are few mandatory differences for mine:
  • Needs to stretch wall-to-wall (approx 4m) and floor-to-ceiling (approx 2.35m).
  • Needs to have LED strip lights running at the front underside of each shelf. I have 5m lengths of LED strip already, but will need to ensure each shelf has a recess or oversized lipping to avoid glare. I will also need to accurately cut holes between the verticals to allow the strip to run the full length across each horizontal run of shelves.

Tools available:
I will get the large sheet materials cut by my timber yard. I have a tracksaw, router, domino, random orbital sander, drill. I don't yet have any large clamps, nor pocket hole jig. My ability to press together such a large piece is one of my considerations. Not sure if just regular screws will do the trick, but conscious that large clamps aren't cheap... and I might need a few! I also don't have a brad nailer, which I think might be quite useful for this project?

Construction approach:
This is where I'd really like some suggestions. I can think of a few ways to build this - each with various pros and cons, but grateful for some experienced suggestions.

  • Shelf Width: For my size, I thinking of 5 horizontal shelves across the 4m span. This means each shelf will be around 75cm wide once verticals, edges/ scribing allowance is taken into account. I could go for 6 which would leave each about 62cm wide. A nicer width perhaps, but I think I prefer having an odd number of shelves. Any strong views on this?
  • Shelf lipping: Given I'm looking at 75cm shelves that will be full of books, I'm assuming I should be lipping the front of each shelf for strength. Given that I also want to hide the LED strip, the lipping will help with that. I'm wondering whether I ought to also route say 5mm of the shelf material so that the led is slightly resessed into the shelf.
  • Separations of the Units: At 2.3m tall I could just about build this full height, but I think it would be really heavy. Minded to build 5 separate cupboard base units, then screw them together when complete. I'm less clear about the shelving units. Easiest seems building 5 different shelf units to match the bases, but I suppose I could also build it as a single unit, adding on an additional 'column' of shelves one at a time.
  • Shelf thickness: What thickness do you think the shelves are in the attached pictures? Looks like at least 40mm to me? How best to achieve this? The pictured units have shelves flush top and bottom, I'm wondering if they have used really thick wood, or two sheets of 24mm MDF glued together perhaps? Or a hollow construction? I need a lip on mine to hide the LEDs which gives a degree of flexibility, but I don't want say 18mm MDF and a massive 40mm+ lip. I'm also conscious that they will eventually be full of books and want to avoid sag.
  • Verticals / Cupboard Frames: Linked to the above, I'd like same thickness for the shelf verticals and frames. If I am using MDF, I'm conscious about the difficult in painting MDF edges. If I was to use 24mm MDF for each carcass, when constructed it would equal 48mm thickness, then I could double up at the ends. Instinctively this feels like overkill - heavy and expensive; and perhaps a better finish with a different construction method with suitable wood nailed/glued on to provide the desired look. But then I'm not sure how well that will work with the visible hinges etc.
  • Getting the seamless finish: There are going to be joins on this, so will need some careful construction, sanding, filling etc - and exactly what is required will depend quite a lot on the answers to the above two points.
  • Method of attaching shelves: I don't have the requirement to adjust the shelves after construction. They will in any case have LED lighting running through them. I suppose method of attachment will depend on their construction (e.g. two sheets of 24mm MDF/hollow/etc). My assumtion was dominos and glue; perhaps also with screws in lieu of clamps.
  • Painting:I'm planning on building this; then spray painting it with a Graco GXFF. I've heard that painting one side of MDF can cause it to warp, but am assuming that won't be an issue given the size and weight of this. Alternatively, I could prime and or initial paint after dry-fit but before construction; but this will be a lot more work given the space I am working in and I think will still require painting afterwards.

Very grateful for any advice on the above. Apologies for the slightly lengthy set of questions!
 

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woodbloke66

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An interesting project to which you've obviously given considerable thought; I'd advise using the Sagulator to sort out the best material for the shelves in order to end up with barely perceptible sag. As an example, this....

IMG_3305.jpg


...is a recently completed and very heavily loaded, glass fronted bookcase (hence the ugly mug reflection :D ) The 26mm thick shelf is a metre long, adjustable and is made from a laminated pine core, veneered with 2mm thick oak. Although it's loaded with heavy 'coffee table' type books, there's little or no sag. If you're after top quality brassware for adjustable shelves, then I'd recommend Marche's. Whatever you do, I'd advise NOT using mdf or similar for the shelves - Rob
 

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petermillard

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Jeffo":1pj0ss8m said:
Hello,

I'm about to embark on a large bookcase project, but it is a step above the basic 18mm MDF with Domino construction I've used in the past...
Looks like a fun project. I did something not dissimilar last year (see “Big shelves” video series, starts #184, YouTube link in sig) with 65mm chunky shelves made ‘torsion-box’ style with a spacer between two 18mm outers, and a front lip, all in MR MDF. Shelves were attached to the carcass with noggins the same thickness as the spacer, and just glued on; worked great.

Construction approach:
This is where I'd really like some suggestions. I can think of a few ways to build this - each with various pros and cons, but grateful for some experienced suggestions.

  • Shelf Width: For my size, I thinking of 5 horizontal shelves across the 4m span. This means each shelf will be around 75cm wide once verticals, edges/ scribing allowance is taken into account. I could go for 6 which would leave each about 62cm wide. A nicer width perhaps, but I think I prefer having an odd number of shelves. Any strong views on this?


  • 5# shelves at ~750mm sounds OK, you might want to mock up a section of shelf to check for sag under load, but I wouldn't expect much over that span, at a decent thickness - especially if they're fixed at the side and onto a back/the wall. Sagulator's good, but not much help for doubled-up torsion-box style shelves

    [*]Shelf lipping: Given I'm looking at 75cm shelves that will be full of books, I'm assuming I should be lipping the front of each shelf for strength. Given that I also want to hide the LED strip, the lipping will help with that. I'm wondering whether I ought to also route say 5mm of the shelf material so that the led is slightly resessed into the shelf.
    Why not just extend the lipping down so it creates a little rebate for the LEDs to sit behind? I think I'd be inclined to go for more like 10mm, given the height of the upper shelves, but again you can test this.

    [*]Separations of the Units: At 2.3m tall I could just about build this full height, but I think it would be really heavy. Minded to build 5 separate cupboard base units, then screw them together when complete. I'm less clear about the shelving units. Easiest seems building 5 different shelf units to match the bases, but I suppose I could also build it as a single unit, adding on an additional 'column' of shelves one at a time.
    Yes to separate cabinets, and probs to columns of shelves as well. Think I'd be inclined to pre-build the columns with a single skin, join them in situ, then apply the front capping piece on the uprights - you'll need to be quite precise, but filler is your friend. Stagger the noggins/spacers in the uprights, obvs, then it's easy to clamp.

    [*]Shelf thickness: What thickness do you think the shelves are in the attached pictures? Looks like at least 40mm to me? How best to achieve this? The pictured units have shelves flush top and bottom, I'm wondering if they have used really thick wood, or two sheets of 24mm MDF glued together perhaps? Or a hollow construction? I need a lip on mine to hide the LEDs which gives a degree of flexibility, but I don't want say 18mm MDF and a massive 40mm+ lip. I'm also conscious that they will eventually be full of books and want to avoid sag.
    Looks more like 60-70mm to me, and from the pictures you can see lines where the top & bottom shelf skins abutt the shelf inner, so almost certainly hollow IMH.

    [*]Verticals / Cupboard Frames: Linked to the above, I'd like same thickness for the shelf verticals and frames. If I am using MDF, I'm conscious about the difficult in painting MDF edges. If I was to use 24mm MDF for each carcass, when constructed it would equal 48mm thickness, then I could double up at the ends. Instinctively this feels like overkill - heavy and expensive; and perhaps a better finish with a different construction method with suitable wood nailed/glued on to provide the desired look. But then I'm not sure how well that will work with the visible hinges etc.
    There's no difficulty painting MDF edges. Use MR MDF, it's a much better board for not much more money. I'd build the cabinets in the usual way and use a face-frame between them the same as the capping pieces on the shelves.

    [*]Getting the seamless finish: There are going to be joins on this, so will need some careful construction, sanding, filling etc - and exactly what is required will depend quite a lot on the answers to the above two points.
    Glue it, clamp it, sand it, fill it, sand it, fill again if needs be, sand it, paint it. Care needed not to round over the edges, but it's not hard.

    [*] Method of attaching shelves: I don't have the requirement to adjust the shelves after construction. They will in any case have LED lighting running through them. I suppose method of attachment will depend on their construction (e.g. two sheets of 24mm MDF/hollow/etc). My assumtion was dominos and glue; perhaps also with screws in lieu of clamps.
    Dominos, glue, screws, noggins, spacers, whatever works, and whatever you're happy with.

    [*]Painting:I'm planning on building this; then spray painting it with a Graco GXFF. I've heard that painting one side of MDF can cause it to warp, but am assuming that won't be an issue given the size and weight of this. Alternatively, I could prime and or initial paint after dry-fit but before construction; but this will be a lot more work given the space I am working in and I think will still require painting afterwards.
Again, MRMDF, don't bother with anything else. No issues with painting MR at all.

Very grateful for any advice on the above. Apologies for the slightly lengthy set of questions!
Them's my initial thoughts - I'm sure there'll be others.

HTH P
 

Jonathan S

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Jeffo

Nice looking cabinet.

Are you going to make in-situ or in workshop? as both ways would have a different approach.
The easiest approach would be a bit of both and then a hand paint job to finish, as I don't know your situation its difficult to make build suggestions.

For the LED I would deffo put the strip in a diffuser, it takes all the glare away and if needed you can change the light with filters behind the diffuser....also remember with Led you get movement and very quickly the contact with the shelf fails, then the strip drops down....I learnt this the hard way!

Jonathan
 

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It has been remiss of me not to say thanks for the replies on this. Peter, the video was really helpful. Unfortunately I hurt my foot so have been out of action the last few months. But... I hope to get this project squared away during early December.

The above has cleared up many of my questions and I've been taking detailed measurements and starting to think about a cut list.

Shelf size/construction/material is the one sticking point and I'd appreciate any further guidance as to which approach to take.

The things I'm considering:
  • Number of shelves desired / space available means that I don't want to go more than 50mm on shelf thickness.
  • Shelves will be 910mm in length and 350mm deep and will be loaded pretty heavily with books. Weight per linear metre won't be as bad as vinyl records, but still significant.
  • I think I need at least 10mm lip/indent to hide the led strip, 12mm or so might be safer.
  • I'm open to the idea of routing our a 10mm channel to hide the LED strip rather than have an oversized lip on the front of the shelf. I think this will ensure the underside of the shelves also have the same chunky look. On the other hand, I'm worried that a 10mm indent will lead to poor light spread. I'm also conscious that this choice might have implications for shelf design.

I've mainly been looking at torsion boxes. Some of it seems to get quite mathematical but I'm wondering how easily the concepts translate to DIY woodwork. For example, I've read than deep "ribs" and thin "skins" can be very strong - but I can't help but feel that 6mm MDF glued on 38mm ribs will be hard to construct and a bit wavy.

18mm top and bottom skin leaves only 14mm for ribs.

The front of the torsion shelf will need to be lipped for asthetic reasons (otherwise it would be hollow!), but I'm wondering whether I should do this in something other than MRMDF (what instead?) and how thick it might be. One thought for example would be to build a MRMDF box, and lip the front with 30mm of wood, with a 10mm channel cut out of the centre to run the LED.

In short, I'm not sure what the science says would be the best option.

I'm also really open to using the laminate pine core approach mentioned above (or other composite materials) - but can you advise what/where to buy. Presumably I could do it without the oak laminate given I'll be spray painting?

Thanks!
 

profchris

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Jeffo":1ldwxrys said:
I've mainly been looking at torsion boxes. Some of it seems to get quite mathematical but I'm wondering how easily the concepts translate to DIY woodwork. For example, I've read than deep "ribs" and thin "skins" can be very strong - but I can't help but feel that 6mm MDF glued on 38mm ribs will be hard to construct and a bit wavy.
I suspect this is no help, but I have flown torsion boxes. Wooden gliders where the load is taken by a single spar (an I beam about 100mm deep made of 6mm ply, I think), strengthened by a D box (leading edge of the wing) about 100mm high and 150 mm wide, skinned with 2mm ply. This is carrying loads of around 100lb per metre. 7.5 metres each wing, so they did bend somewhat.

I've used 6mm MDF to make musical instrument cases, and I wouldn't use it for anything more structural than that. 6mm birch ply, OTOH, is plenty strong.

What if each shelf had ribs spaced 50mm apart, so 6 ribs plus front skin, all in 6mm ply and clad top and bottom with 6mm ply. Intuitively that feels like it would be really strong, but I'd build one 50 x 50mm box, support each end and load it with bricks or similar in the middle until it sagged. Then weigh the bricks and calculate how the whole would hold up.
 

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Thanks again for the replies.

Profchris: So what do you think about two skins of 6mm birch ply (900mm x 350mm), with 38mm ribs made of MRMDF? Am I right to think the strength comes from placing the ribs width ways i.e. cutting them to 350mm (or perhaps a bit less), then spacing across the length? Is 8 ribs enough? I was thinking one each end, then 6 spaces over the intervening 900mm. Also wondering whether 12mm skins with 26mm ribs would be better. Finally, my plan originally was to have noggins/rails to slide each shelf onto. Is that still viable with such construction?

Robbo3 - Thanks - actually Peter posted further up in the thread. I've watched lots of his stuff now, but his example with chunky shelves results in slightly thicker shelves than my design allows for. Just wondering how I can best scale it down to 50mm (or just a smidgen more).

Scaredycat: Thanks, thats an interesting approach. I could just use two two 24mm sheets with that approach. I guess it would be a bit heavier at 48mm thickness is probably close enough to the 50-53mm that I was aiming for.

I'd be grateful for any views on how MRMDF will match with potentially birch ply shelves. After sanding and spray painting will there be a noticable difference? Wondering whether I need to opt for all MRMDR or all birch.

Many thanks!
 

profchris

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Jeffo":3io2c96b said:
Thanks again for the replies.

Profchris: So what do you think about two skins of 6mm birch ply (900mm x 350mm), with 38mm ribs made of MRMDF? Am I right to think the strength comes from placing the ribs width ways i.e. cutting them to 350mm (or perhaps a bit less), then spacing across the length? Is 8 ribs enough? I was thinking one each end, then 6 spaces over the intervening 900mm. Also wondering whether 12mm skins with 26mm ribs would be better. Finally, my plan originally was to have noggins/rails to slide each shelf onto. Is that still viable with such construction?
My suggestion was purely theoretical - I've not made anything like this (I mainly make ukuleles, where the stresses are rather different!).

I'd definitely make a test piece - just a single box the full width of the shelf and however wide you think you will space your ribs - you seem to be suggesting 150mm spacing running the full length of the shelf. Then place the ends on a couple of bricks or whatever you have, load up the middle, and see what happens. I'd probably include some sideways stiffening, probably a couple of triangles each half the cross-section, at 1/3 and 2/3 length, though you might not need these for the actual shelf, but it would be easy enough to do - make the test piece (and the shelf) by glueing ribs to base, then glue in the stiffeners, then glue on the top.

You're right that all the bending loads should be taken by the ribs, so maybe MRMDF would work for top and base, but if I were building it I'd be happier using ply because it is so much stronger. 6mm ply seems to cost around £12 per sheet more than MRMDF, which I calculate to come to £4 per shelf. I'd think that worthwhile for my peace of mind :D

Remember, I'm just hypothesising, testing is definitely needed!
 

Jeffo

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Thanks again for the advice. I looked at my design over the weekend and decided to move from 4 columns of shelves to 5. In effect, this seems to solve much of the concern over sagging. In terms of sagulator, I am now looking at a shelf 700mm long, 33mm deep, which even with just 18mm MDF is in the "acceptable" range for sagging.

However, I'm still minded to err on the side of cuation and over-engineer a little if I can.

I'd be really grateful for some advice on the plan:

Slide1.JPG


The above shows the construction, minus face-frames which will cover both the shelf fronts, the verticals between the units, and the filler panels on all sides. I'm planning to use more 18mm MDF, which once fitted, will need some filler and sanding to get a flush finish.

For construction, I intend to use a domino for alignment, with glue, and screws to do the 'clamping. Do you think I'll need clamps as well? I can invest in a few and can likely borrow a few more that would span the circa 700mm unit width.

Do I need to worry about the cumulative weight? The joint between the bottom horozontal (where the legs are attached) and the bottom verticals looks like it is going to be taking the weight of the entire shelves and books. Will 6 dominos/glue/screws hold that? Or do I need to change the design logic in that section?

You might have other observations, but my big question is the best way of attaching the bottom 'cupboard' unit to the top 'shelf' unit. I could make the vericals of the cupboard 18mm longer so that they touch the verticals of the shelf section. Could be glued and aligned with dominos?

My second question is back to the shelves... As I've thought about how to hide the LED strips (that I want properly hidden and at the front undersides of the shelves), I've stuggled with what would be the best approach. The torsion box design, with an added overhanging lip to hide the LED strip makes for excessivly thick shelf fronts. But routing a channel into the shelf, seems to then defeat the purpose of the lipping/torsion design.

Slide2.JPG


These are the thoughts I had... Going for a 30mm MRMDF takes me into clear 'no perceptable sag' territory and allows for a lip to hide the LED in a 'right angle' profile. The other ways I can think of all seem inferior, but really grateful for views.

Thanks again for all the help with this. I realise many of my questions are probably pretty basic.
 

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siggy_7

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I've made a few torsion boxes, so speak from some experience. I think your design is way over-spec. The strength of a torsion box comes from the thickness of the overall structure, not the thickness of the materials used to make it.

A bit of theory, if I may. The stiffness of a beam in bending increases with the cube of its thickness. Think about how a simply supported beam responds to a point load - it tries to sag (form a curve). The top of the beam forms the inner part of the curve and the bottom part the outer. To form this shape, the bottom has to get longer (tension) whilst the top has to get shorter (compression). The greater the separation between the top and bottom, the greater this stretching/squeezing is for the same deflection. This is the principle behind how a steel I beam works - the bits of steel at the top and bottom of the beam (flanges) are what provides the stiffness; the web in between the two is just to hold the two parts together and transmit the forces between them.

If you don't believe me, take a look here at a torsion box supporting a load of bricks over an 8' span. It's made of 3mm hardboard: https://www.ncwoodworker.net/forums/ind ... ong.19885/

I would make your torsion box skins out of 6mm material, connected by similar or perhaps slightly thicker material (standing thin pieces on edge can be a little tricky for gluing up, so I generally work with 9 or 12mm thick material for the internal parts). Anything thicker is overkill and will make the shelves unnecessarily heavy and costly to make. I've built torsion box shelves using cheap 6mm ply over a 3' span and had no issues with strength - the overall thickness was only 30mm so with a 50mm thickness you'll be absolutely fine using similar thickness material.
 

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Siggy / Chris - Many thanks. One additional question, which after reading some of the links and FWW articles I'm still not clear on is the relative importance of the torsion box having a grid vs ribs running in only one direction. Does it actually make a difference if it is maintaining the distance between the skins that is most important? Intuitively, I would have thought length ways ribs would work best, but I've seen various constructions with width ways ribs (Peter Millard's shelves and others); and grids. I can't say I've seen any with only length ways construction.

I will need a way to attach the shelf to the bookcase verticals. Previously my chunky 18mm based construction lend itself to sliding onto a 18mm noggin. I wondering if I'd be best placed to ensure there were ribs flush with the ends of the shelf, glued together, then dominos (and screws) to hold the shelf to the verticals?

And presumably MDF is fine for all of this? (I'm intending to spray paint the finished shelves, so slightly reluctant to mix ply with MDF.)

Many thanks!
 

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I've not seen torsion boxes built with the internal ribs in only one axis, but my intuition tells me you're right in saying that the lengthwise ribs are the most important for your application. For the dimensions you're looking at, I would suggest in addition to a rib along the front and the back of the shelf you put one down the middle of the shelf - that's what I would build anyway, but it may be unnecessary. If you're going to include front to back ribs (again, I would if only for belt and braces comfort), I would space them at something like 200mm intervals - over a 900mm span, one each end plus three in between at 225mm centres would be fine I should think.

Regarding how to install the shelves, my first choice would usually be the little metal shelf supports that fit into 5mm holes in the carcass sides. If you want fixed shelves, then dowels (or dominos if you have the machine) would be the way I would do it - bump up the rib thickness on the end of the shelves to 18mm so the fixings have plenty of purchase. Housing joints would also work well, but fit and finish may be a bit harder to get a really tidy look.

I've not used MDF like this in a structural application, but I imagine it will be fine. I've had bad experiences with solid MDF shelves sagging where I've under-specified it, but for a torsion box of this thickness I can't see you running into issues. Someone more familiar with MDF may be of more use here.
 

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(Belated) Thanks siggy!

TLDR: Is attempting a seamless join between tulip and MDF a disaster waiting to happen?

One of the few upsides of this lockdown is that I've had time to return to this personal project, which to my regret hasn't progressed much since I last posted...

By way of an update, I decided to make the shelves themselves out of 25mm MDF, lipped front and back with tulip wood. The rear tulip is flush with the shelf (25mm x 25mm), but the front is 25mm x 50mm. This provides a dropped lip for my hide the LED's behind.

For the verticals, I've taken a bit of inspiration from Peter Millard's approach and am sandwiching some 15mm MDF noggins between two sheets of 18mm MDF (giving a total thickness to the verticals of 51mm). The verticals will be faced by an additional piece of 18mm MDF.

As per the picture in my original post, I've cut all of the wood so that when it is constructed, the front lip of the shelves will be flush with the face of the verticals. I've only done a partial dry fit so far, but as I'm building this in-situ, inevitably (at least with my skill level) there will be some gaps between the (tulip) shelf lips and the (MDF) verticals/filler panels. I'll be using a combination of pocket holes, dominos and regular screws (each with wood glue) to assemble.

I've been investigating options for filler that I can use. Someone has pointed out that the tulip and MDF will move differently and that cracks might be inevitable...

Seems obvious now it has been pointed out to me. Has anyone any experience in creating a seamless joint between MDF and tulip (or similar)? Will a decent amount of wood glue and careful assembly mitigate the differential in movement? Any other tricks?

Otherwise I'm tempted to trim 10mm off the rear of each shelf so that the front lips sit back 10mm from the verticals. I won't be able to do this for the bottom shelf (that forms the top of the cupboard, with inset door); so there is a chance for some cracks there.

I sort of wish I'd followed suggested practice in designing in lines where lines naturally exist from the outset, rather than going for a flush finish. I do prefer the flush finish look and was prepared for the effort of sanding, filling, sanding, filling - but this potential for cracking is making me think again.

Open to opinions - do I take the risk, keep it flush and hope that cracks don't appear? Or redesign?

Thanks again for the advice.
 
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