Under-stairs cupboard + WIP

[RogerS]

Well, it's only been around 20 years or so. We have an under-stairs area that needs sprucing up.



So the plan is to make this. One large door and a sliding drawer nearer the foot of the stairs for the Hoover.



I have some nice old elm in a large slab that Chief Designer has selected as it's the closest match in colour and texture to the old oak beams in the adjoining room.

My original plan was to rip it down the middle to give me thinner panels that I could maybe bookmatch together to make a larger panel. Then use some other elm or similar for the frames. A quick look at the elm slab - it's too warped and cupped and even using it for the frame is questionable. We shall have a go.

I have some elm veneer which I suggested to CD would make a good panel but CD objected. So Plan B...after cutting some of the elm slab into frame components I still have some left to try and make my own veneer and glue that onto a stable substrate for the door, at least. That is the current plan.

Note to burglars:

1) The safe has nothing of value in it
2) Burglars will be shot

 

[RogerS]

Ripped the slab down into smaller pieces and planes some up. As expected, many of them are all over the place. I know that if I keep on planing them and trying to get them square straightaway then I'll end up with matchsticks. So I've relieved the convex side of quite a few of them and we'll see if they straighten up - even slightly - overnight.



Next morning, no improvement and by the time I'd got most of the twist, curl and cup out of some of them, I could see that this was going to end up with the wood only about 15mm thick. Way too thin to be used by itself. So it's going to need a frame on which to fix the panels.

Et voila...



Nice big hole for the door and also to drag the safe out (if/whenever we move). Does give a bit of a problem with the door frames only being 15-17mm thick. Might end up laminating several pieces together to balance out the cupping etc.

One thing I can't decide on but which needs deciding sooner rather than later is whether or not to rip up the step and front riser and replace taking the wood all the way across to the panel. It will mean that the bottom line of the panel won;t follow-on through the rest of them but I think it might stand on its own merit especially if the step goes all the way across.






Problem 1...faffing about with Van **** crystals trying to match the colour of the new step and riser.

Problem 2 ... I think that the second riser probably needs to go all the wall across as well. But the wall bows out and is plastered and sods law says that there will be brick sticking out as well. What does the team think? I'd probably then have to take the top threshold step all the way across as well. Is it really worth all the effort?

Ripping the veneers
Meanwhile back on the veneering side...I knocked up a high fence on the bandsaw. Also came across an excellent article here http://www.timothycoleman.com/publicati ... rticle.pdf I spoke to Ian at Tuff Saws to see what blade he recommended and ordered up a couple but while waiting for them to arrive thought I'd run a short piece through with my existing blade and was quite chuffed at the result. 2mm think and pretty even across the width and down the length.





The challenge is going to be the longer piece. It has some really nice figuring



but oh is it warped. It has the full works....twist, curl, cup...you name it. However provided I can get the convex side reasonably flat and square then I'm in with a chance,



The drawer is going to be challenging, I think as access to where it is going will be tight. I'm planning on using these runners. http://www.hafele.co.uk/Hafele35a1/imag ... 06-138.pdf

Thinking that I need a three sided MDF outer carcass which can be fixed to that upright holding the stairs up (nice of my builder to fix it vertically - NOT). That will anchor the righthand side and I will need something for the lefthand side, I'm guessing otherwise the front of the carcass can twist. Need something at the back to support it. Also adjustable from inside the carcass as that floor sure as hell isn't going to be level or plumb. Screws through the bottom of the carcass until the they bear onto the floor (concrete AFAIR) and then screw up./down until the front of the carcass is coplanar with the stairs/rest of the panelling. I'm guessing in the dark here as I've never fitted these type of sliders before.

I also have a sense that the house might be moving slightly..what with all the rain...so better plan for retro-adjustment

How accurate do they need to be fitted in the front-back direction? Is there any adjustment built into the sliders ?

 

[Phil Pascoe]

That's near identical to mine - the wine rack next to the safe!

 

[RogerS]

Progress has been slow as other projects jumped the queue.

Because I've had to use a softwood frame, I didn't want to see it when the door was opened and so I've been applying thin pieces of elm to the visible faces.



Slight ****-up on the top diagonal softwood frame. If I'd reduced the depth I could have used it as a stop for the door. Now I'll have to rebate the top of the door but that''ll have to do.

I also discovered that the stairs aren't straight (made by my builder a long long time ago) plus when he put that support in, it projects a bit too far underneath the stringer and doesn't leave me with much room to get the panelling in. I foresee lots of fiddling about.

Meanwhile I bit the bullet and ripped down those long bowed pieces to get the veneer that I need for the panels and door. Some went OK but others, as you can see, wandered offline. I cocked up the first one because I fed the board in convex side to the fence...rather a dumb thing to do. In between veneer cuts, I lightly planed the face before cutting the next veneer. I have enough for the door and longest panel...just.



Time to glue the veneer to the longest panel substrate. Being a tight sod and not really doing much sheet work, I rarely have much MDF around but I had a few offcuts and so with a bit of judicious fiddling around with scaled pieces of paper to represent the top and bottom of the veneer platen (to sandwich the veneer and substrate in the vacuum press) I decided I could get away with just getting one sheet. I cut all my sheet stuff into manageable 'table-saw-able' pieces by using the TS55 on top of a sheet of Kingspan.

My last sheet lasted me about four years but as it was on its last legs, decided to treat myself to a new sheet. Last time I used the 25mm sheet but decided this time to go for a thicker 50mm sheet. Big mistake. While it is light, it is bloody slippy to hold and damn awkward compared to the 25mm sheet.



While the sheet was on the floor, I thought I'd try a technique I'd seen on the web for trimming the veneer down its length and getting a straight edge. These pieces are 1.6m long....too long for a shooting board. The idea is quite simple. Just use the Festool guide rail, stick the two pieces on top of each other and run the saw (carefully) backwards rather than in the normal forwards direction. Worked a treat although the veneer is still frisky and keeps wanting to become a banana.

Check for fit ...sort of bookmatched.


That ridge part way down one of the pieces is where the bandsaw ripping started to go pear-shaped.

Coax the boards into line and tape up. Normally I'd use veneer tape but because these boards needing serious coaxing to stay straight, I had to resort to using duck tape. Normally I'd run a mile from using this on veneer but as the veneer is 2mm thick, any gunk from the tape will come off in the scraping/sanding. The glue side of the veneer pieces were lightly sanded with the Mirka to get a smooth surface.



Try the new bag for size...left over from an other project, I just had enough. Mind you sliding in the veneer platen single-handed was tricky. Then had to get it back out again as I;'d forgottem to knock off the corners (I do this to minimise any chance of the bag puncturing).



Hunt (and fail) looking for the veneer glue roller so resort to Plan B which in retrospect was a pretty dumb decision - see later.

Get out the trusty 'home-made' vacuum pump. It's an air-particle sampler that has an automatic control mechanism so i can quite happily leave it on all night if need be. A very, very cheap vacuum pump.



And we're good to go. Momentary panic when the bag didn't seem to have any air sucked out of it. I waited and waited as I thought maybe it was because the bag was a bit large but still no signs of evacuation. Unplugged the connector and felt for some suck...none..then remembered that the connector was one of those that was self-sealing and needed its mating companion to open up. So reconnected it....properly this time...and rewarded with a quick suck.

I left the pump on all night as my last bag seemed to leak slightly and lose its vacuum. As it turned out, I needn't have worried as in the morning I disconnected the pump and left the bag for an hour or so and there was no visible loss of vacuum.



OK..time to check the results. Unfortunately, while being beautifully tight, some of the joint line failed to glue properly.



So I had to resort to using a syringe and then clamping it back. I use greaseproof paper as a barrier to stop the glue sticking to the clamping piece. It was tricky getting the veneer up as the joint line was so tight.


Next time I might try using mitre mate as it's less viscous then the glue I'd used for the veneering plus it would go off quicker.

I have various theories as to why it didn't stick very well down some of the joint line.

1) Not enough glue (I have now found my roller )

2) The glue side of the veneer might have had some hollows which was compounded by insufficient glue.

3) Because the veneer isn't of uniform thickness, it means that in some places where one side of the joint line is proud relative to the other side then when the MDF board is laid on to and the bag evacuated, the MDF is going to be held away from the shallower piece and so not press down on it. Given that the door panel has a lot of pieces of veneer I am thinking that I will dispense with the top piece of MDF so that the bag will press down all over.

Comments always welcome

 

[RogerS]

Veneering the door panel.

As I mentioned above, I'm not really kitted out for sheet work so for the substrate of the door panel I paid a bit over the odds and bought a couple of smaller sheets of 12mm ply. Ripped one down to give me the extra width I needed. Ran one edge on both the whole sheet and the 'extra' bit past the groover on the spindle moulder and glued a bit of oak I had spare into the slots so giving me the size I needed. Not rocket science.

Why 12mm thick rather than, say, 6mm? Well, for the size of the door I thought 6mm might be a bit too floppy and could bow in time.

As it is a door, I need to balance the outer veneer with something suitable on the inside. I found some sheets of elm veneer bought many moons ago for peanuts at a Pugh's auction. Only trouble was they were a bit wrinkly.



I tried flattening them over several days and got reasonably close to flat but as soon as I took them out from underneath the MDF top cover, they started to move again. This was about the best I could do so decided to suck it and see.



Six pieces all taped up and ready to go.



It's the largest piece of veneering I've done and a bit of a struggle to get it into the bag single handed. Quite a few raised lumps in the veneer but off we go.



I know that I'm going to have to do some fiddling about tomorrow. That's the trouble with those lumps. All that 'extra' veneer has to go somewhere! This one, for instance, will need a bit of TLC. God knows what I'm going to find when I remove the MDF top.

 

[RogerS]

The Moment of Truth

Taking off the MDF top revealed to my pleasant surprise that nearly all the lumps and bumps were laid flat. There was this small lump that I knew about



This raised piece (although it looks as if it is a dent...optical illusion)



But much too much bleed through of the adhesive which you can see in the photo above and when I peeled off some of the tape a fair bit of part of one of the sheets came with it.



Nothing that can't be sorted.

The first one is the easiest. Cutting through the two lumps and judiciously paring the cut back, I was able to press and reglue the offending lump back. As an experiment and much to my surprise, the glue I am using (a D3 PVA cross-linked) was remarkably sympathetic to a use of a little bit of heat from my iron, softening and getting sufficiently tacky that pressing the iron was all that was needed.



A bit more finessing and this is the final result. Not my best but good enough for the inside face of the door. With a little bit more sanding and finishing it should improve a little bit more.



Next up was the long thin lump. I wasn't sure how many times that D3 glue would let me go through the reheating process. Ideally I would have run a cut down the length, ironed down the two halves on either side of the cut then cut through both, re-applied heat to lift them up again to remove the offcuts then re-applied heat again and ironed them down flat. So I decided to play around with cutting out the lump and then gradually trimming the sides using a tiny shooting gauge !



Lots of fiddly little cuts later and here we are



Bit of sanding and finishing should hopefully sort it.

And lastly the large lump. I got a matching piece of veneer



Put it in position and cut around the offending area. I did forget the angle the scalpel at 45 degrees

That gave me the replacement piece and also the area that I need to remove. Again, using a sharp chisel and the tip of the iron, it was very easy to soften the glue and gently remove the old veneer.



Reglued in the new piece and ready for a little finishing off. To give some idea of scale, the piece is about 6" long by 3/4" wide.



And here is the finished side prior to final sanding and finishing.



Out of interest, I found a photo of the original auction lot



Next up is the other side of the panel using my home-cut veneer.

 

[RogerS]

Drawer

While the vacuum pump is doing its thing on the other side of the panel - of which more anon - thought I'd turn my attention to the drawer. It reminds me a bit of the Irishman, on being asked for some directions, said "Well, I wouldn't be starting from here". It would have been so much easier just to have had another door and simply grovelled around inside for the Hoover and dragged the bits out one by one. :idea: Actually as I type this I am starting to think that there might be a halfway house......anyway ....

Plan A is to have a flush mounted elm panelled door sitting on the front of a drawer that will contain the Hoover and stuff. I rather fancied those push to open/push to close runners from Hafele and that's what I've bought. But how to mount it all ? Plan is to treat the drawer as a stand-alone unit and pre-make it on the bench, adding the front door when it's all in situ. So first we need an outer carcass on which to mount the runners. But space is tight under there and every millimetre counts as I will lose precious space with the actual drawer.

So three attempts later, having discovered that the builder had not levelled the concrete underneath the stairs very well, the carcass is temporarily stuffed in the hole.





and therein lies the rub as I can't really see my way forward. Theory says that it needs to be perfectly level and vertical. Not only that it needs to be coplanar with the front of the panelling otherwise when I mount the door, it is going to stick out of line at some point or another. Thoughts are to stick a batten on the stair riser to the left of shot and then screw the lefthand carcass side to it. But I can guarantee that the riser won't be coplanar to the front panelling. I can also guarantee the riser is not parallel to that grotty softwood support frame to the rh side.

Wedges underneath? I can just about get some in down the lh side but not a snowball's on the rh side because of the bottom bearer of that softwood support frame.

Another idea is to fix some of those nut inserts into the base plate and run a threaded studding down through until it touches the floor. If I put a slot in the top of the threaded studding then I could screw the carcass up or down.

Maybe I need to sleep on it.

OR maybe you guys can help?

Plan B

Make the front door simply hinged. The drawer stays as it is. So open the door..push the drawer in to release it and pull it out. Somehow that seems like cheating.

 

[flying haggis]

dont build, cheat

http://www.ikeahackers.net/2012/12/old- ... -look.html

 

[RogerS]

Moving on swiftly from that ghastly melamine-faced MDF monstrosity from Ikea, time to veneer the main face of the door panel.

These are my home-cut veneers all taped up and ready to go



Those with sharp eyes will notice that at the top LH corner the veneer is missing. This was because I had some blade wander when cutting the veneers and so had to jockey around the available veneers. This bit is going to get cut off anyway as the top of the door is triangular. In an ideal world and if I planned ahead then I would have laminated the whole sheet of substrate and that triangular offcut would have married up nicely as the front piece for the drawer. Isn't hindsight wonderful?

Also at the top there is a slight gap. This was the best I could do as I found that no sooner had I cut a straight edge on a veneer then it started to go banana shaped immediately. Taping (using more traditional brown sticky tape) gave me two sheets of three veneers on each and ones that moreover matched reasonably well. That small missing piece can be filled in later.

As mentioned at the beginning of the thread, on the first panel I'd had problems getting the two veneers of different thickness to stick down properly and put that down to the fact that the MDF top sheet wasn't transmitting the pressure through to the thinner sheet. So with this side I'd planned to glue up, stick down the veneers and whack it all in the vacuum bag pronto. Sods Law applied and as soon as my veneers got a sniff of glue they started to curl up big time. No option but to stick the MDF sheet on top.

And voila, out of the bag the next day, it is all flat. There is a slight line down the RH side where the veneer is thinner that that surrounding it. I'll either sand everything and see how it pans out or simply leave it as a 'feature'.




After a bit of sanding with the Mirka Ceros, it's all starting to look quite good and I'm quietly chuffed at the joins.

 

[MickCheese]

Thanks for posting this, really interesting.

Mick

 

[marcros]

Thanks for posting this, really interesting.

Mick

+1

 

[RogerS]

Thanks guys. The lack of response, despite quite a few views, was beginning to make me wonder if it was worth the effort!

 

[Orcamesh]

Thanks guys. The lack of response, despite quite a few views, was beginning to make me wonder if it was worth the effort!

Sorry Roger, definitely worth the effort, I guess a lot of us are either lazy or just so busy getting ready for Christmas that there is only time for a quick scan! Anyway, I'm picking up some good pointers about how to do veneering, something which I have only ever done on a course on a tiny scale. Never at home (yet). But definitely will try one day...

Keep up the good work, it is useful, interesting and definitely worth the effort!

cheers
Steve

 

[RogerS]

(The Christmas and New Year festivities plus work took their toll and not much was done hence the lack of posting.)

The financial aim of this project has been to use up as many offcuts and odd bits of elm as possible. To make use of warped and twisted boards that otherwise would be cut up and burnt. So far estimated total outlay of elm used is £30. So the door frame is next.

The door panel being veneered 12mm ply meant I needed a more substantial door frame. Because I didn't have any thicker elm that I was prepared to use for this project plus some of the boards were a bit bowed, I opted to glue various lengths together such that the bow in the two pieces counteracted each other. End result 25mm thick. The door panel at 12mm thick is also going to be a constructional part of the door and so I need to cut a groove down the middle of the rails and stiles. I used an adjustable groover on my spindle moulder but no reason why I couldn't use the router table. My set-up was this.



I mark up the rail and stile with a wiggly pencil line just so's I don't make any ****-ups and groove them the wrong way. The groove is offset to allow for the 4mm domino's.


and just kisses the domino's




One frame later and lay it on the panel to work out where to cut the panel.



and here's one I prepared earlier



As soon as I offered it up in situ I decided that a design change was in order. The original plan was to simply use normal brass butt hinges but I rather liked the idea of the whole understairs cupboard being 'seamless' with nothing other than wood showing. The drawer was going to be 'push-to-open' and I thought that the door should also be the same. But how to do it?

After asking for suggestions over on WoodworkUK (thanks, guys, for all the input) kitchen cupboard type hinges seemed to fit the bill. Specifically 'inset' hinges. The Blum catalogue is very detailed (and complicated) in terms of hinge setback from the edge of the door for any given gap between door and frame. Compounded by the fact that normal hinges are designed for doors up to about 22-23mm. My door at 25mm needed a special type of hinge. Duly placed on order.

Of course, going down this route meant that the hinge stile was not going to be deep enough to take the hinge (at least on the inside) and so, while waiting for the ironmongery to arrive, an extra piece was glued into place



and also it meant that the door frame also needed an extra piece glued on. Nothing like a plan going wrong. What plan, I hear you say? Well, one of the 'benefits' of making do with whatever scraps happen to hand. You can see the bleed through of the glue which I mentioned further up the thread. Luckily it's inside.



The paper underneath the pads is to prevent them marking the wood as I'd found that these clamps (especially when new) leeched something that left a stain on the wood.

Also took the opportunity to knock up a drilling jig for the hinge...the lip gives me the correct spacing from the edge of the door. Ignore the ****-up of the extra holes.



I also made up the veneered panel for the fixed panel between door and drawer



As for the first fixed panel, it is narrow and as I am fixing it in place didn't bother with a balancing veneer as no real need. But just to show that if you were going to put it in a door, for example, that a balancing veneer is a 'must', I stuck this edge on it (after 24 hours removal from the veneer press)

 

[the_g_ster]

Interesting post.

And, thanks to you, I shall be off for find a sheet of 25mm kingspan, genius idea!!!

Thanks, look forward to see the rest.

 

[newt]

Roger, done something similar recently. I used kitchen cabinet type hinges, I used 3 as the weight was just on the limit for two. All went well until I tried to open the door and the top right hand corner on the sloping edge fouled the frame, difficult to explain but if you think about the geometry it's got to happen, I had a 2 mm gap all around the door. I found I had to relieve the inside top edge by planing a 30 degree chamfer for about 50 mm down from the point, of course the thicker the door the more it will foul and more will have to come off. You would only see the chamfer on the inside, so the outside appearance is unaffected. Also a bigger gap would solve the problem but you would not want to do that. Some under stairs doors have a small horizontal flat area to avoid this but to me it looks wrong. Good job so far particularly the veneering. My door was a built up frame in 18mm MDF with a centre panel in 12 mm all painted. Fitted an oak threshold to match the oak floor.

 

[RogerS]

Pete...you are psychic! I am a little behind in my posting and did hit exactly the problem you outlined. We had a thread about it over on woodworkuk. This SketchUp drawing shows the problem. I rotated the door slightly and as you say it fouls the top corner.

 

[RogerS]

As Newt (Pete) mentioned, pointy doors have one disadvantage in that as you open them they will bind. I found this out the hard way. The solution as suggested by the guys on WoodworkUK is to chamfer off the top of the corner. So I didn't cut off more than was necessary I tried it out on a bit of softwood of the same thickness as the door. The SketchUp drawing shows this binding in graphic form.



The new hinges arrived and the door hung. I have four hinges on the door due to height and weight...any less and the chances are that the top of the door will get pulled away from the frame due to weight/leverage of the door. However, for trial purposes only needed top and bottom.



Watching the way the door opens is quite strange as the front corner of the hinge side of the door swings behind the front face of the frame and so a small radius on this corner helps. As you adjust the hinges with the door partly open you can see the gap close up between door and frame...too little and it binds, too much and there is a large gap between door and frame. It's possible I got the distance between the hinge and the door edge slightly wrong but I don't think so. It is critical though.

And it was this point that a wee problem reared its head namely how, if I wanted to maintain a clean uncluttered line, was I going to open the door? I'd originally planned to have a push-to-open fastening. Or maybe two but I wasn't convinced that they would be man enough to push the door out far enough against four sprung hinges. Finger-pull in the edge of the door...breaking fingernails as you wrestle it open? I think not. Knob? Definitely not. Again, the guys on WoodworkUK pointed me in the direction of some hinges from Hettich that are sprung the opposite way round. In other words they are trying always to open the door a bit. Result! Spoke to the technical guy from Hettich...very helpful..walked me through the right part numbers online with me including the complementary push-to-open fasteners. Expensive though as the quantity I was buying in meant them splitting packs with a resulting financial loading. Ah well, if it works......

So while I waited for them to arrive, turned my attention to the drawer problemette. Posed this problem and several solutions were suggested. In the end, I went for one suggested by SBJ (Sainty) which was to make a small plinth and get that level. But how to execute? I came up with the idea of putting screw inserts into an offcut of ply. Feed bolts through and adjust them until the plywood plinth was level. I'd then fix the plinth in place somehow, remove the screws, cut their heads off to the right length, cut a screwdriver slot in the ends so that they'd sit below the surface of the plinth. Sounded like a good plan. And so it was.

Until we came to how to keep the plinth in the right place. Expanding foam, I thought. Unibond the cement to seal it and give the foam a dust free surface, stick a heavy weight on top and let it go off. BAD IDEA :evil:

Ever see a grown man cry? Too much foam and I had no idea of the pressure it could create. Result? A nice dished plinth with the centre nicely in place and all the corners all over the place.



After much fettling, cursing and cussing, I eventually managed to bludgeon, coax, screw, rescrew the f*****g thing down and, using a couple of winding sticks, level and without any wind. In the process I also realised that the screw inserts I'd used were not ideal for the job as they pull out to easily. But I had a lot spare and so that's why I went for them. Much better to have gone for the screw inserts that themselves are screwed into the plywood with an allen key.



While the foam was going off, I made up the actual drawer from MDF. This is destined to house one of the vacuum cleaners - a household utensil that seldom sees the light of day in our household So making the drawer out of MDF rather than some elm seemed reasonable. I used pocket screws. They work. But I've never managed to find a way to stop the two pieces sliding out of line as you tighten up the screws. Especially something slippery like MDF. I've tried the Kreg clamp...no good. I've tried clamping a batten behind. Failure. I've tried everything but still they slide out of line.

The sliding rails are also push-to-open. Fitting them to the inside of the carcass I don't bother with any measurement or lines. Just use a piece of square offcut as a spacer up from the bottom..job done.



You have to make sure that you allow a 2mm gap for the drawer to be pushed in to unlatch the slider. Only I then found out that the drawer wouldn't close ...



because I'd cocked up my measurements and forgotten to factor in the end panel of the carcass.



So what to do? Shift the sliders in the carcass or cut down the drawer? At this point I had a panic attack..would I be able to slide the drawer onto the slides once the carcass was in situ? The hall is quite narrow here with a radiator opposite. If I pushed the carcass right back under the stairs (the carcass is 850mm long) would I have enough depth available to fix the front elm panel. So rather than measure I decided to take the whole lot in and try it for size. It all fitted....just.

A check of the level of the carcass showed it to be level...at least as far as the spirit level is concerned ...but a quick look at how the centre fixed elm panel is looking tell me that I am going to need some finessing if the drawer panel is to be perfectly co-planar with the rest. Main reason being that because of the length of the drawer, a tiny tiny mm or fraction out at the back will be magnified at the front. I know I can glue the carcass down in place with it aligned but know that the front panel will need adjustment. Some more thought needed on this one, methinks.

 

[Graham Orm]

Entertaining stuff, thanks for posting. It's hard to give advice because of the danger of mis-understanding the problem. Going back a page (I've only just arrived on this thread) I would have said put in a frame of some sort and level and plumb that up. The adjusting feet were a good idea. I would probably have used them to level it then take it out and make shims up the same thickness that each leg protrudes, then screw down through the base and newly glued on foot/shim. The first problem (above)....after measuring the vac!! cut down the drawer. Not sure I can visualise the second problem just posted enough to respond.

 

[AndyT]

I think this is a very useful post. Far more valuable to see the things that can go wrong - and how to put them right - rather than 'I did this and it was all perfect.'

It's a bit late to say it, but in case you have to take out your level plinth... I think I would have put a block in the unreachable back corner and screwed down through it into the floor. I'd then have put a slender wedge in each of the other corners, knocked each one in until the board was level, then screwed down into each one to stop it moving.

The trouble with doing jobs like this is that you will always look at it and see all the little snags and how they were solved - but everyone else (apart from us on here) will just think 'he took a long time fiddling about with that cupboard before he finished it!' ;-)