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By RogerS
#1327464
The initial design ideas and exploratory thoughts/problems etc can be found here

This project is definitely something you wouldn't want to tackle as a paid job. Way too many if's and but's and 'How the hell am I going to do this?'. A lot of interdependencies affecting the sequence and timing of the work.

First off is getting the sub-frame sorted. Starts of with the bottom piece fixed in position. A simple job until you find that in the time-honoured tradition of the builder who resurrected our wreck back in 1975 for the then-owner, his refusal to ever use a spirit level continued.

So that bottom piece has to be wedged, glued and screwed in place to level it up.

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Last edited by RogerS on 11 Feb 2020, 06:19, edited 1 time in total.
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By RogerS
#1327465
Managed to get out into the workshop yesterday to veneer the arc for the bottom step in the vacuum press. Not used it since we moved three years ago. Ran it up and it seemed to suck OK. Veneer pieces all cut. A nice bit of veneer for the top and some constructional veneer for underneath to bring the overall thickness to that of the floorboards that will be inset. Bought a sheet from Capital Crispin at an astronomical price TBH and glad it's underneath as there's virtually no 'figuring' of any description. Maybe I'll try Mundy's next time.

First time veneering something as thin and curvy...bit of a 'mares TBH. Stuck it in the bag and turned the pump on and waited. And waited. And waited. Air was going out but not very fast. Cranked it up (or so I thought) but after 15 minutes I could see that it wasn't going to do the biz anytime soon and so I invoked MPM (Mad Panic Mode) .

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We shall see tomorrow.

In the meantime I investigated the pump and discovered that numbnuts here had misunderstood the scale and had tweaked down to minimum suck. So with a bit of luck it will be OK for the other stuff. Nonetheless I will try and do a trial run before committing.
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By RogerS
#1327466
'Compulsory' holiday got in the way of much progress :evil:

But tolerably pleased with the veneer after the earlier panic. Obviously still some finessing to do.

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Attention now turning to making the vertical veneered curved panels. I think the two 'critical' points for fixing are at the extremes. As per this diagram -

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Proposing to have blocks glued and screwed at each end and also others distributed around the periphery. The blocks will be then screwed into large pieces of timber (fitted radially) that are themselves fixed to the bottom baseboard. The edge of the bottom baseboard will be glued to the bottom of the vertical panel. The blocks at the extreme ends will be double the height that's needed thus allowing me to screw a long batten across the chord to keep the vertical panels curved and in place while everything (glue etc) goes off.

Once the vertical panel has been fixed to the bottom baseboard but before it's all set, glue the edge of the top baseboard and push that into position to give as tight a fit as I can manage to the top of the vertical panel.

So basically that vertical panel is glued all the way round at the top and bottom. Plus intermediate blocks screwed to it prior to veneering that are fixed to the radials. My one concern though is this. Seems to me that most of the stress is at the two extremities by the wall. Just glueing blocks won't work as the MDF will delaminate I think and spring back hence small screws through the MDF into those blocks prior to veneering. Just wondering about them pulling through the MDF.

I've put the MDF (6mm) in tension around a former to encourage it to stay bent. Don't think I can wet it 'cos it's MDF.
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Any thoughts ?
By profchris
#1327498
I've made a guitar case from 6mm MDF, which bent fine over a hot pipe. I reckon heating the MDF with a heat gun (to Ouch hot but below scorched, practice on an offcut) will make it take up the curve.

But it will soften your glue joints, which will harden again but be a little weaker. If you haven't glued it yet, that's my solution. If you have, you'll need to take a view on the glue question.
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By RogerS
#1328626
I’ve had two suggestions for ‘easing’ the curve on the 6mm MDF risers : cutting a load of kerfs (RogerM TWH2) and using a hot air gun (ProfChris UKW). Since it’s over 2m long, the thought of cutting all those kerfs didn’t appeal and so I gave the hot air gun a go and it worked a treat. You have to be careful not to get too close to any strapping

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The allen key underneath is to spread the strap load evenly over the width. I’d noticed that without it, the MDF was starting to distort under the pressure of the strap.

Still thinking about (a) how to fix the riser to the subframe and (b) keeping it bent between taking it out of the vacuum press and fixing it to the subframe.

The solution to (a) is several blocks glued and screwed to the riser ahead of the veneering..since I don’t really want screw heads in the veneer !!
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In an ideal world with a level floor I might have considered making the bottom step as a unit, gluing and screwing the riser on and then veneering but, as mentioned earlier, the floor isn’t level and I would like a nice tight fit down to the floor with the riser so it’s going to be …(a) fit the bottom subframe to the floor (b) veneer (c) fit the riser to the subframe.

The solution to (b) is to have the two blocks at the lefthand and righthand extremes (where the riser meets the wall) extra tall and then have a plywood bar between the two. Using two screws at each end minimises any tendency for the riser to skew. Thus …

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This was Plan A. It lasted two whole days.

Remember I’d not done any veneering for over two years and had forgotten what little I knew. First thing was to check the pump was OK and that this time I’d set the ‘suck’ to the right level. It’s also a damn great bag. Test 1…put the riser in the bag but without veneer or glue, started the suck

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Not much happened. Then … I found out that it also helps to actually fit the vacuum connector on properly. :oops:

Test 2…well on the way. Success. Image

What next ? I remembered some of that breather membrane needs to go in but I couldn’t remember where it should go …alongside the workpiece ? On top of the veneer ? Did I have to moisten the veneer ? Did some reading around, spoke to a few folk. Membrane goes on top of the caul. Caul ? So thought to use some 6mm MDF as a caul. But speaking to Steve Maskery, he rightly pointed out ‘Why fight 6mm MDF…why not get some 3mm hardboard or picture backing board ?’. He was bang on the money.

Did you know that you can roll up 3mm hardboard and stick it in the back of your car ? No, I didn’t either until yesterday.

Then the thought struck me…looking at that photo…I couldn’t see how it was going to work properly. Surely the underside of the riser needs a better support. Or does the vacuum ‘wrap-around’ as it were and provide equal pressure on the underside? Would it all twist and stretch out of recognition once I’d fully applied the vacuum ?

More Googling…more looking at Youtube. Couldn’t find anyone daft enough to be attempting what I was doing but gut feel suggested that belt and braces dictated a decent support underneath. So unscrew the bottom panel of the subframe from the floor, take that and the upper subframe panel back into the workshop. Screw the riser using those blocks onto the bottom panel …fudge fixing the upper panel fitting all together into some semblance of a support et voila.

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Turn on the vacuum pump.

I’d knocked off as many sharp corners as I could and added padding as I didn’t want to tear the bag.

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Even then, I think I could have provided more padding.

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Doing this has also highlighted one thing…namely that glueing the top of the riser to the upper subframe panel is going to be challenging given the gaps…they will pull in but how ?

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I have a cunning plan but that will have to wait.

Oh yes…that scream you heard this afternoon? That was me realising I’d been a muppet because when I went to apply the veneer to the freshly glued surface, it was then that this eejit had cut it 3” too short. That’s something else to sort out. But we are making progress.
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By RogerS
#1328628
doctor Bob wrote:I'm either missing something or you have way over complicated that.


Probably the latter or perhaps I've not explained things very well. Would welcome any suggestions. You've been at this way longer than I !! Happy New Year, btw.
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By Jacob
#1328636
RogerS wrote:
doctor Bob wrote:I'm either missing something or you have way over complicated that.


Probably the latter or perhaps I've not explained things very well. Would welcome any suggestions. You've been at this way longer than I !! Happy New Year, btw.

Said it before will say it again; simplest would be to modify the very commonplace trad detailing of a bull nosed step. You'd have to look in the older books for info as there seems to be little on line (lost art?).
The essential detail is the curved riser constructed from a solid board with the curved part reduced to a thickish veneer but the ends left intact for locating to a made-up backing block. Various crafty fixings here - bevelled half dovetail and folding wedges etc. It wouldn't need steaming or pre-bending but a quick soak in hot water would be enough to help fit it.
The 'veneer' nowadays more easily done with saw kerfs instead.
The whole riser plus block (s) would be a unit and the boards for the treads simply laid on. The blocks quite substantial made up of layers of 2" timber
It's on page 93 of vol3 of WB McKay 1954. May not be in later editions, but will be in Ellis etc and many older books.
I've done it once! Worked fine, a bit of a challenge but nothing went wrong. I've got some snaps will post if I can find them.
PS you are getting closer to the idea in your pencilled diagram above. The blocks would be much more massive than anything you have shown in your pics. The curved risers would have no screws, nails or other fixings visible on the face
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By AndyT
#1328869
I realise this is probably way too late to be any use, but I have only just remembered where I saw someone else doing something a bit like this. It was Mitch Peacock, on YouTube. He's a British woodworker who works commercially, has done hundreds of videos, but seems to not get talked about on here very often. I can't remember how he did his big curved step but it had some similarities to yours and might be interesting to watch.

This is part 1 of 5 short videos.


youtu.be/8gLKfamfcyo
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By RogerS
#1329299
Jacob wrote:

The essential detail is the curved riser constructed from a solid board with the curved part reduced to a thickish veneer but the ends left intact for locating to a made-up backing block. Various crafty fixings here - bevelled half dovetail and folding wedges etc. It wouldn't need steaming or pre-bending but a quick soak in hot water would be enough to help fit it.
The 'veneer' nowadays more easily done with saw kerfs instead....


Interesting idea. Curious to know more. I don't have that book to hand.

What thickness board are you suggesting ? How thick is "thickish" ? Not sure about this backing block
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By Jacob
#1329304
RogerS wrote:
Jacob wrote:

The essential detail is the curved riser constructed from a solid board with the curved part reduced to a thickish veneer but the ends left intact for locating to a made-up backing block. Various crafty fixings here - bevelled half dovetail and folding wedges etc. It wouldn't need steaming or pre-bending but a quick soak in hot water would be enough to help fit it.
The 'veneer' nowadays more easily done with saw kerfs instead....


Interesting idea. Curious to know more. I don't have that book to hand.

What thickness board are you suggesting ? How thick is "thickish" ? Not sure about this backing block
You need to look at the old books WBMcKay as mentioned above. Or "Joinery &Carpentry" ed. Greenhalgh Vol 3 shows very clearly how to do a bullnose step with a much tighter radius than your proposal. You'd have to adapt their processes to your design. The most obvious thing you'd do differently is to kerf the board instead of "reducing to a stout veneer" as Greenhalgh terms it - we have handy table saws available for work earlier done with hand tools.
I'll do a photo of the pages later.
PS or any of those old books on Stairs and handrails. All sorted - no need to reinvent the wheel.
https://www.worldofbooks.com/en-gb/rare ... YYQAvD_BwE