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Rogue
27-08-2012, 02:24 PM
Whilst reading around I came across various mention of lights dimming and all sorts of intrigue while turning on equipment. This leads me to wonder if I am going to run into problems with supplying power.

There is a single point in the room I'm using - a standard double socket. It's almost guaranteed to be on a spur as it is a converted attic. Is this likely to cause me any major problems in terms of running PSUs, VFDs etc? I hate the idea of having to reset breakers on a regular basis because the CU is all the way down in the basement, past the dragons and cave trolls and big hairy spiders :nightmare:

Jonathan
27-08-2012, 02:53 PM
What current is the spur fused at? Simple answer is add up the power of everything that could be on at one time, then compare it to what you can get from the sockets.

Running a CNC router (so VFD, stepper motors, computer, water pump, maybe air compressor) should be fine on a 13A socket. Mine certainly uses a lot less than that. It's theoretically possible that the VFD could draw 2.2kW whilst the stepper motors are drawing a few hundred watts along with the computer, which might take the total over 3kW, but that's incredibly unlikely - I don't think I've ever drawn the full power from my spindle.
However if you put a kettle or a heater on there that could easily take you over 13A.

JAZZCNC
27-08-2012, 03:07 PM
You need to find out for sure because VFD's and high powered PSU's come in with a kick.!

If it is a just a spur then wouldn't recommend you pull everything off it and chances are it's rated 13A.? Most VFD/spindles can potentially pull between 7-8A and 3 axis machine/PSU could pull 8-10 under full load and 10-12 if twin screw setup or 4th axis.?
Then you have secondery stuff like PSU for BoB's, coolant pump etc and then there's the PC.! Heater in winter, alarm clock so you don't miss ya dinner or Coronation street etc etc Ye get the picture.!! . . So all in all you could potentially be pulling over 13A under full load.?

I certainly wouldn't be happy running all this off a 13A spur.! . . . I think you'll certainly be needing your shield and sword for the dragons and trolls every now & again.??

JAZZCNC
27-08-2012, 03:13 PM
Ha ha didn't see Jonathans post.!! . . . . No surprise thats Another thing we don't agree on.! But thats ok because it's not my house you'll be burning down after you find out he's wrong. .:hysterical:

Rogue
27-08-2012, 03:17 PM
As to the first question about the current for the spur, no idea. I am not aware of any seperate fuse for this so I guess it's just a matter of checking the fuse for the ring downstairs.

Each work area has an extension lead out to it and I tend to make sure I'm only using one area at a time anyway. All that would be running would be the CNC kit including computer, though what I mean by "kit" is vague I suppose. VFD, steppers, water pump seem certain. Dust extraction for wood, coolant pump for metal are nice ideas but unlikely just now, some airflow into the planned enclosure is likely though.

As for other comments about lights dimming on startup, is that a feature of a particular piece of equipment and can it be avoided?

Rogue
27-08-2012, 03:30 PM
Ha ha didn't see Jonathans post.!! . . . . No surprise thats Another thing we don't agree on.! But thats ok because it's not my house you'll be burning down after you find out he's wrong. .:hysterical:

Yeah I won't be mentioning that last line to the wife :playful:

This might take a bit more planning and balancing then. Steppers and Drivers were going to be 3 x Nema 23 3Nm (http://www.zappautomation.co.uk/sy60sth883008b-nema-stepper-motor-p-24.html?cPath=9_159_42)and PM752 (http://www.zappautomation.co.uk/pm752-microstepping-driver-p-409.html?cPath=9_3_4)s, spindle to be chosen based on price and availability at the time!

I could always run an extension lead up the stairs to run the fan during the summer! :joker:

JAZZCNC
27-08-2012, 03:38 PM
As to the first question about the current for the spur, no idea. I am not aware of any seperate fuse for this so I guess it's just a matter of checking the fuse for the ring downstairs.

Well in this case like I say you need to find out for sure because in this case the whole house is pulling off it and you could be stuffed unless you turn off everything else in house.!!



As for other comments about lights dimming on startup, is that a feature of a particular piece of equipment and can it be avoided?

This would indicate a really high initial draw so could be large transformer or dodgy motor pulling high Amps.? Could be many reasons.!
My lights don't dim and I run high power transformers and large motors with high power draw on startup like my big compressor.! There's many times I'm running CNC machine while I'm using Lathe with mechanical saw cutting in background and compressor kicking in & out blowing chips form machine, sometimes I even have extractor going at same time.

Rogue
27-08-2012, 03:44 PM
Well in this case like I say you need to find out for sure because in this case the whole house is pulling off it and you could be stuffed unless you turn off everything else in house.!!


You're a little bundle of joy, sometimes, did you know that? :whistle: Still, these are things that never occured to me that I'll need to worry about and address before, not after.

I'm stubbornly hoping this will all work out because I've not got another space I can use at the moment.

JAZZCNC
27-08-2012, 03:45 PM
I could always run an extension lead up the stairs to run the fan during the summer! :joker:

Won't matter if they are all pulling off the same ring.? If this is the case now you have to total everything using power and pulling off this ring in the house and be sure it's not going to exceed the fuse rating.? . . . . Don't let the wife put kettle on or hair dryer or take a shower while using machine thats for sure.!!

Rogue
27-08-2012, 03:49 PM
Yeah that's one of the new things I have to worry about. I'm rather hoping that at least the upstairs rooms will be on their own ring, I thought it was usual to have a ring per floor. If that's the case then, thankfully, the only other thing running on that ring during the day would be the aquarium. Oh great, now I have to go home and work out how much the aquarium heater/pumps etc are using

JAZZCNC
27-08-2012, 03:50 PM
You're a little bundle of joy, sometimes, did you know that? :whistle:

Ye I know it's my special gift but I'm going away tomorrow so you'll be ok for a few days untill I find the password for the wifi where I'm staying. . Lol

Rogue
27-08-2012, 03:53 PM
Ok so an extension lead from the kitchen - it can't be more than 10m if I run it outside through the windows, maybe 30m if I run it up the stairs :whistle::wink:

(Just for clarity, I don't actually intend to do this!)

WandrinAndy
27-08-2012, 04:08 PM
There's many times I'm running CNC machine while I'm using Lathe with mechanical saw cutting in background and compressor kicking in & out blowing chips form machine, sometimes I even have extractor going at same time.

And some womenfolk reckon we don't know how to multitask... tut tut

i2i
27-08-2012, 04:14 PM
if there's a spare spur in the main fusebox fit a 32A/40A breaker and run a new length of 4mm or 6mm cable up to your work area and put a breaker there. Run the machine from that.

Rogue
27-08-2012, 05:18 PM
if there's a spare spur in the main fusebox fit a 32A/40A breaker and run a new length of 4mm or 6mm cable up to your work area and put a breaker there. Run the machine from that.

Which would be sensible I suppose, though once you get into fiddling with the fusebox you need proper electricians and paperwork to prove it's done properly?

JAZZCNC
27-08-2012, 05:33 PM
Which would be sensible I suppose, though once you get into fiddling with the fusebox you need proper electricians and paperwork to prove it's done properly?

Don't know what you mean officer it's been like that since I did it.! . . .Err . . mean we moved in.!!. . :loyal: . . . Actually I think the Regs have got so silly you can't even change a socket now without the HSE police knocking.?

Seriously thou it would be worth the expense for peace of mind and allow you to use what ever you like without torching the place or getting eaten by trolls.!!

Rogue
27-08-2012, 05:42 PM
Right, just been down to check. Our basement is designed for midgets unfortunately, which is a pain in the arse when you're 6-foot-something.

Older style (pull out the whole fuse not flip a switch) breakers, no spare spaces and, very helpfully, no indication whatsoever of which one is which.

30 Amp, 15 Amp , 30 Amp, 5 Amp, 5 Amp, 15 Amp, 15 Amp, 30 Amp

I'm guessing the 2 x 5 Amps will be lighting and 1 x 30 Amp for the kitchen. That leaves 2 x 30 Amps and 3 x 15 Amps unaccounted for. This calls for some quality time taking out the brakers to see what affects what I guess, but I'll need to wait for a time when the kids are at school and the wife doesn't have any work to do.

Rogue
27-08-2012, 05:47 PM
Seriously thou it would be worth the expense for peace of mind and allow you to use what ever you like without torching the place or getting eaten by trolls.!!

I quite agree. I'm perfectly happy with having the old CU replaced and some wiring run up for proper power. It's just starting to double the budget. I was looking forward to ordering the first batch of bits on my birthday next week :hororr: This might require some thinking.

i2i
27-08-2012, 05:51 PM
you don't want to call in an electrician then, as he will strongly suggest you change the old fusebox and probably most of your wiring.

JAZZCNC
27-08-2012, 05:51 PM
but I'll need to wait for a time when the kids are at school and the wife doesn't have any work to do.

Bugger them we need to know now.!! CNC rules over all other things or people and it won't kill them for 5 mins plus they can shout out whats wot.? . . . . In the great words of wolfie smith " Power to the People" of in this case "Power off to the Attic". . :loyal:

Rogue
27-08-2012, 07:01 PM
Never I say I didn't give you blood, sweat and tears.

Gashed my head open crawling in and out of the midget basement but managed to work out some of it.

The second 30Amp provides power to the upstairs hall and three bedrooms. I can discount the hall and two bedrooms for various reasons. The main bedroom has an aquarium running 24/7, and provides the socket for the washing machine in the adjacent bathroom. Iron is also here. Hoovering happens, but not often enough :whistle:

I've got some guestimates (http://www.wiltsfire.gov.uk/fire_safety/safety_advice/fire_safety_electrical_safety.htm) in the 1.5-2 Amps range for the aquarium, 8-12.5 Amps for the washing machine. I've gone through and added up a list of things that might happen at from that list. As long as we don't use the washing machine and iron at the same time we should have 12 Amps. If we make sure we don't use the hoover as well, that brings us to 18 Amps spare.

As long as that list provides a decent estimate, I'd say that our realistic max "casual" use on that ring without the washing machine is about 4.5 Amps, going up to about 11-12 if hoovering or ironing. As long as we coordinate to avoid using the washing machine at the same time, I think it's the 13Amp socket that will be the limiting factor.

I still like the idea of getting it all sorted properly though.

JAZZCNC
27-08-2012, 07:10 PM
10/10 for effort.!

Your sorted then with 30A and just leave the washing machine off for good measure.

The dedicated ring is ideal for safety sake and piece of mind but so long has the wirings in good order you'll be ok.

Thou i2i is right a sparky will want to change the consumer unit at a minimum.? Must admit thou they are good when things go tits up.!

Rogue
27-08-2012, 07:16 PM
After wrestling with those bloody fuses with a torch clamped between my teeth, blooding dribbling down my forehead and a big scary spider looking at me like I was dinner... yeah I don't mind swapping out to one of those new ones with little flicky switches :nevreness:

JAZZCNC
27-08-2012, 07:21 PM
a big scary spider looking at me like I was dinner...

Got one in my bathroom big has a sponge.! . . . Been having baths at my sisters for weeks I dearn't check if it's eaten my son or not yet.? . . Hope so. . :playful:

Web Goblin
27-08-2012, 07:25 PM
If you get a spark in then he or she will probably recommend a CU change but you dont have to do it. As long as the board complied when it was fitted then it doesnt need to be changed. They might check over things like earth cabling and bonding and see if it meets current requirements. Depending on what size of cable your spur is wired in you could easily pull full load through two sockets if its a twin socket. You would only be limited to around 13amps if it is connected to a 13amp fused spur. Its been a while since I did any real electrical work but a bit of 30Amp fuse wire will happily run at over 30amps for quite a while without blowing.

Rogue
27-08-2012, 08:13 PM
Got some of that flat grey 6mm for another project, then realised I didn't have any clippy thingies that would cut through the flippin' stuff! Somehow I did it in the past but I've got no idea how?

Edited to add: apart from the obvious "because you had a tool that did it but now you've lost it" :D

John S
27-08-2012, 08:25 PM
Run the spur wiring thru the fish tank, that should keep it cool and allow you to go up to a 20 amp fuse.

Rogue
27-08-2012, 08:29 PM
Run the spur wiring thru the fish tank, that should keep it cool and allow you to go up to a 20 amp fuse.

I'm already wondering when the whole place will end up falling into the fishtank as it is! The maximum loading for the floor is one of the many reasons why I'm not going to use concrete-filled bases :whistle:

JAZZCNC
27-08-2012, 08:44 PM
You could always save some amps and weight in attic by using the fish tank pump and water for cooling the spindle.? Sure Nemo and his mates won't mind.! . . . Then when it's time for water change then use it for flood cooling. . Lol

Rogue
27-08-2012, 08:56 PM
Now that's thinking!

irving2008
27-08-2012, 09:07 PM
You could always save some amps and weight in attic by using the fish tank pump and water for cooling the spindle.? Sure Nemo and his mates won't mind.! . . . Then when it's time for water change then use it for flood cooling. . LolMany moons ago I was working at a large data centre associated with a UK bank... the cooling system for the mainframe did indeed run outside to a large bank of evaporators and the condensate was stored in fishponds which, because it was well aerated and at a controlled pleasantly warm temperature, housed a startling variety and size of tropical fish...

On a serious note though, how thick are the joists in the attic space? Is it a sanctioned conversion or have you just migrated to it?

Jonathan
27-08-2012, 09:08 PM
Not as silly an idea as it might seem - if the temperature of the water from the spindle is greater than that of the tank (i.e. put in a quick op-amp circuit to compare it) you could put a heat exchanger in the tank and pump the water through that so it's an isolated system and the fish keep cosy for free.

m.marino
27-08-2012, 09:14 PM
First find out how many rings you have in the house. We have two rings and if I owned it, they would be divided further. I am US bred and we tend to put heavy appliances on their own, sockets on another (per floor or in some cases region) and lights on their own with a circuit for the garage or external al on it's own. That is there not here. So find out how many rings you have. I run the shop off the ground floor ring and as long as I don't start the washer there is no problem and I am running 4 nema 23 3.1NM steppers, AM882 drivers (4), BOB (PMDX), ESS, Computer, Lights and at times either the bandsaw or the pillar drill.

So it really depends on how you are set up and what the circuit is set up to take. Better safe then sorry and I DO have an ABC rated fire extinguisher just inside the door to the shop. Jazz it pointing out that being on the safe side is always better then having to make regular trips all the way down stairs to rest switches.

Michael

Edit: well thing where going so fast that this is a near worthless post.

Rogue
27-08-2012, 09:58 PM
@Irving: The best way I can answer that is "no idea". I'm in the end-terrace for a row that go back about 100-odd years. I suspect they were built with the attics as habitable by design. Ours has actual stairs that look like they were meant to be there, and I note that all the other houses left from this row also have dormer windows - though ours were replaced with a bigger dormer at some point.

6682

I've stuck my reloading/"clean" bench there for the moment. Well, I say "for the moment", there's no flippin' way I'm moving it. All the benches are designed with no removal strategy other than 30 minutes with a chainsaw :whistle:

@Jonathan: Oh if I could get away with it I would be entirely up for it :D

@Michael: I've identified which ring it is on and what sort of loads I expect on it, so I am quitely confident. Quite quietly. Whisper-like, perhaps. In fact you might need a medium with a ouija board to hear my confidence, but it's there.

Rogue
27-08-2012, 10:05 PM
On a sidenote, I was rather surprised with the workbench in that photo. I put a PC on it to test something and the whole thing vibrated like a drum. I didn't really worry about sound when I built it because it's not for "noisey" stuff, but I didn't expect it to amplify the vibration and it felt like it transmitted it straight into the structure.

Lots of experimenting to be done with isolating and dampening, I think.

irving2008
28-08-2012, 12:11 AM
@Irving: The best way I can answer that is "no idea". I'm in the end-terrace for a row that go back about 100-odd years. I suspect they were built with the attics as habitable by design. Ours has actual stairs that look like they were meant to be there, and I note that all the other houses left from this row also have dormer windows - though ours were replaced with a bigger dormer at some point.

6682

...

Nice bench and a period chair too ;)

You should lift a floorboard or two and check the joist dimensions before you load the floor too much. A typical 100y old house would use 4x2 joists in the attic (my son's from 1903 does), they were never designed as habitable space but for light storage, tho it could be used for 'servants quarters' in larger houses, but the loading assumed very light (no heavy wardrobes etc.). Building regs differentiate between ceiling joists and floor joists. A 4 x 2 ceiling joist at 16" centres spanning a maximum of 8' (the width of a small room below) will support a dead load of no more than 500N/sq metre, an imposed (i.e variable) load not exceeding 250N/sq m and a concentrated temporary load not exceeding 900N. I'd hazard that you sitting at your substantial workbench is close to exceeding that.

Building regs do not allow for more than 1250N/sq m loading, above this they need structural design/calculations agreed by building control - this is why you need building control approval for loft conversions, especially where there is a wet room or bath installation (a full bath of water with a typical male in it is close to 2500N/sq m loading).

Again, don't want to be a spoilsport... but you don't know how the timber has faired over the years and it would be unfortunate for your new CNC build to end up in a crumpled heap on the floor below!

JAZZCNC
28-08-2012, 12:22 AM
Ye what Irving said.!!. . . And if you miss align the ball-screws it will shake the tiles off your roof has well. . :hysterical:

Rogue
28-08-2012, 12:42 AM
Nice bench and a period chair too ;)

If by period you mean "absolute pain in the neck for most uses" then yes. There's a stool around there somewhere that I use, but occasionally the lower seat lets me get adopt a more stable position leaning on my elbows, holding whatever I'm working on right up to the face.


You should lift a floorboard or two and check the joist dimensions before you load the floor too much.

More things to check! And lifting floorboards? I think I'd rather play with the mains again, there's less chance of getting into trouble :whistle:

For various reasons we've got to have some work done on one of the ceilings underneath so we'll probably have to cut away a square of the plasterboard. I assume we can get a look from underneath. Either that or I'll definately have to wait until the kids are at school and the wife is at work!


...scary numbers etc etc... Again, don't want to be a spoilsport... but you don't know how the timber has faired over the years and it would be unfortunate for your new CNC build to end up in a crumpled heap on the floor below!

Nope, don't worry, I entirely appreciate the points you are making. Is it my first choice of location? No. Is it my only current realistic option for location? Yes. Adopt the guest bedroom? Take garden space to build a shed? The last time I successfully convinced my wife to do anything was when I asked her to marry me and, looking back, I'm starting to wonder if I convinced her to say "yes" or if she tricked me into asking in the first place. While I love her dearly, my jedi mindtricks don't work on her.

I assume that if the joists are too small there's nothing I can realistically do, short of miniaturising the build or rebuilding the attic?

Rogue
28-08-2012, 12:44 AM
Ye what Irving said.!!. . . And if you miss align the ball-screws it will shake the tiles off your roof has well. . :hysterical:

The wind does that already...

Rogue
28-08-2012, 12:48 AM
I'd hazard that you sitting at your substantial workbench is close to exceeding that.

Ahh yeah, forgot to mention. I suppose this won't be helping either?

6683


Except now it's got a 2m long double layer of MDF (that was only a temp worktop for the picture) and a pillar drill on it...

JAZZCNC
28-08-2012, 12:52 AM
ah ha ah . .bet there's more bloody timber in them 2 bench's than the whole floor . . lol

Rogue
28-08-2012, 01:00 AM
ah ha ah . .bet there's more bloody timber in them 2 bench's than the whole floor . . lol

Probably - if the floor ever collapses the benches will come out intact, and that's the important thing. The only thing they contain in greater volume that timber is woodglue :cool:

I wonder, is there likely to be enough of a gap between the floorboards that I can poke something thin between them to find the edges of the joists to work out the width? If I can get something with a bend in it then I can find the bottom and work out the height as well.

Rogue
28-08-2012, 01:04 AM
Worst case scenario, I can cut out some of the ceiling and put up some support poles then decorate them to blend in. I'll tell the kids I built them a jungle gym for their room, and tell the wife I bought her some poles for dancing in our room...

John S
28-08-2012, 01:13 AM
I wonder, is there likely to be enough of a gap between the floorboards that I can poke something thin between them to find the edges of the joists to work out the width? .

Measure between the heads of the floor board nails ?

Rogue
28-08-2012, 01:15 AM
Measure between the heads of the floor board nails ?

For the distance, yep, but I think the issue was the actual width of the joist unless I misread it? But measuring nail gap is also going to be done.

irving2008
28-08-2012, 01:38 AM
...stuff...

I assume that if the joists are too small there's nothing I can realistically do, short of miniaturising the build or rebuilding the attic?

Not at all, theres a few things you can do, sadly none of them very easy. The absolute simplest solution is to increase the size of the joists by bolting another alongside it. This is what you do in bathrooms under the bath. Its not ideal as a 4 x 4 still doesnt have the resistance to bending that a 10 x 2 does. Another, better, option is to add a second joist on top of the first a 4 x 2 on top of a 4 x 2 will make a huge improvement, however it does mean that you'll have a step up into the room, headroom is reduced and inward opening doors have a bit of an issue - but this is whats often done for loft conversions.

Another, more expensive option, is to bolt some steel angle alongside the joist. Obviously this has better bending resistance than wood so can use a much smaller cross-section, but it weighs more so some calcs need to be done about the overall floor weight and wall strength.

Jonathan
28-08-2012, 10:14 AM
I notice irving's specified the loads in Newtons per square meter, so surely if you can spread the load by placing the benches on their own 'joists' running perpendicular to the existing joists the area and therefore number of Newtons supported is increased, perhaps enough? You'll probably be tripping over them all the time though...

Rogue
28-08-2012, 11:50 AM
Another, better, option is to add a second joist on top of the first a 4 x 2 on top of a 4 x 2 will make a huge improvement, however it does mean that you'll have a step up into the room, headroom is reduced and inward opening doors have a bit of an issue - but this is whats often done for loft conversions.



...surely if you can spread the load by placing the benches on their own 'joists' running perpendicular to the existing joists the area...

They say that great minds think alike, but then again they also say that fools seldom differ. This is the first thing that occured to me when I read the post. Can the joist be on top of the floorboards? Basically creating a raised platform at one end of the room? Hopefully Jonathan and I have great minds but I must admit I'm not doing our side any justice at the moment.

Edited to add: Ahh, I guess you mean the extra joist being lined up exactly on top of the old joist, not perpendicular to it? Still, same question applies!

irving2008
28-08-2012, 12:01 PM
They say that great minds think alike, but then again they also say that fools seldom differ. This is the first thing that occured to me when I read the post. Can the joist be on top of the floorboards? Basically creating a raised platform at one end of the room? Hopefully Jonathan and I have great minds but I must admit I'm not doing our side any justice at the moment.

Yes in theory, but you'll need to support the joist at the wall at each end using joist hangers and not just terminate it at the wall. Although just having an additional joist on the floorboard will improve the 'bending' aspect by spreading the load, it wont reduce (indeed it will increase) the shear force at the wall and the underlying joist could still fail with the load. The correct solution is to lift the floorboards, add new joists, cutting them back into the wall and then board over with 18mm OSB which will be a lot stronger than the old floor boards. The new joists need to be securely attached to the old ones at no more than 600mm intervals, either drilled and screwed through into the old ones (BIG screws lol) or you can use retaining straps screwed to lower joist and taken over top joist in a notch and back down to lower joist, tensioned, and screwed through into both joists. Tensioning the straps needs some sort of tool...

Incidentally the minimum joist size now acceptable for loft conversions and new builds is 9 x 2 but 10 x 2 is usual as this matches the 10"/250mm insulation depth requirement and allows direct boarding over.

Rogue
28-08-2012, 12:17 PM
Yes in theory, but you'll need to support the joist at the wall at each end using joist hangers and not just terminate it at the wall. Although just having an additional joist on the floorboard will improve the 'bending' aspect by spreading the load, it wont reduce (indeed it will increase) the shear force at the wall and the underlying joist could still fail with the load.

Which realistically means "no" in this scenario. Fair enough.


The correct solution...

...sounds painfully expensive and simply not possible at this moment in time, certainly. Hmm.


Incidentally the minimum joist size now acceptable for loft conversions and new builds is 9 x 2 but 10 x 2 is usual as this matches the 10"/250mm insulation depth requirement and allows direct boarding over.

I think the first step will to be to work out the joist size and then plan around that in terms of what can be safely done. That might scupper things more than anything else.

Rogue
28-08-2012, 01:37 PM
Hmm, I had a brief bit of time just now but only enough to move a bit of the carpet. No nails in sight and my plan to wiggle something between the boards hit a snag - there appears to be some kind of filler between the floorboards. Still, found one that was slightly looser and had a dig!

Found two joists. Each was 65mm wide. Distance between closest faces was 340mm, so centre to centre would be 405mm. What I'm wondering is that, because the measurements were taken close to the stairs, whether this is representative of the rest of the room or whether the gaps are different because of the stairs. Somehow. Or maybe not.

6690
Measurement was taken about a foot away from the wall, roughly in line with the middle of the radiator.

6691
The stairs, viewed from the uncovered part of the floor. The joists I found would be roughly in line with this.

I don't know if the gaps might be different further out to the middle of the floor but didn't have enough time to check. An awful lot of moving might be needed!

The plot thickens.

Edited to add: I plan to check the depth of the joist but I'll need to find something thin and bendy first. I guess the depth is a more critical bit of information.