Mahogany species

[sime42]

Are you concerned about a potential weakness in the top platform, due to the grain direction of the wood? Front right corner, it looks to be diagonal there, not parallel with the rungs.

 

[ucoulddoit]

24 minutes ago, sime42 said:

Are you concerned about a potential weakness in the top platform, due to the grain direction of the wood? Front right corner, it looks to be diagonal there, not parallel with the rungs.

 

Pretty much spot on! So pleased someone worked it out.

 

OK, so here’s an explanation of the mistake I made. It’s the top step / platform as mentioned. It’s especially annoying given my working life in industry as a structural engineer. I tried to fix it, so what doesn’t look like it was intended?

 

The mistake is, the grain should run front to back, not side to side, as the platform is supported by the brass rods on the front and rear edges. When I realized it was the wrong way round, I went back to the photo on the internet, used as the basis for the design, and it had the grain front to back! Just hadn’t noticed that, but should have worked it out.

 

Looking at the photos below showing the underside of the top step, you will see it is supported by the brass rods at the front and back. But the grain runs parallel to these supports instead of the board spanning front to back onto them. So, my weight of 15 ½ stone standing in the middle of the platform could cause it to split suddenly along it’s length and maybe I’d break a leg or worse? There is a joint along the middle where I ripped and rejoined the wide plank after machining to just over an inch thickness, so that might be an additional weakness?

 

 

 

The two bearers screwed to the underside of the platform were an attempt to strengthen it. If they had been part of the original design, they would be on each side and supported by the brass bars so that the loads would transfer from the platform to the bearers then to the brass bars and finally into the legs. But, fitted as an afterthought, they couldn’t be supported by the brass bars. Also, I realised they couldn’t be glued across the grain due to future movement that might occur, so they are screwed into the platform with a slotted hole at one end to allow for the movement. But there isn’t much thickness to screw into and will the screw pull out capacity in tension hold my weight?

 

Need to sort it properly. I’ve thought about making a new platform with the grain turned 90 degrees. But it’s a lovely piece of wood and took quite a while to make it. Am now leaning towards re-using the platform with bearers on each side, made using brass bar, probably about 1” deep by ¾” wide, instead of mahogany. But I need to check that size is strong enough and stiff enough to carry a person. So, the two short brass blocks at each side will be replaced by brass rectangular bars spanning front to back between the brass round bars with the platform supported on top, spanning side to side. That will work with the existing holes in the legs and platform height as I can get a much smaller edge distance on the holes through brass compared to mahogany. I'll get rid of the two mahogany bearers. It might even look as though it was intended to be made that way!

 

All very annoying and the brass rectangular bar will be an unforeseen additional expense, but looks like it will work out fine in the end. Could have happened to anyone?

 

Thanks for all the comments.

 

Andrew

[Doug Tait]

8 hours ago, sime42 said:

Are you concerned about a potential weakness in the top platform, due to the grain direction of the wood? Front right corner, it looks to be diagonal there, not parallel with the rungs.

 

Well done, thoroughly deserve your prize of, well, a pat on the back emoji! 

[Dan Maynard]

I wouldn't change it, I think those brass bars might be intended to support it but they will be much less stiff than the step so would bend under it if you turned the grain. To my mind the grain is the right way in that step.

[Retired Climber]

23 hours ago, sime42 said:

Are you concerned about a potential weakness in the top platform, due to the grain direction of the wood? Front right corner, it looks to be diagonal there, not parallel with the rungs.

 

Good spot. I've been staring at those bloody photos for ages, and couldn't work out what was wrong. 

[sime42]

1 hour ago, Retired Climber said:

Good spot. I've been staring at those bloody photos for ages, and couldn't work out what was wrong. 

Me too. Like half of us on here I reckon. It's only when Andrew narrowed it down to the top platform that the Eureka moment occured.

 

[sime42]

On 02/09/2022 at 09:20, ucoulddoit said:

Pretty much spot on! So pleased someone worked it out.

 

OK, so here’s an explanation of the mistake I made. It’s the top step / platform as mentioned. It’s especially annoying given my working life in industry as a structural engineer. I tried to fix it, so what doesn’t look like it was intended?

 

The mistake is, the grain should run front to back, not side to side, as the platform is supported by the brass rods on the front and rear edges. When I realized it was the wrong way round, I went back to the photo on the internet, used as the basis for the design, and it had the grain front to back! Just hadn’t noticed that, but should have worked it out.

 

Looking at the photos below showing the underside of the top step, you will see it is supported by the brass rods at the front and back. But the grain runs parallel to these supports instead of the board spanning front to back onto them. So, my weight of 15 ½ stone standing in the middle of the platform could cause it to split suddenly along it’s length and maybe I’d break a leg or worse? There is a joint along the middle where I ripped and rejoined the wide plank after machining to just over an inch thickness, so that might be an additional weakness?

 

 

 

The two bearers screwed to the underside of the platform were an attempt to strengthen it. If they had been part of the original design, they would be on each side and supported by the brass bars so that the loads would transfer from the platform to the bearers then to the brass bars and finally into the legs. But, fitted as an afterthought, they couldn’t be supported by the brass bars. Also, I realised they couldn’t be glued across the grain due to future movement that might occur, so they are screwed into the platform with a slotted hole at one end to allow for the movement. But there isn’t much thickness to screw into and will the screw pull out capacity in tension hold my weight?

 

Need to sort it properly. I’ve thought about making a new platform with the grain turned 90 degrees. But it’s a lovely piece of wood and took quite a while to make it. Am now leaning towards re-using the platform with bearers on each side, made using brass bar, probably about 1” deep by ¾” wide, instead of mahogany. But I need to check that size is strong enough and stiff enough to carry a person. So, the two short brass blocks at each side will be replaced by brass rectangular bars spanning front to back between the brass round bars with the platform supported on top, spanning side to side. That will work with the existing holes in the legs and platform height as I can get a much smaller edge distance on the holes through brass compared to mahogany. I'll get rid of the two mahogany bearers. It might even look as though it was intended to be made that way!

 

All very annoying and the brass rectangular bar will be an unforeseen additional expense, but looks like it will work out fine in the end. Could have happened to anyone?

 

Thanks for all the comments.

 

Andrew

I don't think I can claim much glory actually. I thought you were intending to have the grain from side to side, having seen the bearers underneath, I just noticed that it wasn't aligned in that corner. I think your fix has worked; the retrofitted bearers make it look as if it was always part of the design.

 

The brass bearers sound like a good idea, but I don't think they'll be required, it'll be perfectly strong enough as it is. I would leave it alone now, as it looks so nice already. Anyway, if a failure does occur it won't be a sudden split that would cause the user to fall. It'll be a gradual process so you'll get plenty of warning that the platform is not strong enough.

 

I can tell that you're a structural engineer. I feel that you may be over-engineering the steps a tad! I mean no offense, no criticism, I'm the same!

[ucoulddoit]

5 hours ago, sime42 said:

I can tell that you're a structural engineer. I feel that you may be over-engineering the steps a tad! I mean no offense, no criticism, I'm the same!

 

The steps are pretty chunky. In fact my wife seems to be struggling to move them about. So maybe they will get a home in my workshop!

 

But, joking apart, although some projects might be over engineered with components that are too large, structural safety comes in part by having clear load paths and simply making everything bigger isn’t necessarily safer. The top step doesn’t in my opinion have a good load path to the legs. So I’m going to change the design by adding the brass bars and will post a picture in due course.

 

This really got me thinking about my design objectives. I’m sure I’ve developed a track record of making stuff that ‘won’t break’. Thinking about that, I recalled a pitch pine cupboard we have for our bed linen. I first saw it as a child and the key has a hand written label with the note ‘Made from a pitch pine tree bought standing’. It’s dated 1895. It’s been in the family since then and we now have it, 127 years on! That label was part of what inspired me at a young age to dream about turning trees into beautiful furniture. I now dream about what I make being treasured by my grand children and their decendents. So, the aim of things I make is for them to stand up to a long life of use and abuse. As well as a design which hopefully stands the test of time, rather than chasing the latest fashion. Time will tell if I manage to achieve that, but I’ll not be around unfortunately to enjoy going into the next century!

 

127 years from now is 2150, a century on from the date being talked about to be carbon neutral. Maybe these steps will still be used by a family member? The timbers may have worn, but there should still be enough section left to be strong enough. There is no reliance on glue, tenons are wedged. All the holes for bolts and the brass rods have brass bushes to minimize wear. I've done what I can to give them a long, long, life.

 

Not sure where those thoughts came from. Maybe the bottle of wine I just enjoyed sharing with my wife! Off to watch a film now and fixing the steps is for another time.

 

Andrew

[sime42]

1 hour ago, ucoulddoit said:

 

The steps are pretty chunky. In fact my wife seems to be struggling to move them about. So maybe they will get a home in my workshop!

 

But, joking apart, although some projects might be over engineered with components that are too large, structural safety comes in part by having clear load paths and simply making everything bigger isn’t necessarily safer. The top step doesn’t in my opinion have a good load path to the legs. So I’m going to change the design by adding the brass bars and will post a picture in due course.

 

This really got me thinking about my design objectives. I’m sure I’ve developed a track record of making stuff that ‘won’t break’. Thinking about that, I recalled a pitch pine cupboard we have for our bed linen. I first saw it as a child and the key has a hand written label with the note ‘Made from a pitch pine tree bought standing’. It’s dated 1895. It’s been in the family since then and we now have it, 127 years on! That label was part of what inspired me at a young age to dream about turning trees into beautiful furniture. I now dream about what I make being treasured by my grand children and their decendents. So, the aim of things I make is for them to stand up to a long life of use and abuse. As well as a design which hopefully stands the test of time, rather than chasing the latest fashion. Time will tell if I manage to achieve that, but I’ll not be around unfortunately to enjoy going into the next century!

 

127 years from now is 2150, a century on from the date being talked about to be carbon neutral. Maybe these steps will still be used by a family member? The timbers may have worn, but there should still be enough section left to be strong enough. There is no reliance on glue, tenons are wedged. All the holes for bolts and the brass rods have brass bushes to minimize wear. I've done what I can to give them a long, long, life.

 

Not sure where those thoughts came from. Maybe the bottle of wine I just enjoyed sharing with my wife! Off to watch a film now and fixing the steps is for another time.

 

Andrew

Looking forward to the seeing  photos of the upgrade.

 

An honourable design rationale indeed. Especially in today's rubbish world of massive over production and consumption of throw away goods.

[ucoulddoit]

Got around to sorting out the problem with these steps. Photo below shows the underside of the top step / platform which now has a 3/4" square (19 x 19mm) brass bar each side. So, the timber step with the grain direction side to side spans onto these two bars which in turn span onto the round brass bars front and back which are supported on the legs. Feels very solid! The screws are just to hold each bit in place and take no load now, and the back screws are in slotted holes in the square brass bars to allow for movement in the timber step which could be 2 to 3mm if they are moved from inside the house to an unheated garage / outbuilding at some point (over the next 100 years or so).

Still annoyed with myself for getting this wrong, but with hindsight, I prefer the top step having the grain side to side instead of front to back. So, it's worked out OK in the end.

 

Andrew