Modified Nimbewill Wood Stove - Part 2

[scoops_uk]

They say never work with animals and children. Well add stainless steel to that list, blimey it's hard stuff but I finished the stove...see here . Afraid I couldn't resist lighting it before photographing it, so it's not the shiny masterpiece it once was.



Aside from the problems of working with stainless steel (i.e. going through a lot of blades and cutting disks and wearing out a file!!) it wasn't too tricky to build. If you fancy a go you can download templates from here . Just print off the PDF choosing the no scaling option in the print options dialog.

First off I laid out the templates on my piece of stainless steel, before sticking them in place with a spray adhesive.



Then I did a final quick measure before doing any cutting. Last chance saloon, once you've started cutting it's too late to go back!



Next to make handling easier I rough cut out the parts with a jigsaw. WEAR SAFETY GLASSES - Eyes and flying metal bits don't mix.

I found that a normal HSS metal blade worked best, although they wore our fairly quickly. Things like progressor blades were too aggressive for the sheet material and caused the piece to bend horribly on some of the finer cuts later on.



After the rough cuts, I trimmed as close to the line as I could with the jigsaw. I then did the tricky bits like the slots before finishing the piece by filing down to the line. Best to get the slots right rather than crying into your beer if you've messed up a slot and wasted all that filing effort. Stainless steel is HARD!!

The best method I found for the slots is to use a heavy duty cutting wheel on a dremel at about 3/4 full speed and cut into the center of the slot just enough to fit the jigsaw in. Then used the jigsaw to cut the slot out *exactly* as marked. Note my nifty homemade "vice" to make working on the sheet easier! I basically drilled a big hole and put a clamp through my bench! For the larger air slots I first drilled the ends (see tips below) and then use the slot cutting technique before finishing with a half round needle file.



After a bit of research I decided to drill the holes so I could control the volume of airflow and it's position through the grate, rather than my original BBQ mesh idea. For drilling the holes I found a normal 10mm HSS bit and running the drill slowly worked best. Centre punch the holes first. Don't get the bit hot or the stainless will eat it. I always kept the bit cool enough to touch. Keep some water handy to quench it in if it gets too hot. I'm sure oil is better but the stainless is probably going to kill the bit anyway before you have to worry about rust! (BTW I used a proper punch not the nail in the background for marking the centres. Nails don't touch the stainless, I tried it!) I have used nails to help stop the piece sliding aound under the force of the drill.



For the bends I used a ball pein hammer and one of those mini vices, worked a treat but you need the hammer to get the bend nice and tight.



When filing the sides, leave cutting the tab slots till last. Without the extra bit of material they are too flexible to file easily. When your ready to cut the slots use the jigsaw and tidy them up with a needle file.



Once finished put the bit's together and tada!



Scoops

[leon-b]

nice one mate
leon

[scoops_uk]

Cheers Leon,

Just been reading about your day with Fenlander, you're a lucky guy! Keep up the great work and I'll look forward to attending one of your courses in a few years time!

Scoops

[Ogri the trog]

Scoops - nice one buddy,
I read about your modified top plate on another thread, how does it work in practice? ie without getting air to flow up around the sides of your Crusader cup.

You've done a good job there, I left the pieces of my attempt quite rough, just cleaned up the edges that I'll either catch my fingers on, or might damage a mesh bag in which the whole thing is carried.

ATB

Ogri the trog

[scoops_uk]

The results are a bit mixed, the top plate works but I've tended to remove it for cooking and add it to slow things down.

Adding a chimney has a dramatic effect (see below), and I'm thinking about redesigning the top plate swapping the hole for a rectangular chimney across the the back of the top plate. This will also provide a larger area on the rest of the top plate to be used as a hotplate for cooking bannock, simmering or drying tinder etc...

I made my first chimney in a hurry, can you tell



A problem though is it getting too hot for the stainless with the chimney on and the stove enclosed. The grate glows bright red and sags and the sides get pretty soft too! An aluminium version would probably be a puddle!

Scoops

[Stew]

I guess it's too early to tell, but I'm curious how you'll find the height adjusters.

Personally I suspect that you won't see a big difference in performance but I'll be interested to see how you get on (ready for me to make my version! )

[Stew]

Also, did you change the location/quantity of ventilation slots in the end?

Looks like it's the same as your model but it's a bit hard to tell...

[scoops_uk]

I actually tried to move the air flow forwards by drilling the grate to create a particular area where the primary air comes in rather than using the indescriminate BBQ mesh. The holes are in the front 2/3 of the grate and are sized to open up about 30% of the area. (If you look at the bending picture you'll see what I mean).

I opted for that solution as it still allows the stove to be set up as a normal nimblewill with the vents at the back.

In that sense the height slots do make a difference as they allow the different configurations. The problem I have encountered is that without a chimney and the stove enclosed you get a lot of smoke which pops and flares(wood gas generation). Put a chimney on top and this all vanishes to be replaced with a continuous roaring flame from the wood gas.

Need to do some more experimentation before I decide how to progress.

Scoops

[Glen]

Nice one.

The results are a bit mixed, the top plate works but I've tended to remove it for cooking and add it to slow things down.

Adding a chimney has a dramatic effect (see below), and I'm thinking about redesigning the top plate swapping the hole for a rectangular chimney across the the back of the top plate. This will also provide a larger area on the rest of the top plate to be used as a hotplate for cooking bannock, simmering or drying tinder etc...

I made my first chimney in a hurry, can you tell


A problem though is it getting too hot for the stainless with the chimney on and the stove enclosed. The grate glows bright red and sags and the sides get pretty soft too! An aluminium version would probably be a puddle!

Scoops

With the micro chimney it's begining to look like a miniture kifaru stove.
http://www.kifaru.net/stovspex.htm
Click on the link for single tube pipe for chimney idea.
They make their stoves out of stainless steel, though I've not found out how thick, so would have thought you'd be OK, they do give a lifetime guarentee on them.

Image intensive link to one used with a tarp http://forums.kifaru.net/cgi-local/u...4;t=000972;p=0
Half way down shows surprising pack size which amazingly includes the chimney.

[anthonyyy]

Very very nice work.

I wonder if part of the exhaust pipe of a truck do as a chimney pipe?

[fred gordon]

Fantastic work. I made an environmental fireplace, based on the Bill Mason model, some years ago and it has worked very well over the years. However, it has had its day and needs replacing. Are there any plans to make the drawings available for sale or on the site for downloading?

[Stew]

Are there any plans to make the drawings available for sale or on the site for downloading?

He already has:

If you fancy a go you can download templates from here . Just print off the PDF choosing the no scaling option in the print options dialog.

[fred gordon]

Abject apologies! Missed that. Thanks for the reminder.

[scoops_uk]

Thanks Glen the kifaru is exactly the type of thing I was aiming to build. That was a very interesting link! Can't afford one and I have reservations about things like wing nuts which are easily lost on a woodland floor, but it's getting the juices flowing for my MkII version!! The roll up chimney is a great idea.

Fred - I would suggest if you want to build something now, knock up a quick basic nimblewill, they are great little stoves I found having a rough version to mess around with made me more patient making my modified version MkI. There's gonna be a MkII along soonish (off to Scotland for a couple of weeks first).

The MKII is going to be larger, that means heavier. What would people regard as a maximum weight? Bear in mind there's always the option to configure it as a basic nimblewill and leave the other parts at home. An Optimus Nova weighs 420g plus say 600g for a full half litre fuel bottle. We don't need to carry fuel so would a top weight of 1kg be OK or could we go higher for the full stove say 1.5kg? The stove is 650g at the mo, doubling that weight will provide a much bigger stove with a larger firebox and if I can find a source for 0.004 tempered stainless foil a chimney too!

Scoops

[jdlenton]

scoops that's a great piece of work even more so because you made it by hand out of stainless I've always contemplated making one of these but i would only have used mild steel for the prototypes as it a fire place who cars if it rust a little. let us know who you get on with the next ones a bigger stove wold be great i recon. If your going to make some more in stainless i recon you need to find a friendly engineer with a laser cutter that accepts beer as currency.

[scoops_uk]

Thanks for all the positive comments, much appreciated.

JD - got a mate who might know someone with a laser cutter, so I might have to explore that avenue. If anyone knows of anywhere that can laser cut stainless please let me know!

Scoops

[woodwalker]

the engineering departments of some universities sometimes have them. Not sure if they will let you use it though.

woodwalker

[Spikey DaPikey]

You could always ask the student to make it as a project for you, and pay in beer tokens

[wildrover]

What thickness of stainless did you use?

[scoops_uk]

Hi Wildrover,

Sorry for the delay in replying I've been away in Scotland for the last two weeks.

I used ~1mm stainless offcuts that I got cheap from a local sheet metal workers. I think the actual thickness is 0.9mm but I've not actually measured it, I just asked if they had any sheet stainless offcuts around 1mm thick and used what I got

Scoops

[wildrover]

Ta for that
what thickness do you think you'll use for the bigger version?

[stevec]

if the chimny was made a bit more subsantial, three h shaped strips of metal, and put a small wok on top of the chimny, might be worth trying out with a tin can and some coat hanger wire perhaps?

looks good in any case
steve

[scoops_uk]

Wildrover,

I'm going to stick with the same thickness for the larger version, I might opt for interlocking tabs on the top and bottom plates that connect to the sides in the same way as the back currently does to prevent warping, although it only seems to be a problem when you stuff it full and give it loads of air and a chimney

stevec,

I love the wok idea stir fry anyone?

I can see I'm gonna have to get the CAD going again, although for the next one I'm going to try and get the parts cut. I have a mate whose an engineer and knows someone...

Scoops

[stevec]

the reason why i suggested a few pot stands on the chimny was that quite a while ago, i was round a mates house who had a chimnina(sp) and it wasn't doing too much in the way of heat or flames, so i suggested that we took the "hat" off the top of the chimny, the flames were about 4-5ft high, so i figured that with a long handled frying pan some good cooking could be done. having seen the difference the chinmy made to the flames on your stove, i fugured the same would apply quite nicely.

steve

[scoops_uk]

Hi Steve,

The problem with cooking on the chimney is that it really isn't that sturdy and as the top plate is loose even if the chimney was fixed in place I think the weight of the pan plust the chimney acting as a lever could be a bit to tippy.

Interesting to hear of the effect of the chimney cap though. I was going to add a mesh cap (car body repair aluminium mesh) to the chimney to stop sparks emerging as a precaution for tent /dry woodland use but now I'm pondering having that plus some sort of air flow regulation. Hmmmm.

Scoops

[stevec]

Hi mate, i should point out that the mesh in the "hat" was very blocked with soot. i don't suppose putting mesh over the chimny will be a problem as long as you make sure it doesn't get clogged up.

best regards
steve

[scoops_uk]

That's sort of why I was thinking of using a mesh hat rather than putting it somewhere less accessible. The other option was a slotting it in partway up the chimney but I had all sorts of issues about chimney strength and slotting things into cylinders without cutting halfway through the cylinder etc...

Have decided to make a firebox next as I want to experiment with different fire sizes to figure out how much bigger I need to make the next stove.

Scoops

[Paul Holtom]

Any updates on the stove, have just started one of my own and was wondering if the height adjustable grate is worth the effort.

Great design by the way, it really goes together well and certainly looks the part.

[scoops_uk]

Hi Paul,

I'm still pondering the next incarnation.

The changes I think are most likely are...

Making the stove larger probably going just over 1kg overall weight. (It's about 0.6kg as it stands). This is to reduce the frequency of refuelling.

Changing the connection between the sides and the grate and base so that they interlock with eachother (like the sides do with the back plate). To reduce the potential for the sides to warp away from the grate and base when hot.

I think as a backpacking stove the existing version is just fine. With my planned design I am leaning more towards a tipi stove which has the function of space heating and slow fuel consumption as priorities ahead of boiling a pot of water.

Good luck and please share any lessons you learn

Scoops

[Stew]

Scoops,

For the larger version are you going to go more square or keep it rectangular?

I would think rectangular would be better for the chimney but if you go square you could possibly use pieces from your existing design.