Making springs for NRVs

Hello all,
Thanks lance for reviewing the ones you have on hand and finding that the cant to the spring when slid onto a bucket tail may be normal.

Now that I think about it, a compression spring of this type when it is compressed will assume a larger diameter of the helix coils . If the inside diameter of the helix coils of the spring open up a little when it is assembled in an NRV (and compressed) then the cant of the spring and any issues it might cause may disappear in use.

There are tool positions open on the lathe (this is a rare treat, as there are usually not enough tool positions) so I can add a chamfer tool for the disk end of the bucket body and might get another one in for the other end. Not sure, might have to use a needle file for the back end of the bucket to break the possibly offending corner .

Regards,
Doug

 

Greetings,
I have measured an existing original bucket using a toolmakers microscope to get dimensions and angles, and made some edits to the geometry of the exisiting part made here, then tested the bucket again in a few of the NRV cylinders on hand. Much better, it operates smoothly ! The drawing has been revised, and the revised drawing is here in the thread where the first one was posted, replacing the old version.

This is what the parts will look like now, and the machine is ready to run. Excuse the photo, it was taken off-hand thru the eyepiece of my inspection microscope, hence the vignette.


The part in the photo is complete but the cut off burr has been snipped off, but not dressed. A fixture is in the works to make near full removal of the burr easy with a file.

Regards,
Doug

 

You're nutz Doug!

I love it!

 

Hello,
Here is a photo of Doug with the microscope. It may have been posted before but, it is worthy of another post. He is indeed a madman when it comes to making parts!

Chuck

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Hello Gents,
I promised another photo, so have put together a set of them.

Definately nutz here CB ! This one was a tough nut to crack.

Thanks for adding the microscope photo Chuck, and the compliments of course. That scope is the portable and I use it out in the shop. It was made in England and appears to be about 50 years old.

There are 2 other scopes here used for inspection and measurement.............
This microscope is used for general inspection.


This is the toolmaker's microscope. It is used for measuring unusual features that can't be easily or accurately measured with micrometers or other calipers. It is indispensable for measuring chamfers, angles, and recessed features.


This drop gauge is being used next to the lathe to check the bucket length overall, tail length, and depth of the hole. Hole depth shown.


A micrometer is nearby as well for the body and tail diameters.


This is the setup on the lathe for making the buckets.



So.........the NRV buckets are running and they are of consistent dimension and quality.
The springs take more time than the buckets, so I will work on the spring making method next to see if it can be improved.

Regards,
Doug

 

Hi Doug, Amazing!!!!
You never cease to amaze me with your inventiveness, ingenuity and tenacity.
I now believe that you can do anything mechanical that you set your mind to.
Well Done.
Best Regards,
George

PS I am sure that the Video is speeded up!

 

Great stuff and skills. Please do make plenty, and put me down for a couple as well. Thanks,

Ed

 

Mucho caliente!

 

Understanding Engineers.

Normal people believe that if it ain't broke don't fix it.
Engineers believe that if it ain't broke, it doesn't have enough features yet.

To an optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

Regards,
Engineer Kerophile.

 

If it ain't broke, fix it until it is

 

That's the spirit!

 

Hello,
A quote from George Dyson, author of Baidarka, The Kayak, who took a hill walking motto " never step on what you can step over, and never step over what you can step around" and modified it for working in a workshop " never buy what you can make, and never make what you can find " . Sounds a bit like working on stoves.

I have a camping trip coming up and will be busy getting ready starting on the upcoming weekend. Thought I'd make some parts tonight, and did real well on the springs. I am using some of the advice from Barrabruce and Oops 56 and ran off 40 of them I switched to making the buckets and in my zeal smapped a tool. I hope to regrind it tomorrow and may be able to run off some more.

Two sets of 8 (16 total ) buckets and springs have shipped to friends in UK today.

There are still 17 parts ready in the shop at this time, there would have been 40 if the tool had not been lunched by yours truly. If you are in dire need you can order some now to get out of trouble and I will send them along, or , I will be back July 12. Just send a PM and I will get back to you ASAP.

My friends will probably do some testing, and I plan to take a 00 camping and will retrofit it with an NRV reworked with a new production bucket and spring and give it a workout for 5 days of cooking for 3.

I can offer parts as follows buckets $2.50, springs $2.00, nitrile disk .50 . Post to anywhere $2.50 for moderate sized orders ie 10 pcs or less , and should cover the soft envelopes and postage.

Thanks for your compliments, advice, and support.
ATB,
Doug

 

Hello,
The saga continues. I pulled the NRV out of my test stove which will be used to perform meals preparation at least twice a day for a four or 5 day camping trip. I noticed the NRV looked different, and it is. I checked my recently purchased new spare NRVs and they are exactly the same and appear different from the older style NRV devices I have been working with. All other NRVs I have been recently making bucket /spring combinations for are what I will refer to as the older type. Now I find I must address this new issue and quick.

Here is the old style NRV part, with a newly made bucket and spring


Here is the newer style NRV part with items labeled and a recently made bucket/spring added for comparison purposes.


I took both styles of NRV and measured them on a toolmaker's scope, took data, and then made a composite drawing of both NRVs for my reference and for yours. I also put a .040 inch wire probe into a force gage and whilst watching under a microscope, measured how much force must be applied to open the valve in each case. Those data are in the notes of SHT 3 of the NRV Bucket drawing.

 

Hello,
Previous post was cut off mid post.
This is the comparison drawing



I measured the force to open an NRV under the scope with a pin mounted in a force gage. The results are shown on the drawing
Note that putting an old style bucket and spring in a new style NRV body will result in very low spring force. I suspect the seal will be compromised a bit on a stove that is full and not pressurized (in transit for example)

I have ordered phosphor bronze spring wire in the same size as the reddish spring (new style) in the photo in my previous post, and will make some new springs in phos bronze to match the buckets in production. Also the nitrile disk will have to be thicker if the bucket is used in a new style NRV. On the old style NRV,the seal lip of the NRV body will go down into the bucket and contact the nitrile disk even if it is worn. On the new style NRV bodies, the seal lip of the NRV body will not go down into the bucket so the nitrile disk must protrude above the top of the bucket to work properly with a useful life. .125 inch thick nitrile material is also on order.

The test stove will be operated in the field to make sure a bucket device will work in new style NRV bodies using the heavier spring and thicker nitrile disk. I have just enough time to receive materials and retrofit the stove.

This Opti 00 will be the test stove. It presently runs with a bucket/spring in a new style NRV body but I would prefer more spring force based on data taken thus far. Look Trainmanny, the mug is my favorite road, Norfolk & Western !


Regards,
Doug

 

Could you please give more information regarding the type of wire that you used for these springs. Your source shows a number of different type wires and it would help to know just what you are using.

Thank you for a very informative article.

 

Hi Ken,
No problem. For the standard springs for use with old style NRV I am using .016 diameter spring brass and winding it onto a .116 inch diameter gage pin.

The second material on order is .018 inch diameter phosphor bronze spring wire. With that material I will be winding springs that will fit the buckets I am making with an extended nitrile disk in the bucket, and fitted into a new style NRV body to operate near the higher opening force of 135 grams as measured using an unused , unmodified, new style NRV.

Regards,
Doug

 

Greetings,
An easy method for making springs is shown here.
Following is then a description of experiments using a stove with the test results noted.

Here is a simple way to make the springs:
1. Wrap a square of leather around a hand drill, put a wooden support block in the bottom of the bench vise so the drill will not drop down, and install the drill. with light pressure from the vise.


2. Install a pin (an old drill bit could be modified for the purpose). Mark the pin with a marker at the appropriate length for the end of the spring.

3. Bend a 90 degree section on the end of the spring wire and push the bent tag end into the drill chuck on the farside. You will need to make about 1 turn (under power at low speed) before good tension can be applied to the wire. Having the wire on a spool makes it much easier, and I hold the spool about 9 inches out from the pin. Make 3 turns side by side then stop, but maintain the tension on the wire.

4. I previously placed a protractor set to 5 degrees for visual reference on the bench. A piece of cardboard or paper cut to 5 degrees and taped down to the bench as a visual reference would work as well. Set the spring wire at this angle of 5 degrees and rotate slowly under power once again, maintaining the tension and your angle to obtain a uniform helix until you reach the mark on the pin. Change the wire angle back to perpendicular to the pin and complete with a winding of 3 more turns.


5. Trim with small wire cutters and you're done.


Stove test:
We took an Optimus 00 on a camping trip of 5 days and gave it rigorous testing with a retrofitted NRV. The stove was run about 4 times per day for 5 days, and some of the cooking times were up to about 20 minutes.

This stove had a new style NRV body of the type that will not go down into a bucket to seek the nitrile disk, therefor the nitrile disk must protrude above the lip of the bucket.
I chose .125 inch thick nitrile material of 70A durometer for the disk that would be used for the test.

Punching the disks in the thicker material yields very poor results as there was great mushrooming of the disk. This issue was solved by putting my punch into a drill press, setting a bottom stop so that it would just touch my soft wooden backup block (end grain up), and then cutting the disks at low turning speed of the punch. It cuts instead of shearing the material, and eliminates nearly all mushrooming. If the depth stop is set properly on the drill press the disk stays in the sheet of nitrile material and you can push it out after the cutting. The same results may be had if you use a hand drill carefully to cut the disks. If your punch will not fit in a drill arrangement, a segment of steel brake line tubing or similar can be drilled to the inside diameter you need, and the outside can be sharpened with a file while it rotates in a hand drill or similar to get a sharp punch for rotary cutting.

Springs were wound using a phosphor bronze spring wire of .018 inch diameter (the same original material used in the new style NRV devices with molded nitrile seals) . After testing with a force gage to try to match the seal pressure as measured on a standard new style NRV, it was found that a spring of 3/8 inch length, wound on the same .116 inch diameter pin with the same helix, gave the same 135 to 150 gram force on the seal bucket with the thicker nitrile disk. This is the bucket used with thicker disk, and the photo was taken after a week's use.


Results:
The stove worked well, there were no problems with maintaining a good seal in the NRV, and pump stroke force seemed reasonable. Upon our return, and with 7 days of time on the NRV in fuel, and 5 days of cooking , I removed the seal bucket and inspected it. From the visible wear pattern after a weeks use, I believe it would continue to have a useful lifespan.


Regards,
Doug

 

Hi Doug, thanks for the great tutorial and the comprehensive test results. I too find thet mushrooming is a real problem when trying to punch valve washers from nitrule sheet. I will try you method soon.
Best Regards,
Kerophile

 

excellent work and equipment, just a dream )

What do you think, is brass wire obligatory as a material or it may be changed with steel spring wire?

Have you tried another types of the closing element, which are better protected from jamming?

 

great thread on making springs!

i just realized that when i recently serviced my Optimus No. 1's NRV it did NOT have a bucket! the spring had broken and there was only a hardened nitrile pip and spring inside!

stupid me - i simply punched a suitable piece of cork for a new pip, inserted one end into the new spring, then put the NRV back together

still seems to be working fine after a couple months of daily usage?

i don't think i'd be able to make a bucket using what i have on hand - i wonder if there's a suitable substitute or if it's even necessary to have one?