Mini gas burner

[Blogwitch]

Thanks for the confidence in the method Tim. I'm glad someone has been assisted by my posting.

Back to the main issue now.

For all the ones who have the plans, you will now notice that I will be deviating slightly. There is nothing wrong with all the methods Jerry has shown how to do this part, but I am stuck in my ways a little, and I will be doing it my own way.

This pic shows how the needle is fashioned on a commercial steam valve I used to make. Instead of it being just a straight needle, it has threads that screw into the body of the component. It is a little more work than the type shown on the plans, but after pressure testing many of these items, I know they will easily withstand 120psi, which is a lot more than the regulated gas supply to be used with this burner. I am sticking within my own safety margins.

So after a bit of working out, I have the sizes for the blank to be made to, and a rough sketch working drawing.

I was lucky when rooting thru my stash box, I came across a few short lengths of brass rod. They must have been used in some sort of heating system, because the OD was all different sizes along its length, and there was a deposit of some sort on there, maybe it came out of a nuke reactor or something like it. I always wanted to be able to glow in the dark. ;D
Anyway, I should be able to get the sizes I want out of it.
But first, I need to set up my taps and die.

I have decided to go with 5/16"x40 Whit, a standard ME sized thread.
A 7.3mm hole was wacked right thru a short length of brass bar, and I cut a thread from each end, that didn't meet in the middle. Just to make sure I got standard cut for the tap.

Next, I chucked up a length of my brass bar, and by coming down gradually with the die size, and checking it with the internal threads I had just cut, I got a good match between the two. A thread was cut on each end of the bar. The die will be left undisturbed in it's holder until the job is finished.

The threads fitted perfectly, even when swapped about with each other, but now having tried them on this material, I think I have made the wrong choice. It might be OK for steel, but on brass, I suspect it is a little weak.

I will do the same test, but with a 32TPI thread of the same diameter. I think it will be a lot stronger

You win some, you lose some.


Blogs

 

[Deanofid]

John, do you mean that 40 tpi is too fine for this size, (and material)?

Thanks,

Dean

 

[Blogwitch]

Dean,

I personally think that it isn't correct for this job.

You know the feeling, sometimes you get a gut reaction that makes you feel that it isn't quite right for what you want to do. Crossing threads or stripping out because of how small the threads are for such a large diameter. As I said, maybe OK for steel, but not for brass.

It isn't a problem, it will only take another half hour to test and set up the die for the next TPI size.

That is one of the advantages of Model Engineering threads, you can have the same diameter, but up to three different choices of TPI.


John

 

[Blogwitch]

First thing I did was to set up for the 32TPI threads, and so I set the die and cut a pair.

I am now happy with the result, and this is what I will go with. A much more robust thread altogether, and still in keeping with the scale of the job.

That then left me with getting on with the control valve.
So going with my sketch, I turned down the length and diameter needed.

After I had done the first one, and tried it thru the jet holder, it looked a little too long. The next one I cut was 1/8" shorter, and this looked much better all round.
It is always the same when you are modifying something, it takes a little fine tuning to get it just so.

Now with the new length, the tubing spigot was turned to what is shown on my sketch.

It is at the stage now where I totally disagree with how Jerry has made his tubing nipple.
Thru many years of use of silicone fuel tubing, I have come to the conclusion that having any sort of sharp edge fitting, will cause it to fail very quickly, just a small nick into the material, and it will tear. So I have come up with my own solution over the years, and have found that this causes no failure problems, and grips just as tight, maybe even tighter.
I will explain as best as I can, and hope you understand the process.
Using a normal threading tool, the tip was aligned with the very edge of the end face, then plunged in by 0.020", this forms a lead in taper on the front end of the spigot. The tool was retracted, moved along the spigot by 0.100" and was again plunged in by 0.020", this was repeated twice more along the spigot.

This is what it comes out like, and it has already had a little wipe over with wire wool. The lighting makes it look like it still has sharp edges, but it hasn't. On final polish up, the edges will be rounded over a little more.

The tubing goes over the spigot really smoothly, and where the depressions are, the soft tubing settles into it. But when you try to pull it off, it grips like my wife when she has hold of my wallet.

Just one more little job on this end of the valve, then it is onto the threading and drilling bits at the other end. But maybe not tomorrow, I have lots of other things to do.


Blogs

 

[Deanofid]

John, thanks for the update, and for letting us know what you found regarding the threads.
I like your way of making the barb, too. Not only easier on the hose, but a better way in the machining sense, too.

Dean

 

[Blogwitch]

I'm very sorry that this is taking so long, but I am still trying to shake off the bad side effects of a medication change. It is taking a lot longer than the last time I had it done.

Last post I had made the tubing spigot, this time I am going to be doing first, most probably the most important hole in this part.
On the spigot end, I spot drilled just to make sure that this hole was really in the centre.

The hole needs to be perfectly straight, because the other end of where this hole ends has to be perfectly centred as the control needle will use the edges as a seat for controlling the flow of gas. If it is too far off straight, the needle won't seat correctly on the end and thus will give bad metering of the gas.
Using a 0.040" (1mm) drill, the hole was gently peck drilled to a depth of 0.625" (5/8").

Once all the holes were drilled, after a collet change, the ends for the nut threads were cut to length (1/4")

The previously set die was now used to thread the end.

Then a nice small lead in taper was put onto the threaded end. This doesn't need to be large, otherwise it will intrude onto the flat end face where the o-ring will be seated on.

Each one was then checked for perfect fit into the test sleeve I had made before.

The next time I will be making another d-bit (but not showing the whole process) and getting the inside of the valve ready to take the metering needle.

I know this post is very long winded, but I want to show, if possible, that these things can be made by almost anyone, just by joining the dots.


Blogs

 

[Seanol]

Bogs,
Don't worry about long winded. You show your way and we all can learn from the various setups and ways you approach the work.

That is very valuable information and something I need as a beginner. With no one watching over me as I complete my steps to make a part I have no feedback as to the proper order.

You capture the order as well as the reason behind that order (and even capture why you should have done it a different way) and that makes the post ideal for someone just starting the steep learning curve this hobby has.

Thanks for the informative posts and hope the meds get easier,

Sean

 

[xo18thfa]

This is a great topic. Watching with much interest. One of these may end up in the "Nina" build.

 

[ozzie46]

Bogs,
Don't worry about long winded. You show your way and we all can learn from the various setups and ways you approach the work.

That is very valuable information and something I need as a beginner. With no one watching over me as I complete my steps to make a part I have no feedback as to the proper order.

You capture the order as well as the reason behind that order (and even capture why you should have done it a different way) and that makes the post ideal for someone just starting the steep learning curve this hobby has.


I second seans thoughts.

Keep up the good work.

Ron

Thanks for the informative posts and hope the meds get easier,

Sean

 

[Deanofid]

Seems like you're moving along fast enough to me, John. After all, making nine of everything.

Mine is barely half done, and I'm only making one!

Thanks again for all the photo's and comments you provide.

Dean

 

[Blogwitch]

Thanks gents.

Dean,

I am in fact only making six. But I am always wary of damaging one when making exact numbers. There is nothing worse than going back and having to do all the setups again just to replace one part.

With something like this, which will be an ongoing thing, depending how many engines need them, I am not worried about having bits left over. With very little work, another unit can usually be knocked up out of the left over bits plus maybe one or two newly made parts.

All purpose made tooling for the job, sketches etc, and any parts left over, get put into a little box and then into deep storage in my 'back room'. Ready for reuse whenever needed.

For say a one off engine build, only the required numbers are made, and the tooling reused for something else, if possible, after the end of the job.


John

 

[Blogwitch]

I managed to get this one part finished off today, so away we go.

But before carrying on with making the part, there were a couple of things that needed doing.

I don't have a tap that will cut threads to the very bottom of the nut that I will be making, but by using a mains powered mini drill mounted with a grinding point, and a first cut tap, I will make just what I want.

By having the lathe chuck running fairly slow, and a jet of air to keep things nice and cool, I ground the previously tapered end off.

After the bit on the end was off, the end was gently hollow ground, and by being really careful, I managed to get the first thread ground with a small taper.
This was all done freehand.

It was checked to see if it would feed into the hole by trying it on the test piece I had made. It screwed in perfectly with no sign of wanting to deviate or cut any more metal out, just what I was after.
So that is the first bit of tooling done.

The next was to make a D-bit for flatting off the bottom of the hole that the needle will screw into. This will enable the taper point to make it's own very small seating area.
It was made to 0.090" (2.3mm) diameter. The same size as the drill used for cutting a 6BA thread.
That is the last bit of special tooling required at this time for me to proceed with the project.

Next thing was to make a crib sheet so that things were in the correct place and to the right dimensions.
These things look very difficult to achieve, but in fact it is very easy.
I am a DRO fanatic, and have one on my tailstock, so I can actually drill to a tenths tolerance. But as most of you won't have such a thing, small pieces of tube slid over the drill or D-bit, and by using a vernier to get the length required by pushing the cutting tool so that the correct depth is protruding, then tighten up the drill chuck. The tube will act as a dead stop as soon as it touches the part in the lathe chuck. Very similar to what I show later when tapping to depth. If you need a C-o-C then just ask.

Now come all the boring drilling pics, but they need to be done to show the order to do it in,
First off, gently drill down to depth.

Followed down with the D-bit to depth.

The 1/8" recess in the end was done with a multi flute end mill.

I tried to get a shot of the flat face at the bottom of the hole that the D-bit formed, but it went slightly astray.
If you close one eye and squint with the other while standing on tiptoe, you just might be able to make it out.

So that is the hole to size and depth, next comes the tapping.
I got out a set of matching tap & die as later I will be cutting a bit of tough stuff, and these HQS bits work wonderful on it.
If you look at the tap, I have stretched a bit of silicone tubing over it, and the length of the thread protruding is the depth I need to go to. I can go a bit deeper, but not shallower. Because I power tap, if I had a rigid stop on the tap, and I went in a bit too far, the tap would be liable to snap, this acts as a safety depth stop in case that happens. If you are tapping by hand, as mentioned above about the drilling, you could use a bit of tubing with the right amount of thread showing to get you spot on depth.
This is a plug or bottoming tap for you in the US.

Power tapping all the holes only takes minutes. If you only ever make one or two of something, it isn't really worthwhile setting up for power tapping, but if you do a lot, it sure saves your aching fingers.

Nice clean holes with well formed and perfect sized threads brings this part to it's conclusion.

Just the nuts and needles to make.


Blogs

 

[Blogwitch]

So now we come to the sealing nut for this valve. I redesigned this unit so that if necessary the o-ring can be replaced in a matter of seconds and also it is very easy to put a little more pressure on the ring just in case it does start to leak.
I have just noticed how many pictures I have used in this post already, well over a hundred. For such a small item, I hadn't realised just how many machining operations are required.

The first thing I needed to do was to sketch up the part, with all the critical dimensions shown. The outside surface was left blank, and was tidied up once the main dimensions were hit.

Starting off with a length of 12mm bar, it was spot drilled and drilled to a depth of 0.525" with a 1/8" drill.

The drilling size for 5/16" x 32 is size J or 7mm. Normally this would mean making up another D-bit to give me the flat bottom to the hole after drilling, but in this case, I had a 7mm end mill, which I used to drill to a depth of 5/16". That saved me a lot of work.

The hole was the power tapped with the flat ended tap I had prepared earlier until it hit bottom.

The lead in was given a nice chamfer.

A needle body was screwed in to check for fit and depth. Perfect for what I want.

It was then parted off to a length of 1/2". This was to allow for a cleanup in later stages.

The previous operations were repeated until I had a nut made for each holder.

Now comes the time to shape up the outside of the nut.
A holding mandrel was made to allow me to get to all outside surfaces. The screw thread was a fair amount shorter than the internal thread on the part.

How the nut fits onto the mandrel.

The first job was to face the end until it was the correct length, 7/16".

Skim up the OD to around 7/16"

Then it was time for some heavy stuff. I put a straight knurl on the end.
I have mentioned this before, and I use the generally accepted practice of straight knurls for undoing/tightening, and cross hatched knurls for gripping, as on a centre punch. But the choice is a personal thing.

A nice big chamfer on the end.

Using the same tool, I put a chamfer on the other side of the knurl and turned down the nut to a nice narrow profile.

Same tool again, and a small chamfer was put on the nut end.
By this time, the nut was really tightened onto the end of the mandrel, but with very careful use of a pair of pliers on the knurled area, they were loosened off with no detectable damage.

A little hand chamfering on either side of the 1/8" end hole, and the nuts were finished.

Getting there


Blogs

 

[Deanofid]

Those knurled nuts and valves look top rate, John.
Still with you, and happy for as many pics as you care to post.

Dean

 

[Blogwitch]

Thanks Dean.

I have worked out only five more bits to go until the basic unit is ready to have gas to it, the needle, air control ring, diffuser screen and holding ring, and then of course, the jet, plus any special tooling to get the parts made.

Once those are done, then I will make a couple of right angled ends, a gas distribution block, and I haven't decided which regulator valve to go with yet, most probably the one I posted, as it looks a little less complicated and easier to make.

Unfortunately, lots of things to do this week, and I don't know whether I will feel like doing anything for a while, so it will all be as and when.


John

 

[Blogwitch]

I started on the needle this evening, but didn't have the time to put things into practice, so the needle bit will be done in two parts.

This is the design stage.

I could in fact work everything out mathematically for making this needle, but at this time, I don't think my brain is up to it, and also, by doing it manually, it will show how to make a multi part needle. Most people will only be making one or two of these items, so this is an ideal way.

First off, I needed to find any sort of bar that is just smaller than the root diameter of a 6BA thread. This will allow enough room for the gas to flow into the bottom end of the valve and disappear up the jet. I found a short length of 2mm silver steel just perfect for the job.

From previous experience, I have found that a 10 degree included taper is just fine for this sort of control, where a needle is sitting into a squared off face. It could be made a lot shallower, say 5 or 6 degs, but then you end up with a very long needle, but much finer control, and usually a lot less robust. The one on the plans doesn't give the angle, but a quickie calc gives an included angle of 18.78 degs, which will, of course, give less fine control.
So I set my topslide over by half the included angle, that is 5 degrees.

With a razor sharp tool, and the lathe at 900rpm, I cut a taper onto the end of the bar, trying the gas inlet end of the needle holder onto the taper every so often until it sat about half way along the cut taper. Once that stage was reached, I marked up where it came to. The end of the needle should not end up sharp.

This is what it looked like, about half way along the taper. The taper length ended up at approx 1/4". As you can see, I am not working to decimal places here, near enough is good enough for this job.

By taking the needle and pushing it gently into position (I don't want to form the seat just yet), where it came out of the body was marked up.

The needle was then tried in all the other bodies, and as far as the old eyesight could tell, they were all exactly the same.

By making a near enough measurement, from tip to mark, and referring to my previous sketches, I was able to calculate the rest of the needle dimensions.

This is what the finished needle should end up like.
Unfortunately, making it is a little more difficult, as it is full of little traps for the unwary, and needs to be machined in the correct order to end up with a good needle.

So next time, I hope to be able to make eight of these items.


Blogs

 

[NickG]

Blogs,

Very nice work and a very comprehensive write up and excellent pictures. Thanks for taking the time to do this, it's what the topic needs but I know it takes a lot of time up. I haven't been able to get on myself or in the workshop but thought I'd check in today. Just can't seem to find the time.

I like your method for making the tube spigot and will use that myself for future work.

Your crib sheet for the needles will also no doubt come in handy for a lot of people.

Thanks,

Nick

 

[Blogwitch]

No problems Nick, you will get in there when the time and temperature allows. I am lucky in that I don't work for a living any more, and my shop is a constant 14 degs C throughout the winter, no matter what the outside weather is doing.

I used to have problems when using silicone tubing, of it tearing when using the sharks tooth type spigot, so I started to use this design.

It does have one drawback, when using it for higher pressures, it doesn't hold as tight as the normal sharp grippers, because unlike normal plastic fishtank tube, the silicone blows up, a bit like a balloon, but not to the same degree, and so when the internal diameter grows larger, it pops off. If that ever happens, all I do is to wrap one turn of thin plastic coated garden wire around where the recesses are on the spigot, and twist, then cut off the twisted end to a short length, two of those, and it will go nowhere, but it still won't tear.

John

 

[Deanofid]

It's (they're) getting there, John.
I was wondering what angle you would use for the needle. Thanks for the heads-up!

Dean

 

[Blogwitch]

Sorry this hasn't progressed any. Even though you might see me online, I can't do anything in the shop at the moment.

Anyone who knows me personally, if I mention cold virus, will know why.

Normal service will resume as soon as possible.

John