In THIS post @night_owl answered in response to my enquiry Here’s the inlet orifice of a jet I’ve restored with an insert, the stainless steel needle liner clear to see at 100X magnification. It shows the nature of the problem in getting an auto-pricker tip into that orifice, that the insert isn’t chamfered/tapered on its inner circumference and there’s a chance that even a pricker tip itself rounded or tapered might snag on it and double up on itself. As yet, smoothing off that square inlet circufetence to the hypodermic needle or flaring it so that it will guide a pricker into the jet and not cause it to snag has defeated me. It’s the tiny dimensions and the hardness of the material that make it so. I was successful in reducing the jet orifice with an insert on this stove having an auto-pricker. It worked primarily because the pricker isn’t operated by a rack and pinion but, rotates as it is manually screwed upwards. The rotation prevents it snagging on the insert. So, @night_owl and others, that’s where I’m at. Thoughts, ideas to make progress with the problem would be appreciated. John
If I understand. You want the bottom of the orifice, the part that is now the hypodermic needle, to better take a pricker going up? Try a Dremmel abrasive stone shaped as you want the underside shaped. Like a 'cone'.
Exactly Ken, yes. The difficulty is finding an abrasive ‘point’ fine enough to engage with a hole of 0.32mm in diameter. These are diamond bits but they’re not fine enough. Carborundum or other stone abrasive points don’t have a sharp enough point either - well, none I’ve encountered yet. Maybe something in the watchmaker’s toolkit?
My most recent try with your needle insert technique, @presscall , was on this .32mm standard jet (for a different Primus 71). Here, I modified my technique a bit: (1) First, I enlarged the opening with a needle that is one gauge (about .05mm) smaller than the one for the final insert (here, I enlarged the opening with a 25G needle for a final 24G insert). (2) Then I partially pushed the needle for the insert (still complete) through the jet from the underside, until about 1cm/.4" of the needle stuck out of the top of the jet, so that it can be easily gripped there (more than what can be seen in the first picture). (3) I then cut off the needle near the underside of the jet and tried to clean up the cut as well as possible. (4) I used a combination of pull motion (with pliers, obviously flattening the needle near its tip) and push motion to get the insert to its final position, so that the cut-off end is flush with the inner surface of the jet. The Philips 000 from above turned out way too large for pushing (obvious from the photo, but wasn't clear to me before). But the tip of the pick is actually fine enough to be placed right in the center of the needle insert, for pushing it into the jet. As the tip of the pick is tapered, this helps with very slightly widening/tapering the inner end of the needle insert (as opposed to the use of blunt instruments for pushing, which may deform the cut in undesirable ways). Doing this, the pick likely gets stuck in the needle insert. No problem, though, since the needle can still be gripped with pliers from the top, so that the pick can be pulled from the insert without changing the position of the insert relative to the jet. (5) Finally, I cut off the top side of the needle insert near the jet, ground the remainder flush with the jet, and used a 1.5mm round diamond polishing tip to create a taper towards the opening and deburr the top of the insert. Not only was I able to insert a pricker from the top, but also easily from the bottom of the jet (just didn't take a picture of that, though). As is easily seen in the picture, even a 1.5mm round polishing tip is still way too large to achieve a truly cone-shaped taper, though. Just as @snwcmpr suggested, my idea was to next time use a very fine cone-shaped polishing tip from the inside. This is what I've found in my dad's tools, possibly still too coarse and with too worn a tip already, but likely with the right shape for the purpose: I haven't searched for a finer one yet. So unfortunately, it seems I am about at the same point as you are, John. Best regards, Christina
@night_owl You’ve developed some very good techniques there Christina, which I’m grateful to you for sharing. Push-pull is clever, and the Knipex parallel-jawed pliers are a must-have for that sort of delicate work. Please let me/us know if you make further progress, as will I. Regards, John
TGood morning @presscall and others . This is just a drawing of the cross section of the nozzle showing the thickness of the material between the inlet and outlet of the jet. The inner diameter of a standard nipple is 2.5 mm. I wonder if you used a matched, or slightly smaller drill bit, would the chamfer be appropriately "steep" to guide the cleaning needle out.? Or maybe there are drill bits with a more pointed tip....
I've sleeved the nipple on my Radius range with 23-gauge needle stainless, and put a chamfer on the inside with a 1mm solid carbide drill bit. Easy. You can even grind the bit to a sharper point with a fine diamond plate and some patience... Hopefully there'll be photos when I add it to the reference gallery.... any time..... the vegetables are taking priority at the moment.
You’re onto something there, Stan, thank you. A standard twist drill isn’t pointed, the cutting flukes meeting at quite a flat tip. Some sort of pointed reamer though …? It would be essential to silbraze the insert where it emerges from the jet on the top surface and not rely on a friction fit. Reaming the interior end of the insert would exert a force tending to push the insert out otherwise.
@presscall 1mm solid carbide drill bit worked fine for me. If the grind as supplied doesn't work, it's easy to alter with a diamond plate. Most drill bits are ground to a general purpose angle at the factory, the idea is you change the grind to suit different jobs.....
So you’ve successfully installed an insert in a worn a jet for a stove or lantern with an auto-pricker?
After your reply @presscall What is the compound used to hone? That compound, in the hole, and a tapered pin, just might shape that cone that you desire.
@presscall A 1mm cobalt bit might also be an option, it would be easier to tweak the angles than a carbide bit. Cobalt is probably hard enough, especially as the stainless may well have been properly normalised* during brazing. But I haven't tried cobalt. Either way, easiest to try a 1mm bit as it comes, if not turn it into a specialist tool to suit the job. *Heating to a certain temperature then allowing to cool normally. This removes stress from forming processes, and will remove any hardening heat treatments that may have been applied (Not the same as annealing!). Easy with low to high carbon steels, they become non-magnetic when the right temperature is reached and the phase occurs internally. Stainless is another kettle of fish! It will be in incandescent range but varies depending on the 'ingredients'. Sorry to anybody who finds this tuition in egg-sucking! Edited to add- I wish more of this sort of thing was taught to people, it would help many out... I'm sure many folk wouldn't know to modify a drill bit if they were doing a lot of sheet work for example. And the number of people who throw bits away if they become blunt, or break...
This is a Russian stove. So use simplistic Russian approach: try to use wood toothpick (or a pencil) with diamond polishing paste (the same as used to polish inlet valves in automotive engines. This works.
Problem solved with THIS lantern project, where the delicacy of a lantern jet pricker (0.16mm diameter) and corresponding jet insert were successfully combined.
