No-silbrazing downsizing of worn jet

Alternative title could have been No-silbrazing downsizing of 0.32mm to 0.23mm jet, which is what I did here, but the principle's the same.

All down to Doug L for his clever idea of using a hypodermic needle for a lipstick burner tube repair, featured HERE - Anglo-American co-operation

Earlier Primus 71 stoves and some others require a 0.23mm jet, which have become scarce - unless/until someone finds a hoard of the things to release on the market. Not so 0.32mm jets (as yet) and unless you chuck the things out (I don't) there are any number of jets that became oversized, were replaced and ended up in parts trays in sheds.

This jet is a 0.32mm jet very slightly worn and a little oversized on that pricker wire




The hypodermic needle I use in this repair is (I've since discovered) a gauge 25 and I've another 50 of them in the post to me for £5, so they're inexpensive. The outer diameter is 0.54mm, inside diameter 0.26mm, so a little over the ideal 0.23mm but little enough not to affect combustion adversely I've found.

Needle alongside the jet




The 'no silbrazing' in the title came from the realisation that if I drilled out the hole in the jet to a little bit undersized for the outer diameter of the needle I should be able to create an interference fit to hold the length of needle in place.

I've two or three sets of these drills from bargain racks in places like Maplins




I picked a 0.45mm drill to run through the jet hole, drill in a Dremel. Easy enough job, since all it's doing is reaming out the existing hole and not by very much




Here's the result, drill removed from Dremel




I didn't want any of the needle to project on the other side of the jet orifice, so I measured the thickness of metal involved, which was about 3mm. I cut a short (6mm) length of needle off using a cutting wheel in the Dremel (the diamond-abrasive one on the right, which makes a neater job than the thicker oxide abrasive wheel on the left)






Having put a chamfer on the needle with that same diamond wheel (spinning the needle between finger and thumb while holding the needle up to the rotating wheel briefly) I inserted the end in the jet hole and used a vice to push the required length of needle in - determined as I've said by not wanting any to project inside the needle cavity




Again using that diamond wheel I trimmed the excess needle off ...




... deburring the hole edge using a 0.23mm pricker wire. Because the needle's stainless steel so pretty hard, there was little to de-burr in actual fact




Time to try it out, installing it in my Primus 71




So far so good, still self-pressurising






Pot on board, pretty much up to speed now




Great performance






This works because there's enough metal in a jet to create the bond with the needle. The tip of a lipstick burner tube is thin, too thin to achieve a reliable interference fit. Consequently the needle would have to be silbrazed in place as I did with the burner tube in the 'Anglo-American' repair.

Next time with a lipstick burner tube repair however I'll dispense with the brass insert and will drill out the worn hole to be undersized (relative to the outside diameter of the needle) as with this jet conversion so that I can trap the needle in the burner tube tip to hold it steady for silbrazing.

John

 

Great post John 8)

Well done again , these hypodermics are the dogs danglies , how many inserts can you get from just one needle

Stu

 

In theory it would be eight at 6mm out of a 50mm needle Stu. Those were the ones I got from Doug.

The ones I'm getting from an ebay source are half that length, but at ten pence each needle I'm not going to be grudging about wastage, given that cutting short lengths off an already shortened needle gets progressively more fiddly.

John

 

Hi John.

Can you post a link to the Ebay seller?

Ta.

Terry

 

Of course Terry.

Needles

John

 

well done .
i was Jokingly going to ask you in the other thread why you did not thread it and screw it in

then the thought went through my head if an interference fit would work .

i now know it does ,

cheers
kerry

 

Nice work!

Few days aga I tried to buy syringes from chemistry/apotek to suck out fuel from stove tanks. They said that they don't sell syringes for other that persons that buy medicines that needs syringes.

Maybe I go and get free syringes and needles from the place where they distribute them for drugs/narcotics addicts.

 

Just make sure you get them from the right bin. They will want the shortened needles back though

 

Maybe the stoves will get a real kick from the residues left in the needles then

But on topic, This really is a great and relatively easy way to make these jets suitable for 0.23mm stoves. It would probably also work to refurbish worn 0.32mm jets right? What gauge syringe would that be?

 

If THIS Wikipedia chart of needle sizes is correct (I'll know when I take delivery of the 25-gauge needles) it looks like a 24-gauge needle would get an oversized 0.32mm jet back to specification.

Since it's a tiny bit smaller than 0.32mm bore it may or may not take the appropriate pricker wire (I expect it would) and it might be necessary to use a 0.23mm pricker to clean the jet afterwards - maybe.

John

 

This is great!
If they work as I think they will, this is a great way to make "lifetime" jets. I bet it takes maaaany hours of runtime, or many prickings to wear out a stainless insert.
Well done indeed!

 

Loved the thread too John

Great idea and within reach of many a fettler

Cheers

 

Are those tiny drill bits only available in the UK? They would be handy after peening lipsticks, instead of peening a little and rechecking with a pricker.
Duane

 

Chinese sources originally Duane, so I'd be surprised if they're not available elsewhere. Look for micro twist drills on ebay for starters.

You'll probably find the equivalent of THIS sort of thing, some directly from Hong Kong at worst (meaning, slower to reach you).

John

 

Thank you John. I almost messed up a lipstick over a year ago, I was hand twisting a SAE size bit, then realized the hole would be way too big. Needed to me metric.
Duane

 

Sticky? This one is worth it.

 

Agreed, but it has only lasted one day so far. I think it will be fine but only time will tell.

 

The Yellowdog said,

Vital signs are good so far, implant not rejected. A bit sore around the point where the needle went in but otherwise the patient is holding up well ...

 

Hi John

I have a load of old jets ( i always keep everything ) so this will be a good way to refurbish some back to .23's as these jets are like hens teeth or very expensive to say the least

I found these 25G needles.....

http://www.ebay.co.uk/itm/251820716...49&var=550734334648&ssPageName=STRK:MEBIDX:IT

50 Braun/Terumo 25G needles £2.49 , what have i got to lose & mine are on the way

Stu .

 

That's a better price than I got Stu. I should have scrolled a bit further down the page when I did the search on ebay!

It'll be good to get your feedback on the method and establish any possible issues my first attempt didn't.

I've thought of one, and it's what I've noticed to be the different internal contours and dimensions of jets. There seems to be some variation in the thickness of metal the jet orifice is drilled in.

It was around 3mm on that example I featured as I said, which gives plenty of contact surface for the needle insert to be gripped by. Any less would be fine down to about 1.5 to 1mm I'm guessing. I might be wrong and the needle insert might hold securely even in that thickness.

If not, I personally would do as I'll be doing with a lipstick burner tube (tip metal also thin) and silbraze around the base of the bit of needle projecting on the outside of the jet before trimming.

John