Why do copper soldering tips sometimes work better for me than iron tips? - Page 1
Forum section: electronics / beginners

author: midix
author_rank: Contributor
timestamp: October 20, 2022, 12:36:57 pm
content: Most likely, I've gotten used to a wrong soldering technique, but it just felt so convenient at timesThe long story.In my teenage years when I got interested in electronics, I was living in a poor family. We had only large-ish soldering irons with copper tips in local shops and I could not afford to travel to our capital city and buy a proper low-power soldering iron for small electronics. I did not even know such things existedMy father had a spare soldering iron with a large copper tip for household and electricity tasks, so we repurposed it. We tightly wrapped a thick copper wire around it and sharpened the tip of the wire. It was strong enough to be used for electronics. Much later I bought a better low-power soldering iron that was powered through a simple buck transformer to 24 volts, but that one also had a copper tip.Those tips needed some special care - tinning the tip often and sometimes also reshaping it with a file. Tinning them was very easy. I had a large piece of rosin and I just dipped the iron in it and then immediately I applied some solder to it.I did not have a thin soldering wire, I had only a thick piece of solder. So, my soldering technique was, I guess, unusual. First I melted some solder and let it stick to the tip of the iron. Then I could apply it to the electronic components (that I had to pre-tin). Anyway, the main thing is that it was convenient because I did not need "the third helping hand". I held the PCB with one hand and applied the solder from the tip with the other hand. Somehow I learned to pick up just the right amount of solder with the tip, and the results were clean enough without any spikes or blobs.Some years ago I bought a "proper" soldering station HQ-SOLDER/30 (available from different brands). A cheapie from a local store, but it seems to be doing everything I need for occasional use and has compatible spare parts still available everywhere even after 10 years.Now, the problem is that I'm feeling clumsy with this iron.My old technique did not work because the solder does not seem to stick and flow nicely around the tip. I tried to tin it and tried different temperatures, but it always feels wrong, it just does not flow and stick as easily as it did to the copper tip.So, I had to learn the proper technique that requires some tool to hold the PCB in place and then I preheat the soldering area and apply a thin soldering wire to it. Still, I find that some solder is sticking to the iron tip in unexpected places and causing problems later. For example, while I'm soldering something with the very end of the tip, some solder creeps up and sticks somewhere higher at the tip, and later it can mess up the soldering process by separating from the tip and sticking to a place where it should not be applied. To avoid that, I have to clean the tip often, but then I'm wasting the solder - I cannot reuse the solder that got stuck to the tip because I cannot easily pick it up with the tip and apply it where I need it.At first, I thought it was a temperature problem. I have it set to 350 Celsius. So I increased it to 400, but then I started burning some PCB tracks away, ouch. And it did not solve the problem with the solder not flowing around the tip nicely - the tip just becomes dark too soon, even if I had tinned it recently.I suspect I'm tinning the soldering tips wrong.Can normal rosin flux be used for tinning the tips? What do you use for keeping your soldering tips shiny and to reuse the solder that has stuck to the tip?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 20, 2022, 01:49:39 pm
content: When you need more heating power, do not raise the temperature, you should change the soldering tip instead with a bigger/wider one. See if these helps:Basic Soldering Lessons 1...9 from PACEhttps://www.youtube.com/playlist?list=PL926EC0F1F93C1837

author: DavidKo
author_rank: Frequent Contributor
timestamp: October 20, 2022, 02:11:39 pm
content: Copper soldering tips slowly dissolves in tin. That is the reason why they have plating on them to prevent this. Due to this you should be careful during tip cleaning, not to remove the coating.

author: midix
author_rank: Contributor
timestamp: October 20, 2022, 03:39:36 pm
content: The copper tips on my old and cheap irons did not have any plating at all - they were essentially just thick pieces of copper.Yep, they did dissolve pretty soon, but I could always just cut the end away of my DIY "copper wire tip" and use a file to shape the tip as a cone.But that's not a problem anymore since I don't have those old irons anymore; I'm using a proper iron... which does not work as nicely for me because I seem to be unable to tin the tip so that it behaves the same way as copper tips did.

author: Ian.M
author_rank: Super Contributor
timestamp: October 20, 2022, 03:44:09 pm
content: Without seeing your tip we cant make specific suggestions.Wipe off your tip and try to re-tin it, then post a couple of photos from different angles, with (part of) a ruler next to it for scale.

author: midix
author_rank: Contributor
timestamp: October 20, 2022, 04:45:34 pm
content: Can the iron tips be tinned with normal rosin or do they need a stronger kind of flux?

author: Ian.M
author_rank: Super Contributor
timestamp: October 20, 2022, 04:49:14 pm
content: Maybe. It depends on how oxidized the surface is. That's why I wanted to see photos.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 20, 2022, 05:17:18 pm
content: Quote from: midix on October 20, 2022, 12:36:57 pmyour temperature is too high. your tip becomes black and oxidize, or leave some stubborn flux deposit on it after few soldering job. how i know? because your story is my story even until today, i live like that like nothing happened. keep temperature around 200+ where just enough to melt solder. increase temperature slightly bit by bit if you think not enough for the job. use metal wire tip cleaning to remove those deposit, sometime i just scratch with paper knife (my style, weak hearted cant follow). there is also tip cleaner flux powder online but i havent tried, i always use my Zinc Chloride flux to re tin my tip, several magnitude more potent than fluxes specifically for ee job around here, but i have to clean thoroughly to remove ZnCl and do second retin before doing ee job. people will go against ZnCl (and i agree with them knowing and experienced their reasoning) but i have no other better choice to keep my tip pristine. it can also quickly cool your blackened overheated tip down to temperature suitable for retinning.is it waste solder? yes. so i have a tiny compartment to store solder blobs for repurpose as tip retinning, so i dont waste much. will ZnCl eats tip metal away? yes it happened to my super cheap and super crap iron before, but the $5 china iron (with temp control on handle) amaze me, i've been using it for about 3 years without seeing any significant coat degradation, i even filed the tip (without 2nd thought since they are expendable) to get slightly flatter tip at an angle so i can stick solder on there and do your one hand soldering technique. its been like that since beginning. will i care if my tip damaged by ZnCl? heck no, they are cheap i think i have bought 3-5 spare of it and they are piling up, and i have another 2 more quality irons that i put at rest, in case all of them eaten away. in fact the one i use now is free gift when i bought one of the more expensive iron (Yihua 908D), still cheap actually, but not as cheap as the free gift i currently used. the other one is old school Hakko Presto, its my samurai back then, nothing can beat its high power button when i need demanding job quickly, thats why i keep it in plastic bag just in case, but i havent open it for so many years. both Hakko and Yihua are at rest standing by, fwiw.

author: EPAIII
author_rank: Super Contributor
timestamp: October 21, 2022, 10:50:30 am
content: Modern steel/iron plated tips must be coated or wetted with solder to function well. The small coating of solder will help to transfer heat from the tip to the work. Any corrosion, even small, barely visible amounts, will retard that heat transfer and make soldering difficult. And they must be clean for the solder to wet them.With a modern, usually temperature controlled iron my technique is this: first the hot iron is cleaned. In the past I used a wet sponge, but they sell balls of metal ribbons for that today and they work well without the need of water which also cools the iron (not desirable). Most electronic supply places sell these metal "sponges".Then, immediately after two or three quick plunges into the metal sponge I tin the tip of the iron with rosin core solder. Just a little bit. If I get too much on it, another plunge into the metal sponge will remove the excess. Then, again immediately or with minimum delay, the iron is used to heat the joint.After a few seconds of heating, I apply the rosin core solder which should immediately melt and flow into the joint. A second or two of additional heat to ensure good wetting and the iron is removed to allow the joint to cool.I have plated tips that I have been using for well over 50 years and they are still good.A tip: An old rule is that you should apply flux, then heat, then finally the solder. This may be true, especially for mechanical soldering, but for electronic work I have found that just a small amount of solder on the tip of the iron before heating the joint will help transfer the heat a lot faster. Sometimes it is the only way to actually transfer enough heat to get the joint hot enough for the final application of solder. Not a lot of solder. Not enough so it could be flicked off. JUST a very SMALL amount!

author: EPAIII
author_rank: Super Contributor
timestamp: October 21, 2022, 10:59:36 am
content: When you need more heat, turning the temperature up is never a good idea. The idea of a temperature controlled iron is that is the temperature needed to melt the solder alloy you are using. It is the Wattage of the iron that allows more heat to flow, thereby allowing the iron to remain at that needed temperature. If the Wattage is not enough, then no temperature setting will help.If you have a joint that needs more heat, then go to a higher Wattage iron, not a higher temperature.And yes, I too learned this by needing to repair traces that were peeled off the circuit board. Whenever I took over a shop where an iron on the bench had a temperature knob, it was always cranked to the max. I immediately ordered a Weller WTCP style where the tips had fixed temperatures and threw the one with the knob in the trash. No more peeled traces.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 21, 2022, 11:56:16 am
content: Quote from: EPAIII on October 21, 2022, 10:59:36 amthe temperature is sensed in the heating element, not on the iron tip. so there is latency esp small mass tip. the trick is to increase temp setting during soldering when temp gradient between tip and heating element increased. so you maintain same temperature at the tip (much higher at heating element), just remember to dial down the temp setting when the tip is idle. another argument is to use larger mass tip, but sometime soldering small smd part on large thermal mass pcb cant be done comfortably with big tip. ymmv.

author: JohanH
author_rank: Frequent Contributor
timestamp: October 21, 2022, 12:41:18 pm
content: The generic idea is that a joint should always get fresh flux, or fresh solder (containing fresh flux), otherwise the solder oxidizes and won't flow and stick. Leaving solder on the iron tip more than a few seconds and the work is already ruined, unless you also apply fresh solder or flux the moment you touch the iron to the work joint.That's why I like gel type flux in a syringe so much. I use it all the time with SMD components and sometimes also with through hole (especially when resoldering). Apply a generous drop of gel flux first on the component/PCB, then heat the PCB/component with the iron and apply additional solder if needed. If the component is small, the solder on the iron tip is enough for it to flow with the help of the gel flux. It's incredible in comparison how easily the solder flows when there is a good amount of flux, regardless of how sticky and oxidized solder becomes even after a few seconds exposed to air on the iron tip (the flux burns away from the solder). This method causes more flux residues, but it's easy to wash away with Flux Remover or simply IPA and scrub with a lint-free paper towel and/or brush.That said, regularly cleaning and tinning the tip is crucial. Always have it coated with solder when putting it into the stand. If it becomes too badly oxidized, iron tip cleaner containing some acid can be used. But this is quite rare if you take care of cleaning and tinning the tip. Don't use any tools or sand paper, files or anything on the tip; if you do, it's ruined.

author: midix
author_rank: Contributor
timestamp: October 21, 2022, 09:35:58 pm
content: Quote from: Mechatrommer on October 20, 2022, 05:17:18 pmYes! This must be it, that's exactly what I'm observing.My soldering iron is rated at 30 watts, and many beginner articles recommend this wattage for small electronics, and also they recommend 300-ish C temperatures. So, this might be not the best option and maybe I should try a 40 - 60 watt iron with less temperature. I suspect that my old DIY copper irons were closer to that.One more noticeable difference is that my old copper irons caused immediate steaming when I touched a piece of rosin. My new soldering iron has to touch rosin for a few seconds before it starts steaming, despite 300 C. So, that might be the watts and not temperature thing and maybe also not even iron-vs-copper tip thing.Also, one more thing is that with the old copper iron tips I was used to tinning them far up from the tip, so even if a blob of solder touched a bit higher, it immediately melted and flowed to the very tip. With the new iron, only the very tip is shiny. So, when I accidentally get some solder a bit higher, it does not melt and stays there like snot, and can later mess up things badly by attaching at the wrong places unless cleaned away.Maybe I'll buy a bit more powerful iron. I've heard good reviews about SH72 - still a Chinese cheapie, but it should be able to squeeze more than 50 watts from a solid power supply, and also it's more portable than my soldering station. Portability is important for me - I don't have a dedicated table for work, so I have to put away my iron after work to free the space for other things.

author: Bud
author_rank: Super Contributor
timestamp: October 21, 2022, 10:06:45 pm
content: Going back to your original post, to me the problem is the poor quality tips. Cheapy soldering stations have poor quality tips.The coating may be total shit. Whay you can do is identify what good brand tips are compatible with your handpiece and buy brand tips.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 22, 2022, 07:24:26 am
content: Quote from: midix on October 21, 2022, 09:35:58 pmmaybe you didnt read me correctly, or confusing me with EPAIII's post. wattage is only how quick you need to recover from cold tip. when your tip temperature is too high (as you described in OP), that can translates to "too high wattage" too (but not really that). maybe the problem is your expectation that coated tip should work as your older copper tip. if your reason to get SH72 is portability, then thats reasonable. but if you think is because it has higher wattage, you maybe dissapointed due to your old way copper tip habit. here in video, it only need 5-10W to get the tip to the soldering temperature... ymmv..

author: bidrohini
author_rank: Regular Contributor
timestamp: October 22, 2022, 12:18:11 pm
content: In general, copper tips have some advantages:https://handtoolsforfun.com/why-is-copper-used-for-soldering-irons/

author: smd_hunter
author_rank: Newbie
timestamp: October 22, 2022, 02:39:16 pm
content: Hi, I'm new here, this will be my first messageYou have already been given excellent recommendations, I would like to say that if you can try other brands of tin and different alloys, your story is similar to when I just started and bought the cheapest soldering iron that came with its tin, that was a nightmare and I solved it by buying a "branded" tin, I didn't even need to use flux for most of the things I needed... but of course! it was my particular case! sometimes you do need a truckload of flux!I always leave the tip tinned when I put it on the stand, I always use it between 250 and 300 ºC, when I raise it to ~400ºC is because there is a ground plane that needs great thermal mass and my tip is not able to deliver it , in these cases I have to be quick both to not burn smd components and/or to prevent the best possible that the point does not deteriorate by the high temperature.When I have to clean, I use toilet paper, or jean cuttings from some old pants haha,(any COTTON fabric, don't even try it if you don't know if it is 100% COTTON, if it has any polyester ... oof!, it will be a disaster!) I do this with the tip at working temperature. I do not have any steel sponge stands.And if that is not enough, I use a sponge with fiberglass that is used to polish oysters and kitchen pans, it does not scratch or eat away the tip, but it does fall into the category of abrasive! The latter with a cold tip but after trying to clean with the above step.I would have a lot more to say but I tried to be brief.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 22, 2022, 03:00:36 pm
content: Quote from: smd_hunter on October 22, 2022, 02:39:16 pmyou mean like this? you are not new my friend. those steel wool only for amatuer (steel can on the left picture) i use it to remove stubborn deposit quickly while in soldering job, or excess solder sticking to the tip that made their way up like midix mentioned. i can do with the cotton or paper knife if i have plenty time, like in the end of soldering session, cleaning and tinning the tip before storage.

author: mariush
author_rank: Super Contributor
timestamp: October 22, 2022, 03:28:53 pm
content: Your soldering station is actually a rebranded Zhongdi ZD-929C with an undersized transformer (30w instead of 48w) :http://www.china-zhongdi.com/product/38.htmlYou can get various tips on ebay, here's an example :https://www.ebay.com/itm/162672153337- They look a bit different but I suspect they're same as the classic 900M-T series from Hakko, which was used with Hakko 936 and lots of cloned soldering station. Example :https://www.ebay.com/itm/195134228643Handpiece is 23$ (but probably comes with 48w heater element) :https://www.ebay.com/itm/113739710206You should be able to upgrade the transformer to a 50-65w one easily, and it's not that expensive. It should be a 24v AC transformer, nothing special. It may have a second winding for something like around 12v for opamps/comparators and the microcontroller (using a 5v regulator to get 5v from 12-ish volts)This guy posted schematic here:https://www.eevblog.com/forum/repair/tenma-21-147-soldering-station-repair/msg912353/#msg912353You could use a transformer with a two 12v secondary windings and tap into one of the 12v windings to power the logic (a few mA)You could probably improve heat transfer between heater and the soldering tip by wrapping some aluminum foil to thicken the heater element, and maybe by adding a drop of thermal paste inside the tip walls.Anyway, the undersized 30w transformer means that when you put the tip on a big copper pad, that copper will pull heat from the soldering iron tip fast and then your soldering station will start pumping energy into the heater to bring the temperature back to the configured temperature. With a tip that has small volume (heat reservoir) the temperature will drop fast and take some time to recover ... with a bigger tip the temperature drop will be less pronounced.In normal operation, there's rarely a need to go above 320-350c especially if you work with leaded solder, which melts at 180-183cI clean with a paper napkin / towel and then with sponge like in the video below (at around 1:20 is cleaning the tip) ... if not sponge then I use that "wool" like material

author: smd_hunter
author_rank: Newbie
timestamp: October 23, 2022, 10:32:45 am
content: Quote from: Mechatrommer on October 22, 2022, 03:00:36 pmThe main reason I found it more convenient is because I always forgot to moisten the sponge that comes with the stands, but it is a plus that it does not lower the tip temperature with this methodQuote from: Mechatrommer on October 20, 2022, 05:17:18 pmIs that what is called Tip Tinner? the one that is usually sold in a tin of about 20 grams in a white/grey color? At first I thought it was something similar to what I was recommended a long time ago to clean areas of boards with a lot of corrosion where there was no way to solder, I mean old radio cards for restoration, what they specifically told me was to dissolve zinc in hydrochloric acid until it no longer dissolves, filter it and use it and then clean ... but you do not mean anything like that I think. Either would scare me that it would eat too much of the tip...mmm maybe try with an old tipQuote from: Mechatrommer on October 20, 2022, 05:17:18 pmwhen I read that, I was surprised, I thought I was the only one who did that, I always kept it a secret so no one wouldn't think I was stingy with the tin

author: MrAl
author_rank: Super Contributor
timestamp: October 23, 2022, 10:40:49 am
content: Real quick reply...Copper conducts heat better than steel or iron.Pure copper does erode faster than steel or iron though so will not last as long.Brass works to some degree, but still not as good as copper, although brass does not erode as fast either.

author: smd_hunter
author_rank: Newbie
timestamp: October 23, 2022, 11:04:03 am
content: Quote from: mariush on October 22, 2022, 03:28:53 pmWhat a good idea, I have a "bakku 601D" that I bought on sale at 27€, it came with the box in pieces but it worked well and still works, I will see if I can also improve it by applying your advice.Quote from: mariush on October 22, 2022, 03:28:53 pmI'm curious to know where you learned about the aluminum foil because I've heard it 3 times this week and it can't be a coincidence, some youtuber recommended it in a video?. What kind of thermal paste do you have in mind? the white one that you see everywhere? or a more special one? it makes me think that when the temperature rises and the paste dries out it will stick and it will be a disaster when you want to change the tip.Quote from: mariush on October 22, 2022, 03:28:53 pmI think this was the most professional and elaborate soldering video I have seen so far. Too bad that in the day to day, and I speak for me, not all the steps that he says are done ... but when I had to do a beautiful job, I did clean the tin with alcohol and took more precautions. I would add the advice to leave the tin in a small box with a hole to remove it from so that it does not get dusty or dirty in the coil.

author: mariush
author_rank: Super Contributor
timestamp: October 23, 2022, 12:35:30 pm
content: Quote from: smd_hunter on October 23, 2022, 11:04:03 amI remembered a Youtube video in the past where reviewer of another Hakko 936 clone was complaining about poor transfer between heater and tip and blaming it for too much play, too much air between them acting as insulator. That person used copper foil, but I figure copper foil is much harder to source compared to some plain kitchen aluminum sheet you could cut a strip out of so that's why I recommended aluminum foil.As for thermal paste, I would say use whatever you have - I have a larger tube of some plain white thermal paste but also some half empty syringes of computer thermal paste like Arctic MX-2, Ceramique, MX-4 ... similar pastes should do the job just fine.

author: mariush
author_rank: Super Contributor
timestamp: October 23, 2022, 12:55:17 pm
content: Quote from: smd_hunter on October 23, 2022, 11:04:03 amThere's a teardown of that model in the video below.It seems the transformer has 3 secondary windings : 26v , 10v and 32vI assume 10v is for the logic (microcontroller and comparators, opamps, to produce 5v) so I think you'd be fine with 12v winding instead26v is probably for the heater of soldering iron and 32v is probably for the heater in the air gun and probably the fan is also powered from the rectified 10v ac if it's not a 24v fan.So it's a bit more custom, but there's enough room inside that box that you could easily have a couple toroidal transformers , for example one 24v AC (2x12v - so you could get 24v AC and 12v AC) and maybe one 30-32v AC (maybe 2 x 15-16v AC) secondariesAlternatively you could just get the insides of wallwart adapter that produces 12v DC 0.5a..1a mounted inside and remove the 10v AC winding completely, you could feed 12v DC directly after the bridge rectifier on the board.This way you'd be left with just a 26v and 32v AC windings (should be fine adjusting to 24v AC and 30..32v AC)

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 23, 2022, 02:08:48 pm
content: Quote from: smd_hunter on October 23, 2022, 10:32:45 amsomewhere, its called plumber's flux/paste, it corrodes copper into greenish material (if left on for long period without thorough cleaning), it damaged 2 of my irons, one is the cheap super crap iron, the other one is my first Hakko Presto. i dont care, i just buy new, thats why i love cheap iron. and ZnCl characteristic of creating conductive path between traces (like Mohm to Kohm is possible) and its very hard to take this conductive property off the board. so i will never use it on PCB anymore, esp when higher voltage present, after one brainfart explosion occured because of the flux, once its carbonized (due to heat i guess) it becomes very conductive and in the end a short circuit between traces/pads. but its great when soldering distance is far such as battery tabs, connecting wires/cables etc. one 20g plastic can/tin can last for many years, recently i purchased my third can (no i dont diy chemicals) attached picture, with my solder blobs collection, which is much cuter than yourstake one cold blob, put it on my wooden bench, immerse iron tip in ZnCl paste, press it from its side on to the blob, in a second the whole tip will be immersed in the melting blob, wiggle a bit esp on the very tip to make sure tin properly, and then clean with cotton piece (to take out ZnCl) before soldering job or for storage. the blobs i collected over time when doing desoldering or repair job, yeah i'm too diligent on thatymmv.

author: midix
author_rank: Contributor
timestamp: October 23, 2022, 08:56:22 pm
content: Quote from: mariush on October 22, 2022, 03:28:53 pmYep, it looks like it. I searched copper tips for it but - unbelievably! - this is what AliExpress does not seem to have!There are lots of copper tips for Hakko 900M style though, but, judging by some measurement images, the diameter of 900M is too small for my "Zhongdi".This made me think - why even bother with the transformer if I can get a temperature-controlled iron in a single pen, such as Hakko FX-600 clones. There is a large number of 900M tip options for those, including copper tips. But somehow I don't trust holding a mains-powered device in my hand for hours if it's 100% designed in China by an unknown brand. Also, FX-600 (and clones) seem to be a bit large-ish for my small hand. Zhongdi seems a bit smaller. But I might be wrong, it's not easy to judge from reviews.So, I was searching for small-ish 900M irons with a ~20V jack, but there seems to be such a thing even in China. I found only irons with T12 style tips (and of course TS100 and Pinecil and their clones), and there are no copper tips for those. Sigh. So no small portable low-voltage soldering iron with copper tip options for me.

author: smd_hunter
author_rank: Newbie
timestamp: October 23, 2022, 11:18:38 pm
content: Quote from: mariush on October 23, 2022, 12:55:17 pmThanks!I will definitely make some improvement, I have a ~28V transformer (it was first 32V but I removed some turns) that I had recovered from a stereo, I do not remember well how much power it was but it does not matter much as I will measure the in operation current first from the original one. All remains to be seen ... again , because I had already opened it when I bought it hehebut just to look around and see that nothing was broken.What this station absolutely needs isa main switch, because if you have it plugged in but without activating the tools the transformer is still connected directly to the line ! generating heat and little buzzing noises !

author: smd_hunter
author_rank: Newbie
timestamp: October 23, 2022, 11:48:47 pm
content: Quote from: Mechatrommer on October 23, 2022, 02:08:48 pmI did wash the board thoroughly with distilled water and then with isopropyl alcohol, and when it dried I coated it with solid paraffin, when I did that job. Although it was a circuit that worked with 12 or 9 V, I'll be much more careful next time... and I'll save the idea for an experiment heheYour ZnCl looks like a good brand compared to the ones I had in mind.(Cheap Amazon first result for Tip Tinner)I confess that my tin pit looks bad, but it has another use, the edges of the "donut" are used to scrape without scratching the tip when there is nothing at hand.,,, Also the residues that fall from the tin-sucking piston end up there.