Polishing screw heads with diamond paste

[VWatchie]

23 hours ago, nickelsilver said:

They come in sets, and are tapered. The video shows distinctly not the way to use them hahaha. You slide them in the hole, and give a little twist. Sometimes you give a few twists. They don't really remove any metal (yeah microscopically). They burnish the hole. Going from both sides evens out the taper. You want one that fits, but it could fit anywhere along the functional part of the broach.

So, good thing I asked about it. Thank you very much! I’ve been doing this for a while now and I’m beginning to realize that not even what appears obvious always is.

However, I’m still slightly confused. You mention that these smoothing broaches "are tapered", but when I look at the smoothing broaches on offer on cousinsuk, none of them look like they are tapered. Unless, that is, the differences between the widest and the narrowest sections of the broaches are so small it really can’t be seen in the pictures?

Speaking about what appears obvious; If cousinsuk’s smoothing broaches indeed are not tapered, I suppose there’s no need to “go from both sides”?

Finally, I’d like to ask if the “twist” (or twists) are to be done quickly to create friction/heat “burnish the hole “, or just slowly to make a grinding effect in the hole? 

Apologies if my questions appear redundant, but the “magic world of mechanics" still quite often feels like a riddle to me  I’m slowly getting there though, I hope… 
 

[nickelsilver]

Hahahahaha
They are very much indeed tapered. Maybe not much from a casual perspective, but massively from a machinist perspective. A broach might change diameter of 0.2mm over its length of 50-100mm. The twists- go gently, like 1 or 2, then check. This is a physical burnishing, if you're making heat on more than a molecular level you're over motivated.

[VWatchie]

Now that I think about it, I do understand why you're laughing, if the smoothing broaches weren't tapered they would either be too wide or too narrow to be of any practical use. So apologies for that "stupid question", but I guess that's the price to sometimes be paid for learning... 

Your help is immensely appreciated, so @nickelsilver for president!  

Edited March 17, 2020 by VWatchie
grammar, I guess...

[nickelsilver]

Now that I think about it, I do understand why you're laughing, if the smoothing broaches weren't tapered they would either be too wide or too narrow to be of any practical use. So apologies for that "stupid question", but I guess that's the price to sometimes be paid for learning... [emoji38]
Your help is immensely appreciated, so [mention=4990]nickelsilver[/mention] for president! [emoji6] 

Haha don't worry I had a million "dumb" questions when I was starting out! Also somtimes you overthink things and come out with questions that can only be thought of as dumb dumb, unless the teacher understands. Having been on both sides I understand!

[Endeavor]

On 8/19/2019 at 7:18 PM, oldhippy said:

Start by removing the bur with a flat needle file not to course

I like to "do up" damaged flat-head polished screws of a Le Phare chronograph pocketwatch. However, I don't have any appropriated files to remove burs as a starter.

Looking at CousinsUK, they offer all sorts of different files (Buff-, escapement-, habilis-, Micro-, Needle-files), in different shapes and different "cuts"; 0 being coarse, 2-medium, 4=fine, the number goes up to 6.

Can somebody advise me please what I need; which type, shape and cut?

Thanks

 

 

Edited March 20, 2023 by Endeavor

[nickelsilver]

A square 6 cut, either needle or escapement, will cover deburring and also put a nice bevel in the slot if you want.

 

You can never have enough files, all the different shapes, cuts, types (steel, diamond, and the buff files are like diamond files but use a composite ceramic/diamond coating- these are ultra fine, like a 10 cut).

[oldhippy]

This is a selection of all you will need. Looking at the photo the one on the right is the one you will need and use most. Then you can move onto emery sticks and finish up with the finest. Don't buy cheap ones you will find they do not file well and they soon wear out. 

http://blog.esslinger.com/guide-to-watchmakers-files/

Edited March 20, 2023 by oldhippy

[Endeavor]

6 minutes ago, oldhippy said:

Looking at the photo the one on the right is the one you will need and use most.

Thank you both. I guess "the one on the right" (the top one?) in OH picture seems a flat file, is that a "Needle" file?

Yes, through time I learned that the higher quality last longer and works (much) better

[nickelsilver]

For those interested- some pics of a tripod tool and its use. There are numerous versions of these, best aren't too big, and can take a square head pin vise to hold screws. I have a bunch of little Schaublin P4.5 collets so made the holder in the tool.

 

Start on 12 micron paper, initial adjustment of the feet by eye, fine adjustment after a stroke on the paper, until there's full contact. Screw will be matte grained (but a little shiny) from the paper. Clean well, then to the tin with 1 micron diamond paste. The whole process including snapping pics was about 3 minutes for this screw.

 

Some folks go all the way to polish with different papers, but it'll never be as flat as polishing on tin or zinc or thick plexiglass, as the paper always has a bit of "give".

 

Hard to photograph, but it's called "black polish" because just a tiny tilt of view and the surface will go from brilliant to black when properly flat.

 

 

 

Edited March 20, 2023 by nickelsilver

[Endeavor]

Thank you for your explanation and pictures

For sandpaper I'm used to "grit" (1000 grit etc), so 12 micron didn't say me a lot. Here a "conversion"-chart for people like me

According to the chart; 12 micron is somewhere in the range of P1500 - P2000.

 

Edited March 20, 2023 by Endeavor

[nickelsilver]

Yes, it seems they tend to use micron when the abrasive has been graded particularly accurately. Cousins carries both the "colored" 3M micron graded paper, which goes to very fine grits, and 3M Imperial lapping film, which tends to be larger grits. Both are self adhesive (check for "AB" on the colored ones), and fantastic. Around the shop the most used for finishing are 20, 12, 9, 3, and 1 micron. The finer grits don't get used for flat polishing, but are very useful applied to sticks for beveling and such. 30 and 40 micron do get used too on thick glass backers for flattening large pieces.

 

https://www.cousinsuk.com/product/film-lapping-3m-261x266x?code=P1260M

https://www.cousinsuk.com/product/film-micro-finishing-3m-268l?code=P55609

[oldhippy]

I found the grades of emery sticks are best to use because they have a flat surface which helps to keep the screws in shape. You do not want a cheese head screw with a beveled top. You can use emery cloth, or wet and dry but wet is very messy and dry rips apart. You don't use sandpaper on steel sand paper is used for wood. 

[Klassiker]

 

19 hours ago, nickelsilver said:

polishing on tin or zinc or thick plexiglass

Do you need to return the tin / zinc / plexiglass surface to flat once in a while, and how do you do it? I can imagine the surface becoming concave in time, or does that not happen because of the embedded abrasive?

[nickelsilver]

9 hours ago, Klassiker said:

 

Do you need to return the tin / zinc / plexiglass surface to flat once in a while, and how do you do it? I can imagine the surface becoming concave in time, or does that not happen because of the embedded abrasive?

It does get scarred or deformed or just contaminated with time. I skim the surface in the lathe, but it can simply be filed too, but way way faster in the lathe.. It does need a bit of a textured surface; I use a thin section coarse file to scratch it up after turning in hte lathe (thin so that it lays flat on the suface).

[oldhippy]

You could use crocus paper that is around 1500-2000 grit.