A rolling blog of everyday life on and around the workbench

02/02/2018: As anyone who's been to my workshops knows, I'm a bit of a magpie. I can't help it - I see what looks like a piece of junk and I think "Ooh, that'll come in handy...one day". So I rescue it, stuff on a shelf and leave it to gather dust until that day comes.
In some cases it's not the item itself that's of interest, but what it contains. Take the humble hard drive, for example. It sits there in your computer, merrily churning away, and I doubt you give it a moment's thought...at least until the day it packs up - and you lose your entire collection of Kenny G MP3s, and photos of cats pretending to play the piano.
Most people would whip the broken drive out, pop a new one in and chuck the old one away...which is pretty much what I do - except I take it apart first. Hard drives are a fantastic source of precision parts. The drive platters are perfectly flat, with a mirror finish - and can be used as precision flat surfaces, as mirrors...and, if you hang them up on a piece of string, as a surprisingly good (if annoying) wind chime. There are also a couple of really strong magnets (very handy for making tool holders), lots of tiny screws (you never know when you'll need one), a precision motor and two or three very nice bearings.

"All good and well" I hear you cry "but when will you ever use them?". That's the thing - you never really know, until you're faced with a knotty problem and need to make something to overcome it.
In this case the knotty problem was a need to fit a replacement pearl to a key. Normally I'd fish around in my stock of pearls until I found one of the right diameter and thickness - and while I could find plenty of the right thickness, I couldn't find any of the right diameter. No big deal, just sand the edge of the pearl down until it fits in the holder, right?
Well yes, you can do that...but it takes forever, and you'll be very lucky if the pearl remains round. A much better bet is to spin the pearl on a machine and either turn or sand it to size as it rotates. But how to mount it on a machine?

The classic method is to get a piece of dowel and simply glue the pearl on the end of it. The dowel can then be mounted in the machine (be it a drill or a lathe) and the pearl sanded or turned to size.
The problem with this method is that it's hard to get the pearl aligned with any accuracy, and if you're working with a pearl holder that's a little bit out-of-round (as they often are) you may need to remove the pearl from the holder to test the fit as you go along. This is a complete pain in the nether regions, because you have to glue the bloomin' thing back on the holder each time.
What I wanted was a tool that can hold the pearl in a lathe, that will allow the pearl to be centred and turned/sanded, and that would allow the pearl to be removed for test fitting and easily replaced in the holder for further turning.

There's a well-known way of doing this, and it's known as a friction chuck. A normal chuck grips the part around its circumference so that it can be turned - but a friction chuck grips the part on its faces. If that doesn't make any sense, just think of what you do when you pick up a sheet of paper. You grip it 'twixt finger and thumb. That's (sort of) a friction chuck. If you do the same thing with a coin, and only grip it lightly, you can spin it around between your fingers with your other hand. Engineers will probably baulk at this analogy, but it's close enough for jazz.

There are two parts to a friction chuck; there's the part that goes into the lathe chuck (which provides the spinning power) and there's the part that goes into the tailstock...which provides the friction. However, you want the tailstock part to be able to spin, otherwise it'll mark the part...and it'll get pretty hot in no time at all.
A really simple friction chuck is just a piece of wood mounted in the lathe chuck and another piece of wood held against it with a revolving centre - with the part you're working on sandwiched inbetween. It works very well - but when you're dealing with something as small as a key pearl, it gets a bit unwieldy. I wanted something a little more elegant, and a lot more accurate.

Here's what I came up with.
I took a hard drive motor apart and pulled the bearing out of it. It's ideal for the job because it's small, and it's longer than it is wide.
In order to make it versatile and provide a little more working space I fitted two Delrin (plastic) 'plugs' into it - a standard size for large key pearls and a smaller one for those little fiddly Bis Bb pearls. And to each plug I glued a disc of rubber. This will provide the friction...or the grip. The other part of the tool is a lot simpler, it's just a piece of bar - again, with one end smaller than the other, and rubber discs glued to each end. This end goes in the lathe chuck, the other end is held in the tailstock chuck - and the pearl is held between them.

So far so good - but when you grip a pearl between the friction chuck, it rarely runs true...and it's a complete faff trying to align it by hand and eye. What would be really handy is a tool that automatically centred the pearl.
And here it is - and yes, yet another hard drive had to die in order to make this tool. It's simply a bearing mounted on a steel bar, which is then fixed in the lathe's toolpost. The pearl is lightly held in the friction chuck and the lathe turned on. As the pearl spins, the bearing on the bar is slowly brought into contact with it...and as it touches the pearl the bearing begins to spin. As you push the bearing further in, it pushes the pearl over until it runs dead centre (or true).
Isn't that brilliant? It takes mere seconds to centre the pearl - so if you need to remove it to check the fit, it's a doddle to replace and re-centre it.
Once the pearl's running true you simply snug up the tailstock to increase the friction and hold the pearl firmly in place - and then you can turn it.

It's unlikely to see a great deal of use as a pearl turner - it's not a job that needs doing all that often - but a friction chuck comes in handy for all sort of jobs. It's one of those tools that, once you have it, you find things for it to do. And every time I use it I'll not only have the satisfaction of knowing I made it out of a few scrap parts, but also that it's saving me a great deal of time - and you the price of a pint or two.

25/02/2018: More toolmaking - and this time I've been having much fun with a spot of lapping.
In case you're unfamiliar with the term, or are perhaps wondering whether it's the sort of thing that goes on in seedy nightclubs, it refers to the practice of rubbing two parts together until they're a perfect fit - aided by a thin layer of abrasive between them. OK, maybe that's the sort of thing that goes on in very seedy nightclubs. I'll give you that.
Anyway, it's a very time-consuming process, but the resultant fit is very accurate - and aside from the time factor, it's a very cheap and simple way of achieving a very high level of precision.

Most of the lapping in this trade is about matching a fit between two parts - a particularly common job being that of lapping a crook tenon sleeve into its receiver, or a new rod screw into a barrel. But sometimes it's necessary to lap something so that it conforms to a dimensional standard...and in this case the standard is flatness.

If you've read any of my reviews, or the article on warped toneholes, you'll have seen me using a lump of metal placed over a tonehole as a means of showing the degree of warp in it. This lump of metal is called a flat standard...because it's flat, and because it's the standard against which the flatness of another object can be measured.
I already had a collection of flat standards, but I needed some larger ones...and I particularly needed some thinner ones which could be used without having to remove any keys. These are useful for testing brand new horns, where the removal of keys could technically invalidate a warranty - or where the owner simply wants to know whether to take a horn back for replacement or a refund.

I chose 303 stainless steel for my material. It's tough, it's resistant to corrosion, it's reasonably easy to work, it's quite stable...and I had a sheet of it lying around.
The first job was to cut some blanks out of the sheet. This was probably the most time-consuming aspect of the operation, and after an hour of hacksawing I began to regret not simply buying some ready-cut discs off ebay (where they can be had for two a three quid a pop).
I'd gone for a 4mm thickness. I could really have done with going thinner than that (2.5 - 3mm) but had some concerns about the thermal stability of such thin standards - though I intend to make a batch up and test them anyway. Might work, might not - but if it does, it might provide a means for home tweakers to set themselves up with a set of accurate tonehole testers on the cheap that can be used while the horn is still assembled.

With the blanks cut and roughly rounded, it's time to pop them in the lathe and turn them into rounds - and to do this I used the same chucking method as in the previous blog entry - namely a friction chuck, though on a slightly larger scale.
With the disc now rounded off it's removed from the friction chuck and glued to the wooden backplate with a dollop of superglue. This relieves any stress on the face of the disc and allows for a tool to be run across it to flatten it.
At this point the disc is probably quite usable. It's not perfectly flat across the face (typically slightly dished towards the centre), but if placed centrally over a tonehole any minor dishing is going to be largely irrelevant...and it'll at least be flat enough to give you a general idea of the state of the tonehole.

As I'm going to be using these discs as reference standards, I needed to go the extra mile and make sure they're as flat as possible, which meant they had to be lapped - and in order to lap something flat you need a flat surface against which to lap it. But how do you know that this surface is flat?
Well, you could buy a lapping plate - and you'd know it was flat because it would come with a certificate...and a hefty price tag. Or you could make one. This is the beauty of lapping - you don't need a bunch of expensive machines and sophisticated measuring equipment - you simply need three blocks of metal (usually cast iron, but certain other metals can be used) that can be lapped against each other in turn...and, after a lot of puffing and swearing, you end up with three plates that are dead flat and which can now be used as lapping plates.
It all sounds marvellous, but in fact it's rather unnecessary given the tolerances required. You could lap a disc on a sheet of 600 grit carborundum paper glued to a thick sheet of glass and it'd be well within the level of accuracy needed for the job. So why bother going 'the full English'?
Mostly it's because I can, but also because it's nice to know that my flat standards are really flat - and because I use them in the course of my reviews to point out manufacturing defects, it's only fair that I ensure the standards I use are beyond reasonable doubt.

I used a two-stage lapping process - a coarse lap to rough out the larger imperfections followed by a fine lap to sneak up on the final flatness, and to add an appropriate surface finish to the disc. In this case it's a matt finish I'm aiming for. I lapped the previous set of standards to a mirror finish...which is lovely and took forever, using ever-finer grades of abrasives - but the reflective surface turned out to be a proper nuisance when using a leak light during tonehole levelling. Just goes to show...sometimes you can overdo a thing.
Speaking of which, you wouldn't believe the amount of gloves, tissues, rags, mineral oil and degreasant I got through in knocking these discs up.
It's very much a process of 'do a bit, clean up, check it for flatness, do a bit more'.
And despite it being very grimy work you have to be so very careful to avoid contamination of the lap and the workpiece, because the slightest bit of grit in the wrong place at the wrong time will mean having to go right back to the start of the lapping process.
It's immensely satisfying though, to the point where you almost have to force yourself to say 'enough is enough'. And nothing beats dropping the finished disk onto a flat surface and having it stick to it due to the vacuum between the surfaces.

And while I was at it I knocked up a set of flat abrasive discs. These aren't used to level the tonehole as such (as you would with a rotary or large flat file) but rather as part of my preferred method of levelling, which is to selectively treat only the high spots with a small smooth file and then follow up with the abrasive discs to knock down any tiny peaks. It takes a lot longer than going at the whole tonehole with a file, but it removes less metal and provides rather more accuracy.