Now I'm no expert in this, but have managed to clean and restore the dozen or so slide rules in my collection without too much bother. Most look like the day they were made, and moreover, perform mechanically like they're supposed to.
Let me point you toward some restoration instructions I've found useful. But just a bit of a disclaimer: while these procedures have worked for me, neither the authors of these sites nor I take any responsibility for what you undertake. Sometimes it's better just to accept a little dirt and leave well enough alone. You have been warned!
So anyway, here are some links to washing instructions that have been useful on my end:
Above and beyond the scrub job, there's always that business of making the rule perform well physically. The slide should slide smoothly and evenly with no jerks or jumps, but it should also hold its place when you move the cursor one way or another. Achieving the balance isn't as trivial as it sounds.
Here are a few of my own thoughts on the subject. But once more, bear in mind these things have worked for me and I assume no responsibility for how you use or misuse this information.
Plastic Rules
Well, there's plastic and there's plastic. Some formulations are relatively hard and tend to allow smooth even movement without any other ado (like on my K+E 4181-1). Set the tension of the stator properly and a slide rule like this is likely never to require any further attention.
The same thing goes for the Faber-Castell rules. The plastic in these exquisite units from Germany seems just a little bit softer than that used by K+E, but still is quite silky. The slide moves evenly without hesitation, yet holds its place when needed. I have the Faber-Castell 2/82 and a 2/83-N which are both a delight to caress.
Moving down the Mohs scale of hardness, the next is the plastic used in the wonderful Aristo rules of Germany. I love the fine lines in these; the lettering and colors are so easy on my aging eyes! But being made of slightly softer plastic (as near as I can discern), they do benefit from a bit of paraffin for lubrication. Now here's the crazy thing. Some rules are well broken in and slide too easily, slippery like an eel, while others are redolent of pulling a sled over sand. On some plastic rules, paraffin (used to seal canned preserves) takes care of both problems at once.
I have a beautiful Aristo 803 pocket rule which I bought for a song on eBay. It was a bit loose to the touch, but rubbing down the slide with paraffin made it perfect. And just this week I received an Aristo 903LL which was quite good, but still the wax job made it even smoother.
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| Teflon dry lube on the left, a block of paraffin on the right. |
And then we come to the UTO 601 from Denmark. This is damn near the cutest slide rule ever made; it slips into the pocket easily, is crisp in its layout and quite powerful as Rietz rules go. But, being made of PVC (I think) it really is prone to skips and jumps as you move the slide and cursor, one moment moving smoothly and continuously, the next moment acting like a finite difference operator rather than a derivative. Of all the rules I own, this is made of perhaps the softest plastic and really benefits from a good wax job with paraffin. Just run the slide across the block, then wipe the residue off with a soft towel.
Aluminum Rules
My first "serious" slide rule was a Pickett N-500-ES. While I loved what it could do (everything but clean the lavatory), the smudgy residue left all over the place while using it was driving me nuts. The manual (if I recall) suggested Vaseline as a lubricant, and while that makes for a smooth response it also made the mess even worse.
After a half-year of gray fingerprints, I finally hit upon the scheme that works for me. (Remember my disclaimer from above).
First off, clean the hell out of the rule; get all the detritus out of the way. I just go with a bit of a soak in dish soap and warm water, and lots of rinsing.
Then dry the rule thoroughly, after which set the mechanical tension of the stator.
Finally, make the grooves in the slide slippery with a Teflon dry lubricant for bicycle chains. I use a brand called Finish Line I purchased from Amazon. See the picture, above. Here's the deal, it goes on as a liquid, but then rapidly dries leaving a bed of tiny teflon beads. Wipe up the excess with a soft paper towel. I've never noticed any adverse effects on the printed scales, but some people have reported it may cloud the cursor, so watch out.
While your mileage may vary, believe me, the Teflon lube has made my Pickett aluminum slide rules the silkiest, smoothest and most sensitive units in my collection. For the sake of completeness here, I've got the N-500-ES, mentioned above, as well as the N4-ES and my constant sweetheart, the 1006-ES.
Wooden Rules
And that brings us to wooden slide rules which are almost always made of bamboo. Well, this will be a short section! You see, bamboo really is self-lubricating as the manufacturers claim, and that's the end of the story. I have a Post 1460 Versalog which is smooth acting, yet holds its place and no intervention from me was ever required. I think as a long as it's clean, a bamboo slide rule is good to go from the outset.
The claim is, with a bamboo slide rule, the more you use it the smoother it behaves. I believe it. The Versalog I purchased clearly had never been used. Yet after a month or two I could feel it limbering up daily. It's now one of the silkiest rules I own proving, yet again: use it or you lose it.
A Brief Recap
The best way to make a slide rule smooth acting yet have some grip is by cleaning it thoroughly and setting the stator tension appropriately. After that then consider (recalling my disclaimer from above):
- hard plastics (K+E and Faber-Castell): probably do nothing
- softer plastics (Aristo and UTO): buff the slide tongues and grooves with paraffin
- aluminum (Pickett): apply Teflon dry lube in the grooves
- bamboo (Post): do nothing
Next installment: My Collection