Sunday, August 22, 2010

Roll Pins

Roll pins (aka 'rolled spring pins' or 'slotted spring tension pins') are a very good thing to have on hand. They come in a wide range of sizes; the two pictured give an idea. The large one is 3/8" diameter x 2" long. The small one is 3/32" diameter x 5/8" long. (There are metric dimensioned ones too, of course.)

The two shown here are from a 120-piece assortment I got from Princess Auto. Should I ever need a size or a quantity that the assortment doesn't provide for, I'll have to go to an industrial supply outfit like Spaenaur and buy a package quantity (typically 100 pieces).

The pins are made from quite hard spring steel, rolled into shape as the name implies. The key feature of them is the dimensioning. A roll pin's diameter as you receive it is always slightly oversize of nominal; e.g. a 1/8" (0.125") diameter roll pin will have an actual diameter of 0.131" to 0.135". To install one, drill a hole the nominal size and hammer in the pin. (One or both ends is/are always chamfered for ease of starting.) As the pin is driven, it contracts to fit the hole and effectively gives an interference fit of considerable strength.

An installed pin can be punched out and reused, which means that salvage can be a source of them. (A word of caution about punching them out: be sure to use an exact-size punch, and be especially careful if you're starting on a slightly protruding end of a pin. An undersize punch that manages to get down into the hollow centre of the pin can make a nasty mess of things. There are special punches available that have a centring point on them. You'd have to go to Spaenaur or a similar place for those; they're not something you're likely to find at the Home Depot.)

Uses are endless -- pinning gears or virtually anything to shafts; reinforcing glued up cylindrical assemblies; as motion-limiting stops in adjustable assemblies; what-have-you. Uses have a way of suggesting themselves when you have the pins at hand.

Occasionally, the hollow centre can be an undesirable feature; e.g. on a fertilizer spreader axle where corrosive material could get inside. In such cases, the centre can be filled with a length of soft steel wire or rod and epoxy or CA adhesive.

In closing, I must leave you with a word of caution about Princess Auto's assortment; the smaller diameter pins are poorly formed and seriously oversize, and will not install correctly in nominal size holes. To use them successfully, you have to mike them and select a suitable number size drill. For example, the 3/32" (0.09375") pins are about 0.113" in diameter. That's almost 0.020" oversize, and that's a lot for an interference fit. A No. 38 drill (0.1015" diameter) worked ok.



Here's some information you may find helpful for dealing with oversize fractional inch diameter roll pins. Following is a list of all the available nominal diameters with some added information. Each entry is in the form:

Nominal Fractional Diameter; Nominal Decimal Diameter; Maximum Allowed Decimal Diameter*; Difference (Difference Rounded Off to the Nearest Thou)

* i.e. the maximum diameter that a given pin should have from the factory. A pin whose diameter exceeds this figure will be troublesome to install in a nominal-size hole.

1/16"; 0.0625"; 0.069"; 0.0065" (0.007")

5/64"; 0.078125"; 0.086"; 0.007875" (0.008")

3/32"; 0.09375; 0.103"; 0.00925" (0.009")

1/8"; 0.125"; 0.135"; 0.010" (0.010")

5/32"; 0.15625"; 0.167"; 0.01075" (0.011")

3/16"; 0.1875"; 0.199"; 0.0115" (0.12")

7/32"; 0.21875"; 0.232"; 0.01325" (0.013")

1/4"; 0.250"; 0.264"; 0.014" (0.014")

5/16"; 0.3125"; 0.330"; 0.0175" (0.018")

3/8"; 0.375"; 0.395"; 0.020"; (0.020")

1/2"; 0.500"; 0.524"; 0.024" (0.024")

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SUNDAY, JULY 3, 2011

Addendum -- Application Examples

Here's an example of a pin anchoring a stud at the end of a rod.

And here's a roll pin serving as a valve handle.

Scroll down in either and you'll get to it.

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Thursday, August 12, 2010

Somewhere, a Saucepan Needs a Handle

Right about here, actually.

The saucepan pictured is quite a nice piece of cookware, but its handle went south a long time ago.

The handle attachment bracket that's spot-welded to the side of the pan is still perfectly sound. The bracket contains a square M5 nut for attaching the handle with a machine screw.

I have an idea how to go about this that will make a nice illustration of how common garden hose fittings can be employed as structural mechanical parts. The outcome won't be the most aesthetically pleasing thing I've ever done, but it will serve the purpose and keep this lovely piece of stainless steel manufacture out of the landfill. Here's a photo of some of what I'll be working with:

The hose fitting cap will be drilled for an M5 screw, and securely attached to the pan's handle bracket.

I'll strip the ferrule and hose remnant off the male hose fitting, and wed it to the end of the hardwood broomstick piece. I'll have a sturdy replacement handle for the saucepan with a unique feature -- it can be easily detached to make washing the saucepan easier.

The first thing to do is drill that cap through the centre for the attachment screw. A 3/16" hole will give me a slight interference fit for a 5mm screw, which is exactly what I want to have here -- minimal screw clearance so the final assembly will be as snug as possible. That raises an interesting point about inch vs. metric in the workshop. A little digression is in order.

Inch versus Metric Measure

There's a fallacy contained in the above sub-title; the word 'versus'. The two systems are not mutually exclusive. In working with both of them, I've come to regard them as a complement to one another; in a sense, I tend to see the two as one big seamless system that I happily put to use however it suits me. The 3/16" hole for a 5mm screw just mentioned is a small example. One encounters many such mixed uses of inch and metric in manufactured goods. My old Raleigh Grand Prix bike and my ancient 8" Beaver table saw both exhibit mixes of inch and metric dimensions/items where it suited the designers' purposes.

I grew up with fractional inch measure, and it will always be the system that I'm naturally inclined to think in. But in the workshop, one is well advised to be fully conversant with and equipped for the use of both systems.

I say that quite calmly now in spite of the fact that when Ottawa began to seriously embark on converting Canada to metric decades ago, it got my back up something fierce. Ottawa's embrace of metric measure had nothing to do with technical progress. It was a transparent, ham-fisted exercise in social engineering, and an opportunity to jettison another piece of our 'colonial' past. If nothing else, imperial measure is a cultural artifact of great beauty and utility. Ottawa would have had us discard it as if it were a worthless piece of trash. Ottawa can be pig-ignorant and tree-stump-stupid at times.

There, I got that off my chest. Back to the saucepan. This is a workshop blog, after all, not the op-ed page of the Globe & Star-Post.

Here's the pan with its new handle receiver:

The hose fitting cap had a yellow zinc dichromate plating on it that was a bit corroded in places, so I brushed it with the wire wheel machine and that took the plating off entirely, leaving me with a naked steel part. I spray-painted it with grey primer and some automotive silver paint. What the heat resistance of ordinary spray paints is I have no idea, and I can't find a mention of it on any manufacturer's website. I guess it's a secret. Time and use will tell if the cap's paint job will prove durable.

The original M5 screw was longer than needed, and it had a combination slot/Phillips recess that I didn't care for on a screw that will need to be tightened very firmly. I replaced it with a 12mm long hex socket head stainless steel screw, and added a split lockwasher and flat washer, both stainless steel. (And there's another inch/metric mixture; No. 10 inch washers fit M5 screws perfectly.)

Stainless steel fasteners are outrageously costly, but in places like this where they're truly called for, hang the cost. I happened to have what I needed on hand, but would have gladly parted with a dollar or two to get stainless steel parts if I hadn't. That points up the value of salvage to a workshop. It's a good idea to cultivate an eye for good items that can be found in discarded machinery and the like. You can build quite a valuable stock of useful fasteners and material that way.

I used red Loctite thread locker on the screw, and really tightened it firmly. Handles that loosen are a nuisance I want no part of.

The Handle-End Fitting

This is the part that's to be wedded to the end of the wooden handle so the handle can be screwed into the fitting attached to the pan. I was working here with a die-cast male hose fitting, which complicated things a bit. Were I doing this over, I'd use a fully machined fitting.

The problem with a die-cast part like this is that in its intended application, the precision of the bore is of no importance -- it just has to let water flow freely. Consequently, the manufacturer takes no pains to ensure that the bore has a uniform, concentric diameter.

I'll try to summarize the construction of this part without glazing your eyes over.

The hose fitting's bore was something of a taper. I chucked the fitting in the lathe and bored it through 11mm diameter to get a more-or-less straight, consistent bore. The threaded rod is a piece of undersize 3/8"-16 rod with a 9mm diameter. (Not all threaded rod is created equal. This piece had quite flattened thread crests which made it undersize, and just what I needed for this.) I needed a bushing to take up the 2mm diameter difference, so I turned one from a length of thick-walled mild steel tubing that had a 9mm bore. With those three items done, I had the makings of what you see in the photograph. The missing piece of the puzzle was a suitable adhesive/filler to bond them all together with.

And that brings us to an epoxy product that's new to me; something known as 'J-B Weld'. The manufacturer claims that it will withstand 500 degrees Fahrenheit, so that should make it suitable for a saucepan handle application. I mixed up a batch of the stuff, slathered all the mating surfaces of the fitting components with it and clamped it up in the lathe so it would all be held straightly and concentrically while the J-B Weld hardened. Here's how the setup looked:

J-B Weld is a slow-hardening epoxy (fifteen hours for a full cure). I left it like that overnight, and the next day the outcome looked good. Just for good measure, I pinned the assembly through in two places with 3/32" roll pins, and now I've got my handle-end fitting as you see it in the preceding photograph.

Next, I have to fabricate the hardwood handle. That's going to be a bit of a challenge.

Boring and Turning Wood Parts

Wood turning can produce some remarkable items, but it's a process that needs to be approached with a great deal of forethought. Every wood turning project has its correct sequence of operations, and that sequence needs to be thought out before beginning. An oversight in planning a job can result in a situation where a necessary step gets rendered difficult or impossible to do because a preceding step was taken without regard for its effect.

The wood handle-blank needs to be bored to accept the mechanical interface part that I've just made. The difficulty for me here is that my metal lathe is too small to take the wood handle-blank in its hollow spindle. If I could set up the handle-blank that way, the boring job would be a breeze. But I have to come up with another way to do it.

Another complication is that I decided I'd best add a brass ferrule to the handle for strength of the final assembly. A brass coupling nut for a faucet supply tube fitting will serve for a ferrule. What I have to work out is a sequence to do it all in, keeping in mind how each step will affect the steps that must follow.

Here's a point-by-point list of how it was done:

1) Prepare the handle blank for turning between centres -- spur centre at the headstock; live centre with a point only at the tailstock, not a point/cup style of centre. (The books will tell you not to do that; that the tailstock end must be supported by both the point and the cup of a woodturning centre. I'd go along with that if I were turning a porch column here, but what I'm setting up for will be a very light bit of work, entirely safely supportable by a point centre only.)

2) Mount the work and square off the tailstock end with a parting tool as far as the centre will allow. Turn a 3/4" diameter land to accept the ferrule.

3) Dismount the blank and set it up for boring on the metal lathe. Here's how the setup looked:

With a somewhat unorthodox use of the steady-rest, I managed to get around the lathe's small spindle hole diameter. This boring arrangement worked well. The steady-rest is supporting a 3/4" bore ball bearing, which in turn is supporting the work.

4) Bore 9/16" diameter sufficient depth for the hose fitting's barbed nipple.

5) Bore 9mm diameter sufficient depth for the threaded rod.

6) Dismantle the boring setup. Do a trial fit of everything. Glue it all together with J-B Weld and mount it in the wood lathe to clamp it up like so:

This worked out nicely in that the cup of my wood lathe's live tail centre just fits the inside diameter of the hose fitting. I have a perfectly good setup here for turning the handle.

7) Turn the handle blank to a uniform cylinder to eliminate any out-of-roundness.

8) Determine the length dimension, and imagine/sketch the profile to be ended up with.

9) Turn and sand. (N.B. This is a nerve-racking place to be at. By this point, you have a lot of work invested. One blunder with a chisel can ruin the whole thing. Be sober as a judge and proceed with caution.)

10) Part off and dismount the finished handle.

And here's the handle out on the job. A good example of how humble, dirt-cheap bits of hardware and material can be put to very good use, but by no means a claim that it's 'easy'. A lot of thought went into this, and a lot of resources were brought to bear on it. Beware of publications that make repair/fabrication work appear to be a breeze. It's not.



I appear to have the makings of a system here. A good thing, too, because our household just lost a frying pan handle to time and metal fatigue. Pictured below is the wreckage. Fortunately, no one was injured in the incident. A frying pan handle breaking while one is pouring hot bacon grease from the pan could be a frightful bit of business.

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Here I have the opposite case to the saucepan handle -- the handle still exists, but the attachment point at the pan is a ruin. If I can salvage enough of what was a threaded boss, I can fit a hose fitting cap to the pan and attach the saucepan's handle to it.

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Here's what I did to 'renew' the handle attachment boss, and prepare it to receive a new handle:

1) Saw off the boss remnant at an appropriate angle. (On an object like this one, you just have to eyeball and guesstimate angles as best you can.)

2) File the sawn-off boss smooth.

3) Drill through the pan's wall with a tap-size drill for a 1/4"-20 thread. (No. 7 drill -- 0.201" dia.)

4) Thread the hole 1/4"-20.

5) Bore through the centre of a machined, solid-brass hose fitting cap with a No. 7 drill and thread it 1/4"-20.

6) Round up a stainless steel screw and flat washer. Cut the screw to a length that's just a little longer than needed. (To cut a stainless steel screw, use a 1 1/4" diameter reinforced cut-off wheel in a Dremel hand grinder or equivalent. Stainless steel is hard stuff.) Do a trial fit of everything.

In the following photo you can see the prepared boss and hose fitting cap.

Next, I installed the screw w/flat washer in the cap very firmly with red Loctite applied, then I installed the cap/screw assembly in the pan's boss very, very firmly with red Loctite applied.

At the inner wall of the frying pan, I had a slightly protruding screw-end that needed to be ground flush with the pan's wall. I didn't want to do the grinding until the Loctite had cured, but I didn't want to wait for that overnight. I stuck the pan in the oven at 170 degrees Fahrenheit for about twenty minutes, then switched off the oven and let it cool on its own. (Heat is quite an effective accelerator for Loctite curing.)

I used the Dremel cut-off wheel to grind the protruding screw-end flush, swiped the handle from the saucepan and installed it, and here we are; the frying pan has a handle again.

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Now I have to make another handle. I hope this is the last of broken pan handles around here. Mass-production is not an interest of mine.

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