All the making out tools you need for most jobs..
All the making out tools you need for most jobs..
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Combination set, in this case made by Starrett.
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Small protractor for laying out angles.
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Depth gauge.
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Your scriber should be quite long - at least 5" - 6" to be comfortable. A selection can be made with various body widths, turned from drill rod and hardened by the methods described in the appropriate section. Take some trouble to turn the body to a slim gently tapering point, the very end should be about 1/16" dia., whilst the point itself should be ground and honed to an angle of around 60 degrees. Trim the point by spinning it fast in the lathe and stroking the point with a flat Akansas stone at an angle that does not leave concentric marks. Take care of your scriber (keep it in a piece of drilled wooden doweling or a hole drilled in the edge of a wooden shelf), don't let it bang around loose or it will get blunted. A good test for the scriber, and also the points of your dividers, is that they should not slip if placed on your thumb nail held at a 45 degree angle. In use the marks should be very fine yet you should still be able to 'feel' the line if you run the scriber across it - hence the need for a very sharp point.
Toolroom-quality squares are all that is needed for marking out purposes, super high-precision squares costing 3 or 4 times the price will not offer any advantages for this job. So use the money you save and buy a smaller square in addition to the standard 6" one - a small square is really handy for tight corners sometimes. Even though squares are hardened and ground they are still very susceptible to damage, nicks and burrs are easily formed by knocking them against other hardened tools. Periodically run your fingers round all edges to check for such defects and correct any found with a rub from an oilstone.
You need good quality dividers than can be adjusted to fine limits - you may on occasion wish to open or close the points by just a couple of thousandths of an inch. So, buy a well-known make like Starret or Moore & Wright (though new examples of the latter leave a little to be desired in my experience). Nevertheless, avoid like the plague cheap imported dividers, and try if you can (if you wish to save a little cash) to buy good used examples. Very useful are small pairs of architect's dividers, I have a pair that opens to barely 1 inch and these are superb for small radii and stepping out bolt circles. Further, the points are replaceable and are easily removed for sharpening in the lathe.
'Odd-leg' or 'Jenny' calipers (not quite the same thing, one has a small stub to rest on a datum edge, the other has a simple flat end to one bent leg) are essential for marking off lines relative to one edge of the work, and are useful for quickly determining the centre of a piece of rectangular barstock by marking short lines from opposite sides and estimating the centre point by eye. Many examples of these tools use a simple stiff-hinge rather than screw adjustment, but properly set this is no drawback.
Your reference rule also needs to be of the highest quality. The criteria for this are that the divisions be engraved in the metal such that the points of the dividers can be 'felt' as they slip into them, also, at least 1 inch or so should be marked in 100ths of an inch and the engraved marks should be about 1/3 the width of a division. A photo-etched rule is essentially useless for serious marking out. My best rule is a Moore & Wright 18" rule from the combination set of the same make. I have several other rules and of the smaller ones the thin 6" rule (only 1/4" wide) that forms part of a depth gauge probably gets most use (a very similar one forms part of my protractor).
When marking out for centers it is useful to use a fine light punch to locate the exact position with a small 'prick', this can then be more easily located by the center punch for marking the drill center. Again, the prick punch needs to be very sharp so that it 'drops into' the fine trough of a scribed line. A cross-mark is much more difficult to locate accurately as the punch will only drop into one or other of the lines, the position of the other needs to gauged by sight. Use a good light and perhaps a magnifier if you need one. Always place the work on a firm base for punching (that doesn't mean the lathe bed!) and hold the punch vertically. Strike the punch squarely with a single blow, and adjust the diameter of the punch mark by using different weight hammers - don't try making a big punch mark with a light hammer. Automatic center punches have something to offer and are worthwhile (I never did find mine after losing it one day...).
For steel barstock it's useful to use engineer's marking blue to show up the markings better. It depends on your eyesight really, but certainly it is useful on steel which has been rubbed with emery as the scratches so formed tend to hide the scribe marks when they run parallel to them. There are many formulae for home-made marking blue, but it has to said that you are only ever likely to buy it once or twice in your life (it goes a loooong way!). I'm still using a tube I bought 20 years ago and there's still 3/4 of it left. Marking rough castings or cast iron is very awkward as the lines don't show up at all well, and here it's useful to use something like white emulsion paint or an aerosol can of cellulose undercoat paint to provide a base to show the markings better.
OK., that covers the basic tooling, so how do we go about actually marking a piece of steel? A useful example might be the frames of a locomotive. It's unfortunate that, should you take a new interest in this aspect of the hobby, you are suddenly faced with such a significant and critical piece of marking out at such an early stage. Never has it been more true than to check and re-check you dimensions than here as a hole for a main hornblock cut in the wrong place cannot be rectified. Anyway, take it slow and proceed with caution and all will be well. With all marking out you need a datum edge to work from, in the example given it is necessary to file one edge of the two pieces of steel quite flat and true. From this edge you will be able to mark off vertical lines using the square, and horizontal lines (parallel with the datum) using the Jenny calipers. Only where there is no other choice should the rule be used to scribe straight lines.
If you look at the drawing you'll see a complex set of dimensions, and you will be wanting to transfer that information accurately onto your piece of steel. Start with the most significant dimensions first - these would be upper edge of the frame, centers for the hornblock openings, and positions of the cylinder openings and bolting holes. Use your best dividers to mark distances (usually from the bottom-left hand corner) and check these are correct. Minor dimensions are often given relative to major dimensions so you will need your dividers again to locate these lines from those previously scribed. Normally, only the minimum number of dimensions are given to enable the determination of the positions of these lines and this frequently involves some mental arithmetic - perhaps adding or subtracting half a dozen other dimensions to find the one you want. Take great care here that you don't make a mistake. For the top edge of the frames it might be safer to use measured vertical distances joined by a ruled line rather than rely on the Jenny calipers off the bottom edge, the calipers are less accurate used wide open over longer distances. For the hole centers try to determine which are critical and which are not - the position for the weighshaft bushing (for example) needs to be accurate but those for rivet holes are not so important. Prick-punch the hole centers first to provide a more accurate locus for the dividers to work from, then go over these marks later with the center punch.
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The height gauge is extremely useful and once you start to use one you will wonder how you got by without it. The only disadvantage is their high cost, but as always it is possible to find used examples at a more reasonable price. My current one is a vernier type, and this replaced a digital height gauge in which the display failed and rather put me off the electronic versions. I have to admit the digital version offers advantages in that it is easier to set to zero and thus mark off differential dimensions, but once that display has failed that it - so much scrap iron. To mark a center line down a block of steel it is merely necessary to measure it with a micrometer, set half the width on the height gauge and run it's scriber around the block. In the example given earlier for the locomotive frames, the distance to the top edge of the frames would be set on the gauge and, with the steel on the surface plate resting against an angle plate (to hold it square) the scriber is run all the way across the top. Easy and quick. The second instrument, a scribing block, consists of a simple block and adjustable scriber point. It is set using a rule held vertical with the angle plate (or in a purpose-built rule holder), or by reference to another line or machined edge. Scribing blocks are quite easy to make for oneself, and could form a useful exercise for a quiet weekend. Personally, I find it difficult to achieve good accuracy using a scribing block, it is difficult to 'feel' the point registering in the ruler engravings, and the point is usually at an angle to the engraved lines making it very difficult to judge just where the point is. Still, useful for rough marking out.
A surface plate comes into it's own marking out un-machined castings as it's difficult to mark them using just a rule, square and scriber. One face is going to be a datum face and this is normally machined flat prior to marking out. It may well be that the datum face is a vertical face in which case it is easier to mount the casting onto an angle plate for marking out. Where a bore center needs to be located in a cored-out casting it is usual practice to plug the bore (or simply glue a scrap of brass sheet over the hole), this can then be marked and machined away as work progresses. Round objects can be mounted on V-blocks for marking, and a pair of these with clamps will be found to be useful not only for marking out but also for testing the truth of lengths of round bar in combination with a DTI.
Apart from V-blocks you are going to need a selection of parallel bars of steel to stand work on for marking. Commercial parallels are quite expensive as they are hardened and ground, and whilst I do have a couple of pairs of these I have also made several more pairs from lengths of ground stock (gauge plate - oil-hardening tool steel) simply cut to length. Perhaps not as accurate as commercial parallels but they are good enough for all but the most critical of jobs. These parallels can also be used on the lathe or miller for holding work in position for machining. Take the example of the casting again, it might be that the datum surface is not the lowest face, or that a lug extends below it preventing the casting resting on the surface plate. In this case the required edges would be machined and the casting rested on a pair of parallels of known dimension, and it's simple math with a surface gauge to take this extra dimension into account whilst marking off.
Remember your surface plate is just as much a precision instrument as your micrometer, and probably more delicate. It is NOT an anvil despite the fact it appears to me made solidly! Granite blocks are an alternative to cast iron but to my mind they are more susceptible to damage than are cast iron plates. The odd nick or scratch is bound to happen sometime during it's life but is not detrimental provided care is taken to ensure no burrs are left. Indeed, my plate is criss-crossed by deep grooves as manufactured. It's as well to keep the plate covered when not actually in use and a car rubber mat is a good way of ensuring it is well protected. The real problem with surface plates is to ensure no strain is put on them because, despite the fact that iron plates are substantial castings, they will warp if treated badly. Most iron plates should rest on 3 points, and these are usually cast lugs on the base - don't for any reason leave the plate propped up leaning against a wall, or resting on anything other than it's feet.
A dial gauge is a slightly different beast, it's dial is usually larger in diameter than that of the DTI, and the travel of it's fixed direction plunger is usually greater having a range up to half an inch or so. The standard plunger 'foot' is a hardened steel ball, but these are screwed on and can be interchanged with other 'feet' for special purposes. A useful variant is the 'elephants foot' - a wide flat foot useful for traversing along shafts (with the gauge set horizontal) where the ordinary foot, by virtue of it's point contact, would register a change with any slight movement in the vertical direction. The elephant's foot ignores such vertical movements and so only registers changes in the horizontal direction. Dial gauges have a fine cut rack connected to a complex set of multiplicative gearing which turn the gauge's pointer. They are far more delicate than the DTI which will stand some rugged use (relatively speaking). It is very important that the dial gauge plunger not worked rapidly from one end of its range to the other, or that it be subjected to abnormal vibration, and sideways pressure on the plunger is definitely to be avoided. Again, NEVER oil the plunger of a dial gauge, I found this out to my cost many years ago when I thought it was a good idea to do so, it wasn't long before the gauge started to stick and small movements simply didn't resister any more. I'm determined one day to strip it down and soak it in solvent!
(c) Chris Heapy 1996.
17.2 Using the Surface Plate
A surface plate is a definite advantage for speeding up marking out and improving accuracy. Moreover, for castings it is sometimes indispensable. To be useful the plate needs to be at least 12 inches square, mine is 18" x 12" and this gets a little cramped at times. Whilst it is possible to use a flat lathe bed for the odd marking job, rubbing rough cast iron castings across it is not a good idea. A serviceable plate can be made from a section of thick plate glass (about 3/8-1/2" thick) provided it is mounted at 3 points on a firm wooden base. At a pinch, it is even possible to use a piece of laminated kitchen worktop - again provided it is given good support and is not warped to begin with. To make best use of a surface plate you really need a height gauge and a scribing block, together with a pair of V-blocks and an angle plate.
Using a height gauge on the surface plate.
Simple home-made scribing block.
17.3 D.T.I. and dial gauges
A dial test indicator (DTI) is an important tool in work setting of all types, whether in the lathe, the milling machine, on the surface plate, or whatever. You cannot really do without it, and they are quite reasonably priced these days so there is little point in trying to make do without. I have several, and the cheapest (a Chinese import costing just 28UKP) is very accurate - at least as accurate as a 'Verdict' brand I have costing several times more. It is necessary to buy or make some sort of base, if not already included, and this could usefully be of the magnetic variety. Importantly, the DTI will come with several stub adaptors which attach to the back for mounting the gauge, and to be of use the DTI needs to be finely adjustable to many different working angles and heights. The working range of a DTI is quite small, usually the equivalent of 0.015" inch each side of zero, which is sufficient for the uses which are intended. The indicator lever is normally pear-shaped, made of hardened steel, and is set at zero on the scale when at rest. It is possible to move the lever round to a working angle other than vertical by a simple friction joint arrangement, thus it can be used to measure movements either parallel or at 90 degrees to the gauge body. For use in the lathe it is set up with the probe touching the chucked work, and any eccentricity upon rotation of the work will register as a deflection on the scale. The scale might be as fine as 0.0001", but even if it's 0.001" the divisions are usually so widely spaced that fractions thereof can easily be determined. Similarly, the probe can be brought to rest against the edge of a straight piece of work, or the machine slide itself, which traversed across will indicate deflection from parallel. It's useful to make up special spigots to mount the DTI in the drill chuck (for measuring runout of larger bores in work mounted on the chuck), and to mount in the milling machine chuck to check for parallel setting of work mounted on the table. NEVER oil a DTI for fear that it will find it's way into the mechanism where it will gum up the works causing it to stick.
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