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Simplified Lathe and Mill Operation


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Since there has been considerable discussion of lathes, milking machines direct read outs, and CNC lately I thought it might be worthwhile to present some thoughts on the way that I have used machine tools.  For a number of years I have been interested in building a series of warships’ boats to a common scale of 1:32.  My comments apply to scratch building of these models. If you are say turning a set of identical cannon barrels your needs may be completely different.

 

Almost 20 years ago I bought a Sherline long bed lathe and milling column to replace an ancient Sears metal lathe that had died.  The Sears lathe did have two features that I thought that I wanted that the Sherline lacked: power feed, and a tail stock that could be set over to turn a taper.  As it has turned out I have not needed either of these features.  I have also found that that my work has not required a vast assortment of accessories.

 

Chucks and hold downs:

 

For most of my work, I use a 1/2 in Jacobs chuck attached to a Morse tapered shank that fits into the headstock.  I also have a Sherline three jaw chuck but have only needed to use it two or three times.

 

I also have a set of fractional collet chucks that are great for machining fractional sizes of brass rod.  If I have rod that matches one of these collets I use it.

 

Another highly useful and inexpensive accessory is a set of T nuts and hold downs.  While their application to the mill is obvious they can also be used for making fixtures, sometimes from plywood that can be clamped to the tool post. I recently needed to drill a hole longitudinally down an oar shaft to fit a handle.  Freehand made a mess of things.  I made a U shaped bracket from plywood and mdf, held down to the toolpost with T nuts.  A drill equal to the oar shaft diameter was chucked in the headstock and by moving the toolpost was drilled through the two uprights of the U.  This hole was now centered on the headstock.  A smaller drill equal to the handle diameter was chucked and by feeding the oar shank through the holes in the U bracket a hole concentric to the center of the oar shaft resulted.

 

Drilling:

 

Many projects involve drilling a hole, and for this a tail stock chuck is essential.  I also use the sensitive drilling attachment in the milling column whenever I can.

 

Turning: 

 

I have a vertical sanding machine with a 1in wide belt ( a linisher to our British friends) that I prefer for grinding lathe tools.  I find this to be easier to use than a bench grinder.  A parting tool is essential, but I also have a miniature one made from 1/4 in bar stock that accepts a piece of an Exacto blade. While the regular lathe tools are used for turning stock to a diameter or tapering, much detailing is done freehand with needle files.  

 

Calibration:

 

For much work, I find that cut and try using simple plywood gages is easier than using the calibrated handwheels.  For example I recently made a set of belaying pins.  The raw material was 1/16 in brass rod.  First this was chucked in a 1/16in collet chuck and the shank was turned to 1/32in, the diameter checked with a 1/32in hole drilled in a piece of thin model plywood.  It was necessary to turn a short section of rod to its required diameter, then loosen the collet and to feed out another section until the entire shank had been turned.  Otherwise it would have collapsed.  The head of pin was then shaped with needle files and the pin was cut off with a razor saw. With some ingenuity there are all sorts of simple gages that can be made to produce work of sufficient accuracy.

 

Roger

 

 

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8 hours ago, Roger Pellett said:

For most of my work, I use a 1/2 in Jacobs chuck attached to a Morse tapered shank that fits into the headstock.

Well, I am sorry to say, but this is bad advice - never use a Jacobs chuck or other drill chuck to hold workpieces in a lathe ! Drill chucks are designed to take axial forces only and the workpiece can work loose, when lateral forces are applied.

 

For safety and precision reasons my personal preference are collets. For larger pieces, of course, one would use the three- or four-jaw-chuck, but try to avoid using hand-held tools (chisels, files, etc.) near such chucks, as they can get easily caught by the jaws.

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I think this thread can be most useful to many of us "wana be" machinists. I would vote keeping this alive.

 

For example I have to machine some plexi-glass windows for portholes approximately 14mm in diameter. I have a modeler's vertical mill that I thought I could use in conjunction with a rotary table but I just can't quite get there mentally. Or should I be using another method such as a fly cutter? 

 

Joe

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When you say 'machine' what kind of operation are you referring to ?

 

Depending what your starting material is, there are several options. Assuming that you will be working with sheet material, how thick is the sheet ?

 

One option is to use a circular cutter in the mill. This is a bit like a fly-cutter, but the cutting bit is mounted vertical and the cutting edge aligned so that you can cut pieces with a defined outside diameter. Not sure you find a commercial one for such small diameter, you may have to make one yourself.

 

The second option is to use a 'hole-saw' or disc-cutter, essentially a tube with saw-teeth at the end. The inside diameter is the diameter of your finished disc.

 

If you have a lathe, you can also cut the disc roughly using a fret-saw and turn them down to the right size. To this end you have to chuck two corks, one in the headstock and one in the tailstock and wedge the Plexiglas disc between them. This is the classical method by which watchmakers turned watch-glasses to size.

 

If you have a lathe, you can also start from round stock, face it, polish the face and then cut of the disc.

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Welfalk,

 

In the case of my Sherline, I don’t agree.  First of all, the arbor that the chuck threads on to has a drawbolt that passes through the hollow headstock shaft that securely locks the chuck in place.  Without this drawbolt side forces would cause the chuck to come loose.  As to the chuck itself the workpiece is locked into the chuck with the chuck key, and the lathe itself is not intended for heavy cuts in hard materials.

 

Roger

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The mounting of the chuck is not the problem, its the jaws and the mechanism that tightens them - they are not designed for sideway loads, but only for axial loads. Below (left) is a cross-section through a key-operated drill-chuck. The serrated part exerts forces partially axially and partially radially that grip the drill, while the spiral in a 3-jaw-chuck only exerts radial forces. When you apply a radial force onto the serrated part, it has the tendency to splip axially, being a sort of wedge, thus potentially loosening the grip on the part, particularly, if it is not perfectly round. Also, common drill-chucks are not manufactured to the same tolerances (unless you have an Albrecht-Chuck), as 3-jaw-chuck or collets.

 

Drill Chuck

Source: https://www.mscdirect.com/basicsof/drill-chucks

 

It is better not to perpetrate bad practices, even though you may never experience any problems, say when working on wood or plastics. One day, by way of habit, you will chuck up a piece of metal, the cutting bit hooks and then the whole thing flies around. If you ever experienced how a work piece can be even ripped out of a strong 3-jaw-chuck (as I did once in 30 years working with lathes), when a cutting bit catches, you treat work-holding with great respect.

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