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Gingery Lathe and Accessories

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DavidF:
Do you ever get the feeling that VTsteam could be dropped off on the moon butt naked one day and then fly himself back to earth on his home built space shuttle in less than a week????

vtsteam:
Here is the lathe tailstock cast and ready to break out of the mold. The heat of the molten aluminum has burnt up the binders in the baked sand core. It is now just loose grains of blackened sand, ready to pour out of the hole. The core is till intact outside of the casting.

To the right of the tailstock you see the sprue -- the hole down which the aluminum was poured, and the gate which delivered the metal to the casting proper.

I didn't mention the sprue in previous casting photos, and I hope everyone realizes these are cut off, and not part of the casting. A second sprue like column of metal is also sometimes attached. This is called a riser, and it is a reservoir of molten metal that is used to feed the casting as it solidifies. Metal shrinks as it does so, and the riser is necessary to feed more metal to prevent a castig flaw called a shrink cavity.

vtsteam:

--- Quote from: DavidF on February 11, 2013, 11:29:03 PM ---Do you ever get the feeling that VTsteam could be dropped off on the moon butt naked one day and then fly himself back to earth on his home built space shuttle in less than a week????

--- End quote ---

I wouldn't want to leave all that cheese behind, though.

vtsteam:
Last picture of the evening. This is the lathe in its simplest form assembled to try out a test bar. You can see all of the parts cast earlier (and if you're interested you can probably pick out the pattens for each in the first photo in this thread).

The tailstock is in place, but not finished. It is only bored out but with no hand wheel or taper slide yet. A dead center of pointed rod is in place held by a couple of machinery collars. The headstock and a faceplate have been made, and the motor and drive are built. I haven't got photos of these things under construction, but do have more to say about them next time. You can see that many of the parts have been filed smooth -- this was before I had a milling attachment made up, or any chuck or work holding device other than the faceplate and a drive dog made out of some keystock and bolts (you can see it at the faceplate) for that matter.

The motor, by the way, was taken out of a clothes dryer. I went to an appliance store asking about motors, and they sent me out in back of their building to take as many as I wanted from mountain of broken or traded in washing machines and appliances destined for the scrapyard.

vtsteam:
The moment of truth.  :zap:

This was a test bar I was turning just after I had made and mounted the tailstock and its slide. The idea was to see how far off the tailstock (and lathe in general) was, and set the tailstock over to compensate for the error.

Errors would be a result of headstock bearing bore, headstock bearings, headstock base attachment position, tail stock bore and attachment position, accuracy of bed ways and accuracy of scraping.

When I was finished turning the full length of the bar, I measured the ends and middle with my dial caliper. The total taper was less than 1/2 a thou over the full 12" length of the bar. I couldn't actually read it, since it was just over the line on the dial by a hair. I was amazed that I didn't have to adjust the tail stock set over at all.

How was this accuracy achieved with primitive tools and practically no measurement of position or angular orientation when building the lathe? The answer actually lies in the clever way that the headstock and tailstock are bored, and this is one of the more fascinating things about building this lathe.

To bore the headstock on a Gingery lathe, you complete the headstock base slides. Even though it will later be fixed in place, the headstock still has hand scraped slides, gibs and gib screws initially. You then mount the headstock and adjust the gibs for a close sliding fit. You fasten the headstock to the apron, so that it can be driven -- as if it were the cross slide. The cross slide is not yet mounted on the lathe.

Next you assemble a second temporary headstock, made out of angle plates and pillow bearings -- basically a bolt together structure that will support a driven boring bar. The boring bar is made up out of rod and a piece of lathe tool and placed in the temporary headstock. drive pulleys are added to the boring bar, and it is spun by the lathe motor.

You will start the boring bar rotating, then engage the leadscrew, which drives the apron and attached headstock onto the boring bar.

Now te question comes up, how do you get the boring bar exactly straight, at the proper height and perfectly parallel with the bed ways, because this will have a critical effect on the accuracy of the lathe.

Well the answer is, you don't. You just do the best you can by making a little gage out of sheet metal that the bar rests on while you tighten up the temp headstock bolts, and that's it for measurements.

Yet the bore comes out absolutely parallel (within less than a half thou over 12") because of the way you are boring it! By sliding the headstock over the ways, the bore MUST be parallel with those ways. Even if your boring bar is slightly angled (and it won't be angled much) the bore will be parallel. The hole it bores may be very slightly elliptical, if the bar is angled but nevertheless parallel to the ways.

Not only that but the height is also not overly important either. Because after you bore the headstock, you are going to remove the temporary headstock, and replace it with the  freshly bored casting and fasten it down permanently. Then fit it with bearings in the bore hole, ad the boring bar and pulley and get it ready to bore the tailstock. You will do this in exactly the same fashion you bored the headstock -- driving the tailstock with the apron onto the boring bar as the casting slides along the ways.

This means that not only will the tailstock be bored exactly parallel with the ways, but also that its center height will exactly match the center height of the headstock, and their bores will be exactly concentric!

This is a wonderful thing. At least it was to me, at the time. Precision without measurement, simply by the nature of a procedure. Pure elegance. There are several of these moments in the building of a Gingery lathe -- the making of square angle plates in a rotational machine, the boring of headstock and tailstock concentric and parallel, and the making of accurate surface plates by the method of threes, and hand scraping to high precision by simply looking at the pattern of oil paint on a surface.

These are amazing things that we can do.

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