My Speedway 7x12 Bench Lathe

Update: 2003.05.24

Note Well!
I am not a professional machinist, nor have I ever been one.  Prior to purchasing this lathe, I had used a metal cutting lathe precisely once in my life, for about two hours; that was in 1980, and the lathe I used then was a monster compared to this small, inexpensive machine tool.  Don't take anything written here as a recommendation -- in a machine shop, I'm not qualified to recommend anything other than following the manufacturer's instructions and seeking competent advice.

Anyone who's paying attention will have noticed that it's been some time since my last update here.  I've been busy, though not as much of my time has been spent making chips and parts as I'd have liked.  Life has a way of getting in the way of what we really want to do, doesn't it?

In the interim, however, I've gotten a small but useful assortment of working material together (three sizes of drill rod in addition to the lengths of aluminum and hot rolled steel bar, and aluminum plate that I already had), received more carbide tools and HSS blanks (though I haven't had time to set up to grind blanks into tools yet, perhaps I can do that this weekend), got a dial indicator, and made considerable progress in making an adapter to allow use of an old wood turning 4 jaw chuck I've had around on this lathe.

The chuck in question is a six inch, but unlike six in chucks made for metal turning lathes, this one isn't so heavy as to cause concern for the bearings of the mini-lathe; in fact, it weighs about the same as the 3" 3 jaw that came with the lathe.  It does have some limitations, however; first is that it's made to go on a threaded spindle nose, a thread that turned out to be 3/4" x 10 tpi, standard UNC bolt thread for that size instead of the UNF more common on threaded lathe spindles (for instance, Sherline and many small woodworking lathes use 16 tpi on 3/4" spindle diameters).  That caused me some hate and discontent when I finished turning a threaded adapter for it, only to find out it wasn't the thread I thought it to be.  Further heartburn resulted from trying to cut very coarse threads on this little lathe; the 16 tpi feed screw means that when I set up the change gears to cut 10 tpi (which isn't even on the gearing chart, as if that would stop me) the feed screw was turning faster than the spindle.  This made things interesting in two ways.

First, in cutting a thread an inch long, there's a very limited amount of time from the tool point first contacting the work until I'm through the thread and into the runout groove I'd turned to terminate the thread.  Second, although this lathe can be slowed down to an estimated 30 rpm, it has very little torque available at below 200 rpm.  The threading dial spins quite rapidly, also, and it can be tricky to get the half nut engaged at precisely the correct location on the dial to ensure that the tool matches into the previously cut thread.  The upshot was that I wound up taking cuts of .002" and even, near the end, .001" to avoid stalling the lathe, and then traversing the same cut several times to take up backlash and avoid overcutting on the next feed.  I didn't blow the fuse at any point, but that was most likely only because the controller was putting out so little power to the motor there wasn't enough draw, even when stalled, to exceed the 5 Amp fuse rating.

In the end, however, I was able to cut a thread that looked perfect, engaged the thread in the chuck snugly, and had no perceptible shake when threaded fully into place.  With the backing plate (similar to the adapter plate Frank Hoose displays on his site) already turned, it's now just a matter of turning to a press or shrink fit to join the steel thread insert to the aluminum plate, cutting a different thread on the other end to lock the part in place with a nut (even if the press fit should loosen), and mounting it up.

This chuck has its limitations, of course -- the jaws won't close to 1/16" the way the jaws in most small metal lathe chucks will do, and I'm not completely certain they're reversible (though I think they are, I haven't tried to remove them yet).  Conversely, however, I paid only (IIRC) $20 for the chuck, and I've had a good learning exprience and made a lot of nice chips when converting a piece of 3/4" x 3" aluminum plate and a short length of 3/4" drill rod into a threaded nose adapter for the Speedway lathe.

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