My small lathe has been sitting idle in the shop since I bought it. I've not gotten around to making a suitable stand for it, as I had a bit of material shortage - so yesterday morning I ordered two 6m lengths of 50x50x5 angle iron; these were delivered late today, so now I can get cracking on making the stand.
In the meantime, there were some other issues to attend to. The lathe as I bought it is pretty basic, and one of the worst things is that it did not come with a tailstock drill. A fair warning to would-be hobby lathe buyers: Always make sure you buy a tailstock drill along with a lathe; it's indispensable!
A while ago I bought a small but good quality drill chuck for this purpose, but nobody in Windhoek could supply the suitable "shortened" MT1 arbor needed to fit the lathe's tailstock. Finding bigger tooling is easy here, but small things are rare, as there's no hobby market, so the chuck unfortunately needs a threaded arbor to boot, instead of a Jacobs taper. With our currency currently on a very low point in the international scene, buying one from overseas is a tad expensive for my taste.
So I decided to do what I always do; make my own
A C-o-C was drawn up, and a bit of 16mm silver steel (drill rod) cut:
To turn the Morse Taper (MT1), I did some calculations for using the Myford's top slide to turn the taper. I do have a taper turning attachment for the Myford, but that's currently already conveniently set for another project:
"Cross slide" in the image above should be "Top Slide"...
Anyway, to explain a bit of the above:
First off, there are multiple and easier ways to do this, but I felt like taking on a bit of an engineering challenge - that's part of the fun for me. It's also another bit of experience; with this method - if I can pull it off - I can turn pretty much any taper needed without a "reference" piece.
To cut the taper the top slide have to be set at an angle of 1.4287 degrees - not easy to set by eye on the top slide's rotary scale. A sine bar would have been nice to have here, but I must still make one. I have a nice precision protractor, but that's only accurate to 1/100th of a degree - and thus not quite good enough for this purpose.
One way is to use a dial indicator mounted on the top slide measuring against a parallel bar mounted in the lathe to get the "y" value, and to use the top slide's dial to traverse along the hypotenuse of the triangle formed by the taper ("z" in the photo above) for a known distance.
The longer the distance one can measure over, the more accurate you can set the topslide, especially for a very shallow taper like this, so I cranked the Myford's topslide in and out, counting the turns to get a good balance between where its on its maximum "in" (lock up) and "out" (before coming off the feedscrew and still have adequate hold in the dovetails) - this ended up in 25 turns. At 100 thou per full turn, that comes to 2.5" or more conveniently for me 63.5mm.
With a bit of trigonometry, it ended up that the top slide would be set at the correct angle when I could measure 1.583mm travel on the dial indicator over 25 turns of the top slide.
Still a tough call - I only have 0.01mm dial indicators, so I'd have to "read between the lines"
Enough maths, on to the setup. I set the topslide on an angle of about 1.5 degrees on it's scale, and mounted a dial indicator as square as possible to the lathe axis. If you look at the DI's tip, you'll see it has a bit of U-bent plate on it; I don't have different tips for my DIs, and this is a compromise to get a foot for measuring against a round shaft. The shaft I chucked up is nice and straight:
I know my 3-jaw chuck has quite a bit of run-out radially with the outside jaws in it (about 0.1mm!), but is pretty accurate parallel to the lathe ways (less than 0.01mm over 300mm) - but I checked the chucked bar just to make sure on the axial travel. Over the length sticking out and cranking on the apron, the DI barely moved, so that's still OK, and I don't need to turn down a bit of bar to get a more accurate test piece.
Then I locked the carriage down, and started by setting the DI to zero at with the topslide at maximum-less-a-bit infeed and on a zero reading on the topslide dial, with backlash taken up in the direction of it's feed:
After cranking the topslide out 25 turns, I got a reading of 1.32mm:
(The small mm dial on this CCC DI runs the wrong way :big:)
Too shallow a taper then, so I needed more offset on the topslide. I needed ~1.58mm, but the topslide pivots, so it's no good to just set it over to read 1.58mm - it has to be set to less than that. So I split the difference between the earlier 1.32 and the 1.58 - and I lightly tapped the crosslide over a bit more to get 1.45 on the dial. I then repeated this a couple of times, with the different readings - splitting the difference each time. I ended up with this on the dial:
A fuzzy photo with the focus in the wrong place
- a click on the above photo should show more detail - you want to look at the DI face. Earlier on, I mentioned that I'd have to "read between the lines" - and this is it - a reading of 1.58something - between what I would think 1.580mm and 1.585mm, and what I'd guesstimate at 1.583mm. That's as close as I can do in my home shop.
The next step is actually turning the taper. First things first, and the toolbit has to be set spot-on on height:
My crappy-looking very-newby-project height gauge still does the job adequately
The bit of 16mm silver steel (drill rod) turned down to 12.1mm diameter on 32mm length, and marked at 28mm for the end of the taper:
Taper turned part way down:
Time for a final check; some engineer's blue smeared on the taper:
I have a good quality MT2 to MT1 reducer - so I used that to check the taper; slid it on and turned it a bit:
The result - the taper is ever so slightly tighter at the big end, but that's OK by me:
A final finishing cut:
And the end counter bored 8mm deep:
I wanted as much taper as possible on this arbor, and the counter bore is needed to add an additional bit of travel on the small lathe's tailstock; every bit helps...
To turn the thread on the arbor, I need to mount it in the MT2 to MT1 reducer sleeve, and mount that lot in the Myford's head stock. There is a problem though; if I tap the arbor-in-making into the sleeve, I'd have a bummer of a time to get it out because of it's shortened taper. A bit of rummaging around my scrap bin produced an old 1/8" drill with a MT1 shank:
The shank on drills normally is not hardened, so I gave it a test with a file to make sure, and the file cut it, so I clamped it in the vise and hacksawed it off at an appropriate length:
A quick trip to the bench grinder to clean up the sawn end, and I had a nice insert:
With the insert lightly tapped down into the sleeve, followed by the arbor-in-making, and I can use a Morse key to remove both:
While I had the top slide set up on the lathe, I turned two more taper blanks from silver steel:
The original arbor was then fit in the lathe headstock, and tidied up a bit:
Next, turned down to fit the register in the chuck, a thread run-out groove added, and the section to be threaded turned down to 9.52mm (3/8"):
A quick test with a very light threading groove to check the thread pitch:
The thread turned for a good, but slightly tight fit in the drill chuck; it's better to have it a bit on the tight side for a chuck arbor:
Chuck screws on pretty much perfectly - I'm a happy chappy
:
Finally, in it's place on the small lathe:
Then I had a thought
... That's dangerous, but what the heck; I gathered some bits 'n bobs and one of the other blanks I'd turned up earlier:
The MT1 blank was drilled and bored for a push fit for the bearings - leaving the drill bit cone in the end of the hole intact:
I decided not to use the 5mm silver steel rod shown in the photo before the last one; instead I used some 6mm silver steel rod and turned a 60 degree taper on the end:
Then turned it down to 5mm for a tight push fit for the bearings:
The bit was then parted off - leaving a 2mm long 6mm step at the end. I then mounted it in a 5mm collet, and faced off the parted end, and with a big center drill put a cone on the end:
A quick brass spacer and a PTFE ring turned for a press fit in the body and a running fit on the shaft, and this is the lot together - ready for assembly:
The PTFE ring is just to keep swarf and dirt out of the works. The step left at the end of the shaft is so that I can use the shaft to pull out the bearings for servicing.
All assembled up with a good dollop of high-pressure grease on the bearing ball, and I have a small running center - I think it turned out quite well
:
Of course, it's a light duty running center, but I've needed one for a long time.
Couldn't resist a quick test; it works a treat
:
Wow - this was a mammoth post; I hope I didn't bore anybody to death!
, Arnold
