View Full Version : Mandrel

12-14-2003, 09:35 PM
I've been making an expanding mandrel for my SB9 this weekend. It is intended for use with change gears as dividers, as a spindle crank and as a spindle brake. The whole point is that it gives an attach point for stuff on the spindle. This was way more difficult than I thought, but it has turned out well. It has some features that are not apparent. The main body is turned .005 undersize of the spindle. At the shoulder that bears on the end of the spindle is a slightly raised 3/8ths area that is a light, very light press fit into the spindle. The taper is 10 degrees so it doesn't lock. It seems to hold very well. More projects are in the works.




John Stevenson
12-14-2003, 09:47 PM
Nice Evan,
May I suggest you tap the tapered plug all the way thru and that way it can double up with a stud fitted to the large end as a back stop for repeatedly registering lengths.

John S.

12-14-2003, 09:56 PM
I don't have a tap long enough but it is a good idea. Hmm...


Sure, I can tap the large end separately. Then any size of 1/4x28 bolt can be inserted as a stop. Only thing is that I don't recall ever doing a job where I needed that capability. Oh well, you can never have too many tools.

[This message has been edited by Evan (edited 12-15-2003).]

Michael Az
12-15-2003, 01:52 PM
Nice work Evan.

12-15-2003, 02:11 PM
A "go-by" just in time. Can't wait to se the other projects in the works.


12-15-2003, 03:14 PM
Looks great, also I see your Southbend has lots of scrape marks, are they present on the entire bed?

12-15-2003, 03:51 PM

No, the scraping is worn off on the front vee way near the headstock. However, the way only shows about .002 wear in relation to the part beside the headstock which on a SB9 is scraped in the same as the rest of the bed and makes a good reference. That is something that always impressed me, that they would scrape in the entire bed even though some parts will never be used.

The part of the bed in the photo showing the nice scraping is the tailstock way.

I am the second owner of this lathe since it was made in 1937. The first owner who bought it new was a HSM same as myself and took very good care of it until he passed away in 1981. My dad bought it from his widow and brought it up to me as a gift. I have very complete tooling for it, two three jaw chucks, one 4 jaw 6", full set of MT3 collets, live and dead centers, bullnose center, center steady rest, dog plate and dog, MT3 drills up to one inch, drilling center, abouut six tool holders, three boring bars of various sizes and many other small goodies, some that I have made.

[This message has been edited by Evan (edited 12-15-2003).]

12-15-2003, 06:28 PM
Your Dad bought you the perfect gift,
You do allot of nice work on your lathe.

12-16-2003, 01:52 AM
Good idea and execution (as always) looks like it will prove a pretty versatile accessory!

12-16-2003, 02:26 AM
So that is a Mt3 or MT4 expanding taper?
Pretty neat idea, tighten it up, wont slip, dont need to leave a mandrel in chuck for repeatability. The Spindle taper on my chinese lathe is off by .001, Im sure my southbend is dead on.

12-16-2003, 03:11 AM
The mandrel in operation:

You can't see much of it, duh. I can now hold a change gear for dividing purposes on the end of the spindle. The set of change gears provided gives nearly all possible combinations up to 80. To do 100 I will have to make some strange Rube Goldberg (my hero) device that allows a 36 tooth to drive a 60 tooth gear. The aluminum stop arm fits on the end of the lead screw. The tooth of the arm fits the gear exactly (filing and then a couple of light taps with the small ball peen http://bbs.homeshopmachinist.net//biggrin.gif) so there is exactly zero play. The spring holder doo-dad slips over the change gear on the quadrant and keeps every thing locked in place. You can reef on the chuck and it doesn't go anywhere. I love tools.

One prime objective when I make stuff for this lathe is to NOT modify the lathe in any way. So far, so good. I'm waiting for the day when I think of some really cool device that will require me to drill a hole or something. That will be a drillemma


12-16-2003, 03:23 AM
Looks good Evan.

If you have problems with slipage you could contact cement some 1200grit SiC Mylar film to the outside suraces of the expanding mandrel. You can also buy this film in PSA (pressure sensitive adhesive) form from www.leevalley.com (http://www.leevalley.com)

I like the Carrage stop you made too.

[This message has been edited by Thrud (edited 12-16-2003).]

12-16-2003, 03:26 AM
Thanks, Dave. It doesn't slip at all, really solid.

12-16-2003, 10:34 AM
An easy way to get 100 divisions is to use a 100 tooth saw blade, fine plywood blade for instance. Divisions are plenty accurate.
Most people, when looking for more divisions than readily available with the gears at hand, build a worm driven indexing attachment similar to a dividing head, and go to division plates. Much simpler than compound gear trains, and more useful in the long run.

12-16-2003, 01:21 PM

That is the object of this divider, to make a real dividing head. Bootstrap method.

12-16-2003, 02:03 PM

[This message has been edited by pgmrdan (edited 03-08-2004).]

12-16-2003, 02:04 PM
The dividing head I made from Phil Duclos' plans was made without any dividing equipment. The only need for any indexing could be to gash the blank for the 40 tooth worm gear if you choose to make that. It is possible to make even this by careful hobbing in the lathe.
You might want to ask Santa for "The Shop Wisdom of Philip Duclos" from Village Press it is an excellent book for the HSM.

12-16-2003, 02:44 PM

If a circular saw blade doesn't have the right number of teeth, use a section of band saw blade. A 14TPI blade 25.71" in length has 360 teeth, and it will fit in a recess machined in a wheel about 8.25" in diameter. You can see it here:


12-16-2003, 03:26 PM

[This message has been edited by pgmrdan (edited 03-08-2004).]

12-16-2003, 04:17 PM
The idea is not original with me, just passing it along. I have seen the saw blade and bandsaw dividing attachments mentioned several times.
Terry Sexton wrote a short article a while back on making gears of any tooth count by running shim stock, or similar thin, soft metal strip through lathe change gears, and mounting on a wood blank backed up with bondo to make odd count change gears.
There are lots of easy ways out if you use your imagination.