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View Full Version : An Idea That Works Well: Big Crank for Lathe/Milling



Paul Alciatore
04-11-2009, 03:26 AM
My lathe, like many, is used and somewhat worn. This makes it hard to adjust the gibs for equal performance at all points along the travel. In particular, I was trying to mill some simple parts on my SB and having a bit of trouble getting the finish I wanted. The problem was the small size of the ball crank on the lathe's cross slide. It has only a 1" radius from the screw to the handle. Any reasonable setting of the gibs makes for hard cranking at the forward end of the travel. So I came up with this:

http://img.photobucket.com/albums/v55/EPAIII/P1010005-1.jpg

It is made from a scrap of pine 2X4 and mounts on the original ball crank. A single set screw that tightens against the handle of the ball crank holds it in place. I rounded the end nicely so it wouldn't chew up the handle.

http://img.photobucket.com/albums/v55/EPAIII/P1010004-1.jpg

With turning radii of 2.5", 4.5", or 6.5"; selected by mounting it's handle in one of three holes; it makes turning the lead screw as easy as pie and as smooth as silk. Here is a picture showing two identical parts with the "before" surface finish on the right and the "after" finish on the left. I couldn't believe the improvement.

http://img.photobucket.com/albums/v55/EPAIII/P1010006-2.jpg

The ONLY difference in making these two parts was the handle. And, I even changed hands (twice) during the cut with no noticable areas in the surface finish. I should have thought of this a long time ago.

winchman
04-11-2009, 08:21 AM
Suggested reading:
http://bbs.homeshopmachinist.net/showthread.php?t=34277 "Where to buy ball cranks?"

Roger

tony ennis
04-11-2009, 10:28 AM
I think the idea is that he likes the leverage provided by the enormo-crank, and that it is instantly removable.

Paul Alciatore
04-11-2009, 02:29 PM
I read the thread about buying ball cranks just AFTER I made the large crank. Good info, but totally irrelevant. The ball crank on my lathe is in perfect condition and the wood crank is attached to it. My point is the original ball crank is too small for good work. A larger crank is really a tremendous help. It is both easier to turn and it can be turned a lot smoother so the surface finish is a lot better. It really was A LOT BETTER. I expected it to be somewhat better, but was truly amazed at how much. This is the real reason for my post, to share this discovery: Larger Crank = Smoother Motion = A Lot Better Finish.

And yes, it is instantly removable with a single set screw.

This wood version is just a quick proof of concept thing that I whipped up in an hour or so with scraps laying around the shop. Now that I see that it works so well, a nicer version will be a future project. Oh dear, another one of those.

QSIMDO
04-11-2009, 02:39 PM
That's interesting.
Looking at the "before" finish I get that sometimes on my mill with a power feed.
I've been thinking the gib might be too tight. Hope it's not the power feed going south.

x39
04-11-2009, 05:55 PM
Good thinking Paul. A friend of mine told me about a toolmaker in a shop he worked at that made a larger crank and dial for a Hardinge tool room lathe. It made very precise movements easier to make.

topct
04-11-2009, 06:35 PM
If it could be made to fold in some way.

I'm also looking at the carriage feed. For anything other than rapid traverse it kinda sucks too.

Paul Alciatore
04-11-2009, 07:48 PM
If it could be made to fold in some way.

I'm also looking at the carriage feed. For anything other than rapid traverse it kinda sucks too.

No real need to fold it, it comes off in less than a minute and the original crank is still there. I don't expect to use it for turning. Perhaps a smaller, large crank would be better there. And a larger dial.

I'm not sure what would help the carriage feed. I wonder if a stepper could be geared to it. Or a timing belt drive. Using the lead screw for a fine feed does work, but you have to set up the gears.

RichardG
04-11-2009, 11:30 PM
A friend of mine used a speed wrench with a socket on a project he was working on, worked great.
Richard

J Tiers
04-12-2009, 01:10 AM
Good idea there, "EPA"!

I also have thought about the carriage feed issue. I don't particularly like using the power feeds, since on this one it is the halfnuts for turning.....

For much of the fine feed turning work, the feed rate is more "pressure dependent" than it is controlled... due to the fast feed via the handwheel. But the larger crank is a bit less practical there.

So I have thought about gearing a worm to the carriage feed, so that a fine feed could be had with a side crank, which could be pulled out of mesh for fast feeding. A gearmotor could be used for a power feed without any reference to the threading feeds, similar to at least one well-known lathe (Hardinge? Rivett?)