A Logan Lathe Story

[Bernd]

I had a big surprise this past Saturday from my Logan lathe.

I was going to finally finish another long "Round-tuit" project. It's another Guy Lautard project, a
"finger plate". All I need to do was make the rocker clamp and the 5/16-18 threaded post used to
clamp down the "finger".

For the newer memebers who have never heard this term or of this tool, here;s what it looks like.


I was going to finish it up by making the 5/16-18 clamp rod in the center of the tool. Guy suggested
using a ready rod. I didn't have that size or a die to make one so I decided I'd single point it using the
Logan lathe. I set up the tool put the levers in ther proper place on the quick change gear box and
took a light cut to make sure I had the right number of threads per inch. Imagine my surprise when I
counted 20 threads instead of 18. Yet the lever was in the right hole for 18 threads. It does go into
the hole a bit hard ever since I got the lathe. I quickly checked to see if it would cut a 16 thread. Which
is on the left of the 18 thread and then on the 20 hole for a 20 thread per inch. They were fine. So what
was going on.

To make a long story shorter,I decided to remove the gear box and check the gears.

Here's a diagram to help better understand what's inside a QC box.



The left lever selects the letter and the right lever picks the actual thread. So if the left lever is in the "B"
position and the right lever is in the 18 postion you will be using the gear that I've marked "wrong gear"
and hopefully cut an 18 threads per inch thread. Since that gear is the same size as the one to the right of it,
it cut a 20 threads per inch.

I wrote about my plight on the Model Engineering list I belong to and Scott Logan of Logan Actuator Co. is
a memeber. He e-mailed me back said he had one in stock. I recieved an order forum and will be sending out
the order Monday.

I think what happened was that the lathe got rebuilt at one point in time and somebody put the wrong gear on.
Scott even said that it would have never left the factory like that. He also provided me with a bit of info. The lathe
left the factory on May 28, 1971 and was sold to Falk Mill Supply in Rochester New York. It's nice knowing a bit
of history behind the lathe.

So now I'm without a larger lathe for a while. Guess it's back to using the Sherline lathe to make some small parts
for the up coming project.

Bernd

[dsquire]

Hi Bernd

That could be a very frustrating surprise. Good thing that you decided to check the gear box. It's amazing sometime how things can go unnoticed for long periods of time without creating any problem. Now that you know about it would affect how you used the lathe everyday as you would always be thinking about this gear. Glad to hear that you have a replacement gear on the way. 

Cheers 

Don

[Bernd]

Ya it was a bit of a surprise. I had single pointed 20 and 13 threads per inch on the lathe and they wored fine. I can remember wondering why the lever wouldn't go into that one position easy. I tried it several times for a feed rate but never tried to cut a thread. So I never used it until this last Saturday. I've had the lathe for quite a few years now. I guess nobody ever single pointed threads on it.

The best part is that it's nice to know there are parts for it on the shelve ready to ship. I won't want to repair to many lathes though. The gear goes for $50.52.

Hopefully I'll have the gear by next weekend.

Bernd

[andyf]

Bernd, I've got a similar story. I bought a new Chinese lathe 4 years ago. It's an imperial rather than a metric version, though the only truly imperial thing on it is the leadscrew. The cross-and topslides both have dials marked in thousandths, but their feedscrews are each 1mm pitch.

After all this time, I have only just noticed that, while the cross-slide dial is graduated OK, if you accept the 1mm = 0.040 fiction, the one on the topslide is etched to the effect that one division = 0.001" but has 50 divisions on it. So one revolution of the dial only gives me about 0.04", not 0,05" of movement. 

Actually, it's never caused me any trouble. This must be because the only time I take any real notice of the topslide dial is when I'm screwcutting with the topslide at the appropriate angle, but I use the "work to zero" system where you get the cross-slide to do the Pythagoras stuff, so the only topslide mark of interest is the zero one.

But noticing it a week ago has started an itch which can only be assuaged by making a new dial - the existing one is a collar which is too thin to stamp numbers on without causing bumps on the inside.

Andy

[Bernd]

Andy,

Check this page on my web site. I think might like it. Mini-Mill

Bernd

[andyf]

Hi Bernd,

Ha! You had the same problem as I did when fitting a handwheel and dial to my 12 TPI lathe leadscrew, which moves the carriage 0.083333" per turn. Well, it would if Chinese leadscrews were that accurate, which I doubt.

I worked round it with gears:

 http://andysmachines.weebly.com/leadscrew-handwheel-and-dial.html

When I make a new topslide dial, I think I'll put new graduations on the leadscrew one. As the pics show, the divisions vary a bit in size, due to backlash in the changewheel spindle indexing.

Sorry about the  . This thread is about your gearbox, not my dials.

Andy 

[Bernd]

Quite alright Andy. It's not that far off  .

Sent off the order today with the $$ to the Logan company and hopefully I'll have it sometime next week. Hopefuly this week but I don't think our snail mail isn't that fast. 

Bernd

[75Plus]

Bernd, I just visited your mini mill site and found that you have made a mistake in your assumption that one turn of a 16 TPI lead screw moved the table 0.063". It actually moves the table 0.0625" per revolution and exactly one inch in 16 revolutions. It was having to deal with the half thousandth that promped me to upgrade to the 20 TPI lead screws.

Joe

[Bernd]

Are you picking "nits" here Joe. 

Sorry,    Couldn't resist that one.

      

Bernd

[Bernd]

Well I got the gear today at 3:30PM. Had it all back together after dinner and gave it a quick test.

Yup, it now cut's 18tpi when set at that lever position. One happy camper and cudo's to Logan Actuator Co.

It's abck to finishing that finger plate and on to other projects....oh, that includes the kitchen cabinets. 

Bernd

[dsquire]

Well I got the gear today at 3:30PM. Had it all back together after dinner and gave it a quick test.

Yup, it now cut's 18tpi when set at that lever position. One happy camper and cudo's to Logan Actuator Co.

It's abck to finishing that finger plate and on to other projects....oh, that includes the kitchen cabinets. 

Bernd

Bernd, you must have known that I was going to see this. Oh well, they say that the best defense is a good offense. 

Glad to hear that you got the part and now it's working the way it was supposed to work. 

Cheers 

Don

[Bernd]

Of course Don, I knew you'd make some comment on that.    That's why I added that.