Installing a Logan QCGB. Logan 9B to 400 adaptation.

[Redlineman]

Matthew;

I must preface this by saying I really have no idea how the gearbox works. I stared at the pics of it upside down to see at least what it all looks like, but I still have no real understanding of what activates what, and I'm not experienced and/or smart enough to intuit its function just from staring at it. I don't even know what the parts are called. Assuming that the problem is internal to the gearbox, and having said all that;

My gut reaction is that there is a fundamental misalignment between the selector shaft (the shaft the handles are on) and the gear shaft (the shaft the change gears are on). When both handles are engaged, this creates opposition, where it does not with only one.

I can think of a few reasons for a shaft or gear sets to bind. One would be they are not running parallel. Two might be that the tolerances of the end bushings are actually TOO TIGHT, and do not allow the gears to seek their natural, comfortable angle to each other. A third might be that the tooth overlap of the gears is actually too high. These teeth are not designed to run against the valleys of their mates. It seems like you might be able to have one or some combination of all of these going on.

I reiterate that I don't know squat about this stuff. I only hope that my wandering may trigger a thought or observation that brings positive results.

 

[mjhenks]

Thank you guys. I spent some quality time with the lathe today and made some progress and some understanding.

Jim. I had the box back on before i saw your request so sorry no picture from the back side. I do have pictures in this thread of me rebuilding the box though that should the gear train.

Robert. With everything disengaged all spins freely but that is what lead me to figure out part of the problem.

So while the unit was on the bench and the lead screw was not end supported i noted that things would bind up so i know the lead screw alignment is affecting things. I mounted the box up and left the lead screw end support loose. I then ran the lathe and engage the half nut and found it would run better. So, first problem was alignment of the lead screw. I moved the saddle all the way to the head stock and engage the half nut. I then locked down the end support. A few tests showed that things were running alot better.

I also again re-did the alignment of the half nut. Problem 1 & 2 taken care of. Old fashioned careful alignment.

As i went through and tested the gears things were fine until i went to gear A and B. When i get below ~22TPI things just go south. The motor bogs down and the belt slips. After re-alignment and testing i have come to the conclusion that the motor is just not strong enough below 22TPI. The B gear goes up to 28TPI. 22-28 things are OK but i bet if i add the load of actually cutting material it will bog down. My conclusion right now is the little Logan 400 just does not have enough Umph to use the A or B gears. I will avoid that for the time being. That limits what threads i can cut but honestly i will use the power feed for cutting OD's more that threads. I will overcome the finer thread issues when i need to later on.

Now, i did not try going into the back gears which gives more torque. I will try that but still think the motor will bog down.

The other curios things i have is the half nut really needs to be pushed open with moderate force sometimes. Like it is sticking. Not sure if that is a wear in thing or not. Can't tell yet if it is a certain part of the lead screw (local screw wear) or something else. Do not think it is alignment. Interesting. I was used to a floppy half nut before the rebuild but this really feels like it is grabbing or being pulled in as you try and open it up.

Big picture is i am looking high and low for a Logan 9B-17 apron and saddle for power cross feed so i will likely not dig too much into it.

I am also looking for the nut that keeps the main apron handle on. I managed to loose that.

Scary thing happened today too while my middle son was watching me. All of the sudden parts flew off the chuck. Scared me. Glad my head was not over the chuck as two of the jaws went flying.... :talktogod: Thank you lord. One hit the wall and the other flew across the room. I did not realize the chuck was that far open as i never do anything that big. Otherwise it was opening up on its own as i had nothing chucked. That may be the case as i just rebuilt it and it is really smooth. With the constant start and stop the inner gear may have been turning as i started and stopped.

Long post but i feel i made some progress and understand what is going on.

Matthew

 

[Redlineman]

This is very good factual, archival information you have added here. Very helpful to others on the path!

:thumbzup3:

 

[mjhenks]

JimDawson.

Here are a few pictures of the inside of the gear box i located. The last one is all the parts layed out before restoration.







Matthew