Need back gear help, atlas 10F lathe

[Paulsv]

I'm relatively new to machining, and this is my first call for help here, tho I have been lurking for a while, and enjoying all of the knowledge you all are sharing.

I restored an Atlas 10F-54 some time ago, and hadn't used the back-gear much. The other day, I needed about 80 RPM, so I engaged the back gear, set the belt on the proper pully for that RPM, according to the Atlas Manual of Lathe Operations, released the pin in the bull gear, and flipped the switch. It ran OK for a few minutes, but suddenly there was a nasty crunching sound, and the bull gear and the back gear it engages were stripped of a number of teeth. :-\ I was not cutting on the lathe when it happened- I was just bringing the tool to the workpiece. I think the lever that engages the back gear may have popped out of its fully engaged position before the crunching sound came, but I am not sure. It was kind of half disengaged when I turned the lathe off.

I'm not sure what could have caused this, other than perhaps the gears weren't meshed properly- perhaps too much or too little lash? The gears were both already on the lathe when I got it, and appear to be original. When I reassembled it, in the original re-build, I did replace the shims under the brackets that hold the back gear shaft. Those shims are 0.010" thick. The back gear shaft turns smoothly, and has no play in it that I can detect, in any direction. Having just bought two new gears, I sure don't want to have this happen again. How do I determine the proper engagement of those gears? Are there different thicknesses of shims that adjust the engagement of the gears? Any other ideas of what could have casued this, and how I can make sure it doesn't happen again?

 

[GWRdriver]

Paul,
I don't think it had to do with shims or fits although you are right to pay attention to that. I also restored and still have an Atlas 10F (mfgd ca 1953). At the time of its last restoration (ca 1975) there were a number of missing teeth in the headstock gears. You are no doubt aware that all Atlas/Craftsman gears were die-cast in zinc-aluminum (Zamak - or Mazak in the UK) but what many people don't realize is that zinc-aluminum castings grow brittle as they age.

Improvements in die-casting metalurgy are continually being made so it is not a problem now but the older the die-casting the more embrittled it will have become. Collectors of pre-war toy trains, such as Lionel standard gauge, discovered this when after 25 years in the attic the die-cast wheels and other parts began to crumble. Add to that the tendency for the Atlas 10 and 12 back gears to "buck" against each other under power and you have the possibility of tooth breakage. Then there were always some (many?) folks who used the back gears to lock the spindle against an impact, say for removing a stuck chuck for instance, and sheared off gear teeth in the process. If you reassemble properly and don't abuse the mechanism you should have at least 25 years of time on the clock.

PS - I have always been told to run Zamak gears dry. Certainly a little lubrication would help BUT what is more injurious to Zamak gears than lack of lubrication is lubrication that attracts and traps airborn dust, dirt, grit, and chips. There will be less potential for wear without lubrication than with.

 

[Paulsv]

Well, shoot, I bought replacement gears on ebay, and while they were a lot cheaper, I now wish I had called Clausing to see if I could get new ones.

 

[Blogwitch]

Paul,

Like yourself I restored an Atlas 10F and it gave me many years faithful service.

I recognised a back gear problem very early in the restoration, in that under certain conditions the back gears were trying their very best to jump out of gear, and if they did, they were liable to do exactly what has happened to yourself.

Here are a few very bad pics showing just a few of the mods that I did to the lathe, to make it more rigid in operation and easier and safer to use. This is the order I did the mods in.

This was the backgear mod, I put a ball and spring detente between the fixed pivot and the collar on the shaft. Once the collar was located into the right spot, this cured forever the tendency for the backgear to jump out.

The next major mod was put a support under the fwd/rev end of the leadscrew. When you were cutting under heavy pressure, the gears tried to force down the end of the leadscrew and was leading to very bad wear on the gears. This cured it completely.

The other end of the leadscrew this time, a thrust washer either side of the break off bracket. This made a massive difference when cutting threads.

This one was more to do with safety. I found it was difficult to pull the cross feed knob in and out. So I replaced the knob with a grooved collar, and moved the operation onto the front of the saddle where it was easier to get at and operate.

Using a cheapo ratchet ring spanner, I fitted it to the tailstock clamp screw, so with the flick of a switch, it could be put into slackening or tightening mode.

These are just a few of the mods I did, a lot were never catalogued, but these might give you a few ideas to improve your machine.


Blogs

 

[Paulsv]

Some great ideas, Blog, thanks.


I spent some more time reading the manual, and in a totally different part of the manual from where they give the belt speeds, they say not to run the back gears at the higher speeds (i.e., with the belt in the faster of the two positions). I'm thinking that the mesh may have been too tight, and, with the higher speed in back gear, popped it partially out of gear, and with the brittle teeth, they just disintegrated. The new gear on the back gear shaft seems to have a looser mesh with the bull gear, which is what got me thinking about the mesh. I like the idea of a detent in the engaaging lever, and I'll look at that this weekend when I put the new bull gear on. So I guess I'll check out the detent idea, bolt it back together, run it with slower speeds, and kind of hold my breath. If they break again, I'll try to buy new gears instead of used. I might measure the clearance with the gears in mesh and post that with some pictures to see if anyone has any advice on that.

 

[GWRdriver]

under certain conditions the back gears were trying their very best to jump out of gear

This is the "bucking" I mentioned in my post. The back gears on an Atlas can also "ring" as the teeth mesh and on a long turning job this can become irritating. I managed to ignore it.

 

[Blogwitch]

Paul,

If you look at my picture, the casting with the handle stops on. I drilled into the edge of that with, I think a 3/16" hole, popped a spring and a 3/16" ball in there, with the ball only just entering the hole, being held out by the spring length. The collar is free to rotate around the shaft once the grub screw is loosened. I just drilled in it's edge with the tip of the same sized drill, to make the detent pit for the ball.

All that was done then was assemble everything, put the back gear into position, and rotate the collar until the ball located into the detent, and then locked the collar up.

Never any more problems with it.

The two lead screw mods, are the next major things that should be done. They really do stabilise the lead screw.


Blogs

 

[Paulsv]

Blogs-

Great mod, and thanks for the explanation. Sounds very do-able. I like the idea of the thrust bearings on the tailstock end of the leadscrew too. On the other end, I have a QCGB, and the leadscrew engages pretty deeply into it, so I don't think I have any instability on that side, but I intend to check it out. I like the operating handle for the cross-feed, too. Than knob can be very difficult to engage and disengage.

It sounds to me like you guys have identified the problem for me. I'm betting it popped out of engagement, and that trashed the gears. I'll work on it this weekend. Many thanks!