Hendey Lathe Thyratron Drive Diagnostics

Hello All,

The company I work for recently purchased a Hendey lathe, however the speed control seems off. The machine runs, but the control dial only changes the speed over a narrow band and the motor appears to have low torque. As a recently graduated sparky I would appreciate any recommendations regarding drive diagnostics. Attached are some schematics. I think it would border on criminal to replace the drive with an AC motor and VFD. As a note it is setup for a 220 single phase input.

Thanks,
Josh

Here are a few questions for you.
Did the lathe ever work right after purchase?
What is the supply voltage for the Thyratron's measured by you?
What is the nameplate voltage for the motor and what does it read when running when the speed knob is at half














?

JNelson94 said:

Hello All,

The company I work for recently purchased a Hendey lathe, however the speed control seems off. The machine runs, but the control dial only changes the speed over a narrow band and the motor appears to have low torque. As a recently graduated sparky I would appreciate any recommendations regarding drive diagnostics. Attached are some schematics. I think it would border on criminal to replace the drive with an AC motor and VFD. As a note it is setup for a 220 single phase input.

Thanks,
Josh

View attachment 228093View attachment 228094

Click to expand...

Josh,

It looks like there is more to the schematic in the second picture. Looks like the left part is missing or folded under.

Cal

Did the lathe ever work right after purchase?
What is the supply voltage for the Thyratron's measured by you?
What is the nameplate voltage for the motor and what does it read when running when the speed knob is at half

Click to expand...

The lathe functioned as described when we evaluated so I don't think so. The lathe has not yet been hooked to power in our shop so I am uncertain of the answers to the other two questions.

And here is the rest of the diagram.

Very Hard to trouble shoot with no power it may even work when you hook it up.

Diagnosing something like this from a distance is difficult enough and working from the pictures is impossible. You need a good scan or make full sized copies, not a bunch of segments, and mail them to some of us and we may be able to help. I have access to a large printer if you send a scan.

Second, do you have an oscilloscope? If you do, there is a good chance you can watch the signal through the system and see where it gets lost.

Bill

Is that the one from DMT? If so I looked at it a while ago, powered it at shop but just did not seem right so I passed. Glad you got it so its off my radar. If I would have bought it would scrap all the old electrics and replace with 3ph/VFD.
Bob

I now have a good scan. What is the best way to distribute it, as it is rather large? Thanks for your patience.

When the lathe was hooked to power to evaluate and run, it did not work properly so by the time it moves I am not expecting that to change.

Second, do you have an oscilloscope? If you do, there is a good chance you can watch the signal through the system and see where it gets lost.

Click to expand...

What kind of signal should I be looking for, doesn't the drive rectify to DC?

JNelson94 said:

I now have a good scan. What is the best way to distribute it, as it is rather large? Thanks for your patience.

Click to expand...

I'll PM you with my email address. I'd like to see it.

What kind of signal should I be looking for, doesn't the drive rectify to DC?

Click to expand...

It really acts like a big-ass lamp dimmer - it switches the voltage on with the zero crossing and off after a time determined by the drive speed. So the output looks like a chopped DC from rectified AC. The inductance in the motor tends to spread the waveform out some but you'll still see the 120hz bumps. So on the drive side you'll see something like a ~300VDC signal at 120hz for the armature - but there's going to be some bitchin' back EMF from the motor so be ready to snub that.

On edit: I forgot to mention that often a problem like this is a failure of one tube to fire. If you can get to the tubes while operating the drive you might look to see if both seem to be firing the same amount - you can easily see the glow in a well lit room. If one looks a lot dimmer than the other try swapping the tubes - if the problem follows the tube it might simply be a tube problem that's easily solved with a suitable application of money (I'd suggest the tube replacements, myself).

JNelson94 said:

I now have a good scan. What is the best way to distribute it, as it is rather large? ...

Click to expand...

You could put it on a Google drive or use DropBox. Then you can post a link here.

Do you have the manual for the machine as well? There may be a troubleshooting section in the manual.

Cal

Josh,
I acquired a T&G with the electronic drive back in 2005. I ordered a schematic for the electronics from Hendyman - DEDA-1-1 and received the identical drawing as shown above (22 by 35 inches)

The understanding I have with Hendeyman is that I can make a limited number of copies to assist other Hendey owners but Hendeyman does not want a pdf file out on the web. He makes a small profit by selling these drawings which supplements his retirement.

JNelson94 said:

I think it would border on criminal to replace the drive with an AC motor and VFD. As a note it is setup for a 220 single phase input.

Click to expand...

Not "criminal", just more work and expense than repairing the OEM DC drive or providing a modern DC drive so nothing mechanical has to change but the external wire terminations, if-even.

Best is usually to restore the OEM drive you have. They are not actually problematic. If they were fragile, they would have all been gone 30 years ago. They are actually very rugged and are superior to most solid state DC drives or VFD at not being affected by line noise, electrical storm spikes, heat, condensing humidity, and even airborne dirt that can mess with a VFD's fans.

Once repaired they can AGAIN last such a long time even the same owner has forgotten what he did a decade and more ago to troubleshoot a fault.

So.. take photos. Make notes. A voice recorder can run for a long time capturing remarks as "notes" when both hands are too busy or too dirty to write or aim a camera. Make the written notes later.

Store copies under your own roof. On quality paper as well as electronic media. You are the most likely person to have the next need of that information. Treat that poor sweaty bastid to a break! Time cometh, he may appreciate it enough to treat you to a nice dinner.. and even buy the beer!



This can be repaired, just as other Hendeys have been, not to mention many 10EE and other DC creatures.