Crashed my lathe

Using a carriage stop when power feeding or threading has to potential to do some serious damage to the gears, the lead screw, or the half nuts. One trick that I have used is to loosen the drive belt so that it will slip when subject to a heavy load. Threading is a relatively light load so this works. For power feed you can always cut away from the headstock rather than cutting to a shoulder.

I have the Chough42 ELS on my lathe and the stepper motor has fairly low torque. I could use a carriage stop there but the stepper would lose steps and would have to be resynchronized before I could resume threading. Still, better than crashing into the chuck.

Some time ago, I designed an auto release for the half nuts which would in theory stop feed within a few thousandths. However, since then , I replaced the OEM motor with a dc motor which can be slowed to 5 rpm if need be. I can thread up to the exact same point on each pass which removes the need for an auto release so it never got built.
 
90% of the time, threading is simple and straight forward. But there's that 10% (which declines over time) that can be intimidating. Air threading, ie, use a sharpy to print the thread is good to work on the skills. Another thing to try is cutting pvc pipe. Chuck up some 1/2" pvc pipe and practice until things seem like second nature. Once you get in the groove, it goes very smoothly. You are trying to build up muscle/eye/hand coordination, so you should practice it at very slow speeds first, so that your hands know what to do. Later, as you build confidence you can go faster.

But there's always one of those jobs you are working on that intimidates you. For that, I strongly recommend the reverse threading. It makes the job into a piece of cake. As time goes on, and you get better at it, the amount of times you get intimidated goes way, way down.

In the beginning, I used a spindle handwheel to do some threading. It worked well, but I found I rarely use it much anymore.

I agree with @RJSakowski I'd be wary of using a carriage stop, unless there was a clutch or some other slip mechanism.
 
I haven't tried it but reverse threading sounds like a good approach. A runout groove in the case of threading toward the headstock can be helpful, too. Gives you a little bit of leeway.
 
It seems to me that people get all hung up on doing things as fast as they can. Speed, speed speed. Is there some adrenalin rush to do things as fast as you can? If you are doing this for a living then you need to get things done quickly. But for us hobby guys time is meaningless. Who cares how long it takes to do something.

When I first started in this hobby I didn't know how to do anything. Absolutely clueless. I am still pretty clueless. I started with PVC pipe. And I practiced and practiced and practiced until I had the motor skills down pat. I did external and internal turning. External and internal threading. Turning and threading into shoulders. Both internal and external. I put in at least 40 hours. Maybe more. Whenever I had some free time I would go into my shop and practice.

I often use a carriage stop as a guide. Especially for internal threading and turning into a blind hole. The carriage stop is just a guide. It isn't intended to stop the carriage. I use a piece of paper to determine when to disengage the half nuts. As the carriage gets close to the stop I move the paper. When I can't move the paper I disengage the half nuts. Nothing else matters.

And there is no rush to do anything once the carriage is stopped. The lathe can continue to keep spinning. Its not going to hurt anything if you don't immediately back off the tool bit. If you don't believe me next time you are turning something after disengaging the half nuts got have lunch or watch an hour or two of TV. Your lathe will still be happily spinning away when you return.

The point of this is to practice until you have the motor skills down.
 
Turning to a shoulder is tricky even with lots of practise.
Relief grooves, turn by hand using a crank on the outboard end of the spindle or turn going away from the chuck have helped this learner prevent a second crash.
 
homebrewed said:
A runout groove in the case of threading toward the headstock can be helpful, too.
Click to expand...
I prefer a radiused runout groove to stop stress risers. I have had to machine new factory OEM bolts to include radiused runout grooves a couple of thousandths below the minor diameter to keep customers from breaking off the heads of M25 x 2, gr 10.9 bolts in high shock incidents, (i.e. Crashes). It actually strengthens the bolt.
 
Simple technique to prevent crashes: just turn off the motor just before the end of each pass. Then, pull your tool out from the work,
run the carriage backwards (you do have a reversing motor, don't you?) and start a new pass. Just have to keep track of your DOC.
Trying to do it the other way is too freaking difficult for a cave man like me.
 
RJSakowski said:
One trick that I have used is to loosen the drive belt so that it will slip when subject to a heavy load.
Click to expand...
That's actually a pretty good idea, until I at least get my system down. After all, I'm in there messing with my change gears... doesn't take but a second to lighten up on the tension of the belt. Obviously not enough for it to slip on its own, but enough that this would be the point that gives way if I bumble this again.
 
mickri said:
It seems to me that people get all hung up on doing things as fast as they can. Speed, speed speed. Is there some adrenalin rush to do things as fast as you can? If you are doing this for a living then you need to get things done quickly. But for us hobby guys time is meaningless. Who cares how long it takes to do something.
Click to expand...
You speaking in the abstract or are you making an assumption as to the speed I was running the lathe?
 
Speaking in the abstract. I often see people posting about how they get stressed trying to do things as quickly as possible. Especially when threading. Like I posted above I did massive amounts of practice when I started in this hobby. I practiced until I was comfortable doing things.

I treat my machines with a lot of respect. They can be extremely dangerous if you are not careful. I only wear short sleeve shirts and rarely reach over the top of the lathe when it is running. Another example. I made a spider for the outboard end of the spindle on my lathe. I only put the bolts in the spider when I am using it. To be honest those bolts in the spider scare me. To easy to get something caught in them.

I have only crashed my lathe once. No damage was done to anything My lathe is belt driven and the belts are probably a little loose.

I don't know what speed you run your lathe. I tend to run my lathe at the slowest speed that will get the job done. Especially when threading. For threading I run my lathe at its slowest speed. 28 rpm. For turning I try to run my lathe at the right speed and feed for the type of material. I only use HSS tool bits. You can run at slower speeds when using HSS. If I have any doubt as to the proper speed I error on the slow side.
 
You must log in or register to reply here.
Back
Top