Material extended out of spindle.

[zeusrekning]

I just remembered a few accidents I have seen after reading Bob Warfields post on connecting rods. This post is about the safety issues associated with extending material out the back of the spindle in your lathe. Every material type and size will be different, but if your material hangs out too far it can be very dangerous.
I had a 1" diameter Teflon bar hanging out of a Hardinge HLV about 18". This was stupid. I was going to cut it down but put it in to set the collet and forgot. It whip around instantly after turning the spindle on. No accidents it just hit a tool box behind the lathe. The other two times this happend were on the small CNC lathe where I currently work. I was 2ND shift lead and had a guy setting up the lathe to turn the ends on some 1" diameter 48" long conveyor shafts. This program was used on shafts that were only 12" long previously and he did not catch that the RPM was too high. For the long shafts we were to run the spindle speed slow and when we had short ones to do we turned the spindle speed up (another ignorant idea). I went behind him to do something and started it up ! The shaft completely ripped the chip conveyor control off the machine behind it ( a steel box approximately 8" x 12" x 4" bolted to the conveyor). A few months later I had a female operator running this job and she insisted on standing her parts to run up behind the lathe. This was so she could pull a finished part out of the spindle then quickly load the next one. So about every fifth part she was behind the lathe while it was running. I kept telling her not to be behind the machine but a she couldn't get it. Well I don't remember how it happened but I think she turned the spindle speed override up and a shaft whipped.
A 1" steel bar with 18-24" sticking out of the machine whipping is probably the most dangerous thing I think I have ever seen. If she had been behind the lathe the shaft would have easily ripped her in half length wise. BE CAREFUL The first thing I did after being moved up to shop manager was build a bushed steady that was anchored to the floor behind the lathe. It only took about 1 hour to build and install :
Never extend material out the spindle any more than necessary. If it is necessary to extend it more than a couple inches figure out a safe way to steady the work. I always turn the spindle all the way down, start the spindle then slowly work the speed up to my desired RPM to make sure it is safe. You should be able to tell when the RPM is too high. This is a long winded post maybe but this is the most common accident I have seen.
Tim

 

[BobWarfield]

Funny how you'd think 1" steel would be super strong, but it isn't strong enough!

That's why I was careful to say in my post that as far as I'm concerned, I don't want much to stick out the spindle at all--1" maybe. Any more and I'm going to be building a support system too and making sure that even with a support system there is a solid shell all around it.

I recently read an account on the PM board of an operator cutting 2" aluminum on a lathe. The setup was intended for 42" stock and they were making parts that were 6" long. Sure enough some guy loaded a 72" long bar, the rpm zinged up to 4500 rpm, and that bar was whipping around bent 90 degrees. Crazy thing moved the machine about 3 feet (a big heavy Cincinnati CNC lathe!) and took a divot out of the wall.

I'd be hitting the deck and crawling under a bench if that sort of thing was going on anywhere near me!

Cheers,

BW

 

[shred]

Is there a 'slow enough' for this sort of thing? A while ago I had to clean up the ends of some 1" steel tubing. Mindful of the 'whip' and a foot or more of tube out the back of the headstock, I used the slowest speed I had (~50 rpm) and they did fine, but maybe I just got lucky...

 

[rake60]

My mini-mill is mounted to a bench very close to the headstock end of my lathe.
I had a little "neighbor" job here where he wanted the end of a 24" long rifle barrel
crowned and threaded for a flash suppressor. (I've told you before this is Red Neck country!)
I wanted to work close to the chuck, and the area to me machined was less than 1" at the end.
A steady rest mounted to the mini-mill table supported the stock protruding out the spindle
very nicely. It was shimmed to the proper height, then being able to move the mill table in the Y axis
made the mounting of the steady rest less critical.

Sometimes it pays to have your machines all jammed together.

Rick

 

[BobWarfield]

Rick, that was a clever set up!

Makes me think that if I ever need to support something aft of the spindle, I need to concentrate on making some sort of base that will take my lathe's steady rest.

Cheers,

BW