Putting a break on a lathe. Safety...

Well here's a fun question. Place I just started working at today had a nice visit last week from safety inspectors. It's a VERY nice shop. Nicest and probably safest one I've ever been in so far.

Problem is these inspectors are saying that every lathe needs a type of break that stops the chuck in 1 or 2 revolutions. Dynamic breaks ? or something. Is it as simple as having the motor rewired for it ?

One of the lathe is a early 80's DSG about 17 or 20" swing. Bought new, beautiful machine. I don't have the exact model #. I'll get it tomorow.

Other lathe is a Hardinge HLV-H also bought new in early 80's.

They both take a little while to stop, as every normal lathe does. I've only ever seen 1 lathe that had the type of stop that they want. It was on a 20" Mazak and it was pretty scary to have it stop in only 2 or 3 revs. I usualy just turned that break off because I felt like it really couldn't be good for the machine.

There's a 3rd lathe but we probably won't do much to it. Unless it turns out to be a simple fix.

So what can be done ? How is it done ?
If its just about electric's we'll get a good electrician in who hopefuly knows about this type of thing. If there's nothing to be done at all. They say they'll shut us down and get a new machine. But we all know that finding a new machine as good as a DSG is pretty well impossible. Might as well go into CNC.

>Problem is these inspectors are saying that
>every lathe needs a type of break that stops
>the chuck in 1 or 2 revolutions.

That's insane. What state are you in (I'm assuming these are state inspectors)?

You could put a VFD on the lathes with braking resistors, but the best that will do will stop the chuck from rotating in 1 to 2 seconds, not 1 to 2 revolutions. There's a VFD forum on this forum site.

Paul T.

We just went thru this at work and the company opted for new "CHINA" machines. They won't let us bid on the old LeBlonds because they are afraid we will get hurt on them at home and sue them. So the 16" LeBlonds complete with collet's and chucks are sitting uncovered in the parking lot. We can't get anything from work now because of that new law that somone has to be accountable for everything they own. SO THANK YOU MR. ENRON...Bob
http://groups.yahoo.com/group/southbend10k/

I would be very highly unpleased if they got rid of these machines and I couldn't get the hardinge.
I better not think about it.

Before your shop makes any decision about this, where are these inspectors from? I think you'll have an impossible job trying to stop any lathe in 1 or 2 revolutions.

Doesn't sound like a reasonable request. I question what safety regs would support it.

Teach them the difference between a SAW and a LATHE. Apparently they don't know.

Do you know that OSHA requires no guard on a saw as long as it 2" diameter or under? You could rev up a 2" hss, solid carbide or whatever blade to a ZILLION rpm and it would pass OSHA printed requirements.

Inspectors came from the company(based in another country) who owns the place I work for.


Maybe if the chuck stopped in 1 or 2 seconds they would be ok with it. I know they want some type of break on it that will stop it as fast as possible. Whatever it is that some other machines have.

If I remember correct you are in Nova scotia. I have been in many shops throughout the province including where machine shop is taught at NSIT and have never heard of this requirment. I would suggest that you go over the inspectors head and talk to his boss who might be more reasonable. If they end up forcing the issue your best bet would be a variable frequecy drive . They can have an emergency stop feature which uses regenerative breaking and can stop a motor in less then a second.

He is in Canada. So OSHA is totally irrelevant. They have their own laws.
I know its technically possible, but its probably economically absurd.
I have a machine that has a electronic brake on the motor that will stop it within 1 degree of rotation- but its a very slow motor to begin with.

I imagine that they are thinking of an emergency stop, not necessarily something you would use all the time.

A VFD with a huge set of braking resistors (like a bunch of stove elements) might be able to dump some heat, but it would depend on the size of the load in the chuck at that moment.

What about rigging up a rotor and caliper assembly from an automotive application? I bet it doesn't take a lot to quickly stop just the chuck and spindle.

In this case it isn't about the requirements of this country or province. Just what the head company half way across the world wants. They make the rules.

They would probably be ok with putting VFD's if its the most affordable or simplest way to solve this issue.

They may have been refering to an E-stop that would stop the spindle in a few revs if anything bad was to happen. May not need to kick in every time while in use. Although I am under that impression at the moment.

I wasn't there when the inspection was done so I'll get more info.

SND you posted your second comment while I was wrighting mine . I had assumed that it was a provincial inspector that was gining you a problem. For my sake I am happy to hear that It was a company inspector so this foolishness is not likly to spread around the province. On the other hand since it was a company inspector you will likly have to comply. If you like I can introduce you to a lathe which is set up with a vfd incliding a emergincy stop. so that you could see how well it would work for your application.

I'd give them a cost of the VFDs and the time it would take to stop the machine vs the cost of a set of brand new lathes equipped with such brakes. I'll bet they will suddenly see these lathes as much safer as-is.

Agree that traditional manual machine tools can't be made "fuzzy-safe" unless access to them is denied and that safety inspectors have never been on the other side of the coin...at least the ones I have met.

Most of them get paid to "find problems" and damned be you if you stick your head up and put up resistance in the name of common sense.

That said, the original poster asked how this could be done.... if you are truly interested in having a brake, a magnetic friction brake (google Reuland) can be attached to nearly anything via this:

- buy another sheave with 1 or 2 more belt grooves than current. Install on the motor and put the existing v-belts back on (of course i am assuming that a v-belt drive is in there somewhere!!!)

- buy a Reuland brake...a 35 ft-lb version seems to work quite nicely in conveyance on motors from 5hp to 7.5hp.

- sheave the Reuland brake and v-belt this to the motor...there may be engineering requirements but it seems like a 1:1 ratio will be appropriate

- The brake releases on being energized, so I think you can run this off another electrical contactor (parallel in function to the motor starter). The general idea is that motor energized, brake energized (released) and motor de-energized, brake de-energized (applied).

This is a cockeyed setup involving probably $1000-1500 of components per machine plus the labor to install it, reconfigure the electrics, and redesign the v-belt drive, bracket for the foot-mount on the brake. But it will work.

The last option is again expensive...figure out what the frame size is on the motor...buy a "brakemotor" which has a similar brake attached directly to the motor's shaft...kind of an add-on end-can, and the wiring is usually integrated with a lever to manually release the brake (if needed). The can is definitely longer than the standard motor, but less work is required in all that belting and sheaving and electrical work. But they aren't cheap. Baldor has them.

-Matt

"I'll bet they will suddenly see these lathes as much safer as-is"

Depending on the individual(s) involved, if they are of the "clueless" nature, they can make the shop shut down. It has happened before and modern management doesn't have the balls to stand up to them and reach a reasonable compromise.

I agree it is possible do stop the lathe but... Just because the lathe and chuck stops does not mean the part being worked on can stop in that amount of time.
If it is small and delicate it may twist and break under the stopping load and fly off into the operators face. Leaving a small chunk behind in the chuck. If it is big and strong it may simply overpower the brake and or break some expensive internal drive parts.
Centrifical force and rotational torque build up slowly as rpm inceases. that force has to go somewhere for the motion to stop. The less time it takes to stop the higher the force. square of the speed sounds possible. Meaning stop in 1/2 the time increaeses braking force by four times.
Bill D.

There are friction brakes too...the Clausing Colchester 8000 series has a foot-brake pedal (a bar) that both disengages the clutch and also applies pressure to a friction material wedge.

The wedge presses against a v-belt sheave on the opposite end of the headstock input shaft.

To be clear, no v-belt runs in the groove but the friction material is shaped in the profile of a v-belt. (Similar in function to the spindle brake on a Bridgie milling head)

Works pretty well but one can make the spindle coast by just depressing the lever on the outboard end of the carriage....so it's not a requirement to use the brake-pedal-bar.

-Matt

Last post on this subject then I'll go away.

The Monarch EE has pretty impressive spindle braking performance...it uses two fat resistors and the armature is (electrically) "dumped" into series with those.

Even with an 8" 4-jaw "battleship" chuck and a decent sized workpiece it stops quickly and very quietly.

-Matt

just make sure that none of the lathes have thread on chucks or a good brake will mean the chuck will roll across the floor

That could be a problem with the hardinge as the chuck is held by a pin in a tapered slot. Stopping it too fast could loosen it.