Why Would You Want a Lathe to Run Backwards?

Is it so the thing can be used in the Southern hemisphere as well ?

I dunno, but it sounds like a highly dangerous system. Which side of the lathe were you standing on ?

Sounds like your bro is a good sort, but he might not like you mentioning his personal hygiene . My own siblings would stand about laughing.

No mention of what make/model of lathe ? As ever, I'm posting on something I know nothing about (well, CR4 would hardly be interesting if I couldn't read up on such). My dad had a lathe of some sort, but when he died it wasn't really practical to get it shipped here from Milton Keynes.

dvmdsc, in BAhamas

Thanks for answer. I undwerstand the part about threading, but do exmplain what upside down work is.

Most lathe men work with the mandrin or shaft spinning towards them. Workpiece spins counter clockwise (view from the end of the machine). Knife tool is centered a little bit

"under" the center. Depending on speed, pass taken and nature of the work piece, the lathe reaction is to lift the shaft up to the bearing play. This causes jitter and vibrations and you see and measure that in the end product. When you work with hard steel bits, they can even crack and diamond knives lose their diamonds this way.

By letting the lathe turn the opposite way - clockwise - and installing your knife point a bit higher than the center, the reaction of the lathe is to reduce the bearings play to almost zero. The knife has to be upside down for this cutting.

Safer for the operator also, but less view on the work. A relatively worn out lathe can work with a far better precision.

And some new ones get 0,005-0,001 mm as tolerance used this way. These are about milling machine tolerances. But keep it between us.

GA.

I'm surprised that I was the first though.....

I am amused by some of the posts here.

Running the lathe backwards ... reversing the metal removal process, when you have cut too deeply. I have thought of that, but never did get it to work out for me. I do not have one of those metal-applying tools, plus you could cut your fingers, while feeding that curly strip of metal.

The photo posted of the wood lathe is incorrect. Its frame and supports are clearly steel, not wood. Anyway a wood lathe is a bad idea, the material is not strong enough, and swells in moist weather. Would it have warp-drive for humid summer days?

Same for a glass lathe... would it not crack if bumped? Does a glassblower, rolling his blowing pipe on his bench, as he smooths the hot work, consitute 'lathe turning of glass'?

Seriously, I find that reverse is best for cutting the inside of a surface. I like to look at the tool, and if it is inside a piece, reverse makes this simple. If I need to polish an item, I prefer to use reverse. My 8" chuck is attached by a simple right-hand thread, but I make it tight enough that it never comes loose in use.

David

You are not far wrong. In my apprentiship I was shown how to add material if the bearing fit I had just turned was a bit loose. You just put a few thou cut on the tool and ran the lathe backwards and as if by magic the bearing fit was tight.

It is also the only way to get most precision out of your lathe and less problems with

the cut-off material. Why?

First prize: the new Toss Lathe....... link.

I didn't see anyone talk about the chuck mounting method on your lathe. If it's a threaded chuck, you never want to be cutting with it in reverse, as there is a high probability that it will spin off.

But as Anonymous hero has indicated, for left handed threads.

I'm not quite sure what type of lathe you have, I'm assuming a wood lathe. I recall in my earlier years there where lather where you could turn larger object such as over sized bowls.

It's just that the thread had to be correct so your faceplate wouldn't fall off as your turning.

The there are accessories that you get for tool mountsfor this type of turning.

back in the 70's, our industrial arts dept. (Woodworking) in Junior high (7th-8th grade) had lathe like this.

Picture is only used for discription.

Also, if it is a wood lathe threading is done with a die.

If its a metal lathe there are plenty of application where it would have to run in reverse.

Wow, the words 'industrial arts' brought back memories. Nobody calls it that these days. Too bad too. The current vernacular seems to be calling it the trades or vocational studies. There really is art to the process of making things and it's a damn shame "we" have lost sight of that as a society.

I took every shop class I could throughout junior high and high school because I loved working with my hands and making stuff. One part of the day I was banging around with the rough guys in shop class and another part of the day I was in AP calc or physics with the rest of the geeks.

And yes, that lathe looks EXACTLY like the ones we used in shop class.

A glass lathe can run either direction. But it seems glass workers are a dying breed.

I guess you would have to call that "Not your ordinary lathe"!

Reverse is a standard function on most every metal working lathe and mill.

Its used for a lot of things. High precision surface grinding in one. Threading is another.

Inside dia threading and boring are often done backwards as well putting the cutting tool at the back side of the workpiece.

Think about it for a bit. If the workpiece is spinning counter clockwise facing the chuck and you cut a thread where will your tool be traveling towards?

Now put it on the back side and spin it the other way. Now what happens if you overshoot your threads?

On my smithy 1340I I use reverse in about 1/4 of the things I do.

Thanks for all the replies guys (even the teasing, sniff)
For the record it's a Myford 7 metal turning lathe. My Dad has tons of kit for it, milling attachment, draws full of collets etc.

I have a tiny lathe myself which I've used for things like turning an arrowhead out of Antler, great stuff to turn.
I was hoping to turn a new headstock shaft on the Myford, but my enthusiasm outstripped my expertise. I'll do it next time I'm down there.

Shame I didn't get some tuition off my Dad when I was younger, but once I left home it was too late. Mind he taught me how to strip down an engine and re-build a Vespa scooter which was what I needed to know at 16 years old. (E.G. Vital for exploring the world and finding girls!)

Del

It could be worse.

I had an idiot manger send back an order of 10 bandsaw blades along with a nasty note to to the manufacture because they were "manufactured inside out" and when put on our shop band saw the teeth would point the wrong way.

The thing was we had ordered 10 blades two weeks before and the box had shown up a day or two earlier. When us shop guys wore out the last blade we asked for one of the new ones.

At that point our manager said that when they came in he went to put a new one on and it was backwards. From there he checked all of them and they were all made that way so he said he wrote them nasty note regarding poor quality control and shipped the whole lot back for a refund.

BTW for those who don't know when bandsaw blades are shipped they are usually rolled up in a coil and you have a 50/50 chance of them flipping right side out or wrong side out when you uncoil them. If they land wrong way out you just give them a twist and pop them right side in!

"manufactured inside out"
Yeah, that had me foxed for a minute first time I came across the problem.
I put a blade on and the teeth were pointing up. I tried again and this time they were pointing down but at the back of the blade.

Then the penny dropped.
I popped it inside out and it was fine.
It took me ages to get the hang of re-coiling a blade when I wanted to swap from coarse to fine (I cheated and looked on Youtube to see how to do it). It's a good trick to show people who haven't seen it done.
Del

It took me ages to get the hang of re-coiling a blade

But it's a nice feeling when you do get it......... and in front of someone is a bonus.

Clearly you are overqualified for a management position.

But then you didn't reason out why metalworking lathes would have a switch to make them run both ways so.... Maybe not?

Managers on a power trip

What fun times and good memories at the workplace are made from!

I rarely take vacation for the first 25 years in the work force.

But, friend of mine got married in Colorado Springs, and my dad needed help baling hay, so I took 10 work days off, Went to the wedding, afterwards on my way to my dads farm, I stopped at work to straighten out some issues.... about 6 hours.....

Anyways the owners nephew (Jason) took off the same time, when I got back, no one notice he was gone, Me on the other hand had to put in 70+ hours/ week for the next 2-3 months just to catch up, (math does not add up).

Anyways when I returned, Jason also returned after coming back from vacation anounced he had to take another week off...... poor lil' feller, work must be hard on him.

Things run really smooth when they're gone.

A busted tool is not the worst thing that could happen, running lathe in reverse. Especially if your chuck or faceplate is threaded on lathe spindle as I understand was common attaching method for UK lathes. All it takes is a little tool biting, e voila, big iron wheel, chasing cat. S.M.

Very few metal working lathes have thread on chucks. Most have quick change cam lock types being that the machine is designed to run both ways at full power if needed plus it's fairly common to need to change out chucks during some machining processes.

I think this particular lathe, the Myford 7, has a screw-on threaded spindle of 1-1/8" and not a cam-lock chuck.

When parting off it is a lot easier with the lathe in reverse and the tool upside down.

Many lathes have the parting tool upside down and coming in from the back with the lathe still turning in forward direction. The parting tool is generally left in this position constantly with the cross slide bringing it into play when wound right out.

This only works if you have a rear tool post. Most older lathes don't have these.

If its a metal turning lathe then parting off is usually done in reverse as it puts the thrust of the headstock bearings into the bed (against gravity) and not the reverse. i.e. parting tool upside dwon.

Oliver Dunthorne

I have seen that, but the direction of force is opposite than what you describe.

The reason given for doing parting upside down is to let the chips drop off the blade, rather than accumulate.

I assure you it is nothing to do with the chips it is the force. If you do not believe me try it.

Oliver Dunthorne

The force will be exactly equal, only the sense changes. It is simple physics. Or are you talking about the load on the outer race of the spindle bearing?

The other issue is that it is really better to have the turning force applied downward onto the tool anyway. That way the force is transferred downward onto the top of the ways instead of lifting the carriage off the ways.

Any machine tool will kill you, do not turn one on if you do not know how it works. Most have no safeties on power or feeds because they are designed for people smart enough to use them and to take the dumb ones out of the gene pool. Go to your local voc school and take a night class in basic machine tools. Lots of reasons to run a lathe backwards, feeding out from the chuck, reversing an internal tap. Some machines are stiffer on the back stroke. Too bad Dad didn't show you how to use it, some knowledge can make the difference between a maker and a taker.

Any machine tool will kill you, do not turn one on if you do not know how it works.

There goes our appreticeship program shot to hell.

"reversing an internal tap"

Or an external die...

Hooker

Many lathe processes run backwards like threading, boring processes, to cut corners, positioning, to make grooves in back faces, to make chamfers at the exit of the holes, etc.

Actually, while not common, depending on the tooling and operation performed it is not at all unusually to run a lathe spindle "backwards". Many lathes, especially for production applications have an easily accessable lever to reverse the spindle quickly, while others like yours use a switch to reverse the direction of the spindle motor.

what do you mean "not common"? Many CNC machines for production has two spindles, for second spindle the machine run backwards. In this types of machines are very common processes.

I've been thinking about inventing a lawnmower that runs backwards...for when you only want to punish the grass for growing so fast, but not really cut it.

It could also punish you!

Yet another weak attempt at humor...

I was wearing my Monte Python hat, and imagining an earth friendly lawnmower that just bent the grass over; followed by "greenies" standing in line to buy them.

If you put the blade on upside down so the cutting edge is facing the wrong way and you reduce the engine RPM's it won't cut worth a darn.

It would use way less fuel too. Another big selling point!

There is also a technique where you are cutting a thread and instead of disengaging the half nuts, you reverse the lathe and run the threading tool back to the beginning.

That's the way I was taught. You just have to remember to pull the threading tool out with the cross slide so slop in the feed lead screw doesn't cut away thread you need to have.

Then, increment the compound in and run another pass. Rinse, repeat.

Hooker

Hi Dell,

The lathe function requiring reversing the lathe's rotation is screwcutting worms (for worm gears) and metric threads on inch leadscrew lathes (or inch threads with metric leadscrew lathes).

With same measurement threading the leadscrew half nuts are opened after each cut, the saddle moved to the thread's start, and the chasing dial viewed. As the job and leadscrew rotate the chasing dial indicates when to re-engage the half nuts. This system is only workable for simple ratios between job and leadscrew pitches, so with your inch based Myford cutting metric threads it is best to keep the half nuts engaged to avoid cross threading. To return the tool to the thread's start the lathe has to be reversed.

You can use a crank handle in the back of the lathe's spindle but electricaly reversing is usual.Happy turning, Zaf.