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Turret or Gang Tooling on a CNC Lathe?

May 16, 2017   //   by Bob Warfield   //   Beginner, Blog, Products, Techniques  //  12 Comments

This is one of the many topics that seems to engender religious fervor from one side versus the other.  I personally went through several hundred online articles and correspondences I’ve had with our G-Wizard customers about this choice.  For my upcoming Tormach CNC Lathe, I initially had ordered it set up for gang tooling based on my needs, but then hastily added a turret after several conversations with the turret afficionados just so I could write about and compare the two more fully, and I’m glad I did.

BTW, here’s a video on the topic that hits the highlights quickly:

For a more in-depth discussion, keep reading.

Let’s start with some definitions and the basic conclusion I reached after all these conversations and research, and then dive into the myriad details.

What is Gang Tooling and Turret Tooling?

GangTurretHybrid

While you can mount a conventional manual lathe Quick Change Toolpost (QCTP) on a CNC lathe, this is typically only done for Toolroom lathes.  For production lathes, tooling generally either mounted on a gang plate or on a turret.  Ironically, the picture to the right shows both formats in use:  each turret tool station has a gang plate mounted which multiplies the number of tools available from each turret position.

Pure gang tooling is the simplest option.  In this mode, the tools are mounted in a row on the lathe’s cross slide.  Accessing a tool is a matter of pulling back from the workpiece along the spindle’s axis to keep the tools from hitting the workpiece, sliding the X axis until the correct tool is in position, and then moving along the Z-axis back to start cutting.

A gang slide typically looks like this with the tools mounted:

The video captures the simple motion of the gang tool change as well as the speed of a tool change well.  Notice the two tooling formats–the rough turning tool is taking a big deep cut and is a typical square shank lathe tool holder.  The rest of the tooling uses a round shank with a flat that is more typical of gang tooling.  It’s more compact and sometimes you’ll even see a single holder mounting two inserts to be used for different tasks.

Now here is a turret in action:

That machine in the video actually has 2 turrets and uses one to hold a neat live center “tail stock” to turn that long thin part.  You get the idea of a turret from it though.  Lathe turrets are very equivalent to the rotary toolchangers familiar to CNC Mill users.

Which One is Better?

There’s a long list of pros and cons for each that we’ll get to shortly, but as promised, let’s start with the top level conclusion:

The choice of gang tooling versus turret on a CNC lathe has more to do with what kind of parts you’ll be making than anything else.  Gang Tooling is very hard to beat for smaller diameter short parts that don’t require a tailstock.  Turrets are hard to be for versatility and of course are a must have when you need a tailstock for your part.

In going through the many articles I researched on the topic, I frequently came across machinists who wished they could use their gang lathes for everything, but had turret machines for parts that were too long and thin to be made with a gang lathe.  In some ways, that almost means that the “competition” between Gang and Turret is a bit misleading.  Perhaps a better “competition” would be gang lathes versus Swiss machines.  The Swiss Machines use a guide bushing and turn from the end towards the headstock so that the work is always well supported with very little overhang to deflect:

SwissGuideBushing

In exchange for more cost, complexity, and the requirement of barstock that is more expensive because it has to be compatible with the Swiss bushing setup, a Swiss machine can turn parts that would be too long and spindly to do with a Gang Lathe.

Gang Tooling Advantage #1:  Speed

Let’s start with the Gang Tool Gang’s view on why their machines are better:

If the part can be made on a Gang Lathe, it can be made faster and more cheaply than on a Turret.

Remember, some parts just can’t be made on a gang lathe because you can’t use a tailstock–the gang tooling would run into the workpiece if it can’t get completely away from the workpiece, which it can’t because the tailstock is in the way.  There are some gang lathes that have retractable tailstocks, but retracting a tailstock each time a tool change is needed defeats the main advantage of a gang lathe–super fast tool changes.

The gang tool change is super fast because it uses slide motion to do toolchanges and requires no turret indexing.  If you think about it, the typical turret has to move to its tool change position before it can start to spin the right tool into place.  Once the tool is in place, it can then move back to cutting position.  This is almost exactly the same amount of motion needed for the worst-case gang tool change, but the gang tool has no indexing to do.  It moves to the tool change position (different for each gang tool) and moves the next tool into place, then moves straight back.  The most commonly used tools are placed in the center of the gang plate and they only move a small fraction of the distance to the furthest toolchange position the turret needs.

Hence the gang tool is nearly always faster.  You hear quotes from gang tool machinists like, “”The gang tool machine can finish the part, part it off, bar feeder advance the material and it’s well into the second part before the turret lathe can finish the second op.”

Gang Tooling Advantage #2:  Simplicity and Low Cost

Turrets are expensive precision devices with lots of moving parts.  Gang tooling is minimalist.  It involves a view blocks mounted on the cross-slide and that’s it.  The lathe’s normal axis servos and leadscrews do all the work for a toolchange.  This means gang lathes can often be a lot cheaper than turret lathes.  In some cases, shops buy 2 gang lathes for what a single fancy dual spindle turret lathe would’ve cost and feel they’re coming out way ahead.

If your part needs live tooling, perhaps to machine wrench flats onto a part or to drill a bolt circle on a flange, it is much cheaper to do with gang tooling.  Pneumatic spindles, cable driven spindles, and smaller electrical spindles can all be pressed into service if the lathe has an indexable C-Axis spindle.  Motorizing a turret drives up the cost in many ways because of the difficulties of transmitting rotary power out to the tool positions on a rotary turret.  It also drives up the size of the turret, making live turret tooling impractical on smaller lathes.

Gang Tooling tends to be cheaper while turret tooling tends to be more costly, but can be larger scale and more robust.  Some of the turret tooling standards require quite expensive tool holders in order to accommodate live tooling, among other things.

Gang Tooling Advantage #3:  Fast Setup

This is one that swings back and forth, but if you look at the ability to swap out an entire block of tools easily with gang tooling, it’s hard to see how setup can’t be done more quickly since it can be done offline or saved as an assembled block of tools for various jobs.  Here is a block with 7 tools installed:

GangBar

Swapping a block of gang tools is fast and puts all the tools needed for a particular part in place…

Alternately, a lot of gang work can be done with a basic set of tools and just changing one block that holds a twist drill of a particular size, for example.

Gang Tooling Advantage #4:  Accuracy

Simplicity and a reduction in moving parts eliminates tolerance stack up and various kinds of slop (backlash) in the moving parts of a turret.  The accuracy issue is all about achieving the correct centerline (Y-axis) position with the tool.  Once shimmed into place, or a custom bushing drilled for a twist drill, it’s hard to get more accurate and most turrets will be less accurate.

Another factor that gives the gang lathe an accuracy advantage is they’re used to moving shorter distances while machining a part.

Gang Tooling Advantage #5:  Robustness

This one is closely related to simplicity.  There’s not a lot to go wrong on a gang lathe.  Certainly a turret has all the wear points and parts to break of a gang lathe plus a whole lot more.  If you crash a turret, you may have an expensive repair bill, or you may simply need to realign it.

Turret Advantage #1:  Flexibility

Let’s turn to turrets before we start thinking gang lathes are the only way to go.  The #1 advantage of a Turret is flexibility.  You can use a tailstock with one, which allows much longer and skinnier parts than could be made on a gang lathe, though there are some tricks like box cutters that can help the gang lathe do more.

In addition to length, turrets allow larger diameter parts.  If you think about it, a gang tool setup needs clearance for the part to fit between any two tools.  This limits the diameter or the number of tools you can put on the gang plate.  The Turret lets you have your cake and eat it too because it leaves room for much larger diameter parts.

Turret Advantage #2:  Easier Programming

While experienced gang lathe users find programming easy, beginners generally will find turret programming to be easier.  With the gang lathe you have to worry about clearing the part for a tool change.  This can be tricky with different setups and part diameters.  Make a wrong move and a tool crashes into the part.

Also, gang users have to deal with the idea of both positive and negative since tools are on either side of the workpiece.  Turret users only have to deal with one sign and generally pick positive since that’s simpler and more intuitive.  Of course the fancier lathes will mount both a front and a rear turret, at which point they deal with positive and negative as well.

Turret Advantage #3:  More Tools

Refer to the top right picture in the article where every station on the turret has multiple gang tools installed.  That situation has been taken to the extreme and will be fairly complex to program, but having two turrets, or even just putting gang holders in a few turret stations still means more tools for the turret lathe.  Here is a 3 tool gang plate intended to go in place of 3/4″ or 1″ square shank tool holders:

GangBlockTurret

Foxwood Machine, the company that offers this product, says they created it for machines that didn’t hold enough tools or that couldn’t change tools fast enough.  I can see where putting the tools needed to drill and tap a particular hole and thread size onto one block like this might make setup simpler too.

Turret Advantage #4:  More Operations, Axes, and Parts Complexity

This one is related to the Flexibility advantage of Turrets, but they seem well suited to more complex machines that are set up with dual spindles, multiple axes, and other features to accommodate parts that would otherwise require multiple setups.

Turret Advantage #5:  Better Hogging?

Turrets can achieve better hogging just by virtue of being more common on larger lathes.  But, a dual turret machine can also perform the trick of using two cutting tools at the same time as portrayed in the turret video above.  Suppose you’ve got a tool that’ll take a 1/8″ cut.  Put one on either side of the workpiece using two turrets and have one lead the other slightly.  Now you’re taking off 1/4″ with each pass and the two tools are counterbalancing each other’s tendency to deflect the part.

This is a pretty neat trick that can really reduce cycle times.

Conclusion:  It’s Horses for Courses

While there is a natural human tendency to want to set up a competition that leads to a single winner, in this case it’s “Horses for courses.”  The choice of gang versus turret tooling is best made through a careful analysis of the types of parts to be made and which set of advantages those particular parts will benefit from.  If you don’t know what kinds of parts you will ultimately make and aren’t willing to accept the limitations of gang tooling to smaller diameter shorter parts, you’ll probably prefer a Turret.  If you want the simplest possible programming and a smaller learning curve, you’ll probably want the turret.  On the other hand, if you want the shortest possible cycle times so you can crank as many of the kinds of parts made on gang lathes out as cheaply as possible, look at gang tooling.

Extra: Check Out Our Turret / Gang Tooling Survey

Please tell us what you’re up to and see what your colleagues are up to as well.

CNC Lathe Turret and Gang Tooling Survey

 

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Turret or Gang Tooling on a CNC Lathe?
5 (100%) 1 vote

12 Comments

  • I like my GT-27, its GangTool. I have vids on YouTube showing it.

  • Hi Bob, at the risk of being torn apart, I could offer a few comments. I believe that for the types of varied work done in the jobbing shop or home workshop, and the wide range of diameters and lengths we are in need of processing, then I think the turret is the preferred option. Yes, the quick change manual tool post works, but is a poor third place when doing serious work.

    A good eight or twelve place vertical turret is a very expensive item, and when they index and lock they are very solid. Yes, I have looked at many gang tooled lathes, at shows, but almost without exception, these seem to be tooled for doing what we would have once seen produced on capstan lathes or single spindle cam autos. They do these parts very well indeed, but how many of your church flock, LoL! are into running thousands of tiny parts?? Almost none, me thinks. It has been very noticeable that virtually every professional toolmaker or jobbing shop that I am familiar with, has a multi position vertical turret rear mounted or sometimes multiple turrets. I think the double headstock and multiple turrets and live spindle tooling is probably getting far away from your following, and is certainly a vast financial investment, both in the machine as well as the huge outlay in highly specialised tooling libraries.Why is it, that no matter how many different holders and tip types we have, often times, we wish that we had another specific tool? I tend to feel that it is not viable for a large number of small shops to even think about the very exotic levels, because of the support they need and the drain on resources. Bigger shops find them to be a fabulous proposition. BUT, think about how many people are busy behind the scenes planning and programming and ensuring tooling is set and ready, and adequate supplies of consumables are on hand. Yes, it is awesome to watch those incredible Integrex type do everything machines running a part, but the workloads you need to keep one running two or three shifts a day is really scary! We are better served by perhaps diversifying and broadening the scope of our shops, than worrying over maybe saving ten seconds per part. It is the old case of “Horses for Courses!” CNC has given us incredible ability and opportunity, but I also wonder if indirectly it is one of the factors that has de stabilised much of your industry and our industry and sent it to cheap third world countries. Just have a look at who is buying up the six star class of machine tools and then cutting the legs from under us, causing further downsizing of our once stable manufacturing bases.

    Another thing that you do need to pay constant attention and care to, is what tool you put in which station!!!! You must be ever vigilant where pesky things like drills or drill chucks and drills etc are mounted, relative to turning and boring tools. Drills might well live 180 degrees away from the first couple of short rigidly mounted turning tools. Fast revolving chucks tend to make a real job of a long drill that comes into its jaw path. In practice, you find that careful planning will allow you to leave maybe three or four general purpose tools to just remain in situ as they get used all the time. It really is oh so easy to have an unexpected tool crash because it isn’t in use, and your attention is focused totally on the current tool and setting its offsets or whatever. Honestly, I think too much time is spent worrying about saving a few seconds, It is not really that important in our type of work. I believe it is more important to pay attention to turning out a nice well finished burr free job, that you can hand over with pride to the end user. And that does not mean making parts to tenths unless it is actually needed for genuine reasons.

    I am looking forward to seeing how you make out with your new “TOY!” They seem to make very nice machine tools.

  • Stephen, given a gang tool user beat you to the punch with the first comment, it would seem premature to assume they’re not part of the “flock”. In reality, the flock is diverse, and every time I do a survey I am reminded of that. It comes down to about 60% Pro and 40% hobbyist, and the Pro segment runs from 1 man shops up to the very exotic stuff you mention. Given we get 2 million visitors a year and are the most widely read CNC blog, that shouldn’t be too surprising.

    The other thing I’ll mention is the two contingents seem to be rabidly in love with their way of thinking. The Gang Tool guys wish every job could be done on a Gang Lathe and the Turret Guys as you say can’t figure out the value of the time savings of a Gang Lathe versus the elegance and flexibility of their Turrets. The controversy is what makes it fun to write about, at least in part.

    Cheers,

    BW

  • Interesting read! Personally the only type of lathes I’ve worked on are of the gang tooling type. They are great for production runs. On the other hand I’d have to agree they are a terrible choice for a job shop that might only run a few thousand parts at a time. Further they are almost useless if your job is only one piece.

    To be perfectly honest I think lathes could really benefit from CNC mill type tool changing, especially on larger machines turning bigger parts. Maybe not as complete turret replacement but rather as an adjunct to what is done now. It would certainly be interesting to see a tail stock that could change tools just like a mill can. You would solve many problems that are commonly run into with turret machines such as tool interference or the lack of tooling space.

  • David, check out the Willamin-Macodel 408MT ( http://www.youtube.com/watch?v=DyN3b1XxVpU ) it uses a CNC Mill type tool changer. That certainly would be fun to use. We also run a GT27 and it is an awesome machine. I love running it. However, the gang style tooling is a pain for us because we usually do very small production runs…10’s of parts and replacing half the tools every other job is simply not efficient. Even removing the plate and replacing it with another one takes longer than actually machining the parts. This is an instance where someone should have given a little more thought to setup time vs cycle time…

  • Tooling a CNC gang tool lathe differs greatly from turret type lathes. The pros and cons for each are very well shared here. Well! most of my experience is with turret lathes, but have used platen ‘ gang tooling ‘ lathes as well.

  • Most of the Swiss machines I have seen are gang machines so I am not sure how there is a competition there. Also Swiss machines can turn parts that are longer and more spindly than could be done on any other lathe even those with tail stocks.

    Does anyone know if there are special tools for turning on a gang lathe or are boring tools used? I’ve searched but not really found an answer.

  • Graham, any time the same budget dollars could be spent two ways there is a competition, so the competition is between buying a Swiss machine with gang tooling or a conventional lathe with gang tooling.

    There are all kinds of special tools for gang lathes, though you can also use boring tools. Check tooling catalogs for Omniturn or for http://www.gangturn.com (ECI).

  • I’m a big fan of gang tooling on CNC lathes simply because of the speed and cost advantages. As you have covered turret lathing has many advantages in its own right. Great article.

  • hi i know this a year old page but i thought i throw my 2 pence worth in,

    i work with a quick change turret on a hass tl1 doing mainly one off’s
    prototype work in the 70mm – 3mm dia range

    and to be honest i might just make myself a gang tool setup with my main 3-4 tools

    i will say quick change post comes stone dead last in speed and efficency

    i can program a mill to run programs that run for hours while programing others
    but the quick change tool post on the lathe means ill always be at the lathe wasting time and money

    ideally for the work i do i believe a proper atc turret so all my tools are on call as and when needed but extacting the paper to pay for such a item is as likely an event as me making the trip to the moon

    its certainly a horse’s for courses situation

  • Im just starting out on a cnc gt lathe, I have about 11 months experience and programming the gt is just starting to make sense, but my main question is if I were to start programming a turret style lathe what would be the differences in programming the two, I heard people talk bout calling for tools on a turret style and was curious on how u align tools at x0 on a turret style and if u have any examples of programs to show the differences between the two styles would be helpful , thanks great article

  • […] #9:  Turret or Gang Tooling on a CNC Lathe? […]

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