Langmuir MR-1 spindle servo - 8000 rpm

Hi,

This is my first post so apologies if it's in the wrong place or wrong format etc.

I've been wanting to make a cnc mill for a long time now but have been struggling to decide on a format. I recently stumbled on a video of the Langmuir MR-1 cnc mill and that seems to pretty much tick all the boxes. They don't ship to the UK and I've already accumulated loads of ball screws, linear rails etc. over the years so I've decided I'm going to make one. I've made one cnc router in the past but I've never fully had the time (or space) to use it to it properly. However because of my job (freelance industrial designer) I really need to get something up and running so that I can make proof of principle mock-ups and prototypes quickly.

At this stage, the thing about the Langmuir MR-1 that I don't know how to do is the spindle. They use a 2.5kw AC servo that runs 0-8000 rpm and is rated at 240v. I would like to build a similar system but I don't know where to start sourcing the servo motor/driver or learning how to get it running.

So far I only have experience of using stepper motors and the Teknomotor spindle that I bought off ebay which was already wired up to a VFD. Electronics aren't my strong point - the control box for my current cnc was a carefully copied version of Joe's one that he kindly worked through with the help of Jazz (big thanks to you both. I am eternally grateful!).

https://www.langmuirsystems.com/mr1

If anyone can point me in the direction of a similar servo system - preferably one that has some documentation or youtube videos that I can begin to understand how to wire it up and get it working with Mach3 then that would be great.

Thanks, Jon.

Hi jon,

Welcome to the forum,

Ok well the spindle in the Langmuir is more than likely a custom setup that is in 2 parts. It uses a standard Servo motor that will be attached to a custom spindle cartridge, similar to how the Milling machine work but with an ER collet shaft and much shorter cartridge. However, I'm not sure how they are getting 8000rpm with continuous torque so I'm slightly dubious about their claims.!

Most servo's and especially large servo's in the 2,5Kw size have a rated speed/torque of around 2000 to 3000rpm with a maximum speed of 5000-6000rpm for a number of seconds, so how do they get a continuous speed of 8000rpm without a gear ratio, that would lower torque.????

How the servo drive connects up to the controller in its simplest form isn't any different from how you would connect to a VFD, you basically feed 0-10V speed reference and Run-Stop signals.
I the simplest form because Servo drives often have several methods of being controlled.? They can accept Step and Direction signals or Analog +/-10v. They also have several modes they can be run in, usually Position, Torque, and velocity/speed modes.

When being used with Step-Dir you would run them in Position mode, this mode is what you would use if using them to drive an axis. Analog +/-10v can also be used for position mode but step/dir is easier to use and setup so this is what most people would use if they have step/Dir signals.

Position mode is what you would normally use for an axis and wouldn't really use on a spindle other than if you needed to rotate the spindle to a specific angle, which you would do if you had an ATC for instance.

Torque and Speed modes are usually used with +/-10v where 0v is at a standstill and a positive voltage is CW rotation and a negative voltage is CCW.

Torque mode is pretty much what it says you control the torque with voltage, so if you wanted a constant torque the drive would try to maintain that torque level base on the voltage being given. You would use Torque mode for driving things like conveyors where you need to hold tension on a belt etc.

Likewise, the Speed mode is the same but the drive tries to maintain the speed based on the voltage given rather than Torque. This is the one you would use for a spindle as the drive will try to maintain the speed as the load varies.

Now the Langmuir spindle uses an ER collet so you can't run it CCW as it will loosen the collet nut, so in this case, then they will just use the analog 0-10v + output which is commonly provided by most controllers meaning it will only run in CW direction.
If you wanted +/-10v analog output you would need a controller which provided this and they are not common.

Many servos have the option to switch between modes using inputs, so for instance using a servo for a spindle with ATC you will want to switch between position mode and Speed mode. You will turn on Position mode to orientate the spindle when changing the tool and then put it back into Speed mode for cutting.
This is done by setting inputs on the drive high or low.


Now, to be honest, I'm very skeptical about what they are offering.? You might not know but others do know that we build routers and small Mills like these so I know the costs and time involved to build them and I don't see how they can make any money at the price they are asking.? At the moment they are just taking orders so it will interesting to see how many people actually receive them and when.?

Hope this helps and if need any help get in touch.

Edit: Forget to say, forget using Mach3, it's long in the tooth and no longer supported, Mach4 is very buggy and difficult to use and I wouldn't use that either.

I now use UCCNC control software and controllers from a company called Cnc Drive, They make both the software and the hardware so are designed to work together which makes them very stable and are very well supported.

HI Jazz,

Thanks for the detailed reply. It's gonna take me a good while to digest!

Thanks for the info on UCCNC, that's very interesting. I've been debating for ages what to use and I've never got on that well with Mach 3. I'll happily give UCCNC a whirl.

Regarding the price/claims of the Langmuir, I know what you mean having bought all the parts in the past. I too can't see how they can afford it. The other thing I have my doubts about is expecting people to pour the concrete into the base themselves. The metalwork alone will have little rigidity and the weight of the wet concrete will pull it into whatever shape it wants depending on how flat the floor is. Once it's dry that's it. I'm sure not everyone who tries it will get it right first time!

Saying that I love the concept and the videos of it cutting steel are jaw dropping. My old work bought a HAAS mill and they guy who operates it wouldn't dare take cuts like that.

I think I saw that they have a 1:2 belt step-up between servo and spindle. Gain speed but lose torque.

They also talk about a spindle encoder although whether that is in the servo or attached to the spindle I don't know. I guess that it doesn't really matter as they are not talking about rigid tapping - they show thread milling instead.

Quote:

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Originally Posted by Neale

I think I saw that they have a 1:2 belt step-up between servo and spindle. Gain speed but lose torque.

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Would make some sense but the speeds and torque they claim still don't stand up to me because the figures don't make sense.? Here's why.

Langmuir state a 2.5Kw and 4.5lbf.ft or 6.2N.m servo motor which would put it in the 110/130 frame class and this is where the figures go wrong to me.?

I'm taking it that they are not claiming peak values, which would just be wrong, so I'm going to use Rated values to compare.

Most servos at this KW rating, even quality units like Yaskawa, are rated at 3000rpm or less, often 1500rpm. The rated torque for a 2.5KW motor is typically around 7.5Nm or 5.5lbf.ft.

So using the motors rated values with a direct 1:1 connection we can't get near the 8000rpm they claim, if we go with a 1:2 ratio we still only hit 6000rpm but now the torque is half the rated and down to 2.75 lbf.ft and if we pushed the RPM to the claimed 8000rpm would drop closer to 1.8 lbf.ft.

However, I doubt they are using a 110 or 130 size motor because they are heavy things, plus they show what appears to be an 80 or 90 frame size motor which is like a NEMA 32-size stepper size and I've yet to see a servo at this size much above 1.2kw and again usually rated at 3000rpm.

So how they are doing it I don't know.? The figures just don't add up and I doubt they have had the motors built special at this money.!

Quote:

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Originally Posted by jon

The other thing I have my doubts about is expecting people to pour the concrete into the base themselves. The metalwork alone will have little rigidity and the weight of the wet concrete will pull it into whatever shape it wants depending on how flat the floor is. Once it's dry that's it. I'm sure not everyone who tries it will get it right first time!

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Surely the customer doesn't have to fill the base with concrete them selfs.? No way can that not affect the frame dimensions and like you say it will distort it to the point of being unusable. The frame would need to be poured and left to dry then machined flat again which all goes into what is setting my spider senses off about this machine because again at this money no way can they be doing this.?

Quote:

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Originally Posted by jon

Saying that I love the concept and the videos of it cutting steel are jaw dropping. My old work bought a HAAS mill and they guy who operates it wouldn't dare take cuts like that.

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He's a pussy then....:hysterical:

Yes that's right, they talk you through pouring the concrete here:

https://www.langmuirsystems.com/mr1/base

It's a good idea but as you say you need the tools to machine everything flat once finished. And stuff like that is not easy to come by.

p.s. I'll tell him you said that. (It's ok, he's only little.)

Quote:

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Originally Posted by jon

Yes that's right, they talk you through pouring the concrete here:

https://www.langmuirsystems.com/mr1/base

It's a good idea but as you say you need the tools to machine everything flat once finished. And stuff like that is not easy to come by.

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That's a crazy idea, no way can that not bend the base which in turn will pull the sides inwards affecting the linear rail surfaces causing the rails to at best bind or shift onto different planes in which case the machine can never be accurate.

Quote:

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Originally Posted by jon

p.s. I'll tell him you said that. (It's ok, he's only little.)

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That's ok I'll just show him how it's done on our Hurco beast, any way us little un's are the worst...:smiley_simmons: