5-axis for machining metals

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    Default 5-axis for machining metals

    Hello community

    I am going to design and build up my project for 5-axis machine, and I would like some advice's, as I avoid to cockup the build with something I simply overlook.

    What I want to cut:

    I am heavily involved in Mountain Bicycle industry, and I want to create some of my designs. Material in question is 7075-T6 aluminium, and its a pretty tough cookie.
    It should be rigid, and reliable, so majority would be used quality parts. I would include Isel ATC spindle.
    All of the axis will be ballscrew, while linear rails blocks will be 25-35 mm.
    Motors will be steppers, as there is no need for Servo ones. They should be quality build, I was thinking the Japanese ones.
    560 Ncm / 6.0A Sanyo Denki Stepper Motor, Stepping Motors.

    80x80 thick extruded aluminium profiles will be the basis for the machine, and I am thinking making a classic router, adding the 4th and 5th axis to the table.


    Drivers will be either DMS-481 digital stepper motor controller and driver.
    or Gecko http://www.geckodrive.com/geckodrive...ves/g203v.html.

    Working area will be 200x200x200 mm.

    For not I am only good with Mach3, and my programming will be in HSM and SolidCam.

    My recent experience with cnc machines goes a long way, as I have built one machine before. End bits will be Iscar and Vfh, which are more then enough.

    I am starting to design it from scratch, and I would very appreciate your input, as I have no experience with 5 axis. 5th axis which can be found on Ebay for 400-500 USD could be good for design sample, and I am considering the similar approach but very much over sized for rigidity.

    I will update this thread with my designs and my progress.

    Cheers,

    Marko

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    Last edited by lopata; 10-03-2015 at 06:42 PM.


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    Default Re: 5-axis for machining metals

    I'm actually trying to figure out why you need five axises for bycycle parts but let's skip that for a moment.

    The first thing that comes to mind is that routers aren't milling machines, in general they don't have the mechanical integrity to compete with a well built milling machine. That being said there is the potential here to do a build that is a bit more than the run of the mill home built machine seen often in these forums. In any event you need to nail down the size of this machine first, as the working area dictates what is possible.

    As to the frame it should be steel weldments made from relatively large square tubing. Check out one of the stickies where much is discussed about gantry beam sizing. What sort of precision you will need will dictate the frame design. My thought is that if you are going to do sprocket stacks and the like, you will want a bit more precision than is seen in a wood working router.

    Now that I think about it, it may be helpful to describe what you expect to be making on this machine. Bicycle parts covers a wide territory it is very possible that I'm leaning towards part more demanding to make thus the expectation of a more rigid machine. Maybe a description about what your current machine is doing and how this machine will supplement it is in order.



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    Default Re: 5-axis for machining metals

    I think if you want rigidity a D your work cube is only 200x200x200_ you may be able to build a better and more rigid machine with another method. Perhaps epoxy granite inside a metal frame. It certainly will help since you will have 5 axis's of force to contend with pushing and pulling in various directions.

    It sounds like you want to use a trunion table style 5 axis setup. This will be a cool build for sure. One thing to note is that rotary tables that don't cost a small fortune have a fair amount of backlash. And aren't designed for continuous cnc operation and will suffer from premature worm gear wear and need constant adjustment and attention.

    If you planned on building a belt driven unit. The pulley system for adequate reduction is complicated, bulky, and requires very expensive positioning style pulleys such as what are used on vmc axis's. They have a non standard tooth profile that creates a pinch fit with zero slop and tend to wear faster then normal belt and pulleys. I know this after recent correspondence with Misumi. It is possible and this would most likely be the direction I went to avoid worm drive issues.

    Or you could consider having something custom made similar to the new Haas style rotary bearing drives which look awesome but I'm sure would be extremely expensive due to the critical tolerance required.

    Being your cube is very small. You could also consider a custom made pulley, linear rail, ballscrew and open ended belt design for the main rotary axis. This would give you the best torque for work holding. I have a few ideas for this type of drive that use two pulleys sandwiched together and held with locking bolts so they can be offset slightly and used with a wide enough belt to cover both of them to add preload in both directions and minimize backlash.

    Either direction you choose always strive for rigidity especially for machining steel and 7075 grade aluminum. Also mass reduces harmonics that create resonant frequencies that will cause poor surface finish vibrations in the machine and cutting tool.

    If you already have a post processor for solidcam and mach3 you are leaps and bounds ahead of the biggest hurdle. 5 axis cam software and compatibility with mach3 is a rare thing. Most I have seen running t axis were using a low cost cam g code generator that looked quite daunting. Having sokidcam, Camworks, master can multiaxis softwares is ideal but the post processors are difficult to come by.

    I look forward to following your build thread, please don't forget to update us on your progress and thoughts on you designs!

    Chris

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    Default Re: 5-axis for machining metals

    Thank you for your answers

    I know its a short read about machine description, but I will do my best to explain what I need it for, and what I was cutting with my machine, until I sold it.
    1st of all, I have build up a Mechmate machine, which was designed for milling wood. It did not sit on me that I cant cut aluminium, so I upgraded my machine, and started cutting some basic aluminium alloys.
    Machine was really big, 3000x2200x1800 and I intented cut wooden products, doors, etc.
    I discovered I dont like wood dust crawling in every part of my body, so I started making some bicycle prototypes. In that time, I have tried to cut a plate of 7075-T651, and had to get some Iscar end bits to manage it, as its pretty hard.

    Here is my company website Shovel · Downhill & Enduro chainguides , as this are the products I am making now. If you see, there isnt much need in 5axis machine. As I have learned much in this few years, and I have some prototypes which can be only done with 5 axis machine, or done on a 3 axis machine, but with lots and lots of Jigs and time spent per each product. Products in question will be very complicated stems, front and rear hubs, cranks, rotor discs, chainrings, and some other stuff I always wanted to do, but cant get closer to any machine, or somebody who would make it for me.

    As a MTB rider, I want for my ride to be as efficient as possible, so I have an urge to design better and lighter parts. Design driven, I love the feeling when I design something, and go to my workshop and create and test it. Cant beat the feeling. Now I have designs I cant produce on standard 3 axis mill, and I need something much more reliable.

    That being said, my cutting area will be 200x200x200 mm, with an ISEL ATC 2.2 Kwh spindle.

    My only problem was how to design a machine, that would be rigid enough, to withstand the forces created by the material, end bits, motors, vibrations.
    I had in mind large aluminium profile, filled with sand, or epoxy tiny gravel to absorb the vibrations, to reduce the rigidity. This issues I dont find that hard to do, as Machine would be heavy around 300-400 kg.

    Precision of the parts must be top quality, as I tend to create those parts myself, and eventually sell them, so rigidity is mandatory.
    My biggest concern is the that bearings are the only thing that actually holds up things from vibrations, and most of the forces will be expressed on bearding, so I was thinking of something like this, but in smaller size, along with bearings.
    Attachment 294202

    Another thing that concerns me is the transition, as I don't trust belts and pulleys, and I was thinking of a real transmission, but as I read here, it tends to wear out.

    I was thinking also with ballscrew, mounted to rotary circular guides, and to be connected something like a fixed ballscrew, connected with radial axis on the on the 4th axis. Just need to sort out the angles and ratios.

    As I write this, I have seen some finished solutions, and they look interesting. Maybe if you have any link and where I can take a closer look on the rotary tables, that would be also a blast.

    Thank you guyz,

    Marko



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    Default Re: 5-axis for machining metals

    for those parts a simple 3 axis router makes all part..

    if you need for other works than you show on your website 5th axis then buy a factory made trunnion.. what made for metalmachines..

    theres a type of machine, used for moldmaking..
    SALE CNC Router Milling, CNC Laser, CNC plasma machine, China, Servo Motor Drive, UK, USA, Italy, Spain, Thailand

    for this you can add a trunnion.. this type of machine made of castiron..

    you need spindle with 4 bearing, and low range..
    cnc spindle motor large torque 6 poles low speed 8000rpm 2.2kw motor spindle 2200w 220V 80mm 325mm length water cooling-in Machine Tool Spindle from Industry & Business on Aliexpress.com | Alibaba Group

    also geardriven machine wont makes the precision you need, you need ballscrew for that



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    Default Re: 5-axis for machining metals

    Just for a point of interest here, any mountain biking I do at age 55 involves keeping both wheels on the ground!!!

    Quote Originally Posted by lopata View Post
    Thank you for your answers

    I know its a short read about machine description, but I will do my best to explain what I need it for, and what I was cutting with my machine, until I sold it.
    1st of all, I have build up a Mechmate machine, which was designed for milling wood. It did not sit on me that I cant cut aluminium, so I upgraded my machine, and started cutting some basic aluminium alloys.
    Machine was really big, 3000x2200x1800 and I intented cut wooden products, doors, etc.
    I discovered I dont like wood dust crawling in every part of my body, so I started making some bicycle prototypes. In that time, I have tried to cut a plate of 7075-T651, and had to get some Iscar end bits to manage it, as its pretty hard.
    Yep the wrong machine for what you want to do!
    Here is my company website Shovel · Downhill & Enduro chainguides , as this are the products I am making now. If you see, there isnt much need in 5axis machine. As I have learned much in this few years, and I have some prototypes which can be only done with 5 axis machine, or done on a 3 axis machine, but with lots and lots of Jigs and time spent per each product. Products in question will be very complicated stems, front and rear hubs, cranks, rotor discs, chainrings, and some other stuff I always wanted to do, but cant get closer to any machine, or somebody who would make it for me.
    In some cases the 5 axis will be required but innovating with cutting tooling might help with some of those parts.

    As a MTB rider, I want for my ride to be as efficient as possible, so I have an urge to design better and lighter parts. Design driven, I love the feeling when I design something, and go to my workshop and create and test it. Cant beat the feeling. Now I have designs I cant produce on standard 3 axis mill, and I need something much more reliable.
    You probably don't want to hear this but ideally you would get yourself a real milling machine. That would mean several thousands of dollars ( probably tens of thousands) to get you started.
    That being said, my cutting area will be 200x200x200 mm, with an ISEL ATC 2.2 Kwh spindle.
    I must have missed the cutting area in my previous post! In any event a small cutting area like that can lead to a very rigid "router" type machine. The problem is to do it right you need heavy steel weldments and access to a machine shop.
    My only problem was how to design a machine, that would be rigid enough, to withstand the forces created by the material, end bits, motors, vibrations.
    I had in mind large aluminium profile, filled with sand, or epoxy tiny gravel to absorb the vibrations, to reduce the rigidity. This issues I dont find that hard to do, as Machine would be heavy around 300-400 kg.
    While it isn't impossible to build an aluminum based machine for this sort of application I wouldn't. It gets to be expensive and you will still need plenty of machining or weldments to get the strength you want.
    Precision of the parts must be top quality, as I tend to create those parts myself, and eventually sell them, so rigidity is mandatory.
    This goes back to the thought that a milling machine would be a better choice, especially if you aren't tooled up to machine the parts of a rigid router type machine.
    My biggest concern is the that bearings are the only thing that actually holds up things from vibrations, and most of the forces will be expressed on bearding, so I was thinking of something like this, but in smaller size, along with bearings.
    Attachment 294202

    Another thing that concerns me is the transition, as I don't trust belts and pulleys, and I was thinking of a real transmission, but as I read here, it tends to wear out.
    I'm not sure where this distrust comes from. I've seen belt drives to ball screws on a very wide array of belt driven machinery. We are talking Bridgeport mills, Diamond turning machines, Large Cincinnati Injection molding machines with huge ball screws to very loose pick and place machines. Sized correctly there is nothing working with belt drives. In many cases we have had to replace leadscrews, bearings or motors before the belts fail. A belt driving a lead screw is so common that I can't think of a good reason to reject the configuration.
    I was thinking also with ballscrew, mounted to rotary circular guides, and to be connected something like a fixed ballscrew, connected with radial axis on the on the 4th axis. Just need to sort out the angles and ratios.
    IM not sure I follow. In any event there are options for even the forth axis, you could consider a harmonic drive or even a heavy duty belt drive.
    As I write this, I have seen some finished solutions, and they look interesting. Maybe if you have any link and where I can take a closer look on the rotary tables, that would be also a blast.

    Thank you guyz,

    Marko
    Not at the moment though a Google search for DIY rotary tables might help.


    I wanted to add that to build a high quality machine to do the types of components you are talking about will be expensive. Further I'd seriously consider enlarging your working areas to handle fixture and tooling machining. Depending upon your parts there may be lots of fixturing required. In some cases it can be better to use lots of fixtures instead of a five axis solution. This isn't a given though. Either way you sometimes make compromises to accommodate the number of axis you want to use. What I wanted to say is don't assume that five axis machining is always the best approach.

    Last edited by wizard; 10-05-2015 at 02:48 AM.


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    Default Re: 5-axis for machining metals

    Hello guyz, thanks for your inputs.

    I have put my website and products as a reference that can be done with simple mill, but now I advance to much more advanced products, and therefor I need a 5 axis machine.
    Very complicated stems, hubs, cranks, pedals can only be done properly on good 5 axis machines.
    I was thinking about only 4th axis, but that would not do.

    For a simple stem, you would need at least 5 JIGs to do it, which is in my mind much complicated to do, than making a good 5axis machine.

    As for budget, I have around 8000 Euros for making this sort of machine, so In general, I think, with good planning, it can be done.

    Belt drives for ballscrew sound interesting, as I will investigate more about it. Do you have maybe some photos you can share.

    @lcvette

    I have found a mach3 post processor here on Cnczone, and made it to work on my machine. It was working on 3 axis, and not sure how will it behave on 5 axis.
    Do you have any other alternative you can recommend in this matter?

    You said you have few ideas about two pulleys usage, can you explain a bit more.

    I will design my idea how to make a rigid axis, but must figure out the ratios. Will show it here in a day or two.

    Marko



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    Default Re: 5-axis for machining metals

    You are on a good track.
    The build cube size, and the mass, are exactly what you need, to be able to make something like this, work.
    The proposed budget is workable..

    Note steel or flat cast iron, is 3x stronger AND 3x cheaper than alu.
    I would never use alu on something like that.
    Steel costs about 2€/kg, so only about 600-800 €/300-400 kg.

    Basic tool steel, industrial prices.
    Any local steel shop will sell to you, and steel pricing everywhere is similar, worldwide.

    For the trunnion, you can use a rigid belt drive meant for cnc use, if the cutters are small, or you are doing mostly positioning.
    Something like HTD-8M ie 8 mm profile, and 30 mm wide.
    Or..
    You can use a low-backlash planetary gear. These are available for about 2-400€ new. You will need 2, 1 each a and b axis.
    Or..
    Use 2 worm gears, preload one with belleville springs, or use one high-precision one (500-700€).
    Look up hpc gears (uk) for example, for data re worm gears.
    Or cross-morse, uk.
    Misumi (EU). Mcmaster carr (USA), have specs and prices for comparisons.

    The belt has less backlash, but is a little softer, ie has compliance.
    The planetaries are not really zero-backlash, but low backlash, and are quite rigid.



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    Default Re: 5-axis for machining metals

    Quote Originally Posted by lopata View Post
    Hello guyz, thanks for your inputs.

    I have put my website and products as a reference that can be done with simple mill, but now I advance to much more advanced products, and therefor I need a 5 axis machine.
    Very complicated stems, hubs, cranks, pedals can only be done properly on good 5 axis machines.
    I was thinking about only 4th axis, but that would not do.

    For a simple stem, you would need at least 5 JIGs to do it, which is in my mind much complicated to do, than making a good 5axis machine.

    As for budget, I have around 8000 Euros for making this sort of machine, so In general, I think, with good planning, it can be done.

    Belt drives for ballscrew sound interesting, as I will investigate more about it. Do you have maybe some photos you can share.

    @lcvette

    I have found a mach3 post processor here on Cnczone, and made it to work on my machine. It was working on 3 axis, and not sure how will it behave on 5 axis.
    Do you have any other alternative you can recommend in this matter?

    You said you have few ideas about two pulleys usage, can you explain a bit more.

    I will design my idea how to make a rigid axis, but must figure out the ratios. Will show it here in a day or two.

    Marko
    Iopata,

    Similar to a preloaded gear set. Pulleys and belts have backlash, even the good ones for positioning accuracy. Misumi ran calculations for me on their 3GT series and came back with a combined calculated backlash figure of roughly .003". That's not terrible by any means and may very well be OK for your purposes. However in my opinion when you start stacking 5 axis positioning errors things can go south in a hurry and that .003" + any other axis backlash will put the parts out of position by a fair margin.

    My suggestion is to use two pulleys for the driven and drive. They would be the same size pulleys relative to their drive or driven position. And the tooth index would be offset such that both the leading and trailing edge of the belt tooth would be in solid contact with a pulley tooth face. The pulleys would be adjustable by simply loosening the clamping bolts and twisting them opposed to each other to take up and space between the teeth of the belt and pulley and re-tightened. This would mean that each pulley would be responsible for the load in opposite directions therefore when a rotational direction change is made the opposite pulley is already in a preloaded position and no backlash will be present (or very minute).

    It is the same principles hamerno described for a dual worm gear drive. Which I agree would be a more rigid solution. I suppose if you ensure good lubrication and the gear sets were properly hardened to resist wear they may offer a decent service life and the ability to adjust a dual worm gear design would allow the constant removal of backlash as needed until replacement gears were required.

    However, you then would need to drive two worm shafts in synch with each other with no backlash between them for the drive design or they would allow backlash to occur from losing their opposing preload or worse I could see a binding issue that would occur if there were and lash in the drive. This would lead to premature wear.

    You may investigate harmonic drives as these are backlash free, not cheap but they solve alot of the problems and they have a significant reduction ratio for driving high torque loads with small motors.

    With your budget. I would look at the 420l small vmc machine frame as a starting point. It will give you a tremendous headstart on your build and still allow you the flexibility to design your trunion table and choose your motors, drives and spindle motor. They seem very reasonable and would leave a hefty sum of your build budget to outfit it nicely. Certainly ly something to consider consideration specially considering it would get you making parts quicker!





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    Default Re: 5-axis for machining metals

    The first thing that came to mind for me was using two robotic joints (actually this is what fanuc uses)
    HD Harmonic Drive Gear Head 25 50 Free Shipping | eBay

    Harmonic Drive and Vigo-drive/Nabtesco are the ones you want.
    Z-axis > Precision Angle plate 1 > Harmonic drive 1 > Precision Angle plate 2 > Harmonic drive 2 > interface plate > spindle

    Assess whether the gear reduction is too low for a stepper motor that you intend on running - and gear it up with a pulley.

    Counterbalance the mess of components above loaded on your z-axis with some brass plate in slides and pulley etc.

    Surface Ground and Rotary Ground steel plate is cheap from misumi (price 1018 and 1049 steels if you will just be drilling holes in it - and that is the idea with selecting misumi):
    Automation Materials.com | MiSUMi | METAL > Plates

    Surface ground will hold parallelism of at least 0.01mm per 100mm of length.

    If you're worried about backlash of the gear reducers above, I would go with an encoder (probably magnetic tape) around the outside of the rotating side of the reducer and look into a program such as linuxcnc that can manage encoder inputs. Or go to a stepper controller that will utilize encoder feedback for positioning.

    Design up what you want using misumi parts and use the 30% off new customers promotion they have going on (order before end of year):
    30% Discount to All New Terms Accounts Customers | MISUMI?News



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    Default Re: 5-axis for machining metals

    Quote Originally Posted by lopata View Post
    Hello guyz, thanks for your inputs.
    Thanks for posting the questions.
    I have put my website and products as a reference that can be done with simple mill, but now I advance to much more advanced products, and therefor I need a 5 axis machine.
    Very complicated stems, hubs, cranks, pedals can only be done properly on good 5 axis machines.
    I was thinking about only 4th axis, but that would not do.
    The problem is building a "good" 5 axis machine is a bigger challenge compared to building a three axis machine. This is why the suggest above to buy a grunion table to install on a 3 axis machine makes sense. I don't know how well equipped your shop is but if you need to start farming out machine shop work the cost of your machine skyrockets and your engineering time increases dramatically.
    For a simple stem, you would need at least 5 JIGs to do it, which is in my mind much complicated to do, than making a good 5axis machine.
    I'm sitting here looking at a mountain bike wondering just how complicated your stems are going to be. I'm also wondering if your machines working area will be large enough. 200 mm or approximately 7.8 inches seems to be extremely tight for things like handle bars and seat stems.

    The obvious problem here is that you don't want to make the machine any bigger than required so that you can keep the machine stiff and avoid Inflating your expenses. The thing is looking at stems on my mountain bike pretty much indicate that you will need more than the 200 mm work area you are asking for. Also these stems really look like problems for a lathe with a live spindle or two.
    As for budget, I have around 8000 Euros for making this sort of machine, so In general, I think, with good planning, it can be done.
    Probably if you already had a machine shop to build everything in. It is going to be tougher and far slower if you are going to contact much of the work out. The thing is for 8000 € you ought to be able to find a fairly decent industrial quality used milling machine. If not that maybe a low end milling machine like Tormach offers. Such a machine can be put to work right away, assuming the used one runs, to expand your capabilities. You can then buy or build the fifth axis support for the mill as needed. I know machinery is irrationally expensive in Europe but I'd really look into the used machinery market before trying to build this machine. Even if you had to replace the controller you would still be farther ahead with most of the structure work already done.
    Belt drives for ballscrew sound interesting, as I will investigate more about it. Do you have maybe some photos you can share.
    No photos at the moment.
    @lcvette

    I have found a mach3 post processor here on Cnczone, and made it to work on my machine. It was working on 3 axis, and not sure how will it behave on 5 axis.
    Do you have any other alternative you can recommend in this matter?

    You said you have few ideas about two pulleys usage, can you explain a bit more.

    I will design my idea how to make a rigid axis, but must figure out the ratios. Will show it here in a day or two.

    Marko
    I'm sure everybody here will want to see what you come up with.



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    Default Re: 5-axis for machining metals

    a 5 axis machine makes simpler that's right..
    but you have a limited budget.. 8000 euro..

    for that money if it were mine biz, I would buy something like the novakon machine and simply set an indexer on the table..
    then after money comes really, then I would invest into 5 axis..
    at this moment a jig cheaper than investing into 5 axis..

    the problem is, while you can get a great small machine for 8000 euro, the plus two axis might makes price 2-3 times or even more..

    in fact even a used starts about 40K.. there are small machines, but they only for soft materials, wood, plastic and wax..



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    Default Re: 5-axis for machining metals

    Hi I Do Alu Milling with an heiz 400T (now Even with toolchanger ) i Do molds with it my learnings if you stay small and Slow you can use a Router but this is really Slow we Talk of 9 to 20 machining hours of a piece. I now have the need to mill Steel (i designed an toolchanger ) so i have now a novakon like machine but build in europe i right now about to do an trunnion Setup which ill Post in that Forum so if you explains more your Kind of pieces i my be able to help or give hint s ..

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    Default Re: 5-axis for machining metals

    Hi guyz,

    After some turbulent months, I am back on track to start designing the machine.

    I have done some research, and turns out 5 axis is a ***** to build up, specially for Iron and steel.

    So basically I would go and build up a CNC router, and then add 4th and 5th axis.

    What I have been breaking my mind, is the motors I would use for this machine.

    Leadshine easy servos (closed loop steppers with digital drivers) are my favorites.

    I would put this 86HS80-EC-1000 motor and its matchin driver HBS86H.

    Idea is to put this 3 motors on each axis of the machine, and then add 4th axis, with this motor (or even 12 Nm motor) with direct ratio on rotary axis.

    I was also thinking the 1:2 or 1:3 reduction via double steel wire reinforced belts.

    What I am considering is this Leadshine sets, but I dont know how they perform, and would they be suitable for such application.

    Link to motors and drivers.
    damencnc.com - Closed-loop Stepper Systems

    @Tkamsker

    I am really interested in the help you are willing to provide. Also, building your own ATC is amazing. I am currently designing the machine, so I can add ATC at some point.

    Help needed.

    Thanks

    Last edited by lopata; 01-04-2016 at 06:21 PM.


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    Default Re: 5-axis for machining metals

    Quote Originally Posted by lopata View Post
    Hi guyz,

    After some turbulent months, I am back on track to start designing the machine.

    I have done some research, and turns out 5 axis is a ***** to build up, specially for Iron and steel.

    So basically I would go and build up a CNC router, and then add 4th and 5th axis.

    What I have been breaking my mind, is the motors I would use for this machine.

    Leadshine easy servos (closed loop steppers with digital drivers) are my favorites.

    I would put this 86HS80-EC-1000 motor and its matchin driver HBS86H.

    Idea is to put this 3 motors on each axis of the machine, and then add 4th axis, with this motor (or even 12 Nm motor) with direct ratio on rotary axis.

    I was also thinking the 1:2 or 1:3 reduction via double steel wire reinforced belts.

    What I am considering is this Leadshine sets, but I dont know how they perform, and would they be suitable for such application.

    Link to motors and drivers.
    damencnc.com - Closed-loop Stepper Systems

    Help needed.

    Thanks
    Like many have said here before, I would design the mechanics of the system before the electrical system (including motors). Mechanical designs tend to evolve over time, and if you have already constrained your motors then you might end up spending more money if you need something different.

    That being said, I would not gear reduce anything if you can avoid it - especially with steppers. Steppers perform best at low RPMs and continue to fall throughout the range. You may or may not need this because of what you intend on machining, but it is something to consider. You will probably not need a greater resolution either, microstep at 4000 steps/rev or similar and you'll have more than enough resolution.

    Those steppers look like good options and leadshine makes good products. There's a note in the torque curve that says "if higher torque at higher speeds is required, you can change the holding torque percentage to 100% [from 40% that the curve is rated at]" They will require some playing around with software, but they should be fairly straightforward.

    Hope that helps a little.



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    Default Re: 5-axis for machining metals

    Thanks Iron man

    I was considering direct drive, and forgot the basics of the stepper drive.

    All 3 axes will be with 8Nm motors, and 4th axis will probably go with 12 Nm steppers.

    Problem which is occuring is the design of the 5th axis, as this motors are Nema 34, and quite large. Feels like I have to design it from the end, and Z axis will be redesigned.



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    Default Re: 5-axis for machining metals

    Quote Originally Posted by lopata View Post
    Thanks Iron man

    I was considering direct drive, and forgot the basics of the stepper drive.

    All 3 axes will be with 8Nm motors, and 4th axis will probably go with 12 Nm steppers.

    Problem which is occuring is the design of the 5th axis, as this motors are Nema 34, and quite large. Feels like I have to design it from the end, and Z axis will be redesigned.
    The 4th axis typically won't need as much power as the other axes. If you know a feed rate that you'll be cutting a material at, and the dimensions of the stock, you can do a ballpark calculation of the RPM required for the 4th axis, then figure out motor RPM (through any belts/reducers/gears). I am sure it will be low, which again, is perfect for a smaller stepper motor. I imagine a nema 23 would be sufficient for most setups, but again without the hardware it's tough to say.

    What's nice about the closed loop steppers is that you don't really care if you are way oversized. You won't hit resonance points and lose torque like in an old school stepper setup.

    Check these guys out
    http://www.tormach.com/product_rotaryproducts.html



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    Default Re: 5-axis for machining metals

    Further to my first advice;

    1. Forget the 12 Nm steppers and direct drive.
    Technically Very Bad Idea.
    You want 100x more angular resolution AT THE LOW END, 10x more accuracy, and 10x or more top speed and 3-10x more acceleration.

    I have an existing belt drive, C axis, on the lathe now.
    Its about 100x better than the proposed solution, and its barely adequate.

    Fwiw..
    I am using a 2.5 kW brushless ac servo motor, of 2.5 kW power.
    With 1:3 belt drive, using good industrial components, 10x more rigid (HTD 8 mm profile and 30 mm wide) and 10x more tension (50-80 kg tension on belts) than typical hobby builds.
    The belts have zero backlash.

    I have 90 Nm torque (30 Nm peak x 3), and 30.000 steps/rev, and it is, like I said, barely adequate for indexing in metal.
    So, the 12 Nm stepper, will only have 400 steps/rev accuracy, and less than 6Nm (half step) torque, for holding position.
    It will be about 15-20 times less torque than needed.

    Simply wont work, for indexing apps, in metal.

    If you use a small servo (stepper) to drive a low-backlash rotary table, then it will work fine.
    The reason is that worm-gear drives cannot be backdriven, but steppers are like springs, and yield easily (upto 1-full-step) near a full step or 1.8 degrees or 1/200 of a rotation.

    Your motors are immaterial, at this point.
    They are also cheap, and easily replaced, later on.

    My suggestion:
    Forget the motors,
    Focus on mechanical drives.

    My suggestion:
    Use some low backlash planetaries for 300€ or so each.
    A stepper will drive these, easily.

    I may even go to the planetaries(likely) or harmonic drives, myself.

    The smaller the stepper (2-3 N, nema 23) the faster it will run, and the faster it will accelerate.
    A big stepper (12 Nm) will typically run at 300-500 rpm max.
    A small one, 2.5 Nm, 600-1000 rpm at 48-68 V DC.

    The same size servo will run 3000 rpm, and deliver 3x-5x more torque at the top end.

    You real torque on steppers depends on the max speed you run at, and is usually about 1/3-1/6 the nameplate.
    Thus, a 3Nm stepper => 0.3 Nm stepper (to 1 Nm, depending).



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    Default Re: 5-axis for machining metals

    Quote Originally Posted by hanermo View Post
    I have 90 Nm torque (30 Nm peak x 3), and 30.000 steps/rev, and it is, like I said, barely adequate for indexing in metal.
    So, the 12 Nm stepper, will only have 400 steps/rev accuracy, and less than 6Nm (half step) torque, for holding position.
    It will be about 15-20 times less torque than needed.

    If you use a small servo (stepper) to drive a low-backlash rotary table, then it will work fine.
    The reason is that worm-gear drives cannot be backdriven, but steppers are like springs, and yield easily (upto 1-full-step) near a full step or 1.8 degrees or 1/200 of a rotation.
    You bring up a good point about the mechanical system - a worm drive is superior for the application for the reasons you stated.

    I have to disagree with what you're saying about the stepper motors though. 400 steps/rev accuracy? No, the stepper motors are essentially servo motors with a 1000 line encoder - after quadrature that's 4000 counts/motor revolution - that's 0.09° resolution. Accuracy is a function of the drive system and tolerance on the encoder. They will have 12Nm holding torque, not 6Nm. Holding torque is always higher in a stepper motor than dynamic torque and typically what the motor is rated for.

    Quote Originally Posted by hanermo View Post
    The smaller the stepper (2-3 N, nema 23) the faster it will run, and the faster it will accelerate.
    A big stepper (12 Nm) will typically run at 300-500 rpm max.
    A small one, 2.5 Nm, 600-1000 rpm at 48-68 V DC.

    The same size servo will run 3000 rpm, and deliver 3x-5x more torque at the top end.

    You real torque on steppers depends on the max speed you run at, and is usually about 1/3-1/6 the nameplate.
    Thus, a 3Nm stepper => 0.3 Nm stepper (to 1 Nm, depending).
    Hanermo, the motors linked provided the torque curves over the operating range. What you said may apply to the junk high inductance chinese stepper motors, but these will reach 1000RPM (at least the 8.0Nm one will).

    Schneider/IMS made a Nema42 sized stepper that will run up to 3000RPM
    http://motion.schneider-electric.com...s/MDM42_AC.pdf

    Some small stepper motors can hit 6000RPM.

    Your real torque depends on the torque curve, not a thumb calculation of the nameplate - that's only something you assume when you are dealing with steppers that have no listed specifications.



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    Default Re: 5-axis for machining metals

    Quote Originally Posted by hanermo View Post
    I may even go to the planetaries(likely) or harmonic drives, myself.
    The Nabtesco Vigo drives and Harmonic Drive reducers look awesome for a rotary table application, and could probably even be driven by a fairly small nema23 motor. I worked on an instrument where we used a Nabtesco reducer and it was a high performer, we ran it open loop as well and never lost steps with some aggressive accelerations. There's over 10,000 of these instruments in the field and these items NEVER break. I have almost been tempted to buy one or two on Ebay when I see them at a good price.



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