585,454 active members*
2,654 visitors online*
Register for free
Login
Page 1 of 4 123
Results 1 to 20 of 65
  1. #1
    Join Date
    May 2009
    Posts
    1332

    How to Select a 4TH Axis

    I have a 3 axis table CNC mill about 4’x3’ with a 800W water cooled spindle all made with 3/8” and 1/2" thick aluminum plate/flat bars. It’s for a hobby use and I would like to install a 4TH axis.

    I do have the space to put the 4TH axis on the side of the table and modify the spindle to go over it. I will prefer to drive this axis with a stepper motor and it will be used to mill aluminum and wood.

    I see quite a few alternatives on the web but since I never used one before what would be the least complicated setup?

    Thanks
    Nicolas

  2. #2
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    I made one. This gearbox has some true grit. Its safe maximum load is 400Nm, that's the limiting strength of the gear teeth and a rated load of 125Nm (output shaft) at 4000rpm (input)
    I did have a stepper on it, but the stepper was inclined to miss steps but worse was slow so I put a 750W Delta B2 series servo on it, the one pictured.
    The servo is rated at 3000rpm and with the 19.5:1 worm reduction I get 153.8 rpm. I rounded it down to 150rpm in Mach.

    Craig

  3. #3
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    That’s a nice unit you got there Craig but you have the knowledge and equipment to make such a unit but for a beginner do you have a suggestion for a smaller unit?

    Besides that I never used a 4TH axis it looks like that I have to learn much more like servo motors and how to go about programming the 4TH axis to work on my cnc. Would the motor on this link be a good start?

    https://www.automationtechnologiesin...o-kit/kl-5056h

    My cnc has 3 axis, 4 stepper motors and works. Would I be able to connect a servo motor to my current BOB on the B axis or I need an extra BOB?

    That’s a lot of difficult questions but to keep going I must have the answers and besides after I figure out and understand the physical questions I must figure out how to produce the g-code to get the B axis working

    Thanks
    Nicolas

  4. #4
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    this is my first foray into a rotary axis and so I have no more knowledge than you. What I did know and always aimed for was that my machine would cut steel and stainless
    and that in turn demands rigidity, ergo the gearbox you see.

    This gearbox is a 63mm size, that is to say the distance between the centreline of the worm gear and the centreline of the driven gear is 63mm. The same company, Atlanta Drives,
    do one size smaller, a 50mm gearbox. The one pictured is a 58 series, that is heavy duty and <2 arc min backlash. They do another higher spec series, the 98 High Torque series
    with <1 arc min backlash. These gearboxes are well represented on Ebay at anywhere from fair prices to expensive. It costs nothing to look.

    As I posted I found a stepper to be a bit slow and inclined to miss steps. This stepper came off my previous mini-mill and so really is just too small for the job. I have used Delta servos
    before and that's why I chose them again. With the gear reduction that means the chuck can do 150rpm, which in turn means that rotary toolpaths don't take an age to execute.
    A stepper would have worked but result in about 25rpm output speed, which would cause rotary tool paths to drag on and on.

    What motor you use on a fourth axis, or fifth come to that, is down to budget verses performance just like any of your other axes.

    I have bought a subscription to Fusions Machining Extensions. The introductory offer was $1200USD/year reduced from the normal price of $1600USD/year, and that's over and above
    the $545USD/year for the basic Fusion subscription. Fusion + Machining Extensions is, as I found, about the cheapest way to get continuous four and five axis. You are right to be
    concerned with how to generate toolpaths.

    You can write some simple toolpaths by hand, but its slow and tedious.

    You might like to investigate Deskproto. Its is a cost effective way of generating continuous four axis toolpaths. It does indexing five axis only.

    Craig

  5. #5
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Many thanks Craig for the help,

    Now I understand the advantage of higher RPM, no one will like to use 25RPM.

    I knew CAM software are expensive but didn’t know by how much, they are too expensive for my needs. I have been fortunate in the past because a friend works in a machine shop close by and I can have access to a desktop with MastercamX5 which I used in the past and learned enough on my own to do basic toolpaths. I have to check to see if MastercamX5 can do a toolpath for a 4TH axis but the Deskproto you suggested looks promising. They have a free version for hobbyist but I couldn’t find out what “free” means. I will download what they have and eventually will find out.
    Nicolas

  6. #6
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,

    Now I understand the advantage of higher RPM, no one will like to use 25RPM.
    It means that you have one slow axis and so the whole machine slows down to match it. There are a few tricks that can improve cycle times with a slow fourth axis but they
    all lessen finish. 150rpm is much better, its still not blindingly fast but it is highly useable.

    I saw that Deskproto was $250USD for non-commercial use, and that is pretty fair value.

    Its when you come simultaneous four and five axis is where the money goes. If you have access to Mastercam then do whatever is required to retain it....boxes of beer, plates of date scones,
    whatever. If you have to buy simultaneous four and fve axis you'll weep.

    Craig

  7. #7
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Can you give me your opinion Craig on the attached kit?

    What the ratio 100:1 and 50:1 means?

    I’m not saying I will buy this kit but it will give me an idea what to look for. This kit is from Amazon.CA and the price is in CDN$

    Thanks
    Attached Thumbnails Attached Thumbnails Screenshot 2023-02-07 231436.jpg  
    Nicolas

  8. #8
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    the 50:1 and the 100:1 is the gear reduction of the harmonic drive.

    A 50:1 harmonic drive powered by a stepper doing 500rpm will have a 10 rpm output, ie pretty slow.
    A 100:1 harmonic drive powered by a stepper doing 500rpm will have a 5rpm output, even slower.

    Harmonic drives are good because they have (theoretically) zero lash, but the typical gear reductions are 50:1 and 100:1 which are excessive for a fourth axis. Those reductions are better for a
    robot arm that you expect to rotate +180 degrees and -180 degrees rather that rotate continuously. Such a large reductions will mean that even a small stepper will have great torque authority over the
    chuck which is good of course. All in all,I'd say that unit looks pretty good just [Uslow[/U]. You could swap out the stepper for a servo doing 3000rpm and at 50:1 that would be 60rpm at the output, which would be useful.

    Craig

  9. #9
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Thanks for the education Craig, much appreciated.

    Are most of the stepper motors doing 500rpm?

    Yes I could change the stepper with a servo but the problem will be if the servo shaft will fit. If not I’m not equipped to do what is required. An alternative will be to ask if they can switch the stepper for a servo before I buy but I doubt they can do it.

    However I found a servo motor kit on this link.

    https://www.automationtechnologiesin...a23-dual-shaft

    What “skewed rotor” means?

    I noticed the shaft is 1/4" and all the NEMA 23 motors I have now are also 1/4" shaft. So perhaps if all NEMA 23 motors are 1/4" shaft I may take the chance and get the harmonic drive kit I mentioned earlier and replace the stepper motor.

    Are the specs on this servo any good?

    Many thanks again
    Nicolas

  10. #10
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,

    Are most of the stepper motors doing 500rpm?
    Depending on the stepper no most will go faster.

    If you have a low inductance stepper, say <1.5mH and a high voltage driver it might get to 1000rpm or even 1500rpm before stalling, but most steppers
    are good to about 500rpm or so.

    However I found a servo motor kit on this link.
    No, you don't want that sort of thing. Its just a DC motor, then you have to add a driver, encoder etc......don't go there. If you are going to spend big money make sure you get
    a great result.

    This is what you want, if you want servos at all, 400W motor, drive and cables, the drive is 230VAC direct off-line eat any stepper ever made:

    https://www.fasttobuy.com/220v-127nm...ol_p28069.html

    Craig

  11. #11
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    a lot of continuous four axis toolpaths are a 'spiral' type of path. The workpiece rotates in the chuck while the tool of the machine descends to the outer surface of the material.
    If you want a nice finish then you might want a 0.25mm step-over. To machine a100mm cylinder would take 100/0.25= 400 rotations. At 10rpm that's going to take 40minutes!
    That is the downside of a slowly rotating fourth axis.

    The advantage of a slowly rotating fourth axis is that the torque of motor is that the deep gear reduction means that a small (low torque) motor can still result in a high torque output,
    enough to resist cutting forces with authority.

    So one advantage is offset by a disadvantage. As I posted earlier harmonic drives have reductions of 50:1 and 100:1, so unless you have a real high speed motor the output speed of the
    fourth axis is always going to be slow. This really brings into question whether a harmonic drive is the right choice.

    Many manufacturers are using cycloidal drives, which can also be made to have very low lash, not zero, but very low. They typical have reduction ratios of 10:1 to 30:1. Lets assume a common
    reduction of 20:1. This will mean that you get a twenty fold increase in torque from the motor (cf 50 with harmonic drive) but a much faster output (3000/20=150rpm) whereas a harmonic drive
    would have 3000/50=60rpm. Note in both cases I'm assuming a 3000rpm motor, which would almost certainly have to be a servo, steppers don't go that fast (normally).
    Unfortunately cycloidal drives of this description are not cheap, and not readily available secondhand.

    For this reason I went for a worm drive, also called a servo reducer. Quality gearboxes can have low lash, for instance my fourth axis is <2 arc min and my new fifth axis is <1 arc min.
    Even that amount of lash is probably considered unacceptable in a million dollar five axis VMC, but thus far I've had no issues with it. I can't even measure it, at least easily....I might try
    at some stage. Most importantly I can't see any defect in the parts I've made with the lash in the gearbox. These gearboxes are not cheap either but there is a fair selection on Ebay
    at reasonable prices. The reduction ratios are quite broad. Multistart worm gears can have reductions as low as 6.75:1 (my new fifth axis for example) up to 50:1 with single start worms.
    My fourth axis is a two start worm and has a reduction of 19.5:1. I consider this reduction ratio about the 'sweet spot' for a continuous fourth axis. It results in reasonable output speed, 150 rpm,
    with a 3000rpm motor and pretty fair torque multiplication. The servo is 2.4Nm rated and I would expect the viscous drag to knock 0.4Nm off that so an effective output torque of 39Nm.

    If you want to try using servos don't go with the cheapest stuff....it'll bite you on the arse. Get a decent modern AC servo. I use Delta, a Taiwanese brand made in China. Another, that will
    interest you, is DMM an Canadian brand made in China. Both brands are good quality, performance, documentation and most importantly free set-up and tuning software at fair prices.
    There are cheaper Chinese made servos, but the documentation is crap, support questionable and no set-up software. If you've not had anything to do with servos don't go there.
    I have no reason to doubt the quality and performance, its just that if you've never set up a servo before you'll struggle with these things. Get Delta or DMM.

    Craig

  12. #12
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Your post “How to select a 4th Axis” is an excellent source of information for me Craig, many thanks for your time.

    How did you know that the servo motor link I sent the motor is a DC motor? The description says servo.

    The link you sent about “Fasttobuy”, I know them. About 6 years ago I bought from them a set of VFD/Water cooled spindle kit and the service/product was excellent. However the price of that quality servo in US$ is quite high for me but I will search to see if a similar 120VAC is perhaps less expensive.

    And you are right, my knowledge on servos is less than zero and when you are talking about “set-up software” I wonder what’s ahead for me.
    Nicolas

  13. #13
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    the picture in the link shows a plain old brushed DC motor. The brush holders are the plastic screw capped mounds at one end. The documentation shows
    the end plate drilling to which you are supposed to put an encoder. You would still have to provide a DC servo drive, something like a Gecko G320.
    Then you have to set it up and tune it.....all-in-all an expensive and time consuming endeavour.

    The 400W Delta I linked to is in fact cheap as quality AC servos go. No doubt you would prefer DMM being Canadian made....but they are similiarly priced.
    Be extremely careful buying cheaper than these, either the quality is not there and/or you will struggle to set them up. Servos are not cheap, you want to be damned sure
    they are going to be not just good but f*****g perfect! Delta and DMM will give you that satisfaction.

    And you are right, my knowledge on servos is less than zero and when you are talking about “set-up software” I wonder what’s ahead for me.
    Modern AC servos have hundreds of tuning parameters, I mean hundreds! Most can be left at factory defaults but there are some that absolutely cannot be.
    You can program the servo by pushing buttons like a microwave but it slow, tedious and error prone. You really need set-up software. It lays out all the parameters,
    the explanation as to what each one does. The tuning part allows you to tweak the PID parameters if you want to or need to, mostly the Auto-Tune feature is good enough.

    Once you have set up a few servos you will find that despite the different naming terms used by different manufacturers they tend to be very similar. Then you can use you
    experience gained on good servos like DMM and then use the same idea to program a cheap No-Name brand from China.

    That Fast-to-Buy company sells Delta but other brands as well, including their own in-house brand called ToAuto. A 400W ToAuto servo is about $150 cheaper than a 400W Delta.
    I have no reason to doubt ToAuto, nor any reason to doubt Fast-to-Buy, but I still buy Delta servos. I paid $588USD this morning, about eight hours ago to Fast-to-Buy for a
    750W Delta B2 series servo kit, $438USD and another $150USD for three day FEDEX shipping from Hong Kong to New Zealand, thats 9,700 kms. The last one I got took
    two days, 19 hours and 40minutes. I trying to guess whether they can break that record. You might say I put my money where my mouth is....and thats the second 750W Delta I've bought
    of them this month. Shame I cant afford to do it more....but you don't make fourth and fifth axes all the time.

    Craig

  14. #14
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    I’m very happy you answered my post Craig, you know your stuff and you have a good way to pass your knowledge along. From the kind of money you spend it looks like what you are doing is your business or perhaps you are also a hobbyist but prefer to get always the best.

    On my side, I’m retired and I build cnc machines as a hobby which after I finish one I sell it to empty the space it takes in my garage/workshop and hopefully recover my cost. It takes me about 1 year to build a cnc which is all made from aluminum plate and flat bars 1/2" to 3/8” thick and since I don’t have the right tools and neither I want to buy ones most is tedious manual work to cut and drill the required pieces precisely. After all is a hobby work and I take my time to enjoy it plus I like the challenge to learn how new stuff works.

    All my previous machines were sold to local artisans or people who like to have a cnc but are unable to build one so my price must be reasonable and that’s why I can’t afford to buy expensive parts.

    My current cnc is my 11TH and roughly 30”x38” table top, 3 axis, 4 stepper motors with HY VFD and a water cooled spindle. It’s for sale now and I was thinking to modify it to accept a 4TH axis but decide against the 4TH axis now because it’s too much re-work and prone to mistakes. So I will sell it as is and in the mean time I will learn how a 4TH axis works and what is needed and I will incorporate one into my next cnc.

    Now I understand how you recognized the motor I posted earlier that is a DC motor, it takes keen eyes to do that and I’m happy you did. I also understand what you are saying about the servo and I think I may stick to your suggestions and go for a good one.

    I also understand that there is a lot to learn about the servo motors and I don’t mind learning. I already have found some articles about them and I read to educate myself.

    My next step is to find a 4TH axis kit which includes the gearbox, servo, a chuck or plate or something to hold one end of my work piece plus a tailstock holding.
    Nicolas

  15. #15
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    I always try to get the best I can afford, but sometimes that not much at all. I mean last week I tried to buy an F16, a used one....no joy.... just could not afford it.

    The thing about a fourth axis is that it takes away Z travel. If for instance you have a max Z clearance height of 150mm then your fourth axis and material must fit underneath that.

    When I built my mill I knew that at some stage I wanted a fourth and fifth axis so I made it so I could re-mount the Z axis up to 300mm higher so that the stack height of the trunnion
    table and fifth axis does not rob me of all that Z axis travel.

    If you do plan to have a fourth axis on an upcoming machine plan to have a lot extra Z travel so you cn put a fourth axis underneath it and still have enough Z travel for the workpiece.

    Craig

  16. #16
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    An F16 Craig? It would have been so nice to have one, I prefer a US WW2 submarine, I couldn’t never imagine how these sailors went inside these vessels and do what they did!

    It’s true that a fourth axis will take away Z travel but as you said if you make provisions you could easily re mount the Z higher up. I do the same in all of my machines.

    I noticed in some videos most they mount the fourth axis lower on the side of the table which means the Z travel doesn’t change but you must have the X axis travel further out on the left/right side.
    Nicolas

  17. #17
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Found the DMM Servos site and for the benefit of other users I attach their site + a link to a 2 part video describing servos installation and setup in great details. Also included is a PDF with their price list of their products

    https://dmm-tech.com/multiaxissolutions2.html

    https://www.youtube.com/watch?v=oi3K_uApVkU

    https://www.youtube.com/watch?v=V4ARIho56ro
    Attached Files Attached Files
    Nicolas

  18. #18
    Join Date
    Nov 2013
    Posts
    4342

    Re: How to Select a 4TH Axis

    Hi,
    yes DMM are good brand, and you speak Canadian already!

    The DYN2 servo drives, the pulse input ones, the cheapest, require a DC power supply, I think 70VDC is common. That would allow you to usee your 110VAC to best advantage.
    The DYN4 servo drives are direct off-line 230VAC, and if you are limited to 110VAC the output of the drives would be similarly limited......not what you are paying for.

    These servos, drives and cables are not cheap so you want to extract the best from them when or if you get some.

    Craig

  19. #19
    Join Date
    May 2009
    Posts
    1332

    Re: How to Select a 4TH Axis

    Craig you confuse me more than I am, lol, you say “The DYN2 servo drives, the pulse input ones, the cheapest, require a DC power supply, I think 70VDC is common. That would allow you to use your 110VAC to best advantage.” How would I use 110VAC to my best advantage?

    Spend the day searching but got nowhere, just more questions!

    Looks like to me that servo motors are only available for 220VAC, am I wrong?

    What is the difference of “closed loop vs open loop” in stepper motors and which one is better?
    Nicolas

  20. #20
    Join Date
    Jan 2023
    Posts
    436

    Re: How to Select a 4TH Axis

    Quote Originally Posted by kolias View Post
    What “skewed rotor” means?
    it means it runs smoother, most modern motors are like this, expect frameless motors that you can buy relatively cheap on aliexpress which use permanent magnets still tend to be 'straight' but for pm's it doesn't matter that much because of their native synchronous nature.

    the motors in the picture look like 1990's tech, you'd probably be better off with a modern closed looped stepper than this.

Page 1 of 4 123

Similar Threads

  1. Bobcad version for 4th axis true 4th axis machining?
    By Tormachmaster in forum BobCad-Cam
    Replies: 34
    Last Post: 12-18-2015, 01:37 AM
  2. Replies: 1
    Last Post: 03-18-2015, 03:35 AM
  3. Handwheel Axis Select Not Working
    By TAProwler in forum Fagor Automation
    Replies: 0
    Last Post: 07-25-2013, 03:59 AM
  4. True 4th Axis vs Fake 4th axis?
    By microbeast29 in forum Wood Lathes / Mills
    Replies: 6
    Last Post: 10-25-2012, 03:37 AM
  5. Cant select surface for 4 axis Wire edm
    By mgb1974 in forum UG NX
    Replies: 1
    Last Post: 09-23-2008, 03:14 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •