[suspension]

hi everyone,

I an creating this thread to get some advice from experts in this forum for the selection of various parts for the new CNC build that I am planning to start for pro-hobby and basic professional work. The design is heavily based on following work:


I've started the design of base using Fusion 360. See the attachment.


In order to finish the cad model for the base, I need to select servos, ball screw and related components like end supports, couplings.
Since this is mostly for hobby type work, the amount I can spend is limited, but it does not need to be super cheap. (I already have a 6040 CNC and the reason I am making this machine is to have better stability and accuracy).

Some questions that I currently have regarding above selections are:

1. Which servos are more suited to this? AC or DC servos? The total weight of the machine would be around 800KG at the end.
2. In this thread, JMC brand is recommended for servos for this build. I think they are reasonably priced and also seem to have good quality. I also checked DMM and their pricing is too high. Also checked Delta servos and those are also too expensive. Apart from JMC, I would like to see if there are any other Chineese good quality brands with reasonable prices. Also what are your thoughts on various servo motor options listed in AliExpress? Such as this one.
3. Which accuracy level is required for ballscrews of this machine? C3? C5? C7? And which manufacturing process is more suited (ground screws, rolled screws, etc)? Which nut (internal circulation, etc)? Preloaded or not? If preloaded which type? any specific recommendations for fixed and floating end supports?
4. Based on above what are some of my options for brands and suppliers for ball screws? I have already looked at brands like tbimotion and terry-machinery. Hiwin seem to be too expensive. (However I will be using Hiwin for linear rails/guides). What about various suppliers/brands from Aliexpress? For example this one?

I will be having more questions on base later in this same thread (for example on how to machine various critical surfaces, how to make the mould, etc), but above are most important at the moment.

Any help is really appreciated.

Thank you
S

[ardenum2]

I've read a few things about those drive integrated jmc's and people were complaining about lack of proper manual and tuning issues.

[suspension]

I've read a few things about those drive integrated jmc's and people were complaining about lack of proper manual and tuning issues.

I think the quotation they gave me refers to this motor instead which does not have an integrated driver.
Not sure if tuning issues are same with this motor and compatible driver (JASD4002-20B).

[Prodipmohato]

I've read a few things about those drive integrated jmc's and people were complaining about lack of proper manual and tuning issues.

It's unfortunate to hear about the concerns regarding the drive-integrated JMCs. A proper manual and efficient tuning are crucial for a seamless user experience.youtubevanced

[suspension]

It's unfortunate to hear about the concerns regarding the drive-integrated JMCs. A proper manual and efficient tuning are crucial for a seamless user experience.youtubevanced

They sent me a comprehensive english manual and also a software although I am yet to see how good they are.

[suspension]

I have changed the base a bit.

[Mr-MaW]

Mineral castings.The standard to measure the static characteristics of machine tool bed and other components is usually the rigidity of materials, that is, the minimum deformation under load. Under the same weight, the rigidity of iron castings is the same as that of mineral castings without considering the influence of shape.

[ardenum2]

there's not much difference between iso30 and bt30, bt30 can also be used without the 2 dongs. Here's a few motorized spindles:

iso20 toolholder https://www.aliexpress.com/item/1005004798512348.html

bt30 toolholder https://www.aliexpress.com/item/1005004206523750.html

here's a real machining center spindle it costs $4500 without tax and shipping, it might be too big for the machine though, refer to the cad file.

https://ctbservo.com/product/motoriz...000rpm-140n-m/

[suspension]

there's not much difference between iso30 and bt30, bt30 can also be used without the 2 dongs. Here's a few motorized spindles:

iso20 toolholder https://www.aliexpress.com/item/1005004798512348.html

bt30 toolholder https://www.aliexpress.com/item/1005004206523750.html

here's a real machining center spindle it costs $4500 without tax and shipping, it might be too big for the machine though, refer to the cad file.

https://ctbservo.com/product/motoriz...000rpm-140n-m/

Using BT30 without dongs may not be appropriate if I were to do some steel milling?

[ardenum2]

Using BT30 without dongs may not be appropriate if I were to do some steel milling?

not a problem, steel depends on the spindle and stiffness of the frame, bt30 without dongs will work just fine as long as there's enough clamping force in the drawbar, there's a chance you could swap the spring discs inside for more clamping force.

You said your machine is smaller than stefs, a c frame at this size might not be stiff enough, but it all comes down to the spindle. If you want to use that proper spindle for $4500 than you probably need to buff up the frame or use a slightly different one. Have to do some structural to make sure how much your frame deflects when under load during steel cutting.

with a router spindle like the first two links, you could be cutting steel but in a different way, check dental mill videos for how it looks like.

Are you sure about 400W and not 600W or 750W?

[suspension]

Would getting rid if the C frame be enough to host a proper BTR30 spindle with a servo?
I will check the dental mills.
If I were to use BT30 driven by a servo instead of a router ATC that use ISO30, what additional benefits do I get? Such as tapering threads?

Regarding power of the servo, I see that there is no much of a difference in price, so for 3 axis I guess 600W or 750W is also ok. But if the price gap is substantial, I would like to stick with 400W if that's possible.

[ardenum2]

Would getting rid if the C frame be enough to host a proper BTR30 spindle with a servo?
I will check the dental mills.
If I were to use BT30 driven by a servo instead of a router ATC that use ISO30, what additional benefits do I get? Such as tapering threads?

Regarding power of the servo, I see that there is no much of a difference in price, so for 3 axis I guess 600W or 750W is also ok. But if the price gap is substantial, I would like to stick with 400W if that's possible.

for a bt30+servo a c frame is probably the best but needs to be beefy to take advantage of it. If you go down this route high speed machining is probably off the table, these bt30 cartridges usually run at max 12000rpm, most cap out at 6000rpm due to the bearings, which is why you need more stiffness to support heavier cuts.

vulcanmachineco(attached) makes a belt driven bt30 but not an a c frame, its a double column raising gantry, the stiffest we in the diy can hope to ever get, but to replicate it in EG could be tricky, you'd probably have to redesign the saddle instead of resizing it and figure out how to fit bt30+servo onto it.

[joeavaerage]

Hi,

Regarding power of the servo, I see that there is no much of a difference in price, so for 3 axis I guess 600W or 750W is also ok. But if the price gap is substantial, I would like to stick with 400W if that's possible.

When I was initially designing my machine I had intended to stick with 400W servos also...but I must confess without any epsecially good reason, size, convenience, cost all seemed to indicate 400W.
When I came to buy them however I found that a 400W Delta B2 was $398 and a 750W B2 was $438....a mere $40 more...so I got the bigger ones.....why would you not?

My first calculations did not include rotational inertia...and that lead me to the conclusion that even 400W would have been an overkill. Once I realised that my calculations were deficient and I re-did them
but now including rotational inertia I realised that 750W was good enough....but I would have been severely disappointed with 400W.

To be honest you are a long way from deciding on the power of the servos. The actual parameter you need to decide is the rated torque of the servo, and that in turn will be ditctated by the pitch
but most importantly by the diameter of the ballscrews. Rotational inertia of a ballscrew is proportional to the fourth power of diameter, ie very VERY sensitive indeed to ballscrew diameter.

A 400W servo (1.27Nm rated) might be fine for a 20mm or even a 25mm ballscrew but would be hoplessly underdone on a 32mm ballscrew.

Once you firm up your design with the diameter and length of the ballscrews THEN do the calculation and determine the required torque to meet your performance goal. That is what determines the power
of the servo.....not some heuristic guess.

Craig

[catahoula]

I went with c5 ground ballscrews, preloaded double nut TBI brand from BST Motion (aliexpress). C3 are quite expensive. C7 (rolled) aren't really precision enough for preload. C5 seems appropriate to me with ballscrew mapping. For preload, the seller made a recommendation that i followed (i think it was a lighter preload than I would've ordered otherwise) and I'm glad I did- they're plenty tight and being tighter might create a lot of heat etc. of course, the tighter preload might last longer, maybe i'll find that out in a couple years.

[ardenum2]

the tighter preload might last longer, maybe i'll find that out in a couple years.

really? I was under the impression the higher the preload the less life the ballscrew/ball bearings will have.

[catahoula]

yeah i would generally agree with you, but i'm also considering the possibility that since the preload will loosen over time on all ballscrews, maybe you get more time at zero backlash with a tighter preload, even if it means the overall life is less. just hypothesizing here

spent years as a bicycle mechanic and saw many an over-tightened hub that survived a very long time, fwiw

[joeavaerage]

HI,

I would like to see if there are any other Chineese good quality brands with reasonable prices.

There are plenty of cheap Chinese servos, and most of them to be fair are 'fair to even good quality'. Its not that I have an issue with cheap Chinese servos but all of them
miss the setup and tuning software. That's the issue. There are hundreds of parameters that need to be set in an AC servo, while many can be left at default values
there are many that cannot. Do you know what those parameters are? Will you be able to decipher the Chinglish manuals?

I recommended Delta and DMM not because they are the cheapest but because they are the 'cheapest of the quality Chinese made brands that have setup and tuning software.
If you want expensive try Yaskawa or Seimens....they'll make you weep!.

The machine in the video link you posted uses 750W (80mm frame size) Delta servos, the identical units that I use, including the electromagnetic braked servo for the Z axis.

The company whom supplied these servos to me (China) have their own brand called ToAuto. I have some history with this company, all positive. I do not have any of the ToAuto servos
but would be happy to buy them on the basis that I feel I have the support of a good supplier. Given also that I have had some exposure to AC servos including Delta, Allen Bradley, Omron,
( a Yaskawa clone), Mitsubishi and Lexium (Schneider Electric) I would be happy enough to program a ToAuto but I still pay an extra $196 to get genuine Delta servos. I vote with my wallet
and pay the extra to get the quality I want and the setup and tuning software to match.

https://www.fasttobuy.com/nema-32-cn...he_p35883.html

Craig

[suspension]

Given also that I have had some exposure to AC servos including Delta, Allen Bradley, Omron,
( a Yaskawa clone), Mitsubishi and Lexium (Schneider Electric) I would be happy enough to program a ToAuto but I still pay an extra $196 to get genuine Delta servos.

Craig

May I know how you arrived at $196? Because I am also prepared to pay that much extra, but a brief glance across prices shows me that ToAuto 750W motor + driver + cables are priced at 242 while for delta its 648 (B2 series).
Th JMC on the other hand quoted 152 for 400W version.

Also, could I please know which type of servo matches CNC machines better? AC or DC?

I also see they offer software for tuning:
https://www.jmc-motor.com/oftware.html

[joeavaerage]

Hi,
the price for a 750W Delta B2 series servo kit from Fast-to-Buy is $438USD, while the ToAuto 750W is $242USD, difference $196USD

https://www.fasttobuy.com/flange-80m...er_p28084.html

I have bought three of these servos in the last two months, two for me (fourth and fifth axes) and one for a friend. All have been $438USD. Shipping to New Zealand has varied from $150USD (3 day Fedex)
to $156USD (3 day Fedex). The record time is 2 days 19 hours and 47 minutes from pick-up ( Hong Kong) to delivery (Christchurch NZ), and the slowest time was four days 5 hours 20 minutes.

Also, could I please know which type of servo matches CNC machines better? AC or DC?

DC servos are going the way of the dinosaur. They are still quite capable of good performance but modern AC servos are just that much better and way WAY more flexible/programmable.

Its your money and therefore your choice. I too made my choice and it was Delta B2 series.

Craig

[suspension]

Thanks for the calculation Craig, really helpful. I wonder if there is any online tool or software that lets me do these calculations by myself.
As per the ball-screw, based on Stef's mill which is much bigger than this, I suspect I will ever need 32mm. In fact I was thinking about using 16 mm or 20 mm. I think I need some advice there as well.
In addition to the ball screw diameter, would the pre-loading has a significant effect on the torque?