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View Full Version : need help! choosing right kit

msacnc
15-09-2014, 06:56 AM
my machine dim. is (2400*1200*250) rack and pinion X Y with gear 2:1 or 3:1 or 5:1 ratio. used for wood, plastic and thin aluminum
i need to choose from to kits

1- 4 Nema 23 425oz 3A 6Hm with 2 power supply 60V 6A

2- 4 Nema 34 651oz 5.6A 3.4Hm with 4 power supply 60V 6A

i need advice please to obtain good torque and speed. all machin built using steel 100*100*3 box
which gear ratio is appropriate?
thanks

Blackrat
15-09-2014, 07:28 AM
id go with the nema 23's

whats the estimated weight of the gantry ? and what size pinion you using on what mod rack ?
and what drivers ?

msacnc
15-09-2014, 08:11 AM
thank you for reply Blackrat

i know that name 23's is better specially for gear reduction for high speed iam looking for without loosing torque but available name23 has high inductance 6mh which mean require 78V PS and the biggest available PS is 60V only
Nema 34 has 3.4mh which mean more appropriate for 60V PS

For gear rack

5:1 ratio(90 teeth-18 teeth) for Nema 34 frame only
2:1 ratio (40 teeth-20 teeth)
3:1 ratio (60 teeth-20 teeth

The pinion on rack 28 teeth

4 Chinese drivers 7.8A 80V

I cannot estimate the weight of the gantry because it is not yet constructed but it will be two welded steel boxes 100*100*3

i order spindle 2.2kw 5.5KG

may be this information help

msacnc
15-09-2014, 08:17 AM
I go to compare smallest Nema 34 stepper 651oz that is near to nema 23 425oz to keep torque drop at high speed to mininum and at the same time can move steel gantry easily

irving2008
15-09-2014, 10:15 AM
of course you can estimate weight of gantry

cross-section of 100mm x 3mm box section is 100*100-94*94=1164mm^2
gantry is 1350mm wide approx. so total volume of steel is 2 * 1350 * 1164 = 3142800mm^3 = 0.0031428m^3 @8750kg/m^3 = 27.5kg
add spindle, carriages, energy chain, y & z stepper, ballscrew/rack, y-rails, z-rails, etc. (all of which you can get from data sheets or calculate), and your gantry is in the order of 50kg which is typical. add 30% safety margin and for sizing purposes use say, 65kg. - its good enough to help decide what motor is needed.

Boyan Silyavski
15-09-2014, 01:06 PM
Definitely the 23 motor

The motor you point to is not a very low inductance motor. You need similar as what Zappautomation sells:

http://www.mycncuk.com/attachment.php?attachmentid=13385&stc=1

Boyan Silyavski
15-09-2014, 01:21 PM
of course you can estimate weight of gantry

cross-section of 100mm x 3mm box section is 100*100-94*94=1164mm^2
gantry is 1350mm wide approx. so total volume of steel is 2 * 1350 * 1164 = 3142800mm^3 = 0.0031428m^3 @8750kg/m^3 = 27.5kg
add spindle, carriages, energy chain, y & z stepper, ballscrew/rack, y-rails, z-rails, etc. (all of which you can get from data sheets or calculate), and your gantry is in the order of 50kg which is typical. add 30% safety margin and for sizing purposes use say, 65kg. - its good enough to help decide what motor is needed.

Just saw his build and did not pay attention here

He is looking at best case scenario of 100x100x3 9kg/m, just checked it, so the gantry with sides depends how he will go having in mind 300mm Z , will weight minimum ~50kg without z and rails!!!

The Z will weight around 30kg + all the rails and motors and so . Especially if he wants a sturdy machine. The lightest gantry possible as i see it is more or less the way i make it right now on my build here (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one/page6) and is not light at all.

My conclusion for my build was to go with servos or nema 34 to be on the safe side. i went with servos.

Another point is that Rack and pinion is not the best solution so better continue at his build thread (http://www.mycncuk.com/threads/7896-Need-advice-for-4*8-cnc-machine-build?p=61700#post61700), as all is interconnected.

http://www.mycncuk.com/images/misc/flags/Egypt.pngmsacnc (http://www.mycncuk.com/members/17280-msacnc),

Its wise first to finish the design, then to decide the motors. Rotating ball nut (http://www.mycncuk.com/threads/3340-Rotating-Ballnut-design-ideas?highlight=rotating+ballnut) on long axis will be better option. Coupled with 2510 ballscrew on your machine size.

msacnc
15-09-2014, 11:15 PM
thanks riving2008 silyavski for valuable information;

Nema 23 number is JK57HS112-3004

I have a limited option for stepper and PS choice, the available stepper are JK57HS112-3004 and JK86HS78-5504 to choose one of them (low cost for me)

Rotary ball nut is not available option in my country and also dust intensity in the air is a big problem for ball screw + high cost thus rack and pinion is easy to maintain specially with big 2400*1220*30 machine

I think the design of gantry with one box 100*100*3 may be reduce the weight

i have a limited time to choose one kit (nema23 425oz+60V PS) (nema34 651oz+60V PS)
what is the best ratio 2:1 or 3:1 or 5:1
thanks

irving2008
15-09-2014, 11:39 PM
No one can answer your questions because we don't have enough information.

To start with, what speed do you hope to achieve? And what pitch is the rack?

Btw this probably won't be accurate enough for machining aluminium.

msacnc
16-09-2014, 06:23 AM
i do not determine certain speed but the faster choice is better for me

rack inf:
20 mm wide and 20 mm thick 1500 mm long Module 1.5 Pressure Angle:20°

commonly the machine is used for woodworking

I plan to reduce the gantry weight using one steel box 100*100*3 welded to two pieces of 150*100*3 gantry side

"this probably won't be accurate enough for machining aluminum" Why?

msacnc
16-09-2014, 06:32 AM
Gantry imagehttp://www.mycncuk.com/attachment.php?attachmentid=13387&stc=1

irving2008
16-09-2014, 10:38 AM
i do not determine certain speed but the faster choice is better for me

rack inf:
20 mm wide and 20 mm thick 1500 mm long Module 1.5 Pressure Angle:20°

commonly the machine is used for woodworking

I plan to reduce the gantry weight using one steel box 100*100*3 welded to two pieces of 150*100*3 gantry side

"this probably won't be accurate enough for machining aluminum" Why?

mod1.5 = 1.5mm dia per tooth so with 28 tooth pinion 1 rev = 28*1.5*pi= 131mm and direct drive gives 131/200 = 0.66mm resolution per full step

for reasonable speed on a rig of that size 4000mm/min would be a good minimum with 400mm/s^2 acceleration
so (to make math easier) 3930mm/min = 30rpm of pinion so gearing 2:1 = 60rpm, 3:1=90rpm, 5:1=150rpm with resolution of .33mm, .22mm and .132mm/step respectively

Assuming a 80kg gantry and ignoring minimal friction in linear slides, the force needed to get 400mm/s^2 (0.4ms^2) acceleration is F =ma = 80 * 0.4 = 32N, which gives the torque on a 28tooth, M1.5 gear is (radius =62.5mm) = 32*.0625 = 2Nm, geared 2:1 =4Nm at motor, 3:1=6Nm, 5:1=10Nm. This ignores losses so add 10-15% for safety.

Boyan Silyavski
16-09-2014, 11:04 AM
This gantry will bend and twist like crazy. Aluminum is out of question if gantry not reinforced. Irving told you also about the rack and pinion and aluminum.

The difference between mediocre machine and a good one is not \$\$\$ but the amount of time you do a proper research and later make right decisions.

Better read some build logs here and things will begin to clear. Or you will regret later. I don't see how rack and pinion will be much cheaper than ball screw at the current China prices. And the rotating nut assembly is not so much different than the RP assembly money wise.

No offence but most of all - Z300mm, seriously? On a first machine, big machine and making decisions about motors without making a detailed drawing not having clear idea about what material you will like to cut mainly.

So why don't you just take a breath, read the forums, make your drawings, show them here, discuss them, correct them, etc. Start from the bed structure, gantry, Z, rails etc.

JAZZCNC
16-09-2014, 04:22 PM
Listen to Silyavski he's given you priceless advice about not Rushing and taking time to choose correct components wisely.!!

If you are going with R&P then forget nema23 and Also forget running Nema34 motors no matter the size with only 60Vdc.
Nema34 motors require much more voltage to get any decent speed from them. This is why they are often run with high power AC drives. Even 75Vdc is on the lower side.

You need to do some careful thinking regards ratios and components you'll use and the feeds and resolution you'll need for the type of work your wanting to do because this relation ship goes all the way thru the component selection and is very easy to get wrong when using R & P.

In general you need an excess of power to compensate for the inefficiency of R & P so if you get the selection wrong and don't have enough spare then it means running the machine at much reduced rate to compensate. This is often why people building with R&P are dissapointed and more often than not this is because of poor Ratio/Motor/Drive/PSU selection.
With 80KG + You NEED at least nema34 motors around 8nm and these need to be run with High power drives if you want the best from them.

Guessing and rushing not doing your home work will result in poor performance and wasted money I guarantee you this.!!

Such a large machine for first time project is a recipe for wasting money and dissapointment so LISTEN CAREFULLY to what is being advised and SLOW DOWN.

msacnc
16-09-2014, 07:11 PM
thanks Silyavski and JAZZCNC for your advices...but
i read many many threads over 2 year from cnczone and other sites and i build a prototype of cnc using wood and it work fine for first build and i build the second one (cheap) since 1 years 2000m*1000 using wood and home made component such as linear rails and screws steppers from old big printer, home made power supply and so on but the machine is Vibrating like crazy when i test X gantry (rigidity problem)finally i stopped.

the big problem is in my county is the difficulty to buy cnc component from uk,usa and china (very very costly...shipping) , and also there is no Aluminum profiles here just thin Aluminum ,wood and steel.
someone bring some standard cnc components from china (like stepper kits and china gear i mentioned above)To sell them then i think to build a big steel cnc (better than wood) using these components(there is no alternatives to choose) he bring a few types of linear rails, ball screws, R&P and electronics and the problem is "i need to choose quickly before he sell them" 3 or 4 from each type no other chance (this is why i not yet begin to construct machine bed structure and gantry)

he bring :
(ROUND RAIL) all size and nuts
(BALL SCREW) 1605,1610,2505,2510,2525 (2m length)
RACK 20*20 2m length
PINION 28 TEETH
HELICAL RACK 30*30 S45c 1.5m length
HELICAL PINION 24 TEETH
gear rack 1.25mod 1:5
power supply 48V and 60V
steppers
JK57HS82-3004-02 (NM 2.2 - 311 oZ 3A)
JK57HS112-3004 (NM 3 - 425 oZ 3A 6.8mh)
JK86HS78-5504 (NM 4.6 - 651 oZ 5.6A 3.4mh)
JK86HS115-4208 (NM 8.7- 1232 oZ 6A)
chinese spindle 2.2kw air
chinese spindle 3kw water

i have already 4 driver microstep 80V 7.8A

msacnc
16-09-2014, 07:23 PM
i need help to select from these components

i appropriate you if you give me link of any steel cnc log

if with these components no chance to build big cnc suggest max dimension i can buid

i go to R&P because i read its suitable for large machines

i mainly use this machine for woodwoking

i need high accuracy finishing parts 2D 2.5D

JAZZCNC
16-09-2014, 10:42 PM
Well you really have got a problem with this selection because the motors and PSU voltage don't match together well.

R&P needs the JK86HS78-5504 (NM 4.6 - 651 oZ 5.6A 3.4mh) or the JK86HS115-4208 (NM 8.7- 1232 oZ 6A) and with only 60Vdc you don't have enough voltage to get good performance from these.

The JK57HS112-3004 (NM 3 - 425 oZ 3A 6.8mh) are not suitable for R&P and are better suited to 1610 ballscrews but again with only 60V and high inductance the performance will be lower. They really need 70+Vdc to get good performance.

My advise would be don't buy any of them has they are not matched nice but if I must choose then I'd say go with 3Nm and 1610 and build to this size.

If you can push the Voltage upto 70-74Vdc and use toroidal transformer PSU then you could get away with JK86HS78-5504 (NM 4.6 - 651 oZ 5.6A 3.4mh) and 28T R&P with 5:1 ratio.
This would give pitch equal to 22mm (Mod1.25 28T DP = 35 x pi / 5=22 ) which would give decent resolution for wood and good speed so you could tune motors down so they run slower where torque is higher and still maintain good feed rates.

Really the only motors you can use are the JK57HS112-3004 (NM 3 - 425 oZ 3A 6.8mh) and JK86HS78-5504 (NM 4.6 - 651 oZ 5.6A 3.4mh) and both these need more voltage, esp the 4Nm 34's.
The JK57HS112-3004 (NM 3 - 425 oZ 3A 6.8mh) with 70Vdc would perform best.

HipoPapi
16-09-2014, 11:13 PM
Hi there,

In My opinion the best way to estimate weight is the following:

First 1. Use Sketchup to build your model.
Step 2. Any components in your build must be converted into groups or components otherwise you are f****d in sketchup.

So for instance if you make a 100x100x3x 1500 solid in sketchup turn it into a group or component as soon as is made.

Step 3. if you right click a group or component and go into entity info depending on your unit setup (which should be mm for this type of work) you will see the exact cubic mm of the component.

Step 4. Go here: http://www.aqua-calc.com/calculate/volume-to-weight

If you dont see the cubic mm option click show more units and will be there.

Search for steel or aluminum or whatever and calculate.

Have a good night.

Vass

msacnc
16-09-2014, 11:33 PM
thank you very much JAZZCNC for your help

i think i will go to ballscrew as you suggest
one 2510 for X (2m long) but what about wrapping..
one 1610 for Y (1.2 m)
one 1605 for Z (0.5 m)

according to eq. from cncrouterpart suitable V = sqrt(mh)*32 which mean that Nema34 with 3.4mh required 59v for best performance which is close to 60v PS is this correct

i know that Nema23 425oz is better specially for speed but as you mentioned it requires at least 72V which is not available

can i use central 2525 ball screw with Nema34 for X and Y axis

Boyan Silyavski
17-09-2014, 05:47 AM
can i use central 2525 ball screw with Nema34 for X and Y axis

Dont do that. Especially at that size gantry and that Z travel.

At 300mm z travel you have to make sure when you design it, that the long ball screws are more or less on the height where the cut happens. One design consideration most people overlook.
That is good for you because you will have maximum actual travel 2000mm long - ball nut legth

msacnc
17-09-2014, 06:54 AM
To reduce the risk i will reduce the overall machine size frame to 2000*1150*400 mm

X one ballscrew 2510 length 1750

Y one ballscrew 2510 length 950mm

z one ballscrew 1605 length 300 mm

msacnc
17-09-2014, 07:04 AM
i also plan to use design made from steel like this

http://www.mycncuk.com/attachment.php?attachmentid=13389&stc=1

X gantry using 50*70*3mm box

all bed made using steel

one central ballscrew 2510 for X gantry

msacnc
17-09-2014, 07:51 AM
also i plan to pay this steppers

http://www.aliexpress.com/item/3-PCS-1-8deg-Nema-23-CNC-Stepper-Motor-Bipolar-114mm-4-2A-2-8Nm-400oz/1789406140.html

i am confused vender say suitable PS 24-48V but acoording to sqrt(3.8 mh) * 32 = 62V ???

irving2008
17-09-2014, 08:15 AM
That's because vendor wants you to buy the PSU he has on his site, the recommendation is meaningless as he doesn't know intended use.

Single ballscrew on that width isn't going to work, the gantry will rack and bind if you cut towards the edges.

Inertia of 25mm screw is too high for a 2.8Nm motor, you'll be severely constrained on feed rates as you won't have the acceleration to change direction quick enough. Unless you go with fixed screws, driven ballnuts.

You may well have made a usable machine before but from your description this is in a different league and needs much more thought and design. We appreciate your supply difficulties but you're wasting your money by rushing to buy the wrong kit.

msacnc
17-09-2014, 08:16 AM
i need advice JAZZCNC for ordering one Power supply 70V~90V 12A in this link

http://www.aliexpress.com/item/800W-70V-11-4A-CNC-Switching-Power-Supply-Cooling-Fan-for-LED-CNC-Engraving-Machine-SM547/1126181657.html

i already have 4 driver 80V 7.8A

and i hope this PS match The JK57HS112-3004 (NM 3 - 425 oZ 3A 6.8mh) with 2510 and 1610

is one enough for 4 nema 23 steppers

thanks

msacnc
17-09-2014, 08:38 AM
thanks irving2008 (http://www.mycncuk.com/members/125-irving2008) for reply i appropriate your effort with me thanks again

Single ballscrew on that width isn't going to work,
2 ballscrew mean double cost what is the max width of gantry that work well with one

what is your opinion about the design of steel machine above

Inertia of 25mm screw is too high for a 2.8Nm motor
i pay this PS 70~90V with previous Nema23 3NM is this work also double 1610 with 1750 mm length work good or not?

JAZZCNC
17-09-2014, 09:41 AM
Ok well it,s been said but will say again to backup. Forget Single screw down centre gantry will twist at this width. Forget 25mm screws unless running nema34 with high voltage AC drives.

Now the sqrt(3.8 mh) * 32 is just a guide and in practice you can go higher without any issues or shortening motor life too considerably. (One thing to note because your in a Hot country I would consider putting cooling fans on the motors, PC CPU fans work well)

The PSU you linked too would work ok but first I would look into making your own.?
It's very easy all you need is toroidal transformer, 1 x brdige rectifier and capacitor/s. Obviously these need to be sized to give the output your require which we can help with.
You must have electrical component suppliers like RS components in your country so I would enquire about costs because Unregulated toroidal PSU is much better for CNC when your running near the drives Max voltage.

So Definately go with 2 x 3nm/1610 running 70V. Will warn thou that at 1750mm length with 16mm screws your at the point when whip at higher feeds can cause problems so you may still need to limit motor tuning to lower rapid speeds.?
Also the mounting and alignment will need to be perfect, which it should be anyway, but if your off just a little then this is amplified at this length which can introduce whip and resonance.!

So hopefully now you see why WE all have been asking you to slow down and think about it becasue so many things affect other parts of the machine and for good machine you need balance and components working in harmoney not fighting each other.!! . . . . In CNC we Make LOVE(chips) not WAR. .Lol