[Biggermens]

I am building this cnc router table and i think i might have over did it and now i am having a hard time finding motors big enought to power this
i understan thare are some formulas the find this out ??

Thomson Linear Guides are 25mm and i have 4 berrings
Thomson Ball Srew is 1inch and 4 turns per inch
the gantry will be about 500 Pounds
and i want to go 90 to 100 IPM

How would i calculate this ??? with aceleration ???

THanks

[Oldmanandhistoy]

Hi,

Have a look here may help you. http://www.cnczone.com/forums/showthread.php?t=8129

John

[Al_The_Man]

There is also many free graphical design programs like Kollmorgen etc.
I did one that had about a 500lb gantry http://cnczone.com/forums/showthread...ighlight=rosta
Al.

[JerryFlyGuy]

It's fairly easy to calculate if you want to do several iterations to find what works best I'd suggest setting up a spread sheet. There are several more questions which need to be answered before you can proceed.
1) Servo or stepper?
2) Reduction onto the ballscrew or direct drive?
3) Time to rapid speed [ how long do you want it to take, if your table is long this could be lower, if its shorter then you may never get up to speed w/ a longer time allowance as it needs to start slowing down before it gets to rated speed]
4) Force at the tool tip [ how much actual lbs force to move the tool through the mat'l at your req'd ipm.

If you post some of this I might be able to figure out roughly what your looking at...

Jerry

[Farmers Machine]

go to automation direct .com and look up sure servo motors and drives they come with encoders and with or without brakes. up to 3 KW call the 1-800 # to speak to tech support and they will walk you thru. Have gotten very good service and parts from these people.

[Mr.Chips]

It's fairly easy to calculate if you want to do several iterations to find what works best I'd suggest setting up a spread sheet. There are several more questions which need to be answered before you can proceed.
1) Servo or stepper?
2) Reduction onto the ballscrew or direct drive?
3) Time to rapid speed [ how long do you want it to take, if your table is long this could be lower, if its shorter then you may never get up to speed w/ a longer time allowance as it needs to start slowing down before it gets to rated speed]
4) Force at the tool tip [ how much actual lbs force to move the tool through the mat'l at your req'd ipm.

If you post some of this I might be able to figure out roughly what your looking at...

Jerry

I have often thought about this, and I know I will be very much underpowered with only 116 InLb stepper motors using Xylotex control boards with a 28V 8 Amp PS.
It is a fixed gantry so that is less work on the motors.

1. Stepper 116 InLb
2. Direct drive 1/2" 10 Acme rod. 1 start/turn.
3. Moving table is 30" long. Not sure what figures to use here?
4. Force at the tool tip. ?? Using 1.74 HP router. say 3/8" 2 flute down cut carbide mill. Cutting MDF. Not sure what kind of force this would be.

Given these knowns and unknowns what should be the stepper size?

[JerryFlyGuy]

Chips, that does pose a bit of a problem. Your steppers are rated up too 16-in-lb's but they will not get ANYWHERE near there w/ the lower voltages of the Xylotex power supply [I don't think anyway..]. Can you tell me what your nameplate spec's are for your stepper [ Voltage and amp's] I'm guessing thats a Nema 23 motor? [256 oz-in max] If you have the make/model that might help as well as I can go to the website [possibly] and get power charts from there also!

Now, w/ more knowledge comes more questions

If its a fixed gantry the weight doesn't matter, what is the weight of your table[ the moving part]??
Also, in your first post you'd stated a ballscrew and then in the last post a Acme thread can you clarify which one?

If your cutting MDF then the tool forces are very low, [you can imagine how much force it takes to operate a router in mdf by hand [ not very much ]

Sorry to pose more questions but until the fact's are known its a bit tough to 'tell' anything. It's kinda like looking at a race car and telling someone exactly how fast it goes or how much HP it has w/out even knowing what engine is in the car. It wouldn't be to terribly accurate. Not that you should expect I can work miracles and will have the exact performance spec's from your router either I can get close but.. you know what 'close' only counts in right?

Jerry

[Mr.Chips]

Chips, that does pose a bit of a problem. Your steppers are rated up too 16-in-lb's but they will not get ANYWHERE near there w/ the lower voltages of the Xylotex power supply [I don't think anyway..]. Can you tell me what your nameplate spec's are for your stepper [ Voltage and amp's] I'm guessing thats a Nema 23 motor? [256 oz-in max] If you have the make/model that might help as well as I can go to the website [possibly] and get power charts from there also!

Now, w/ more knowledge comes more questions

If its a fixed gantry the weight doesn't matter, what is the weight of your table[ the moving part]??
Also, in your first post you'd stated a ballscrew and then in the last post a Acme thread can you clarify which one?

If your cutting MDF then the tool forces are very low, [you can imagine how much force it takes to operate a router in mdf by hand [ not very much ]

Sorry to pose more questions but until the fact's are known its a bit tough to 'tell' anything. It's kinda like looking at a race car and telling someone exactly how fast it goes or how much HP it has w/out even knowing what engine is in the car. It wouldn't be to terribly accurate. Not that you should expect I can work miracles and will have the exact performance spec's from your router either I can get close but.. you know what 'close' only counts in right?

Jerry

Thanks Jerry,
They are 116 OZ IN Nema 23 One Stack (Soerry I said 116 in lb before)

FLUID METERING CO
BYOBBET, NY 11791

116 OZ IN
POWER MAX II 1.8 STEP MOTOR
MODEL P21N8XC – LSS -NS- 03
CUSTOMER PART NO: 110588
IS(DC): 1.75 A BIPOLAR SERIES
Vs(DC) 65V
PO.48W T:90C MAX
CS:1500 RPM DATE 01066790

Hope this helps.
Hager

[Biggermens]

It's fairly easy to calculate if you want to do several iterations to find what works best I'd suggest setting up a spread sheet. There are several more questions which need to be answered before you can proceed.
1) Servo or stepper?
2) Reduction onto the ballscrew or direct drive?
3) Time to rapid speed [ how long do you want it to take, if your table is long this could be lower, if its shorter then you may never get up to speed w/ a longer time allowance as it needs to start slowing down before it gets to rated speed]
4) Force at the tool tip [ how much actual lbs force to move the tool through the mat'l at your req'd ipm.

If you post some of this I might be able to figure out roughly what your looking at...

Jerry

Hay JerryFlyGuy i have some info see if you can help me that would be much apreciated
1) i want to go with servo and gecko drives
2) i was thinking of going Direct drive
3) this i am not sure i never realy used cnc machines before so what do you think is reasonable my table is about 4 feet x 4 feet of work suface
4) i am not sure about that one also i want to cut some 1/4" think aluminium and think plastic ect..

for rapd rate id like to get 250 ipm and for feed rate id like to get 100 ipm i no i no i will not get that in aluminium

if you look at my photo galary i think my machine is built heavy enough for that
http://www.cnczone.com/gallery/showg...r/5656/cat/500

Thanks Jerry
once agine your help is apreciated

[Mariss Freimanis]

1) Power: Watts = Lbs * IPM / 531

Plugging your numbers in: Watts = 500 Lbs * 100 IPM / 531 and you get 94 Watts of power required, which you can easily get from a NEMA-34 step motor. This assumes you want to accelerate at 1G.

2) Screw Torque: in-oz = (8 * Lbs) / (pi * TPI)
Plugging your numbers in: in-oz = (8 * 500 Lbs) / (3.14 * 4 TPI) which gives 637 in-oz needed on the screw.

3) Picking a motor: A Keling KL34H295-43-8B motor wired in parallel (6A / phase) and used with a 72VDC power supply delivers 345 in-oz of torque at 900 RPM when used with a G202 or G203V.

4) Gearing: Screw RPM = TPI * IPM
Plugging your numbers in: RPM = 4 * 100 which gives 400 RPM on the screw. Meanwhile the motor is turning 900 RPM.

Reduction ratio is Motor RPM / Screw RPM. Plugging your numbers in: 900 / 400 is 2.25 : 1. Use a toothed belt and pulley reduction from motor to screw of 2.25 : 1.

This will put 2.25 * 345 in-oz or 776 in-oz on your screw at 100 IPM; you need only 637 in-oz. At low speeds you'll get 1,435 in-oz on the screw for 2,252 Lbs of push. That should shove your 500 Lb gantry around with ease.

4) Resolution: The drive takes 2,000 step pulses per revolution and it takes 18,000 step pulses to move 1" (4 TPI * 2.25 * 2,000). The resolution becomes 0.000055" per step pulse (1 / 18,000).

5) CNC Software: Mach3 tops out at 45,000 step pulses per second. You need 30,000 step pulses per second to get 900 RPM so your'e good to go with Mach3.

Hope that helps.

Mariss

[Biggermens]

Mariss that is some wiked help
i thank you very much

one more question will i be able to jog at 250 IPM ???? with that setup you got
if no what will i need to move it that fast or am i pusshing my luck ???
i also want it to move pretty fast so i can cut fome

I Thank you Very so Much
Bigger

[Mariss Freimanis]

Probably not. 250 IPM would mean 1,000 RPM on the screw and 2,250 RPM on the motor. The motor develops 130 in-oz at that speed and would apply 292 in-oz (2.25 : 1 reduction) to the screw. It would be perfectly happy to develop that speed and torque. Other things would intervene.

The problem would be:

1) Leadscrew whip. What is the critical RMP for that screw?

2) It would require 67,500 step pulses per second; only 45,000 per sec are available from Mach3. That equals 150 IPM.

Mariss

[Al_The_Man]

one more question will i be able to jog at 250 IPM ????

Many overlook the Motor/load Inertia ratio which is largely governed by the required accel rate.
The Kollmorgen program takes the math out of the calculation as outlined here.
Al.

[Biggermens]

Probably not. 250 IPM would mean 1,000 RPM on the screw and 2,250 RPM on the motor. The motor develops 130 in-oz at that speed and would apply 292 in-oz (2.25 : 1 reduction) to the screw. It would be perfectly happy to develop that speed and torque. Other things would intervene.

The problem would be:

1) Leadscrew whip. What is the critical RMP for that screw?

2) It would require 67,500 step pulses per second; only 45,000 per sec are available from Mach3. That equals 150 IPM.

Mariss

Thanks Mariss

i looked it up and thare will be no problem running 250 IPM with my ball screw
so if i need 67,500 steps per second and mach only do 45,000 steps per second how can i get 250 IPM ????


thanks to everyone for thare help

[JerryFlyGuy]

Chips, well I got a few minutes this morning so I plugged your numbers into my spreadsheet. They are fairly rough, I figured you'd get about 50oz-in w/ that power supply. This is all interpolation from the graphin I could find [which I THINK is a close match to your model] I estimated your table at 100lb's [ probably heavier than it is] and called the 1/2 x 10 screw 30% efficient.

This would give you ~400 lb's stall force [stepper stall torque]
You could get 100 ipm rapid, if your stepper will sping up to 1000rpm [ I question whether it could or not] and I'm sure you'd get a cutting rate of 50ipm w/out much trouble, all depending on how deep your cuts will be.

To improve this, I'd switch to a ballscrew of some sort, reduce the lead of the screw to somewhere around 5tpi or less, this is if you want higher rapids and feeds. The tool force is well in excess of what you need [a guess] and w/ the higher efficency of the ballscrew you'd likely not see a linear reduction in tool force as well. It's all a little vague at this point as there are still several un-known's, things like table weight, and knowing the actual stepper power [ knowing I'm using the proper graph etc..]

Mariss, I like your way of calculating all this, would it hurt to use these and apply some efficency factors to various parts of the equations? I guess knowing a person's system efficency [mechanically speaking] is a bit tough.
Anyway I'll have to copy those down, no harm in carrying them around in one's back pocket

Bigger, if you want higher step rates then buy a G100 instead of a BOB, the G100 will send out 1Million steppers per second per axis.. you could hit alot more than just 250 rpm[ infact you could hit 13333rpm w/ a G202, well.. if the screw would take it! thats 30,000rpm at the stepper btw]
Looks like Mariss has worked out what ya need for you system so I won't dig any deeper

Interesting read there AL, thats a bit over my head on first scan but.. interesting anyway!

Best..

Jerry

[Mr.Chips]

Chips, well I got a few minutes this morning so I plugged your numbers into my spreadsheet. They are fairly rough, I figured you'd get about 50oz-in w/ that power supply. This is all interpolation from the graphin I could find [which I THINK is a close match to your model] I estimated your table at 100lb's [ probably heavier than it is] and called the 1/2 x 10 screw 30% efficient.

This would give you ~400 lb's stall force [stepper stall torque]
You could get 100 ipm rapid, if your stepper will sping up to 1000rpm [ I question whether it could or not] and I'm sure you'd get a cutting rate of 50ipm w/out much trouble, all depending on how deep your cuts will be.

To improve this, I'd switch to a ballscrew of some sort, reduce the lead of the screw to somewhere around 5tpi or less, this is if you want higher rapids and feeds. The tool force is well in excess of what you need [a guess] and w/ the higher efficency of the ballscrew you'd likely not see a linear reduction in tool force as well. It's all a little vague at this point as there are still several un-known's, things like table weight, and knowing the actual stepper power [ knowing I'm using the proper graph etc..]
Best..

Jerry

Jerry,

Like many others this is my first machine to build the second.
Table is less than 30 lbs. I had suspecions about the power and wanted a cheap but rigid machine that is why I went with the fixed gantry, and it is pretty beefy. Too heavy for a movable gantry with skate bearings. (I know I tried He He)

Here is a shot of the linerar bearings and ball screws for No. 2. That should reduce some friction. And it will be a movable gantry.
So I need to up the voltage of the DC PS? How would a torrid coil PS be seem they are pretty cheap to build?

Thanks
Hager

[Mariss Freimanis]

Jerry,

1) A ballscrew was mentioned in the original post. I neglected screw efficiency because it exceeds 95% for that type of screw.

2) System friction losses are best determined empirically. If a leadscrew is involved, decouple the motor and wind some fishing line around the screw. Use a fish-scale on the line and measure the force required to get breakaway force. Multiply the ounces required by the effective radius of the wound fishing line to get breakaway torque in in-oz. Plug the results into:

Lbs = (pi * TPI * in-oz) / 8 to get the force necessary to overcome friction.

If it is a rack and pinion or a toothed belt and pulley transmission, just mesure the force in Lbs of 'pull' required to move the mechanism.

3) The torque @ RPM for the mentioned motor was measured on a dyno here at the stated supply voltage. The motor puts out about 230W mechanical.

4) The G100 is expensive and a bit of overkill. Use a G212 set to 5 microsteps instead. Now 33.75 kHz is required for 250 IPM instead of 67.5 kHz. This is well within the Mach3 limit of 45 kHz.

Mariss

[ger21]

so if i need 67,500 steps per second and mach only do 45,000 steps per second how can i get 250 IPM ????


thanks to everyone for thare help

The Mach3 plugin for the NCpod should be ready soon. www.oemtech.com

[JerryFlyGuy]

Sorry Mariss, I got mixxed up as there were two people looking for answer's here, I got focused on Mr. Chip's question and didn't get back to Bigger's till later, I see it all now

Jerry

[Biggermens]

Mariss

Would it be a good idea that i go with a bigger motor and or higher gear reduction for added insurance ?????

cuz i would not mind cutting fome at 200IPM

What would you sugest to run my machine at 250 IPM ????

that would be apreciated

Thanks