Need Help!- Servo Motor Size for Bridgeport type machine

[native34]

What size Servo can i use to convert a bridgeport type mill to CNC?

[jmelson]

Originally Posted by native34 What size Servo can i use to convert a bridgeport type mill to CNC?

Is this a Series I or Series II machine? Assuming an import manual machine, will you be changing to ballscrews or keeping the Acme screws? Do you need to drive the screws by direct coupling, or can you use a belt reduction drive? Bridgeport now uses SEM motors on their EZ-Trak models, and I think on the R2E4 and later servo BOSS machines. These are great motors if you can get a deal on them.

If you want direct drive or 1:1 belt drive, a beefy NEMA size 34 motor could do it, or a size 42 for sure. If you can use a 2:1 or 3:1 reduction, then a size 34 will be no problem. For better acceleration, a long, thin motor is better than a short, fat one.

Anyway, for a series-I machine (9 x 42 table or thereabouts) something like a peak torque of 20 In-Lb should be fine. I'm running my 9 x 31" ancient Bridgeport with some 9 In-Lb peak servo motors, and it works pretty well. I could probably go up, but this drive system came from a smaller machine, and has 3/8" wide belts, which snap if I turn the torque (current) limit up.

Jon

[native34]

how much voltage and amps should these motors be as i currently have a stepper system i would like to use the power supply and everything from exept stepper drivers i plan on buying G320X from Gecko my powersupply is 50V 16A my mill is a Bed mill with bridgeport type variable s peed head on it. For now i plan on using the existing lead screws until i can afford to put ballscrews on. The table size is 9x42. I would like to move the head and not the quill.

[HimyKabibble]

I did mine with 850 oz-in peak servos, 500 line encoders and G320s from www.homeshopcnc.com. I currently have 2.5:1 belt reducers and 1" 4-pitch ballscrews. It is pretty much unstoppable, and *too* fast - It'll do 400 IPM at 70V, but I only run it at 200 IPM.

Regards,
Ray L.

[native34]

What are the motor voltage and amp specs? Are you using a 70V power supply and what is the amperage of the power supply Are all the motors the same specs event the Z Axis Motor? What type of Timing Gears are you using and where did you get them?

[jmelson]

Originally Posted by native34 how much voltage and amps should these motors be as i currently have a stepper system i would like to use the power supply and everything from exept stepper drivers i plan on buying G320X from Gecko my powersupply is 50V 16A my mill is a Bed mill with bridgeport type variable s peed head on it. For now i plan on using the existing lead screws until i can afford to put ballscrews on. The table size is 9x42. I would like to move the head and not the quill.

50 V may limit your traverse speed. It scales linearly, so if you had a 100 V motor and a 50 V supply, you would only get half of the rated motor RPM. That might be enough, depending on the motor, belt reduction (if any) and what rapid traverse speed you wanted to see.

16 A sounds like a lot, but at 50 V that is only 800 W, probably enough for one motor's peak rating.

Move the HEAD not the quill? That would not be a Bridgeport-style machine. Did you mean move the KNEE? That will take more power, as there is a lot of weight in the knee and parts above it.

Jon

[native34]

Ok i am very confused now. Let me start out explaining what i have then waht i am looking for. I currently have a stepper controlled Mill from Harbor freight model 33686 Round column mill. Control specs are as follows.

cnc4pc C11 Multifunction BOB
50V 16A unregulated power supply from Antek Inc
4 G203V Stepper drivers from Geckodrive
3 906in-oz stepper motors from Kelinginc

What i am trying to do is convert this system over to Servo for my new Mill which is in the picture above it is a Siber Hegner RB-1 Rigid Bed Mill with a bridgeport type variable speed head. As i know almost nothing about Electronics i would like information regarding Servo motor and power supply combination. If i go with the 850 in-oz servos on homeshopcnc website i would need 4 of these. What size power supply would i need to power all 4 of these motors? I have motor specs listed below. I also plan on using G320X Drivers/Amplifiers from Gecko. Thank you for all your help so far.

skewed rotor design

continuous torque: 170 oz/in
peak torque: 850 oz/in
terminal voltage: 72 VDC
continuous current: 8.5A
peak current: 38A
inertia: 3.39 kg.cm^
maximum operating speed: 4200 rpm
torque constant (KT): .1757 N. m/am
voltage constant (KE): 15.71 volts/100 rpm
resistance: 85 ohm
inductance: 2.35 mH
weight: 8.8 lbs
7 inches

[Al_The_Man]

My Excello's which are slightly smaller than your mill uses motors over twice the size, SEM 26"/lb torque together with 2:1 reduction.
If you CNC the head you are either going to need a much larger motor or fairly high reduction. The inertia required to move a heavy head when doing rapid operations such as peck drilling is considerable.
The motors you have I would estimate would require a min 80vdc supply at around 2kva.
Personally I would not consider CNC'ing a mill and not converting to ballscrews.
Al.

[native34]

Ok lets say i wanted to use Gecko drive G320X drives for this mill and use 4 Servos what size power supply would i need? or am i stepping outside the capabilities of the Geckodrive, although i find that hard to believe as i have seen people claiming they are using G320's with their bridgeport style mills in other posts. I'm just not savvy enough to grasp the electrical jargon and what it means i am more of a mechanical person. I wouldn't know what a kva was if it hit me in the head, but i do understand "X" Volt "X" Amp powersupply will drive all 4 motors. I'm just trying to the proper parts i need the first time. instead of trying to guess what i need and think i got the right part then when implemented it turns out to be wrong.

[HimyKabibble]

I have run for almost the last year on what is, if you go by the book, an under-powered power supply - 68V @ 11A. However, it's done just fine running all three motors, though rarely, if ever, all three at once, since I do 2.5D milling, not 3D. I've recently upgrade to a much larger supply - 68V @ 24A.

So far, I've been using the knee as the Z axis, with the stock leadscrew and bevel gears, plus a 4.8:1 belt reducer, giving a total of 48:1 reduction, or 96,000 steps/inch. I also have two 200 pound gas springs on the knee. This gives OK performance, but not great. I can get 75 IPM, but normally run only 50. Within the next few weeks, I'll finally be adding a quill drive, and the knee will then be used only for tool length compensation. Moving that much mass with the leadscrew, there has been noticeable wear on the leadscrew and/or bevel gears, as backlash has increased since I first started using it. I would NOT recommend using leadscrews on a bed mill - I think you'll see a lot of wear in a big hurry.

On my machine, at 68V, I have more speed than I can safely use. It is capable of close to 400 IPM, though I've never run it more than 350, and normally run at 200. It's just too scary at those high speeds - no time to react if something goes wrong. Of course, you'll need a hardware motion control, like the SmoothStepper, to get up to those speeds. You won't get there running a parallel port. Running reduced voltage, max. speed will be your only real loss, so unless it's REALLY important to go REALLY fast, 50V is probably OK. And if you're only doing 2.5D milling, then your 16A supply is also probably OK. If not, go to Antek, and buy one of their 45V/1500W transformers, and then go do PMDX.com, and buy a couple of their PMDX-135 "Power Prep" modules. Connect them together, and you've got yourself a kick-a$$ dual output power supply capable of providing as much power as those motors could possibly use.

As far as power, my machine is practically unstoppable. It'll snap off a 1/2" carbide endmill without even losing position, so there's no issue with having enough "thrust".

You can get any kind of pulleys and belts you need, plus all the design information necessary to make your choices, at www.sdp-si.com.

I STRONGLY recommend converting to ballscrews and zero backlash nuts, and using Nook XPR screws. They are only slightly more expensive than commodity rolled screws, but FAR more accurate (0.001"/foot lead accuracy, vs 0.003-0.004" for all the others), and are also much smoother and quieter. They're almost like ground screws, at a rolled screw price. Or, you might check out seller linearbearings on E-Bay. He gets some very nice Chinese ballscrews and zero backlash nuts are VERY good prices. He also has bearings and supports to go with them, and can do the end machining to your spec. If you contact him, and tell him what you need, he'll put up exactly the items you need. His prices are excellent.

Regards,
Ray L.