another servos V/S stepper V/S R&P V/s ballscrew thread

[lgalla]

I was convinced to go with R&P and steppers.After seeing Granite Devices servo drives changed my mind.
With R&P it appears 20to 1 gear reduction is necessary with servos while with steppers a simple 3to1 belt is sufficent.
Rather than go on and on.
R&P is for steppers.
Servo is for ballscrews with the pitch required.
Larry

[Al_The_Man]

That is OK until you come to retrofitting something like an older Linde where the gantry weighs upward >300lb with 4 oxy/gas torches and maybe a plasma torch added.
With AC/BLDC servo's having a constant torque up to their rated rpm of 6000~10,000 rpm, high reduction allows the economic sizing of servo's on something like this, especially if you want 1000 IPM rapids .
I have found there is no hard and fast rule.
Al.

[BobWarfield]

I've seen guys juggling torches in Hawaii. I even saw a guy juggle chain saws in a video.

Haven't seen 4 flaming torches and a plasma flying around at 1000 IPM yet.

Sounds like fun. Where can I see the show?



Cheers,

BW

[lgalla]

Hi Al thanks for the information.I did not realize servos had constant torque.I would assume setting feed rates and rapids would be much simpler than steppers.Granite Devices servo amps and Keling brushed DC servos sure look good as price/performance.Will a servo work on R&P without huge gearboxes?
I must do more research to have better understang .
BTW Al your avatar looks like you may be very young.You should really quit smoking
Larry

[Al_The_Man]

Originally Posted by lgalla .Will a servo work on R&P without huge gearboxes? I must do more research to have better understang .

Gearbox ratio depends alot on gantry weight, some reduction is required to economically size servo's.
Obviously the high rapids are not cutting speed but between parts or plates.

Originally Posted by lgalla You should really quit smoking Larry

I've been told that before.

Al.

[lgalla]

Bob,glad you chimed in.
I suppose your reference to would like too see 4 torches rapid at 1000 ipm refers to the problem they may blow out and where would Al and I get a light!
BTWBOB how did the E/G work out on the mill fill?
I recently did a display at a local trade show for Tosiba Machine tool.They shipped their mini mill,the smallest machine they produce.40,000Lbs/40HP.
No E/G!

[lgalla]

Are servos less costly than steppers?May be checkout Granite Devices dual drives.http://www.granitedevices.fi/index.p...c-servo.1drive Will power 2 servos on the X and one more drive will power Y&Z.The cost would be around $150 per axis about the same as steppers.
Keling has DC servos for about $100.I do not know if they are usable with the Granite Devices dual drives.Basically it appears servos can be more cost effective than steppers.
http://www.kelinginc.net/ServoMotors.html
Larry

[BobWarfield]

Originally Posted by lgalla Bob,glad you chimed in. I suppose your reference to would like too see 4 torches rapid at 1000 ipm refers to the problem they may blow out and where would Al and I get a light! BTWBOB how did the E/G work out on the mill fill? I recently did a display at a local trade show for Tosiba Machine tool.They shipped their mini mill,the smallest machine they produce.40,000Lbs/40HP. No E/G!

I'm very happy with my E/G. The machine is solid. If I had it to do over, I'd do it again, and probably fill even more of the column!

Cheers,

BW

[Xerxes]

Originally Posted by lgalla Are servos less costly than steppers?May be checkout Granite Devices dual drives.http://www.granitedevices.fi/index.p...c-servo.1drive Will power 2 servos on the X and one more drive will power Y&Z.The cost would be around $150 per axis about the same as steppers. Keling has DC servos for about $100.I do not know if they are usable with the Granite Devices dual drives.Basically it appears servos can be more cost effective than steppers. http://www.kelinginc.net/ServoMotors.html Larry

The DualDC drive was developed using Keling servos (Nema 23 and 34) as test motors, so the perfect matching is guaranteed.

DC servos are generally a good choice for machine tools as their high inertia iron rotor provides stability against cutting forces & inertial loads. AC/BLDC servos start shining if extreme speeds & accelerations are required (>3000 rpm & low inertia). In heavy industrial use they also benefit from longer life time.

In my opinion rack & pinion is not very good choice for machines where cutting forces are present. It is one of the least rigid solutions.

[lgalla]

Thanks guys for the answers.A recent computer crash wiped out all my research.Hope I can pick your brains.
My gantry weight is max 500LBS.It is 12"x4"x1/4"x7'.I cut 18mm Finnish birch,5'x5' for speaker enclosures.From experience 400ipm cutting is over max.How many watts of servo do I need for X axis to move this gantry.Ballscrews are OK as C-7 is OK.I assume a one inch screw,one inch lead is necessary to reduce the RPM and not have whiplash.C-7 screws and support blocks are reasionable priced here.http://stores.ebay.com/linearmotionbearings.
Tero since my ply comes from your country are you experinced with it?
Al,do you have any suggestions as to the gear ratio or ball screw pitch required for the cutting speed ?
Thanks guys.
Larry

[Xerxes]

Larry,
The power demand question is difficult/impossible if there is no estimate of cutting force. My guess is that cutting forces probably are between 50N and 500N on most DIY machines.

You can definitely find quality plywood from Finland I have also built some speakers but I used MDF since I coated the speakers afterwards:
http://www.students.tut.fi/~kontkant/audio.php.html

[lgalla]

Hay Tero,I use 18mm birch for cabinets as they are used on the road.MDF is probably the best choice for home cabinets.I attached 2 pictures.One is a 28Hz subwoofer,it weights 250 Lbs.The outher is a stage monitor.To day I had the side panels of the monitor cnc'd on a friends machine.21 parts on 1 60X60 birch.He ran the machine almost 800ipm with a 1/4" bit.Time for one sheet was 10 minutes.By template and hand router it could take me 10Hrs.
Have a good evening Terro
Larry