RE: [CAD_CAM_EDM_DRO] Gecko problems - What is going on?

Hi George,

You'll need a servo of at least 40 lb-in continuous torque (standard Nema 42 servo). With a 2.5:1 reduction. 100volt and 14 amp continuous ampere rating. A gecko320 or 340 will operate a servo this size quite well. I use no assist on the knee and get rapids of 50 ipm. Using the stock screw. Dont need ballscrews on the knee. There is no backlash due to the weight of the table. The only thing that may need to be corrected is backlash in the bevel gears in the screw mechanism. Although there is backlash compensation in the software putting a shim behind one of the bevel gears is an easy fix.

Driving the knee has many many advantages. 14" of Z travel. The spindle can still be operated manually for sensitive drilling, reaming and tapping. Zero'ing out Z is simple as rolling spindle/cutter down and contact workplane, lock spindle, zero out software. No driving the tool into the workpiece. No handcranking 1200 lbs of cast iron up and down anymore (my favorite)

If you need a mount I am in the process of producing X, Y and Z (knee) servo mounts. I have a prototype set made that I am installing on a machine. And very soon I will be producing these to sell. They are standard Nema42 mounting config machined from a solid billet of 6061-T6 aluminum and will include all neccesary hardware i.e. mount, cover, adapter, tapered timing sheave, motor timing sheave, belt and fasteners. I have been in the process of designing and refining them for the last few months and am very close to listing them for sale. Many other projects have come up and have sidelined my efforts. I'll post here and my website when I have sets or individual mounts available.

These are very strong well designed and machined mounts that totally enclose the belt and assemble rather quickly. They presently do not have provisions for handcranks however will retain the standard Bridgeport resolution dial for mechanical proof of position. If the handcranks are an issue for some, I may change the design or offer an adapter to accomodate them. Personally, I never use them. Who wants to crank when we can push a button? :-)

Ron





"George Taylor, IV" <gtaylor@...> wrote:

Ron,

I would like to put a servo on my Bridgeport knee.
What motor did you use, geared/direct drive, and did
you have to do the springs/pneumatic cylinders thing to
get the knee to move? Putting a drive on the knee seems to
provide a lot of advantages in setup, tool changing etc.
plus, I don't really like driving the quill for the Z.
Any pics of your setup? What did you use for a knee screw?

Thanks

George


-----Original Message-----
From: R Rogers [mailto:rogersmach@...]
Sent: Friday, April 08, 2005 10:28 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Gecko problems - What is going on?


I totally agree Les. I rarely read about a G320/340 blowing. I lost one
because I didn't have the 100 volt 1000uF capacitor at each drive. My
machine was idle and there was a few loud clunks and pops. Consulting
Jon Elson and others it was determined that it was obviously spikes on
the line coming in and the power supply was making that noise. Lost a
drive as a result and it only blew the $2.00 cap inside the drive that I
replaced and its back in service. Adding the large Caps at each Gecko is
a must. They help protect the drives from line spikes and also assist in
filtering the current going to the drive. Before I added them the Z
motor driving the Bridgeport knee would warm significantly after an
hour. Now I can drill holes all day and it stays cool. Made a world of
difference.

The stepper drives are the ones that are problematic. It really isnt the
drive itself, they just require more care in setting up and are not as
forgiving as the servo drives. They are much more complex from what I've
read. Servo drives rarely ever blow. Bad connection on a stepper drive
its gone. Bad connection on a servo drive and it just doesnt move until
its reconnected.

Ron

Les Newell wrote:

It is the stepper drives that seem to have a high mortality rate with
bigger motors. As far as I know the servos are rock solid. I have
toasted 2 stepper drives but the servo drives are still working fine.

Les

lcdpublishing wrote:

>There appears to be a number of people reporting problems of "Blowing"
>Gecko servo drives. As Gecko has such a solid reputation overall
>(many, many, positive posts), I am wondering what is going on.
>
>Is there something inherent in the design, wherein if you do "this"
>then the drive will "Blow"? Just seems very strange that something
>that works for a couple of months (years whatever), can suddenly blow.
>I am planning a servo driven machine right now and I sure don't want to

>end up watching the drives blow every couple of months because I
>did "Something" that no one can determine what the cause is. This is
>sort of "X files" spooky stuff.
>
>
>
>
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>
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OFF Topic POSTS: General Machining
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aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it
if you have trouble.
http://www.metalworking.com/news_servers.html

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there,
for OT subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
bill
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