Re: [CAD_CAM_EDM_DRO] BALLSCREWS QUESTION

Thanks. If I'd actually done a conversion that probably would have been very very obvious!


-----Original Message-----
From: R Rogers <rogersmach@...>
To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Mon Jan 24 19:51:29 2005
Subject: RE: [CAD_CAM_EDM_DRO] BALLSCREWS QUESTION


The only reason that I pointed to a two-step configuration is because in a 10:1 reduction using a single belt, the larger pulley being on the end of the ballscrew would surely prutrude past the surface of the table and continually be in the way. And would be virtually impossible to mount a servo in the conventional method. Of course either way won't be conventional.

Ron

"Terrenoire, Adrien L" <TerrenoireAL@...> wrote:


Ron,

Why would a 8:1 or 10:1 need to be a 2 step reduction? Is it to reduce
belt friction (more belt wrap on the large gear) or is it a moment of
inertia concern (large diameter gear = geometrically larger I). I'm
guessing the latter but just looking for confirmation.

Regards,

Adrien

-----Original Message-----
From: R Rogers [mailto:rogersmach@...]
Sent: Monday, January 24, 2005 2:10 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] BALLSCREWS QUESTION



Manel.

You can use those with a higher reduction between the screw and the
servo. Typically, there is a 2 or3:1 reduction with a .200 or 5mm per
revolution screw. You would need approximately 4 times that reduction to
retain the servo resolution per rev. I would go with like an 8-10:1
reduction then use a 200 or 250 quadrature encoder and a Gecko320. The
reduction would undoubtedly need to be a two stage arrangement. Two
belts running in parallel, each one with a 4 or 5:1 reduction. The belt
on the servo could be half the size of the belt on the screw. Lets see,
20 mm/8:1 reduction=2.5mm traverse per servo rev. 2.5mm/1000 servo
counts per rev (250 encoder quadrature)=.0025mm traverse per pulse step.
1mm/.0025 =400 steps per unit in perhaps Mach2 "motor tuning" menu to
calibrate the axies. This represents units selected as millimeters.
This is basically the same as a mill with 2000 steps per unit in inch
units having a .200" lead ballscrew. .0001" traverse per step. 8:1
reduction, Gecko320 and a 250 count encoder 1000 steps per rev. would
work well.

Ron


mfmiranda wrote:



I'm older to this list but this is my first question to the forum.
I'm looking at putting together my own CNC mill. I already have two
superb 40" german x/y linear assemblies and the servo motors (54V, 7A,
3000 RPM), everything saved from junk. I intend to use Gecko 340 and
Mach2.

The question I have regards to the TPIs of my ballscrews -they are 20mm
- (0.8") - per revolution. This seems very large to my purpose.

I would like to know if some of you kind folk would take a moment to
figure the way I can use it with a minimum of acurracy, say 0,01mm,
using belt reduction, I guess.

Thanks very much,

Manel Miranda
Braga, Portugal









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