Machine geometry

[email protected])

Per the recent request for lurkers to de-lurk:

I recently received some linear components from Bill Scalione, and now
have to decide what kind of machine to build with them. I have two sets
of 1" dia. rails, 54" and 66" long. Also two tables, nominally 22"
square with two open bearings at each corner along one edge, and one
open bearing centered along the opposite edge. These tables weigh about
30 lbs apiece.

My question is what geometry will be best for a (mostly) wood router? I
like the greater working envelope that a moving-Y gantry system would
provide, but this requires a longer leadscrew and probably heavier
motor. The moving-X table system, while easier to build, and probably
more accurate, provides only half the travel.

Any suggestions appreciated.

Geoff Roehm

Robert Campbell

#757

Geoff ,

The size of the table depends on what you plan to make.   I have a 4' by 4'
moving gantry system which has some play in it.  I am currently building a
2' by 2' fixed bridge cnc router that should be very ridged.  I cut a lot of
Corian and wood parts.

Bob Campbell

Show quoted text

----- Original Message -----
From: Geoff Roehm <groehm@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Monday, June 07, 1999 5:44 AM
Subject: [CAD_CAM_EDM_DRO] Machine geometry

From: groehm@... (Geoff Roehm)

Per the recent request for lurkers to de-lurk:

I recently received some linear components from Bill Scalione, and now
have to decide what kind of machine to build with them. I have two sets
of 1" dia. rails, 54" and 66" long. Also two tables, nominally 22"
square with two open bearings at each corner along one edge, and one
open bearing centered along the opposite edge. These tables weigh about
30 lbs apiece.

My question is what geometry will be best for a (mostly) wood router? I
like the greater working envelope that a moving-Y gantry system would
provide, but this requires a longer leadscrew and probably heavier
motor. The moving-X table system, while easier to build, and probably
more accurate, provides only half the travel.

Any suggestions appreciated.

Geoff Roehm

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[email protected])

#758

On Sat, 12 Jun 1999 21:37:10 -0500, "Robert Campbell"
<rcamp@...> wrote:

I have a 4' by 4'
moving gantry system which has some play in it.  I am currently building a
2' by 2' fixed bridge cnc router that should be very ridged.  I cut a lot of
Corian and wood parts.I missed the description of your 4X4, if you posted it. Could you say
how it was constructed, as to guides used, gantry framing/structure, and
also positioning method/hardware? I'd most like to hear any insights
you've gained from this "some play" which you've experienced. Most
helpful would also be the Z-travel range you've worked with on your 4X4,
or do I get your drift correctly, that it's even in just the X-Y plane
that you have this play?

TIA,
Gar

Robert Campbell

#771

Gar,

The 4 by 4 was built using Item aluminum extrusions.  The X and Y rails were
Ina bearings on 14mm shafting (top and bottom).  The Z axis uses THK
bearings with about 6 inches of travel.

In order to reduce the racking of the gantry, I built a double cable system
to counteract the racking.  Now when I push on one side, the cables will
pull on the other side.  This has helped a great deal.

After I build my new 2 by 2 fixed bridge system, I will retrofit my 4 by 4
with THK rails and bearings on the X and Y.

Bob

Show quoted text

----- Original Message -----
From: Gar Willis <garfield@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Saturday, June 12, 1999 9:58 PM
Subject: Re: [CAD_CAM_EDM_DRO] Machine geometry

From: garfield@... (Gar Willis)

On Sat, 12 Jun 1999 21:37:10 -0500, "Robert Campbell"
<rcamp@...> wrote:

I have a 4' by 4'
moving gantry system which has some play in it.  I am currently buildinga
2' by 2' fixed bridge cnc router that should be very ridged.  I cut a lotof
Corian and wood parts.I missed the description of your 4X4, if you posted it. Could you say
how it was constructed, as to guides used, gantry framing/structure, and
also positioning method/hardware? I'd most like to hear any insights
you've gained from this "some play" which you've experienced. Most
helpful would also be the Z-travel range you've worked with on your 4X4,
or do I get your drift correctly, that it's even in just the X-Y plane
that you have this play?

TIA,
Gar

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#772

On Sun, 13 Jun 1999 09:55:01 -0500, "Robert Campbell"
<rcamp@...> wrote:

<debriefing snipped; thanks, most helpful to have these comparisons>

After I build my new 2 by 2 fixed bridge system, I will retrofit my 4 by 4
with THK rails and bearings on the X and Y.OK, so sounds like you're expecting that with stiffer/tighter rails,
you'll be back to where you expected to be, in terms of "slop"? Sounds
good to me. I'm always kinda wondering, altho I have attempted to be as
massively stiff as possible (no, not me personally, the table :), what
I'll end up with as far as repeatability. I don't really HAVE any reason
to strain, given my interest in routing foam, thin alum sheet, and
Rayite, but ya know how it goes; everyone wants to see and continually
sanity check how closely their expectations are likely to match actual
results.

Thanks for the input. I tell people I'm building my own "four-by-four",
but it's gonna run on rails, so they needn't worry; I won't get too far
nor do too much damage. B)

Gar

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Machine geometry