using linear motors to build a small cnc
 

Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router and am
wondering if using linear motors is a good idea and where to find some.
Brand names seem pretty expensive.
I would like to have feedrates of at least 1000 ipm so that eliminates
stepper motors.
Travels would be at least 12" if not 24" on all 3 axes.

Also, what could be used for spindle? Ideally 10,000 rpm

--
Paul

It wouldn't be cost effective and/or they wouldn't have enough torque. For
example my CNC knee mill has 880 oz/in servos. They make 10 revolutions to
move the table an inch. You'd have to get 8800 oz/in linear motor to do the
same. That's 50 lb.ft. I remember buying linear motors that big when I
worked at 3M for $5000 or so. My servos are on Ebay every day for $300.

Karl


"Paul Ragot" wrote in message
...
Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router and
am
wondering if using linear motors is a good idea and where to find some.
Brand names seem pretty expensive.
I would like to have feedrates of at least 1000 ipm so that eliminates
stepper motors.
Travels would be at least 12" if not 24" on all 3 axes.

Also, what could be used for spindle? Ideally 10,000 rpm

--
Paul

"Karl Townsend" remove .NOT to reply wrote
in message nk.net...
It wouldn't be cost effective and/or they wouldn't have enough torque. For
example my CNC knee mill has 880 oz/in servos. They make 10 revolutions to
move the table an inch. You'd have to get 8800 oz/in linear motor to do
the same. That's 50 lb.ft. I remember buying linear motors that big when I
worked at 3M for $5000 or so. My servos are on Ebay every day for $300.

....
I would like to have feedrates of at least 1000 ipm so that eliminates
stepper motors.
Travels would be at least 12" if not 24" on all 3 axes.

I don't know if that high a speed would be possible in that short a
distance. My servos max at 1700 rpm or 170 ipm on my CNC knee mill. But I
limit max speed to 50 ipm. (Chicken s%^&t here) You wouldn't need anywhere
near the torque though, if you geared it 3:1 you'd get 560 ipm top. If you
want to go faster, you'll need big servos.I've seen calculaters for table
weight, speed, acceleration, etc. that give the required servo torque, on a
vendor website

I've no experience with routers. Do they make a three phase router head? I
think so. Running one of these on a VFD would give you variable speed.

Karl

On Fri, 4 Mar 2005 12:16:14 -0400, "Paul Ragot"
wrote:

Linear motors would work great, but they are likely to be too costly
to implement on a small machine

Currently one can get linear motors on many high end CNC machines (DMG
seems to be the biggest proponent)

1000 ipm does not need linear motors from strictly a speed point of
view anyways (backlash etc is another matter). At 1000 ipm go with
brushless servo motors. You can buy the controllers from advanced
motion controls http://www.a-m-c.com/ They are pricier that stepper
controls, but reasonable wrt servo brushless.

You may find that building one machine may be more expensive that just
buying a used CNC - or even pretty close to the price of a small newer
one.


Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router and am
wondering if using linear motors is a good idea and where to find some.
Brand names seem pretty expensive.
I would like to have feedrates of at least 1000 ipm so that eliminates
stepper motors.
Travels would be at least 12" if not 24" on all 3 axes.

Also, what could be used for spindle? Ideally 10,000 rpm

My DMG has a linear motor, you should see the size of the drive it uses,
size of a old at case computer. Lotsa lotsa power. fast tho



Paul Ragot wrote:
Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router and am
wondering if using linear motors is a good idea and where to find some.
Brand names seem pretty expensive.
I would like to have feedrates of at least 1000 ipm so that eliminates
stepper motors.
Travels would be at least 12" if not 24" on all 3 axes.

Also, what could be used for spindle? Ideally 10,000 rpm

"Karl Townsend" remove .NOT to reply
wrote in .net:


I don't know if that high a speed would be possible in that short a
distance. My servos max at 1700 rpm or 170 ipm on my CNC knee mill.
But I limit max speed to 50 ipm. (Chicken s%^&t here) You wouldn't
need anywhere near the torque though, if you geared it 3:1 you'd get
560 ipm top. If you want to go faster, you'll need big servos.I've
seen calculaters for table weight, speed, acceleration, etc. that give
the required servo torque, on a vendor website


They have made major advances in linear motors in the last two years.
They are now the fastest accelerating motors you can buy. The cost has
came way down also. There are several machining centers now being
manufactured with linear motors because of the speed.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Paul Ragot writes:

Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router
and am wondering if using linear motors is a good idea and where to
find some.

This seems impractical.

CNC drives for small mills should develop literally tons of linear force.

Do linear motors do that?

"Richard J Kinch" wrote in message
. ..
Paul Ragot writes:

Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router
and am wondering if using linear motors is a good idea and where to
find some.

This seems impractical.

CNC drives for small mills should develop literally tons of linear force.

Do linear motors do that?

No.

--

SVL

In article ,
says...
Paul Ragot writes:

Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router
and am wondering if using linear motors is a good idea and where to
find some.

This seems impractical.

CNC drives for small mills should develop literally tons of linear force.

Tons sounds high, my SWAG is 1000# would be adequate for a Brideport
sized mill. There are linear motors that produce that much force, and
more, but they're certainly not cheap.

Ned Simmons

Do linear motors do that?


No.

--
well, for hundred grand they do

Richard J Kinch wrote:

Paul Ragot writes:


Has anybody built a small cnc using linear motors?
I am toying with the idea of building a small high speed mill/router
and am wondering if using linear motors is a good idea and where to
find some.


This seems impractical.

CNC drives for small mills should develop literally tons of linear force.

Do linear motors do that?
The new fancy Trans do - Mag Levs aren't they!
Martin
--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

Ned Simmons writes:

Tons sounds high, my SWAG is 1000# would be adequate for a Brideport
sized mill.

F = ma. The table and saddle weigh together 400 lbs or more. Add the
rotational inertia of the motor, pulleys/belts, handles, and screw. You'd
like the table to get up to a respectable slewing speed (for a hobbyist) of
100 ipm or better, in some fraction of a second. You must also exceed the
side cutting forces for a typical task by some multiple, from the
_Handbook_, at cutting speeds.

My smallish 0.1 HP PMDC motors at http://www.truetex.com/mcgpd34002.htm
produce about 800 lbs of linear force with 2:1 timing belt pulleys on
ballscrews on a freshly rescraped Bridgeport Series I with Teflon ways. It
is certainly adequate, but like a speedboat, you can never have too much.
Fun to watch at 100 ipm, but you wonder what 200 or 500 would be like.

In article ,
says...
Ned Simmons writes:

Tons sounds high, my SWAG is 1000# would be adequate for a Brideport
sized mill.

F = ma. The table and saddle weigh together 400 lbs or more. Add the
rotational inertia of the motor, pulleys/belts, handles, and screw. You'd
like the table to get up to a respectable slewing speed (for a hobbyist) of
100 ipm or better, in some fraction of a second.

But with a linear motor you don't have all that rotating inertia. If
you're looking for quick acceleration with a lead screw drive, the
torque required to get all the rotating stuff up to speed is usually
much greater than the torque required to move the load at a steady
velocity.

To get to 100ipm in 1/10 sec is only .04g , or 16lbf for a 400lb table.

You must also exceed the
side cutting forces for a typical task by some multiple, from the
_Handbook_, at cutting speeds.

So say you're using the full 1 HP at 50 FPM = 660# at the periphery of
the cutter.

I backed into it from the other direction, assuming a reasonable force
on the table cranks and 50% efficiency for acme screws to get my 1000#
guess.


My smallish 0.1 HP PMDC motors at http://www.truetex.com/mcgpd34002.htm
produce about 800 lbs of linear force with 2:1 timing belt pulleys on
ballscrews on a freshly rescraped Bridgeport Series I with Teflon ways. It
is certainly adequate, but like a speedboat, you can never have too much.
Fun to watch at 100 ipm, but you wonder what 200 or 500 would be like.


Indicate your vice in 1/2 sec g

Ned Simmons

On Sun, 6 Mar 2005 01:52:21 -0500, Ned Simmons
wrote:

In article ,
says...
Ned Simmons writes:

Tons sounds high, my SWAG is 1000# would be adequate for a Brideport
sized mill.

F = ma. The table and saddle weigh together 400 lbs or more. Add the
rotational inertia of the motor, pulleys/belts, handles, and screw. You'd
like the table to get up to a respectable slewing speed (for a hobbyist) of
100 ipm or better, in some fraction of a second.

But with a linear motor you don't have all that rotating inertia. If
you're looking for quick acceleration with a lead screw drive, the
torque required to get all the rotating stuff up to speed is usually
much greater than the torque required to move the load at a steady
velocity.

To get to 100ipm in 1/10 sec is only .04g , or 16lbf for a 400lb table.

Are the Mazaks with 3.5g acceleration not linear motor driven?


You must also exceed the
side cutting forces for a typical task by some multiple, from the
_Handbook_, at cutting speeds.

So say you're using the full 1 HP at 50 FPM = 660# at the periphery of
the cutter.

I backed into it from the other direction, assuming a reasonable force
on the table cranks and 50% efficiency for acme screws to get my 1000#
guess.


My smallish 0.1 HP PMDC motors at http://www.truetex.com/mcgpd34002.htm
produce about 800 lbs of linear force with 2:1 timing belt pulleys on
ballscrews on a freshly rescraped Bridgeport Series I with Teflon ways. It
is certainly adequate, but like a speedboat, you can never have too much.
Fun to watch at 100 ipm, but you wonder what 200 or 500 would be like.


Indicate your vice in 1/2 sec g

Ned Simmons