Mainly intended for drilling PCBs, it's also suited for light drilling
up to 1/8" holes until I get a larger chuck. Got a lot of help from
rec.crafts.metalworking either directly via questions or by Googling.
Link to pictures below;

http://www.pbase.com/eldata/cnc

In article .com,
says...

Mainly intended for drilling PCBs, it's also suited for light drilling
up to 1/8" holes until I get a larger chuck. Got a lot of help from
rec.crafts.metalworking either directly via questions or by Googling.
Link to pictures below;

http://www.pbase.com/eldata/cnc

Cute - I take it the Z azis feed is via the special-built
pinion gear shown in one of the photos? Looks like you built
it around a surplus drill press, what kind was it?

Jim


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==================================================
please reply to:
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I take it the Z azis feed is via the special-built
pinion gear shown in one of the photos?

Sort of....I pressed a precision shaft into the existing pinion gear
shown below before the mod;

http://www.pbase.com/eldata/image/43425746


Looks like you built
it around a surplus drill press, what kind was it?

It's a Cameron MD-70 (aka deep throat), don't think you'll find that
surplus.

http://www.pbase.com/eldata/cnc

Direct couplings between the motors and leadscrews? What takes up the
misalignment?

Nice job

Nice job

Thanks Tim.

Direct couplings between the motors and leadscrews? What takes up the
misalignment?

The bearings of the shafts involved, leading to wear until the
misaligment is less than the potential runout of the shafts. That isn't
the case here though, misalignment is already less than the runout of
the shafts based on the precision of the couplers involved and mounting
methods. I added three more shots showing the motor mounts but there is
nothing to show the precision of the couplers, you'll have to take my
word on that.

That isn't
the case here though, misalignment is already less than the runout of
the shafts based on the precision of the couplers involved and mounting
methods.

If you say so. But it kinda makes you wonder why machines far more precise
than this consider flexible coupling essential.

Richard J Kinch wrote:

That isn't
the case here though, misalignment is already less than the runout of
the shafts based on the precision of the couplers involved and mounting
methods.

If you say so. But it kinda makes you wonder why machines far more precise
than this consider flexible coupling essential.

In my several years of CNC service nearly every machine I worked on had
ridgid couplings from the servos to the ballscrews. Certainly the
Kitamuras did with big Fanuc 10M servos. There was never an alignment
issue with those.'

Pete C.

In my several years of CNC service nearly every machine I worked on had
ridgid couplings from the servos to the ballscrews.

Theoretically, for a stepper setup or servo setup with encoder on the
motor shaft, a flexible coupling is another source of errors due to
possible coupling backlash and angular misalignment IMO. However, no
doubt there are designs that warrant their use but some people seem to
develop a "pet peeve" in this area one way or another. The other
extreme of Richard's view came from another fellow, claiming to be a
CNC buff, who insisted that the only proper way was to use belt and
pulleys and have the encoder on the driven shaft....Anything else was
worthless due to misalignment. While standards and the experience of
others are invaluable when designing something, being able to think for
oneself is also priceless.

However, no
doubt there are designs that warrant their use but some people seem to
develop a "pet peeve" in this area one way or another.

Physical reality is not a peeve. Flexibility must be satisified somewhere.
Ball bearings with runout in the tenths of thousandths are not going to get
along with drive trains that accumulate at least several thousandths of
runout, flex, angle, and offset. You can put the flexibility into belts,
or helical couplers, or just wrench the bearings. housings, and shafts, but
the demand will be satisfied somewhere.

Theoretically, for a stepper setup or servo setup with encoder on the
motor shaft, a flexible coupling is another source of errors due to
possible coupling backlash and angular misalignment IMO.

Only if IYO you omit the helical type.

Physical reality is not a peeve.

But peeves, irrational convictions and misguided energy are a reality
in just about all walks of life. Some scenarios are so convoluted that
people end up doing the right things for the wrong reasons.

Ball bearings with runout in the tenths of thousandths

Not this system....Remember, you were alluding to a design defect
associated with this system. Is this all about more precise and
sophisticated systems that you have designed by any chance?

but the demand will be satisfied somewhere.

It's the magnitude of the demand and the ramifications associated with
any "dissatisfaction" that the designer should take into consideration.
Rigid couplers are not manufactured and sold as table ornaments. There
are systems where they are applicable and used. Mine is one such
system.

Only if IYO you omit the helical type.

MMC sells helical couplers. One suited for Y and Z axes in my system
goes for $20.00 a pop. That's $5.00 less than the DC gearhead motors
I'm using. The relevant load bearing sleeve for them costs 33 cents or
I could turn/bore one in less than an hour. But I'll probably need new
brushes before new bearings.

There is no flexible equivalent of the X axis coupler. It has three
internal diameters, .25", 8mm and 10mm with the 8mm section tapped.
Even with all that, there are no misalignment issues.

... the DC gearhead motors I'm using ...

Didn't know about the gears. So you don't really couple them directly.

In article , Richard J Kinch
says...

... the DC gearhead motors I'm using ...

Didn't know about the gears. So you don't really couple them directly.

I sorta figured that from the fact that he had the
same motor driving the spindle downfeed via the pinion
gear.

Jim


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==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

In article ,
says...
... the DC gearhead motors I'm using ...

Didn't know about the gears. So you don't really couple them directly.


The fact that there's a gearhead on the motor doesn't make
any difference re the sort of coupling required, except
perhaps for the fact that any effects of misalignment occur
at a lower speed.

Ned Simmons

In article ,
says...
Theoretically, for a stepper setup or servo setup with encoder on the
motor shaft, a flexible coupling is another source of errors due to
possible coupling backlash and angular misalignment IMO.

Only if IYO you omit the helical type.


Ugh. Helical beam couplings are suitable for low torque
applications, such as driving encoders, and best avoided
for power transmission, particularly in motion control
apps. They're relatively expensive, not torsionally stiff,
large relative to torque capacity, and can be quite
fragile. In places where a helical coupling will work
there's usually a less expensive and more robust
alternative.

Ned Simmons

I sorta figured that from the fact that he had the
same motor driving the spindle downfeed via the pinion
gear.

Yep, all three motors are the same. I have seven of them, paid $25.00
each. Adding the second shaft for the encoder was a nice exercise in
precision lathe work. Second shaft uses spring loaded ball bearings.
BTW, the Z axis maximum feed rate would be over 700 IPM (too fast to
drill at), X and Y axes are a measly 20 IPM. Still, the 228 holes in
the 6"X4" accuracy sample were drilled in 15 minutes for about 15 holes
per minute. Certainly beats doing it by hand. Furthermore, the drill
motor is controlled by a SSR so I can walk away once the drilling
starts and it shuts off when finished (M05). Pretty standard I imagine.

Ned Simmons writes:

The fact that there's a gearhead on the motor doesn't make
any difference

Gears can take some misalignment by their nature, and because the shafts
are shorter and the bearings looser.

Ned Simmons writes:

In places where a helical coupling will work
there's usually a less expensive and more robust
alternative.

What alternative would you suggest? Timing belts were dismissed out of
hand.

What alternative would you suggest?

There are probably several. Precise rigid couplers and a "flexible"
mount if necessary is one. Each scenario may call for a different type
of mount. Note the flat and angle alu setup in the shot below. An
ammeter was used for proper alignment.

http://www.pbase.com/eldata/image/47162125

Precise rigid couplers and a "flexible" mount if necessary is one.

So you agree that flexibility is needed. My point is that it should be in
the transmission, not the mount. Flexible, er, loose/sloppy mounting will
not accommodate the three degrees of freedom of misalignment (parallel,
angular, and axial). And it worsens the problem, because the mass of the
coupled element makes it sag still further out of alignment.

So you agree that flexibility is needed.

Depends on the scenario. But your drift has too much of a theoretical
bias. If you rigidly couple the motor to the driven shaft without
mounting it, you'll immediately see how best to mount and align it.
Picture "bringing" the mounting surface to the motor while it is
coupled before fixing it to the mounting surface. It's easier to do
than to describe actually.

In article ,
says...
Ned Simmons writes:

In places where a helical coupling will work
there's usually a less expensive and more robust
alternative.

What alternative would you suggest? Timing belts were dismissed out of
hand.

I don't have a problem with timing belts where very high
acceleration and precision are not required, especially
metal corded urethane belts, as long as you take their
stretchiness into consideration, just as you should for any
flexible coupling.

Oldham couplings like those on this page

http://www.lovejoy-inc.com/miniaturecouplings.htm

have worked well for me in moderately demanding
applications. They're smaller(thus less rotational
inertia), stiffer, and considerably cheaper for a given
torque rating than the helicals. Also much more forgiving
of abuse, and if you do damage one, the damage is almost
certainly limited to the delrin spider, which is
replaceable for a few dollars. There is the potential for
wear in the spider leading to backlash (the spider is a
slight interference fit when new), but I've never had a
problem. At least I've never had a complaint, or had to
replace a spider a result of wear. Presumably this would be
more of an issue with excessive misalignment or in a dirty
environment.

The helical beam couplings are awfully cute, true zero
backlash, and true constant velocity devices, but are quite
fragile. Anyplace that the helical's good points are really
required, I'd be more inclined to use a bellows type
coupling.

Ned Simmons

In article 1123347290.524562.10400
@f14g2000cwb.googlegroups.com, says...
So you agree that flexibility is needed.

Depends on the scenario. But your drift has too much of a theoretical
bias. If you rigidly couple the motor to the driven shaft without
mounting it, you'll immediately see how best to mount and align it.
Picture "bringing" the mounting surface to the motor while it is
coupled before fixing it to the mounting surface. It's easier to do
than to describe actually.



Personally, I think you're underestimating the problem.
Through care and skill (and perhaps a little luck) it
sounds as though your system is working well (and looks
very good to boot, I might add), but a simple static
alignment as you describe above will not ensure that the
alignment is true for all possible shaft positions.

Ned Simmons

In article ,
says...
Precise rigid couplers and a "flexible" mount if necessary is one.

So you agree that flexibility is needed. My point is that it should be in
the transmission, not the mount. Flexible, er, loose/sloppy mounting will
not accommodate the three degrees of freedom of misalignment (parallel,
angular, and axial). And it worsens the problem, because the mass of the
coupled element makes it sag still further out of alignment.


This type of mount gives 5 degrees of freedom - X, Y, Z,
and two rotations - but is better suited to a (light)
encoder than a (heavy) motor.

http://www.renco.com/106025.htm

Ned Simmons

but a simple static
alignment as you describe above will not ensure that the
alignment is true for all possible shaft positions.

Well I didn't tell all. Some procedures, if not patentable, are best
kept to oneself. Especially when others are pontificating about what
can and cannot be done.

In article 1123376183.712346.257490
@f14g2000cwb.googlegroups.com, says...
but a simple static
alignment as you describe above will not ensure that the
alignment is true for all possible shaft positions.

Well I didn't tell all. Some procedures, if not patentable, are best
kept to oneself. Especially when others are pontificating about what
can and cannot be done.


In other words it's exactly as I said; the alignment
process is not as simple as you implied. I never said that
a successful implematation of a rigid coupling was
impossible, only that your description of the alignment
process understated the potential pitfalls.

If you've come up with a clever way of solving this
problem, but don't care to share it or even mention it
(why, I can't imagine), then you shouldn't be surprised
when your methods are called into question.

Ned Simmons

Nice work. What software/control are you using? I assume that the z
axis control is fairly rudimentary since it is only used for drilling.
Have you ever thought of putting a miniature end mill in the chuck for
milling purposes?

the alignment
process is not as simple as you implied

I implied many things....Here's another implication in anecdotal form:

About ten years ago a then coworker came to me complaining about some
briefs he had just bought. The opening in front was so small that he
was now having difficulty at the urinal. Just two or three months ago,
a prominent radio announcer in my neck of the woods was complaining
along the same lines, only in his case the new set of briefs had no
opening in front at all. Apparently, their mommies had shown them one
way of urinating while standing and since mommy was always right, there
could be no other way.

then you shouldn't be surprised
when your methods are called into question.

Who's surprised? If I do a Google search on "flexible coupling"
rigid I see a hit as follows;

"I think you'll find it's easier than you think. I've
aligned larger diesels in sailboats with rigid couplings to
much tighter specs while sitting on the engine in the
bilge. "

And guess what, the posters name is Ned Simmons. What a coincidence.
Now that's a surprise.

Nice work.

Thanks.

What software/control are you using?

A laptop running TurboCNC but it could be any software that supports a
parallel interface.

I assume that the z
axis control is fairly rudimentary since it is only used for drilling.

The control potential isn't really any different for the Z axis but
since the spindle only has to move between two positions while
drilling, the operation is rudimentary. In fact, CNC software has made
the entire drilling process rudimentary. A single G-Code drill cycle
command can do everything, just give it the two extremes for the Z axis
along with the X and Y coordinates for each hole.

Have you ever thought of putting a miniature end mill in the chuck for
milling purposes?

Yes, but it's not something I'd want to do. Getting a small mill and
converting it to CNC as soon as I make more space in the basement.

In article 1123452253.350350.279050
@f14g2000cwb.googlegroups.com, says...
the alignment
process is not as simple as you implied

I implied many things....Here's another implication in anecdotal form:

About ten years ago a then coworker came to me complaining about some
briefs he had just bought. The opening in front was so small that he
was now having difficulty at the urinal. Just two or three months ago,
a prominent radio announcer in my neck of the woods was complaining
along the same lines, only in his case the new set of briefs had no
opening in front at all. Apparently, their mommies had shown them one
way of urinating while standing and since mommy was always right, there
could be no other way.

I don't recall anyone saying there was not more than one
way to take a leak, but you seemed to be saying unzipping
is unnecessary, and are secretive about how you keep the
**** out of your shoes.


then you shouldn't be surprised
when your methods are called into question.

Who's surprised? If I do a Google search on "flexible coupling"
rigid I see a hit as follows;

"I think you'll find it's easier than you think. I've
aligned larger diesels in sailboats with rigid couplings to
much tighter specs while sitting on the engine in the
bilge. "

And guess what, the posters name is Ned Simmons. What a coincidence.
Now that's a surprise.

If you care to equate aligning a pair of small shafts, with
closely spaced bearings, driving a presumably precision
mechanism with lining up a prop shaft with 3 feet between
the bearings, one a hydrodynamic rubber bearing with .010
clearance, be my guest. And if you look at that post in
context, I was replying to a guy who already understood
that he was dealing with 5 degrees of freedom and was
fretting about lining up a *flexible* coupling.

Ned Simmons

but you seemed to be saying unzipping
is unnecessary

CDDS = Comprehension Deficit Disorder Syndrome

Heck, if you had to read between the lines, which wasn't even the case
here, you'd probably fall off the page.

Yeah...

until you try it, don't knock it.

we have seen flexible couplers fail multiple times.
Dad made a couple of rigid ones.
I of course had to play devil's advocate, because he is EXTREMELY critical
of design minutae like this.
The have been working in production for YEARS on a seriesII bridgeport we
retrofitted.

"Richard J Kinch" wrote in message
. ..
That isn't
the case here though, misalignment is already less than the runout of
the shafts based on the precision of the couplers involved and mounting
methods.

If you say so. But it kinda makes you wonder why machines far more
precise
than this consider flexible coupling essential.