CNC drilling machine finally completed

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.

Reply to
Richard J Kinch
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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.

Reply to
oparr

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

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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

Reply to
Ned Simmons

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

Reply to
Ned Simmons

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.

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Ned Simmons

Reply to
Ned Simmons

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.

Reply to
oparr

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

Reply to
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?

Reply to
woodworker88

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.

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.

Reply to
oparr

Thanks.

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

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.

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.

Reply to
oparr

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 piss out of your shoes.

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

Reply to
Ned Simmons

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.

Reply to
oparr

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.

Reply to
Jon Grimm

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