Shark HD4 extended isn't cutting square...

Questions/answers/discussion about initial setup of your CNC Shark

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Re: Shark HD4 extended isn't cutting square...

Postby JerkMcLaughlin » Mon Jun 11, 2018 8:36 am

Gotcha. I figured that was the best test because that’s the size dowels that I’ve seen people use for two-sided parts. I re-ran that same test(still with 1/4” holes) but turned my rpms all the way up while slowing the plunge speed down to 10ipm. Same results.
I guess in MY head it wouldn’t matter what size hole as long as each of them are the same. In theory they would all be inaccurate by the same amount yet still be perfectly square to each other.

Either way, I’m still stuck.
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Re: Shark HD4 extended isn't cutting square...

Postby Rando » Mon Jun 11, 2018 9:47 am

JerkMcLaughlin wrote:Gotcha. I figured that was the best test because that’s the size dowels that I’ve seen people use for two-sided parts. I re-ran that same test(still with 1/4” holes) but turned my rpms all the way up while slowing the plunge speed down to 10ipm. Same results.
I guess in MY head it wouldn’t matter what size hole as long as each of them are the same. In theory they would all be inaccurate by the same amount yet still be perfectly square to each other.


Well yeah, that would be the case, but only if that actually is the problem. That's what I'm kinda trying to say: the overall alignment of the system, being that much out, if it indeed is, HAS to be measurable in a simple way. Seriously. Jog to an end, all the way until it loses a step or two. Then let it relax, and see if one side really is not contacting that back wall at the same point. Measure it with calipers to 0.001" accuracy. If there's mismatch, that's where you'll see it. But other than the gantry being misaligned relative to the bed, that's all there is besides spindle deflection.

If what you want is greater accuracy, you have to use even-more accurate methods and tools.

Thom
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Re: Shark HD4 extended isn't cutting square...

Postby JerkMcLaughlin » Mon Jun 11, 2018 9:55 am

Thom,
I just checked the alignment of the bearing blocks to the back of the frame, it looks like that is indeed the problem. I can't get calipers in there to measure but there is around .1" gap on the left while the right is up against the back wall. That would explain it exactly. I just talked with tech support and they explained how to adjust it. I'll make the adjustment and run more tests.

I knew I wasn't crazy! haha
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Re: Shark HD4 extended isn't cutting square...

Postby JerkMcLaughlin » Mon Jun 11, 2018 10:54 am

Ok, I realigned the slide bearings to the back wall and now it's cutting nearly perfect.

Thanks so much for your help Thom!
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Re: Shark HD4 extended isn't cutting square...

Postby Rando » Mon Jun 11, 2018 10:55 am

Awesome! I knew it had to be there somewhere, if indeed it existed. Did they have you take off the bed to get to the center drive point? Or can it be adjusted just by loosening the ends, squaring it, then tightening?

Glad to hear you found it.

Thom
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Re: Shark HD4 extended isn't cutting square...

Postby Rando » Mon Jun 11, 2018 11:57 am

And for everyone reading this at home, this is a perfect example of the medical difference between a "sign" that a Doctor sees,
and a "symptom" that the patient reports.

So, in our case, the out-of-square cutting was a symptom: some bad outcome that is caused by something. The cutting isn't
the actual error, but the correctness of the cut is being ruined by the underlying error.

On the other hand, a SIGN, as recorded in your med records by the Doctor, is something that his trained eyes and hands are
able to detect, that exposes the underlying nature of the problem. Or, in our case, knowing that going to the end, and
seeing if the two sides are different, is a SIGN of what the problem is, leading to a possible cure.

When diagnosing a machine, a painful knee, or any system, it's important to try and tell whether what you're seeing
is a symptom of the problem, or is a sign leading you toward a solution. "Watch for signs" I suppose would be the wisdom :D.

See....learn something new everyday :mrgreen:

Cheers!
Thom
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Re: Shark HD4 extended isn't cutting square...

Postby rungemach » Thu Jun 14, 2018 3:20 pm

FWIW, I have never seen a shark that was perfectly square, and I have worked on several of different generations.

Do not assume that the front and back plates are parallel or square to anything. I have seen good discrepancies between the front to back plate distance on the right and left side. The front or rear plates may not really be square with the bearing rods that run front to back. From the top view you can get a trapezoid or parallelogram thing happening based on the squareness of the bottom plate. The "drive in the center" design is also prone to rocking out of square depending on where the cut is. The older the generation of shark, the worse the problem.

You need to square the gantry with the bearing rods. If adjusting the gantry by hitting the front or back plate still is off, you can put bolts as microadjusters in the front (or back) base plate. The bolts are positioned to touch the gantry bearing blocks. If you square the machine to the front (or back) plate and it not right, you then use a bolt as a microadjuster to make a new stop for the bearing to hit on the offending side.

The good news is that there is usually enough slop in the shark to allow it to be put square, and then tightened down.
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