z axis alignment

Discussion about the CNC Shark Pro Plus HD

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dcsten48
Posts: 2
Joined: Fri Jul 18, 2014 4:12 pm
Location: Florida

z axis alignment

Post by dcsten48 »

How do you align the z axis, mine is out >.08 in 3 "
What a POS......Had to shim y axis on z with .050 shim. X axis off .07 Headaches with this Machine. They used plastic for a lot of framing should have been aluminum plate, (CHEAP) Will sell and buy different.

pdkama
Posts: 2
Joined: Sat Dec 15, 2012 5:53 pm

Re: z axis alignment

Post by pdkama »

same problem here, I sent email to next wave and they want me to level the top.

EdThorne
Posts: 345
Joined: Mon Nov 26, 2012 11:26 pm
Location: Massachusetts

Re: z axis alignment

Post by EdThorne »

Don't be too quick to dismiss the Shark CNC. It is capable of producing some fine work. None of these modifications are required and each of us on this board probably has his personal list of favorites. You don't have to make any and can still create some quality pieces. I agree that this isn't a commercial quality machine but it is priced for people like me that wouldn't have spent more money. I will be willing to bet that any CNC at this price has some limitations. Regardless, with a little effort, it may be improved and produce even better results.

You may use shims or maybe the following link will give you some better ideas. This approach makes the deck of the CNC coplanar with the movement of the router. I haven't found this necessary as I will explain below but it is always in the back of my mind as something that I want to do someday.

http://www.consultingwoodworker.com/cnc ... d_projects

I originally found that the plastic router clamp would slip and cause problems. I had an aluminum clamp made that has worked flawlessly ever since.
Contact Sam at business@dixiebillet.com
I believe that the cost was about $50.

I use Vectrix's Aspire and do lots of 3D carvings. I really love this package. Lots of people on this board only use V-Carve Pro and love it.

I have recently replaced the top support plate with a 3/4" aluminum plate that cost about $80. Mine is oversized in case I wish to add side supports. You could make one from 1/2" aluminum that will probably do just as well. This is equivalent to the aluminum top plate used on the 60th Anniversary model. A picture of mine is attached. The machine is much, much more structurally rigid after this replacement.

I haven't replaced my deck but I did replace the plastic supports that hold the deck in place with aluminum angle. I also used two bolts on each end for each of the aluminum deck t-slot plates. This helps to prevent twisting and movement. I also make sure that I place clamps so that the t-slot used is in the same deck plate that is directly below the clamp. I therefore only clamp on the ends and not on the sides of the work piece. I also use virtual zero if I am worried about variations in my cut depth. This helps to keep the depth constant when v-carving text, for example. My actual cuts depths are almost always less than 1/2". I haven't had any issues since I started using this approach.

I know that you must be frustrated. Things will improve. I started by reading the entire manual before cutting my first cut only to watch it destroy my bit and my work-piece. I had never worked on a CNC before and it was a huge learning curve for me.

There are lots of fantastic people on this board with a tremendous amount of expertise. They have come to my rescue many time and have provide fantastic ideas. I'm sure that you will also find these people helpful.

Good luck and hope you make happy sawdust, soon.
Ed
Attachments
Alum Top.jpg

Rando
Posts: 757
Joined: Tue Jan 06, 2015 3:24 pm
Location: Boise, ID
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Re: z axis alignment

Post by Rando »

Okay, I have a very odd, but seemingly effective way of getting rid of **most** of the Z-axis being non-perpendicular to the bed.

The way I think about this, the Z-axis is getting error because of weight-induced (and motion-induced) deformation from two main places: Firstly, from the plastic deformation of the z-axis carriage and router mount, from the weight of the carriage and router and accessories. This tends to pull the tongue of the mount closer to the bed, as we know. The second part is the twisting of the gantry plate as that weight pulls on the bearing rods. Depending on where the Z-axis is in its travel, that could be a reasonably supported load, when the carriage is between the two horizontal x-axis bearing rods. But, once the router goes below that, it become more of a torque on the bridge/gantry itself. Thus that mondo plate they put into the unit. Both those forces cause deflection OF the Z-axis ALONG the Y-axis.

There are, of course, bit+material torque that shifts the carriage with angular force, but other than replacing the entire thing with super-rigid Gold plated Unobtainium, the more-proper way is to use speeds&feeds that minimize torque on finish passes...which we already do anyway.

I was looking at the various mounts, seeing if there was a way to adjust or even shim, and there really didn't seem to be a GOOD way. So instead, I cheated. The results won't be exactly directly applicable, since this is being done as part of an upgrade from a router to a "real" spindle with a Variable Frequency Drive (VFD) controller.

I went and found the drawing (here on the forums somewhere) for the mount. I modified it for the diameter of the spindle (80mm in my case), and then cut that out of Aluminum, using the router. As I watched it cut, three things occurred to me:

First, gosh darn it, the bit isn't hanging perfectly perpendicular to the table again! Grrrrr.....
Second, it dawned on me that once the part is done, if I flip the bracket over, it will actually cancel out nearly all of that sagging error.
And third, make sure to mark the "top" of the part before it gets machined, so you'll know which is which. I used the tab locations to keep track of it. If your z-carriage sagging is minimal, it can be difficult to tell which way to put it in, and then you'll have the same error.

The requirement, however, is that when you cut that bracket out, the direction that the clamping slot goes along has to be the direction that the mounts are sagging. That is, along the width of the bed. (Y-axis normally, I changed mine to be the X, but you get the idea). That way, the error in angle of droop will be (with very gentle cutting!) represented in the walls of the mount hole.

Now, this can be futzed up somewhat if there are z-axis lifts on the left-hand (y-positive) side of the hole, since the end of the bit will be dragged "straight up". Typically those lifts happen only in one place, so it hasn't seemed a problem when I've noticed it.

Additional sources of error can come in from the weight difference between the (new) aluminum bracket and the (old) plastic one. So, maybe use HDPE or similar like they do, to eliminate that source of additional sag. For me, with the new (heavier, torque-i-er) spindle, Aluminum just seemed the right choice.

Okay, so now you have your new bracket, and you know the top. Flip that sucka over, and the error **might** be gone. I say might because, after all, there's the bottom plate of the carriage. If your router press-fits into the non-clamping bottom bracket, it's entirely possible you won't be able to get all of the sag-correction. In my case, this isn't an issue, since the spindle doesn't contact that bottom bracket's mount hole.

Don't imagine you can do an iterative thing: make one that gets close, install it and make another. In order for that ONE bracket to compensate for ALL the error, the cutting tool has to cut ALL the error into the surfaces. If you have a partially compensated spindle, then you won't really get all the compensation needed.

Anyway, that's what I did...it seems to have removed maybe 90% of the error, but I suspect it will back when the heavier spindle arrives...which means I'll have to figure it out again :D.

(Added....what a doofus...to get the droop-angle right for the spindle, when I'm making the part with the router, I should add, say 80% of the weight difference between the two, and put (okay, SECURE) that directly on the top of the router, thus simulating the spindle's weight...Ooooh...I like it!)


Regards,

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

rungemach
Posts: 460
Joined: Mon Aug 02, 2010 8:24 am
Location: Sarasota, Florida

Re: z axis alignment

Post by rungemach »

Z axis alignment can be a tricky thing. You must have the z bearing rods perpendicular to the x/y cutting plane, as well as have the router in alignment with the z rods.

If the z assembly is shifted slightly clockwise, and you compensate by mounting the router the same degree counter clockwise, the bit may be perpendicular to the cutting surface, but it will not travel up and down along a perpendicular path. The result of this is that the walls of a hole, cut in multiple passes, will not be at 90 degrees to the workpiece, and/or the hole can get slightly oval if you do a full depth finishing pass.

Unfortunately, there is no substitute for having everything in alignment.
Flex and sag in the machine can complicate things as the machine may be out of alignment in some areas, or may flex out under heavy cutting loads.

Rando
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Location: Boise, ID
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Re: z axis alignment

Post by Rando »

I just printed a small piece with T-glase, and I can add one more:

OOpsies...wrong forum!

Cheers,

Thom
Last edited by Rando on Tue Mar 24, 2015 10:58 pm, edited 1 time in total.
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

Rando
Posts: 757
Joined: Tue Jan 06, 2015 3:24 pm
Location: Boise, ID
Contact:

Re: z axis alignment

Post by Rando »

Very good points. Having everything square without any shims or weird stuff is best. But on this machine, I'm not seeing much of a way to make actual adjustments. Far lower costs in production, I'm presuming. I was going to leave the torque-induced stuff alone for now, since rigidity seems harder to achieve than is lower torque at the cutter.


{Edit] Now I can give a more definitive answer. Yes, Z-axis rods need to be vertical. One component is the back plate; mine has 0.0025" (0.06mm) deflection when the router is in the middle versus 5 inches in +X or -X. The displacement at the very tip of a nominal-stickout bit just due to the plastic between the aluminum z-axis mount plate and the router deforming is closer to 0.020-0.030 (0.5-0.75mm), maybe even more. Thus, the router-platform sag is 8-10X the size due to the rear gantry plate, and clearly should be addressed first.
rungemach wrote:Z axis alignment can be a tricky thing. You must have the z bearing rods perpendicular to the x/y cutting plane, as well as have the router in alignment with the z rods.

If the z assembly is shifted slightly clockwise, and you compensate by mounting the router the same degree counter clockwise, the bit may be perpendicular to the cutting surface, but it will not travel up and down along a perpendicular path. The result of this is that the walls of a hole, cut in multiple passes, will not be at 90 degrees to the workpiece, and/or the hole can get slightly oval if you do a full depth finishing pass.

Unfortunately, there is no substitute for having everything in alignment.
Flex and sag in the machine can complicate things as the machine may be out of alignment in some areas, or may flex out under heavy cutting loads.
Last edited by Rando on Sat Mar 28, 2015 4:11 pm, edited 2 times in total.
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

SawDust913
Posts: 23
Joined: Thu Dec 29, 2011 9:19 am

Re: z axis alignment

Post by SawDust913 »

I have the Shark HD and I use .75 MDF as a base on top of the aluminum table top. I use a .75 center cut router bit and program to shave off .02 first running a raster of 0.0 then 45 deg, and final pass at 90. These are run all at the same Z and most of the tooling marks are gone. I then put grid lines with a .125 v bit, both X & Y at a space of .5; now whatever board I'm working with is easy to line up and then i run the same planing raster I use on the MDF base. I used this method to plane down a desk top,
Y= 60" X=24" which works out great as long as the last past is at Raster, 90deg or on the Y axis. This method is working for me.

Tab
Posts: 20
Joined: Thu Jan 29, 2015 8:24 am

Re: z axis alignment

Post by Tab »

I feel your pain! I had my machine for less than one week and had a control go out.. multiple issues with the software. I called Rockler and they are giving me a full refund.

I just ordered a Stinger from Camaster.. more expensive but a quality piece of equipment.

good luck!

Rando
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Joined: Tue Jan 06, 2015 3:24 pm
Location: Boise, ID
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Re: z axis alignment

Post by Rando »

Using a freshly-planed spoilboard can "help", but it doesn't solve the underlying problem of the rotating shaft and bit not being truly perpendicular to the table along both the X and Y axes. There are a variety of multi-pass ways people have gotten around it with spoilboards, but in the end, the outboard part of the bit cutting circumference is lower than the inboard edge. It's especially noticeable on larger bits, like 1/2 in and up.

To make matters worse, the flex in the system means that the bit perpendicularity changes based on whether the bit is being pushed into or pulled onto the uncut material. When it's being pushed, that outboard side dives down even more, and when it's being pulled, the inboard force swings the bit toward the outboard side, arguably making the bit more perpendicular.

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

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