Author Topic: Wheels!  (Read 1672 times)

beikeland

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Wheels!
« on: November 03, 2016, 03:38:41 PM »
So I've settled on wheels being the culprit of my issues of wavy output. I can see the wheels wobble when moving, which corresponds to the wavyness.

The width of my wheels range from 6.8 to 7 - roughly. The gap in the rail seems to be 6.3mm, with a 0.5mm groove on either side. Does this line up with your machines as well? From the good 'ol internett I see that the wheels are mostly available as 7 or occationally 7.5mm width. 6.8 sounds way too thin.

In adittion to new 5x21.5x7mm wheels I've ordered some wider OpenBuilds wheels, 3D0004P, smaller outer diamter, wider and with a chamfer on either side instead of a fillet, or U shape. But since the diamter of those are smaller the current holes won't fit, so new holes or new plastic pieces.

But curious to learn what dimensions you had delivered and if it matches my numbers, and if your profiles have this 0.5mm step down on each side of the grooves; seems to be a smooth transaction on most pictures and drawing I've seens so far.

ggallant571

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Re: Wheels!
« Reply #1 on: November 03, 2016, 03:55:37 PM »
When I first assembled my Y module I used a wrong length spacer such that the plate was skewed relative to the Y rail. This caused a non-linear repetitive error. The wheels were also very stiff and some light oil fixed that.
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ROSS

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Re: Wheels!
« Reply #2 on: November 04, 2016, 12:18:12 AM »
Wonder if as anybody thought of replacing the wheels with ball race type?? 
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beikeland

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Re: Wheels!
« Reply #3 on: November 04, 2016, 04:40:20 AM »
Ball race type? How does that differ from the ball bearings?

ROSS

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Re: Wheels!
« Reply #4 on: November 04, 2016, 06:43:52 AM »
Ball bearings  are usually loose (individual)
In a  BALL Race they are caged.  (See two types  below).  They come in various sizes.
 
BALL RACE  is the correct term.
« Last Edit: November 04, 2016, 06:47:59 AM by ROSS »
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Lasers are wonderful machines..not ONLY  can they cut a finger off BUT  they can also cauterise it at the same time.....

SAFETY -  IS NO ACCIDENT

beikeland

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Re: Wheels!
« Reply #5 on: November 04, 2016, 07:25:03 AM »
Ah, thanks for clearing that up, I ended up with ball nuts type tings when i tried finding out the difference.

Wasn't easy getting the wobble on video, but its almost possible to make it out here: (The leftmost wheel wobbles and gets slightly caught).
https://www.dropbox.com/s/ebvvnh565uwhfmj/2016-11-03%2012.30.00.mp4?dl=0

I think it V-slot profiles and matching wheels would do more good though. Sadly I can't seem to find the profiles for less than 60$/meter after delivery. Might just buy a 10mm chamfer bit and mill a v-slot in my existing profiles to avoid having to deal with Banggood to get this machine to run straight. Seriously regretting buying this off  Banggood, no matter what the problem is their offer is 200 bangood points, starting to piss me off. Defective laser, no problem we offer you 200 banggood points (and after checking, they have a value of 1 cent, so 2$ coupon for dead laser)

ggallant571

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Re: Wheels!
« Reply #6 on: November 04, 2016, 09:50:20 AM »
That looks for like a defective wheel. On mine, the bolts are 5.0mm while the center of the wheel is 5.5mm. Applied some pressure between top and bottom wheels when tightening everything. To me it is a design flaw that there is so much slop and no alignment mechanism. A machinist friend suggested making axles that are 5.5mm smooth in the center with 5.0mm threads on each end.

I just love the Chinese craftsmanship. Makes me want to go to China and ride the high speed rail.
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ROSS

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Re: Wheels!
« Reply #7 on: November 04, 2016, 10:04:07 AM »
Hang on a while and you can get to ride in the new "Jumbo"  China and Russia are going to build to rival Boeing and Airbus  (but tell the wife where the insurance policy is first!!)
« Last Edit: November 04, 2016, 10:04:58 AM by ROSS »
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Lasers are wonderful machines..not ONLY  can they cut a finger off BUT  they can also cauterise it at the same time.....

SAFETY -  IS NO ACCIDENT

ggallant571

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Re: Wheels!
« Reply #8 on: November 04, 2016, 10:48:02 AM »
I just did a etch with a long x-axis (45mm) and the results are less than spectacular. They are definitely worse that the same etch yesterday. Must have used up the 10 meter max distance built into the bearings!!!   
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beikeland

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Re: Wheels!
« Reply #9 on: November 04, 2016, 01:30:42 PM »
If its wheel related then you'd expect to see a pattern repeating every C=2πr=2*3.14*10.75mm=67.54mm This tracks with what I'm seeing, goes +1mm to -1mm and back to+1mm every full rotation of the wheel. And the video shows the wheel wobbling twice on the 140mm travel along the X axis, the three other wheels are fine, or a lot better at least.

beikeland

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Re: Wheels!
« Reply #10 on: December 01, 2016, 10:33:15 PM »
Cut new parts last night. Front and back X carriage + eccentric spacers for the top row of wheels.

Initially modeled the eccentric spacer identical to the open builds one, but found it to have a little to thin features for the somewhat soft HDPE plastic I used, so I re did them with a 5mm inner bore, 8mm "shaft" and 10mm M5 nut perimiter. Increasing the "shaft" from 7.11mm to 8mm giving the section that protrude a little thicker wall. This meant I had to put a washer on the head of the M5x50 bolt to keep it from going through the 8mm hole of the X carriage.

Anyways, I cut hole distances 53mm (center to center) and the eccentric spacers make it super easy to adjust the pre-loading and tension of the wheels to eliminate all play. This was for the smaller openbuilds wheels.

Just need to cut some non eccentric spacers for the lower row of wheels and try to make some eccentric spacers what have a 8mm surface against the wheels to only contact the inner race of the bearing, or some shims. Using the larger wheels removes that issue.

Really pleased with the result, still a little issue remaining with a section of the profile that runs a little tight after installing motor and belt, but hopefully I can figure it out. Using the eccentric spacers probably did more good than the new wheels.


Zax

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Re: Wheels!
« Reply #11 on: December 02, 2016, 04:39:30 AM »
Very nice, those look like F1 racing slicks. Hope they're better than the Pirelli's though  ;D

beikeland

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Re: Wheels!
« Reply #12 on: December 02, 2016, 07:05:36 PM »
"Racing slicks"  8)

Unfortunately I talked the Chinese seller into selling me 12 instead of 10 wheels and he forgot to add the 2 extra wheels I paid a little extra for (instead of buying 2 lots of 10 wheels) .. but when I get them I'll be doing the same for the Y axis, although I don't think the machine will get any squarer by updating the Y axis.

On the other hand the X axis uses the cardboard shims I used for the mock up, so the delay just gives me plenty time to come up with a design to make spacers that don't contact both the inner and outer race on the bearings of the smaller wheels, and some plain spacers to complement the other row of wheels

ggallant571

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Re: Wheels!
« Reply #13 on: December 02, 2016, 08:04:17 PM »
Did you cut the eccentric's with this machine?
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beikeland

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Re: Wheels!
« Reply #14 on: December 02, 2016, 11:52:08 PM »
No, bits are cnc'ed, doubt I'd be able to get any precision in z depth when cutting on the laser? And I still await my replacement laser module, although the manufacturer have approved a replacement for the 2nd time now, so waiting to see if they ship one or ask for yet another video, again. Fingers crossed for having the machine somewhat usable three months after buying it.

I have a small 3040 Chinese CNC, the rough edge cut is a combination of old PCB drills re ground into cheapo straight flute endmills and me being a noob at cutting plastics, suppose I could have tried adding a finihing pass, but the machine is old and

More pics and the cad model over in this thread: http://benboxlaser.us/index.php/topic,1056.msg14427.html#msg14427