V-Wheel Washer Issues

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twforeman
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V-Wheel Washer Issues

Post by twforeman » Sat Jan 30, 2016 9:19 pm

In this thread http://www.shapeoko.com/forum/viewtopic ... her#p59647 it was noticed that the bearings in the v-wheels have some back and forth slop in them.

I also have experienced this and I decided to do some research. I took the four v-wheels off my Z plate, took out the bearings and washers and measured some things.

According to this drawing, the ridge inside the v-wheel should be 1mm +0.00/-0.08. Since I'm old-school I use inches, so that means it should measure between 0.039" - 0.036".

The ridges in my wheels measured 0.031", 0.032", 0.033" and 0.036". Which means they are out of tolerance and too small.

The washer that is sold by Inventables and Openbuilds is supposed to be 1mm thick. The drawing on Openbuilds shows the thickness as 1mm +0.076/-0.00. Which means it should measure between .039" - .042". My washers all measured .043" which means they are barely out of tolerance on the thick side.

All of this taken together means that there is 0.007" - 0.012" of play in the wheels. Which doesn't sound like a lot until you think about the upper wheels being pushed one way and the lower wheels being pushed the other way, which equals 0.024" and over a distance of about 6" gives us about 0.3 degrees off.

So the wheel ridges are too small and the washers are too thick. This is the worst-case tolerance condition. Even if the wheel ridges were small but still in tolerance (0.036") and the washers were too thick but still in tolerance (0.042") we would still have slop of 0.006". Which is not great.

But as it stands we are double that.

I'm not sure what the correct fix is. It would be nice if the wheels were in tolerance at least. Washers that actually measured 1mm would help.

McMaster-Carr sells precision shims that are 6mm id x 9.78mm od x .031" thick (yes, they are listed using both metric and imperial units) which would give a little pre-load on some of the bearings. They are $10.54 for 10, and of course I need 12. :evil:

I'm going to poke around some more and see if I can't find other shims. I'm also sending this info to Carbide support.
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twforeman
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Re: V-Wheel Washer Issues

Post by twforeman » Sat Jan 30, 2016 9:22 pm

Another option would be new V-Wheels. Openbuilds used to sell polycarbonate "Xtreme" V-Wheels, but I can't find them on the site anywhere. They have their Solid "Xtreme" V-Wheels, but those won't work on the S3 rails.
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AnonymousPerson
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Re: V-Wheel Washer Issues

Post by AnonymousPerson » Sat Jan 30, 2016 9:33 pm

So... suggestion for your next project... make a lathe. :)
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TomDChi
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Re: V-Wheel Washer Issues

Post by TomDChi » Sat Jan 30, 2016 10:28 pm

I'm about to finally install reinforcing bars to stiffen the Z plate, and that has me thinking about all of the different sources of slop/flex. After the plate flex is reduced, the v wheels seem like the next thing to focus on, so I'm interested what can be done there.

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Re: V-Wheel Washer Issues

Post by LTEPM » Sat Jan 30, 2016 11:36 pm

twforeman wrote:Another option would be new V-Wheels. Openbuilds used to sell polycarbonate "Xtreme" V-Wheels, but I can't find them on the site anywhere. They have their Solid "Xtreme" V-Wheels, but those won't work on the S3 rails.
AIUI the extreme V wheels shattered so they stopped selling them. I have a pack of 50 open builds delrin V wheels which are wider than the ones which come with the SO3. As far I I have researched they are the same diameter as the SO3 wheels.

How do you measure the internal flange thickness?

You will also need to check for X axis carriage slop as well.

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Re: V-Wheel Washer Issues

Post by WillAdams » Sun Jan 31, 2016 12:21 am

This came up to some degree previously: http://www.shapeoko.com/forum/viewtopic.php?f=12&t=909 --- wonder if Reactive Substance is still selling them.

More at: http://www.shapeoko.com/wiki/index.php/Parts#All_Axes
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twforeman
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Re: V-Wheel Washer Issues

Post by twforeman » Sun Jan 31, 2016 2:03 am

LTEPM wrote:
twforeman wrote:Another option would be new V-Wheels. Openbuilds used to sell polycarbonate "Xtreme" V-Wheels, but I can't find them on the site anywhere. They have their Solid "Xtreme" V-Wheels, but those won't work on the S3 rails.
AIUI the extreme V wheels shattered so they stopped selling them. I have a pack of 50 open builds delrin V wheels which are wider than the ones which come with the SO3. As far I I have researched they are the same diameter as the SO3 wheels.

How do you measure the internal flange thickness?

You will also need to check for X axis carriage slop as well.
I measured the thickness of the wheel and then the distance from the face to the ridge on each side.

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Re: V-Wheel Washer Issues

Post by JohnP » Sun Jan 31, 2016 2:25 am

During my S3 build, when running the assemblies up and down the V-rails (before snugging up the eccentric nuts), I noticed a "slight up and down" wobble along the slide rails, as if the V-bearing assemblies were just a smidge out of round. This thread makes me wonder if I was really seeing runout/slop caused by a side-to-side seeking/hunting behavior caused by the tolerance issues raised here...

I'm seeing a slight wobble in MDF straight line cuts in the +/- X direction, even after making sure everything in the gantry is tight.
WiggleCut.jpg
Test cut, notice the low near "12" and the high near "10"...
WiggleCut.jpg (486.19 KiB) Viewed 1497 times
(and don't notice the ragged/dirty fingernails :? ...)
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twforeman
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Re: V-Wheel Washer Issues

Post by twforeman » Sun Jan 31, 2016 10:10 pm

That's possibly the issue, but the bearings are a pretty tight fit in the wheels usually, so it takes a bit of pressure to move them back and forth. I wouldn't expect them to be the cause of your wobble when moving it by hand, but they could cause the issues you see in your cut.
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apspurgeon
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Re: V-Wheel Washer Issues

Post by apspurgeon » Mon Feb 01, 2016 12:19 am

Just saw this post....same issue and the bearings for the bottom 2 v-wheels on the z-plate have changed. The 2 bearings now longer hold the plastic wheel.
I too could get very noticeable movement (bottom 2 only). The bearings may have quality issues, or need to be replaced regularly.

I used a thinner washer and problem was solved (I made them out of copper sheet). This solved 90% of the Y axis movement, the stiffening in the Z-Plate made little difference

http://www.shapeoko.com/forum/viewtopic.php?f=37&t=7572

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