I started assembling assembled my LitePlacer and tried to do the wheel alignment but the movement
of X gantry and pick up head as well may not be smooth enough.
When the eccentric spacers are aligned, the movement is not completely free.
There is quite some friction. I’m not sure if that’s correct or not.
To be able to describe the amount of friction I did a simple experiment.
I moved the X gantry fully to the front of the machine and then lifted the front of the machine up
to create a slope for the X gantry to slip on. It starts moving downwards
when the front of the machine is lifted by about 10cm. Is that too much
friction or is it acceptable? This is when the eccentric spacers are in the positions when
the friction is minimum.
I also noticed that when I tighten the wheel screws the plane of the wheel changes a little.
That may be causing increased friction. How tight should the wheel mounting screws
be torqued?
How sooth should the movement of X gantry be?
Re: How sooth should the movement of X gantry be?
There is some friction. What you describe sounds a bit much but not excessive. However,
> I also noticed that when I tighten the wheel screws the plane of the wheel changes a little
This is not good. Do check that the bearings sit good in the wheels (a wheel on a table and a flat object on top should have the object parallel to the table), that the plates are not bent and that there is no burrs or something else between the washers and the plate, so that bolts fit straight.
There is no specific torque. The bolts can be tight, the bolts with eccentric spacers obviously not so tight that you can’t turn the eccentrics.
> I also noticed that when I tighten the wheel screws the plane of the wheel changes a little
This is not good. Do check that the bearings sit good in the wheels (a wheel on a table and a flat object on top should have the object parallel to the table), that the plates are not bent and that there is no burrs or something else between the washers and the plate, so that bolts fit straight.
There is no specific torque. The bolts can be tight, the bolts with eccentric spacers obviously not so tight that you can’t turn the eccentrics.
Re: How sooth should the movement of X gantry be?
I checked the bearings, they are installed properly.
When the wheel screws are not fully tightened, the v-grooves of the wheels don't make contact to both
sides of the slide, just on one side like on the attached picture.
When the eccentric spacer is turned, the v-groove falls in place and both sides make contact
but as a result the mounting plate is slightly deflected and tensioned. This seems to be causing
the friction and resistance in movement. I used light to see the gap between the sides of the wheels and
the surfaces of the slide to adjust the eccentric spacers so both sides of the v-groove make contact
and don’t tighten them any more. Y direction movement has quite some friction now but it is consistent
in all positions.
The same problem is more visible on the X movement wheels. The mounting plates bend so much when the eccentric
spacers are turned that I had to use two washers to offset the wheels. X movement is still very stiff.
I will look more into it.
Do you recommend shimming of the wheels to offset them so they align better with the slides
or should the lateral position of the wheels be preset by the structure of the machine.
BTW, the mounting plates are not flat, that may be the source of my problem.
When the wheel screws are not fully tightened, the v-grooves of the wheels don't make contact to both
sides of the slide, just on one side like on the attached picture.
When the eccentric spacer is turned, the v-groove falls in place and both sides make contact
but as a result the mounting plate is slightly deflected and tensioned. This seems to be causing
the friction and resistance in movement. I used light to see the gap between the sides of the wheels and
the surfaces of the slide to adjust the eccentric spacers so both sides of the v-groove make contact
and don’t tighten them any more. Y direction movement has quite some friction now but it is consistent
in all positions.
The same problem is more visible on the X movement wheels. The mounting plates bend so much when the eccentric
spacers are turned that I had to use two washers to offset the wheels. X movement is still very stiff.
I will look more into it.
Do you recommend shimming of the wheels to offset them so they align better with the slides
or should the lateral position of the wheels be preset by the structure of the machine.
BTW, the mounting plates are not flat, that may be the source of my problem.
- Attachments
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- wheel.jpg (8.69 KiB) Viewed 6671 times
Re: How sooth should the movement of X gantry be?
If the plates are bent, it is a manufacturing or shipping damage. Email me with info about what plates are not straight and I’ll replace them.
One trick to try when you get the new plates is to loosen the screws that hold the rails. There is some play in the screw holes; loosening and retightening them lets the wheels to push the rails to position where they want to sit.
One trick to try when you get the new plates is to loosen the screws that hold the rails. There is some play in the screw holes; loosening and retightening them lets the wheels to push the rails to position where they want to sit.
Re: How sooth should the movement of X gantry be?
The wheel mounting plates are bent/deflected only when the wheel screws are fully tightened.
When the wheel screws are completely loose, the wheel plates are quite flat.
The problem may be in the lengths of the front/back beams and the X gantry beam
or they way I assembled the machine.
I'll do some experimenting to see what's causing this issue.
No need to send any replacement parts at this time. Thank you.
When the wheel screws are completely loose, the wheel plates are quite flat.
The problem may be in the lengths of the front/back beams and the X gantry beam
or they way I assembled the machine.
I'll do some experimenting to see what's causing this issue.
No need to send any replacement parts at this time. Thank you.
Re: How sooth should the movement of X gantry be?
It looks like the main culprit is the distortion of the flat washers at the wheel
screws where the eccentric spacers are. That's the spacers between the wheels
and the mounting plates. If the screw is torqued too much (I thought I didn’t use
excessive torque but apparently I did), the washer becomes distorted and formed
into a ‘bowl’. The wheel bearing doesn’t have a flat plane to sit on. As a result
when the eccentric spacer is turned (the wheel screws turn along with them,
the wheel doesn’t just go up or down, it starts moving in an unpredictable trajectory.
This is also causing some lateral offset of the wheel.
I replaced the distorted washers and added spring washers so I can apply minimum
torque without risking that the nuts will get loosened due to vibrations (hopefully).
I also rebuilt the machine in slightly different way than escribed in the documentation.
I bolted down one side of the machine to the table, then I removed the X gantry but
left the wheel plates on the Y movement rails. I made sure the rails were perpendicular
to the table top, installed and adjusted the wheels, made sure the movement of the wheel
plates was smooth and them installed the X gantry. I installed the first part of the X gantry,
perpendicularly to the table top, then the second part and made sure the ways on both parts
formed a plane parallel to the table top (I used a level)
Now the X gantry movement is much smoother but there is a little problem
with the X gantry itself. The two parts have slightly different lengths and there is
a gap between them. I wonder if that needs to be corrected or if it’s acceptable.
Please see the attached pictures.
screws where the eccentric spacers are. That's the spacers between the wheels
and the mounting plates. If the screw is torqued too much (I thought I didn’t use
excessive torque but apparently I did), the washer becomes distorted and formed
into a ‘bowl’. The wheel bearing doesn’t have a flat plane to sit on. As a result
when the eccentric spacer is turned (the wheel screws turn along with them,
the wheel doesn’t just go up or down, it starts moving in an unpredictable trajectory.
This is also causing some lateral offset of the wheel.
I replaced the distorted washers and added spring washers so I can apply minimum
torque without risking that the nuts will get loosened due to vibrations (hopefully).
I also rebuilt the machine in slightly different way than escribed in the documentation.
I bolted down one side of the machine to the table, then I removed the X gantry but
left the wheel plates on the Y movement rails. I made sure the rails were perpendicular
to the table top, installed and adjusted the wheels, made sure the movement of the wheel
plates was smooth and them installed the X gantry. I installed the first part of the X gantry,
perpendicularly to the table top, then the second part and made sure the ways on both parts
formed a plane parallel to the table top (I used a level)
Now the X gantry movement is much smoother but there is a little problem
with the X gantry itself. The two parts have slightly different lengths and there is
a gap between them. I wonder if that needs to be corrected or if it’s acceptable.
Please see the attached pictures.
- Attachments
-
- A gap in the centre of X gantry
- X gantry centre gap.jpg (47.92 KiB) Viewed 6609 times
-
- Different lengths of the two parts of X gantry
- X gantry halves length difference.jpg (52.79 KiB) Viewed 6609 times
Re: How sooth should the movement of X gantry be?
An update on the gaps between the two parts of the X gantry.
The gap is actually needed as the spacing between the wheels
of the X-direction moving assembly is bigger than the spacing between the ways
of the X-gantry. The wheels were pushing the two parts apart creating the gap.
Different lengths of the two parts of the X gantry is a real problem.
When the screws fixing them to Y direction wheel plates are screwed in,
the wheel plates are slightly bending and the wheel geometry changes.
The gap is actually needed as the spacing between the wheels
of the X-direction moving assembly is bigger than the spacing between the ways
of the X-gantry. The wheels were pushing the two parts apart creating the gap.
Different lengths of the two parts of the X gantry is a real problem.
When the screws fixing them to Y direction wheel plates are screwed in,
the wheel plates are slightly bending and the wheel geometry changes.
Re: How sooth should the movement of X gantry be?
The different rail lengths is a manufacturing defect. My apologies for that and for the troubles and extra work! I will get a new shipment of rails in a few days; I'll send you replacements early next week.
Re: How sooth should the movement of X gantry be?
No worries.
Thank you very much for your support.
Thank you very much for your support.
Re: How sooth should the movement of X gantry be?
I used thicker washers to offset the wheels on X movement, most of the gap between X rails is eliminated but there is some twist
in the beams, probably because they are of different lengths. The X wheels make noise on one side of the machine while they are quiet
on the other side.
BTW, what's the maximum scanning speed in X and Y direction? I was able to get Y to work at 20,000 but not at 25,000.
Can this be used as an indication of the resistance in the movement?
I didn't try X as it's nor fixed yet.
in the beams, probably because they are of different lengths. The X wheels make noise on one side of the machine while they are quiet
on the other side.
BTW, what's the maximum scanning speed in X and Y direction? I was able to get Y to work at 20,000 but not at 25,000.
Can this be used as an indication of the resistance in the movement?
I didn't try X as it's nor fixed yet.