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Back to Tutorials |
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Part 1 Guide Roller Design Consept
Linear Guides |
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| Many engineering
situations require the movement of machine parts along
set axes. On traditional machine tools this was historically achieved
by using accurately machined and hand scraped guides that run on planed
or ground slides. This method of construction when done correctly
offers a great deal of rigidity between the components but still
allowing movement in one axis. The drawback of this type of slide is
the initial high load required to overcome the starting friction. On a
traditional machine tool this simply meant the operator would have to
exert a little more force on the hand wheel to start the slide moving. |
Traditional Dovetail Slide |
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Recirculating Ball Guide | On Industrial CNC
machines overcoming friction to allow increased speed
and or smaller drive units has brought about the development of linear
bearings. These usually contain re-circulating balls or rollers that
run along hardened and ground guides. Alternatively larger drive units
are fitted to traditional slide ways. In both situations overcoming
friction can be a costly process.
As an alternative to recirculating ball races, some industrial
processes use a ‘V’ roller guide running on a pre
formed
track. |
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V-Roller Guide |
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Though not offering the same rigidity or accuracy of the
recirculating ball races they are perfectly adequate for a light duty
machine. |
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As a hobby engineer the use of expensive OEM components such as linear
bearings is not affordable, therefore an alternative must be used. The
original router used “Oilite Bushes” running on
18mm Bright
drawn steel shafts. The shafts proved amply strong enough for the
job. The problem was the inability of the stepper motors to
overcome the starting friction, especially when the shafts became
slightly contaminated with dust from the machining process.
Though Industrial 'V' rollers are still quite expensive it is
a
simple process to machine an alternative that will run on the existing
18mm BDMS slides. The following
tutorial shows how the 608 bearing model was used as a base to
construct the ‘V’ roller and axle.
If you are currently using Blender save your work Ctrl-W and start a
new project Ctrl-X.
Delete the default cube X.
This section assumes you have completed and understood the 608-Bearing tutorial. | |
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As the components will be
built from the 608 Bearing geometry the first
step is to append the low vertices 608 bearing into the scene. Press Shift-F1 and
navigate to the folder containing the 608-BearingSmall.blend made in the Bearing
tutorial. Click
on Object and select the OB:608-BearingSmall model, Press Load Library and
the Bearing
will be loaded into the scene. (A
more detailed description of appending is given in 608-Part
8.)
Split the 3D view and
open an Outliner window. (If
you cant remember how this is done it is described in 608-Part
4.) |
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Some of the design
constraints I have are based on the material
available to me. I currently have slides at 18mm diameter so I will
reuse these. The ‘V’ Roller will be made the same
width as
the slide to maintain as small a footprint as possible. I have some
45mm diameter BDMS that I will use for the rollers, so I need to make
sure the outside diameter is less than this.
In side view NumPad 3
Copy the Bearing Shift-D
and move it in the Y-axis
11mm. |
This will set the bearings with an external width of 18mm.
Next we need to add a cylinder to represent the 18mm diameter
slide, centrally to the bearings. Shift-RMB
select both Bearings and
snap the cursor to the middle of them Shift-S
Cursor>Selection.
Add
a Cylinder press Space
Bar to open the Toolbox then select Add
>
Mesh > Cylinder. From the popup menu change radius to 9 and
length
to 20, press Enter to accept. Tab back into Object Mode and with the
cylinder still selected, move it
below the bearings G
(move) Z to
constrain it to the Z-axis and drag it
to a position below the bearings. |
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We will now use the outer
profile of the bearings to form the bore of the V-roller. Shift-RMB
select both bearings and copy them Shift-D
then press Esc
to leave the copy
over the top of the original bearings. With the two new bearings still
selected join them into one object Ctrl-J.
In the Link and materials
panel rename the object OB:V-Roller. Press NumPad / to go into
local
view for the V-Roller and Tab
into Edit Mode.
Now is also a good time to save your work. Pres Ctrl-W and save the
file as V-Roller.blend |
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Shift-Alt-RMB
Select the second outer loops of vertices from the bearing outside
diameter and the loops indicated between the bearings. If you added
chamfers to the bearing choose loop A otherwise choose loop B. In total 4 loops should be selected.
Delete
these 4 loops X
Vertices.
This will isolate the outer section, from the inner part of the bearing. |
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RMB select a vertex
on the far left side of the bearing and snap the cursor to it Shift-S
Cursor>Selection.
Change
the Pivot point to 3D Cursor.
Alt-RMB select the
loop of vertices on the outside diameter of the bearing. Scale these along
the Y-axis
to the 0
cursor position. |
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Repeat
this on the Right hand side of the other bearing.
Press
A
to deselect all vertices then with the cursor over the inner portion of
a bearing press L
to select all linked vertices. |
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Delete
the selected Vertices X.
Repeat
this on the other Bearing.
You
are now left with two bores where the bearings sit inside the V-Roller.
These
now need to be joined together. |
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Shift-Alt-RMB select
the inner loop of both bearings.
Press
F
to open the Make Faces menu. A new option is available Skin
Faces/Edge-Loops. |
Pressing
the
Skin option will automatically build faces between the two vertex
loops. It works the same as the Loft function in many 3D CAD packages.
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| The bore of the V-Roller
could be called finished
at this stage, but its not really good engineering practice to have the
inner fillet radius of a bore the same size as the object that is going
to fit into it. |
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To facilitate a better
fit for the bearing it is better
to have a bore fillet with a smaller radius than that of the bearings
outer edge. To achieve this we need to delete the loops making up the
fillet and re model them.
Shift-Alt-RB Select the inner loops of the two fillets and
delete them X. |
| RMB select the inner
loop of the left hand bearing location and move the loop G on the Y-axis 0.3mm. This will
allow us to reconstruct the fillet with a radius of 0.3mm, half the
size of the outer fillet on the bearing. |
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Select the inner loop of
the right hand bearing location and move this -0.3 on the Y-axis.
In
front view NumPad 1
press Z for
wire frame view then B-B
to open the paint select tool, select the top vertices.
Hide
all the other vertices Shift-H. |
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Go into side view NumPad 3 and RMB select the first vertex that will be
used to spin the new fillet radius (A) and Extrude it on the Z axis
-0.3mm. This gives us the centre point for the fillet.
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the cursor to the extruded vertex Shift-S Cursor>Selection. |
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Reselect vertex A (the
vertex we are going to spin to make the new radius) and in
the Mesh Tools panel set Degr:90 and Steps:5, Press "Spin" to form the
new radius.
Select the vertex on the fillet centre and delete it X.
Select the two vertices shown opposite and add an edge between them F.
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Repeat this for the Right hand side, selecting vertex B, but in the
Mesh
Tools panel deselect "Clockwise" so the fillet is spun in the opposite
direction. |
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Shift-RMB select
both sets of fillet vertices including those that join to the existing
V-Roller bore.
Go into front view NumPad
1 and Tab
into Object Mode.
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Snap the cursor to the Object Centre Shift-S
Cursor>Selection then Tab
back into Edit Mode. |
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In the Mesh Tools panel
set Degr:360 and Steps:32, press spin to generate the new fillet.
Select All
and Remove Doubles W. |
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Go back into Global View NumPad
/ and you will see the bearings sitting in the newly
created
bore. At this stage we don't need the Bearings in the view. In the
outliner click on the eye icon for the bearings which will close, and
remove them from
view.
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In side view NumPad 3 select one vertex that is sitting on the
V-Rollers horizontal centreline. Extrude this vertex in the Z-axis
-22mm, snap the cursor to this vertex. This will be used as a reference
to set the outside diameter.
Select the two bottom vertices on the outer edges of the V-Roller. We
will build the cross section of the V-Roller from these.
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In order to cut the
angles on the roller we first need to cut a central groove. On my lathe
I will
do this with a 3mm parting tool. To add the groove select the two
central vertices. Change the Pivot to "Median point" and scale them by
a factor of 0.5
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To
give a small flat at the edge of the V-Roller Extrude the bottom
left corner vertex in the -Z
direction then Extrude
this vertex in the Y-axis
1mm,
then Extrude
this vertically crossing the bottom edge. This will be used to cut a
new vertex 1mm from the corner of the bottom edge.
Select
All the press K
for the Knife tool, select Knife (Exact) from the sub menu and holding
down Ctrl
snap the cut line to the reference edge crossing the bottom edge. A new
vertex will be created. Delete X the reference
vertices.
Repeat this to cut a vertex from the right hand corner. |
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Select the two centre vertices and move them G in the Z-axis 6.5mm. This will
create the V profile with an angle of 45 degrees.
To
complete the groove Extrude
"Only Edges" the central edge in the Z-axis 2mm, then delete the
lower central edge X
"Edges".
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The roller profile is now ready to spin around the central axis. Select
all the vertices of the profile, including those attached to the bore.
Go into front view NumPad
1 and Tab
into Object Mode. Snap the cursor to the object centre Shift-S
Cursor>Selection, then Tab
back into Edit Mode.
In the Mesh Tools panel set Degr:360 and Steps:32, then press Spin.
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The profile will be
created around the bore. Select All,
Remove Doubles W
and Set Smooth W.
In the Modifiers Tab ass an Edge Split modifier and keep the default
settings. (A more
detailed description of adding the Edge Split modifier is contained in 608-Part 4)
The V-Roller is now complete. In the Outliner open the eye icon for the
two bearings to bring them into the view.
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Save
your work Ctrl-W
This has been a fairly long-winded way to construct the roller, however
I have chosen to do it this way to introduce the Skin Face/Edge loops
tool and methods to accurately modify a 3D mesh. In practice it would
be much Quicker to simply construct a complete cross section and spin
it around the centre axis.
In the next section we will construct the axle |
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