a rab3D: V-Roller Guide - part 1
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Part 1 Guide Roller Design Consept

Linear Guides





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 Divetail Slide
Traditional Dovetail Slide





Reciprocal Ball Guide

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. 
V-Roller Guide

V-Roller Guide


Though not offering the same rigidity or accuracy of the recirculating ball races they are perfectly adequate for a light duty machine.




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.





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.)
608 Bearing





Centre Cursor to Bearings 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.
Bearings and Guide





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
Local View





Select Outer Loop
Inner Loops
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.
Select Loops





Position Cursor
Pivot-3D Cursor 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.
Alt Select





Bore depth = Bearing width

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.
Select Internal





Delete Inner Vertices
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.
Repeat on other Bearing



Select Inner Loops
Skin 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.
Skin Between Loops





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.
Select Loops 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.
Move Edge





Repeat 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.
Paint Select





Shift H
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.
Snap the cursor to the extruded vertex Shift-S Cursor>Selection.
Extrude Centre





Spin 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.


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.
Add Edge





Select Verts 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.


Snap the cursor to the Object Centre Shift-S Cursor>Selection then Tab back into Edit Mode.
Spin





New Fillets In the Mesh Tools panel set Degr:360 and Steps:32, press spin to generate the new fillet. Select All and Remove Doubles W.


Outliner

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.

Global View





Vertex on Horizontal Centre Line

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. 
Extrude -22mm





Scale to Centre Extrude the two bottom vertices in the Z-axis with a length similar to the reference vertex.

To position them at the same Z-axis location as the reference vertex Scale them constrained to Z and to a scale location of 0.

Delete X the reference vertex. 

                Add Edge
Subdivide Multi - 2

Subdivide Multi W the bottom edge with 2 divisions.

This will split the bottom edge into three equal divisions of 6mm each.





Scale 0.5 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

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.
Cut new vertex





Move Centre vertices 6.6mm
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".
Eetrude Edges





Remove Edge
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.
Front View





Spin 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.
Completed V-Roller





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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