Sanding Block - #5 Completing Knobs, Danish Oil Finish & Done

This post is a little longer that most because at the end I have included the sequence of operations including material and hardware sizes.

After turning the knob blank to a cylinder, marking the beginning point of the dome and the blank’s overall length the blank is turned down to final length.  With that done the dome part of the knob is turned.

Adding the six faces to the cylinder is next.  It did take a while come up with a process to get them the same size and 60 degrees apart.  First, a jig is needed to hold the knob in place while the face is made and second the jig has to be able to control the rotation of the knob (60 degrees) so the next face is in the proper orientation.  The top photo below shows the top of the jig.  On the right is business end that controls the location of the cut and its depth.  The hole is for the threaded rod while the partial hole on the left is where my thumb sets to control the depth of cut.  The bottom photo is the back side.  You can see where the threaded rod comes through.  A nut is used to tighten the rod which holds the knob in place.  The recess allows the threaded rod to be below the face of the jig.

Next the knob is mounted in the jig as shown in the top photo.  The bottom photo shows the first face completed.  I will show the jig in use and how the faces are made in just a bit.

With the first face made the nut holding the knob in place is loosened and the knob rotated 60 degrees clockwise.  The first face is now parallel to the long reference edge of the jig at the bottom of the photo.  The nut is tightened to hold the knob in place and the second face is made.  This is shown in the top photo.  This process is repeated to make the third face as in the bottom photo and continues until all six faces are made.

Here in both photos all six faces have been made.  The bottom photo is simply a different view of the knob and jig.

Now with an idea of how the knob and jig work together the only thing left out is to explain how the faces get made.  Of the options available using the disk sander seemed to make the most sense to me as the rate and amount of material removal is easily controllable.  The photo shows sander with the miter fence set so the jig presents the to be made face parallel to the disk.  In use the miter fence is moved back and forth to prevent the disk from burning the wood while the jig is gradually fed into the disk until the proper depth is reached. 

After the six faces are finished, they need to be sanded since the grit on the disk sander is certainly not smooth enough.  To maintain the flat face at the proper angle the knob is set in another jig and each face is sanded with 220 and 320 grit sandpaper to remove all traces from the disk sander. 

The last two bits of work on the knob is first to remount it on the lathe then hand sand to ease the transition between the dome and the faces then do the same thing with the sharp points between faces.  When done with the 320 paper the lathe gets reversed and the rounded edge between the faces gets sanded to make the feathering even on both sides.   Last the piece is removed from the jig and the edge between the faces and the base of the knob gets softened with sandpaper.

Everything went well except for the last knob.  When it was turned down to the cylinder, I saw a faint crack in the blank.  I had hoped that it would get turned away as the piece was cut to length and domed but no such luck.  The straw that broke the camel’s back was when the first face was made.  There right across the face was the crack that probably ran most of the way through the piece.  Not what I wanted but so it became scrap and another one made.  Looking back the knobs were the hardest most time-consuming part of the build as they were all made individually with little benefit of reusable machine setups. 

Below is what the five sanding blocks look like ready to apply three coats of Danish Oil Finish and buff out.  This type of finish is used rather than my usual lacquer as an oil finish can be rejuvenated down the line a lot easier than a film finish. 

Here are the pieces with one coat of Danish Oil Finish on them.  There are seven knobs because I made one to replace the prototype and ended up finishing the cherry one with the crack.

With all three coats of Danish Oil completed the cork bottom needed some attention.  No matter how careful when applying the finish invariably I got some on the cork.  The top photo is typical of what happened.  As I wanted to have an unfinished cork bottom it needed to be fixed.  Cleaning is pretty easy. a sheet of 220 grit sandpaper is clamped down to the table saw extension and a few passes cleans it up as shown in the bottom photo.

The top photo shows the five completed sanding blocks plus the prototype finished with the final buff done.  The bottom photo has two of the blocks with sandpaper loaded on them.  I know this project may seem like overkill for sanding blocks but I like working with nice tools and enjoyed the build. 

Once completed I built a storage case to hold them along with some cut sandpaper.  Five of the blocks are loaded with different grits of sandpaper from 80 to 400 grit.  In general, the darker the sanding block the finer the grit.  In addition, I wrote the grit on the end of the sandpaper.  This is what it looks like and will get mounted on the peg board for easy access. 

Early on I wondered if the parts would be interchangeable between the six blocks.  After giving it a try they are and if desired, the parts could be all mixed up and still work just fine.  Don’t think I will do that as I like the continuity of the woods but it is interesting that it would work.

For anyone who wants to make these here is the sequence of operations along with material sizes I used.

Sanding Block Sequence

1. Thickness two blanks 2” x 7” x ½”
2. Thickness two blanks 2” x 7” x 1/8” (one contrasting)
3. Glue thin blanks to upper base
4. Cut angled notch in lower base
5. Glue cork to lower base
6. Cut glued stack and lower base to 6.25” length and 1.83” width
7. Sand cork on lower base to 5/8” total thickness and sand smooth edges
8. Clamp upper and lower bases together, drill 5/16” dowel hole centered 13/32” from edge
9. Turn 5/16” dowel
10. Using dowel for registration drill 5/16” hole vertically through stack and just into base for ¼” rod
11. Countersink underside of stack with ½” Fostner bit 1/8” deep
12. Drill 10 mm hole in base for insert & chamfer
13. Temporarily install ¼"-20 brass insert & remove
14. Finish sand base upper face
15. Glue in dowel
16. Sand excess off dowel ends
17. Epoxy insert in place
18. Route top edges of stack
19. Final sand top stack
20. Finish using DOF

Sanding Knob Sequence

1. Layout knob blanks, 1 5/8”+ diameter with compass.  Drill 7/32” hole 5/8” deep for rod.
2. Bandsaw knob to rough circle
3. Cut 1¾” long ¼”-20 threaded rod
4. Thread knob hole & epoxy rod into knob blank
5. Put fixture in lathe and use live center to true center
6. Do not take fixture out of lathe, take chuck & fixture off lathe then put cap in fixture
7. Turn to a 1 37/64” diameter cylinder
8. Turn dome shape total 7/8” tall with lower ½” still a cylinder
9. Take chuck off lathe, remove knob & install in jig
10. Sand 6 flats with jig on disk sander, remove from jig
11. Use sanding jig to sand flats to 320
12. Put back on lathe fixture then using 120, 220 & 320 sandpaper feather dome & edges between flats knocking of sharp edges.  At very end reverse lathe and sand with 320 to help feather both edges
13. Remove from lathe fixture and break base to face surface