Toolpost Grinder Part 21: Tightening Fixture

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This week, we finish up the wheel arbor and make a tightening fixture to make wheel changes easier for those of us who only have two hands.

Spanner Holes in the Arbor…

The first thing we need to do is poke some holes in the arbor so we have something to use when tightening it on a wheel.  I held the arbor in aluminum V-block soft jaws in the mill vise and found the center with an indicator.

Indicating the Center
Indicating the Center

To make the holes, I used three operations.  First, I spotted the holes very gently to try to prevent flex in the mill from pushing them off center.  Then I drilled out the bulk of the material with a #31 drill.  Finally, I brought the hole to size and location by plunging with a 5/32 end mill.  The 5/32 end mill I have has a 3/8″ shank, so I had to grind the shank down to clear the arbor.  I did this by chucking it up in a Deckel tool grinder and spinning it against the wheel at 8 degrees to provide some clearance.

Drilling out the bulk of the material
Drilling out the bulk of the material
Custom-ground End Mill
Custom-ground End Mill
Milling the hole to size
Milling the hole to size
Deburring with the spotting drill
Deburring with the spotting drill

…and in the flange

Next up, the flange needed the same holes.  I indicated the flange using the chamfer around the edge.  This isn’t perfect, but it worked well enough.  The flange was a little easier to deal with because the arbor wasn’t in the way and I could use my Noga deburring tool.

Indicating the flange
Indicating the flange
Noga deburring tool
Noga deburring tool
Finished flange
Finished flange

Milling a Taper

For the fixture itself, I re-used the aluminum hex that we used when turning the taper on the lathe.  It isn’t much good for anything else now that it’s out of the 3-jaw chuck, and it was handy.  The first step was to cut the taper.  I did this in two steps, roughing out the bulk of the material with a 1/4″ carbide end mill and then finishing the walls of the taper with a ball end mill.  I finished it in .030″ steps, which left about .0004″ of roughness, but this is just fine for a fixture like this.

Roughing out the taper
Roughing out the taper
Finishing the taper
Finishing the taper

The arbor dropped in to the taper and held firmly with no rock.  I was actually surprised how well it fit.

Nice fit!
Nice fit!

More Pin Holes

The last milling step on the fixture was to put in a pair of holes for the drive pins.

Pin holes
Pin holes
Measuring the hole size
Measuring the hole size

The hole size in the aluminum came out to exactly .060″, the same as in the steel, so this is our target when we drill the pins.  As an afterthought, I decided to go ahead and drill a through-hole behind the pin, just in case we need to knock them out later for some reason.

Through-drilling
Through-drilling

Making pins

I turned the pins out of W1 drill rod on the lathe.  W1 is not my favorite material to turn, but I have a lot of it, and the Kyocera CCMT0602 inserts made short work of the job.

Turning the pins from W1
Turning the pins from W1
Finished pin
Finished pin

Assembly

After machining, I got a closer look at the taper.  It turned out really well–better than I expected.  As it turns out, the taper didn’t fit quite as tightly after taking the part out of the mill.  I was confused for a moment until I realized what had happened.  When I mounted the part in the mill vise, I applied enough pressure to distort it.  The part was already drilled-through, so it was able to compress a little.  I milled the taper round, and the arbor fit perfectly while it was still in the vise, but when I released the vise pressure, the part relaxed and the hole is now not round any more.

This isn’t a problem for this fixture.  It doesn’t have to be a tight fit.  But I learned something.  I’ll have to remember that in the future.

Close-up of the taper
Close-up of the taper

I installed the pins with Loc-Tite 609 permanent retaining compound (green) and pressed them in using the vise jaws.

Fitting the pins
Fitting the pins

The arbor dropped in and the fixture held it securely.  Now, if only I had a pin spanner wrench…

The arbor and the taper
The arbor and the taper
For want of a spanner
For want of a spanner

Up next…

I made this arbor to tighten with a pin spanner, but it turns out I don’t actually own one.  We’ll make one next time.

If you’re following along with the build, or if you’re just curious, here are some of the tools used in this video:

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