...allows the vacuum line to rotate freely and to deviate nearly 40° side-to-side.
So, while the consensus online is that an external vacuum is a good idea, these random orbital sanders don't tend to come with adapters, so I had to make one, and being a huge fan of these swivel plugs for my pneumatic tools, I wanted to copy that functionality in my hose line adapter.
The linked pneumatic swivel plugs are two simple parts: a ball with a stick attached to one end, with a hole bored through for air flow, and an enclosed socket - a "cage" - that holds the ball... we could copy that design, but since we are connecting a vacuum line here, we can actually skip the "cage" bit, omitting half of the socket, and just use the low pressure to keep the socket on the ball. (A hollow peg then becomes necessary to keep the socket from rotating too far and blocking the vacuum connection.)
So far, I've been happy with the ability of the vacuum to hold onto the sander, but if I decide otherwise, it would be a fairly simple retrofit to complete the cage.
(Please note: the design I present here actually requires a lathe to make, but by substituting a 1" coupler for the fancy turned socket, and an oversized hole and some glue for the tapered bore, you could probably make a fairly good copy with only a drill, a grinder, and some hot glue.)
Step 1: Design
Design is pretty simple; set up a single 2D parametric sketch and figure out the best way to achieve the following goals:
- The largest possible opening for the socket, to maximize the area of low pressure which holds the swivel connection together.
- A mating angle of at least 20° per side between the socket and the golfball. (much less than that and they will jam together, in the same manner as a machine taper)
- A large amount of possible angular deviation.
- A reasonable wall thickness, both for the pin and the socket.
- General manufacturability
I ended up with the above design, based on a 1" coupler (further machined with fancy socket shapes) glued onto a bit of 1" pipe (which handily fits into my vacuum hose), with a pin made from 1/4" steel pipe turned down to .43" so that it press-fits nicely into a 27/64" hole.
Step 2: The Ball
A golf-ball gives us a slick surface for the socket to bear against, and a rubber core for the sander to mate with... and as a bonus, is actually surprisingly machinable:
- Find the dimensions for your sander's vacuum-in port. (mine was 0.85" min and 1.5° of taper per side)
- Chuck the golfball in the lathe... fairly gently. It is rubber, and you don't want to distort it too much.
- Drill a hole to a depth of about 1" into the golf-ball. Do this in multiple steps; something like 1/4" → 3/8" → 1/2", so as not to tear the golf ball out of the chuck.
- Finish the tapered bore in the golf-ball with a boring bar. You can use the outlet on the sander as a go/no-go gauge, enlarging the bore until you are happy with the fit.
- Flip the ball around and drill a 27/64" hole. With this Makita sander, some angular misalignment is preferable, as it allows the center of the allowable deviation to be set parallel to the workpeice, rather than angled upwards with the vacuum port.
- Turn down the outside of a bit of 3/8" pipe to 0.43", add a small taper to one end, and cut to a length of .7" or so.
- Press the pin (bit of pipe) into the golf-ball, leaving something like 0.125" protruding.