My Ryobi leaf blower served well for many years until recently when the polypropylene impeller died. As replacement impeller parts are no longer available, 3D printing came to the rescue of what was otherwise still a good leaf blower.
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The original impeller fractured around its shaft, causing a massive impeller wobble within its housing. This produced lots of noise and the bad smell of melting plastic!
The original Lightwave design necessitated lots of supporting material – too much, which couldn’t be broken off cleanly. The challenge was then to design the parts so they would fit together easily, but could be printed with the minimum amount of supports. In considering the actual shapes, it was also necessary to consider which parts would best be printed upside-down. The one-piece design of the 3D print in the photo below was abandoned (shown here with its support material still attached).
As it was impractical to print the whole impeller as a single part and remove the supports cleanly (see above), the design was changed to that of a minimum number of parts which would be Superglued together. In the image below, the vanes (grey) and the base (green) would be a single printed part. The shaft (yellow) and shaft collar (grey circle) would be separate parts, as would the top disc of the impeller (not shown).
PLA plastic was to be used; ABS was a backup option if the PLA failed during blower use, but so far after a couple of months of operation blowing leaves and drying washed bicycles (yes, it’s great for that!), the PLA is just fine.
Instead, a revised top disc design had small triangular protrusions equally spaced on its face around the edges to serve as vane alignment guides during gluing. This would also ensure that the base (to which the vanes were printed as a single integrated unit) would self-centre and align with the top disc. In the Lightwave screengrab below, the triangle guides are visible on the white top disc section (shown here rotated upside down, with the base not visible).
The 3D printed components. Clockwise from bottom left: top disc (triangular vane guides are on the under side in this shot), collar and top disc alignment jig, collar, shaft, base strengthening disc, base and vanes. This design required little in the way of support material.
To strengthen the bond between the vanes and top disc, extra Superglue was spread along the vanes so it oozed out along the length of each vane, and the impeller was quickly plunged into a tub of bicarb and moved around to make sure the bicarb covered every nook and cranny of the impeller. Superglue and bicarb baking soda set off like rock very quickly! The left over baking soda was tipped off back into the tub. Wearing nitrile gloves helped to ensure that my hands didn’t get stuck with glue.
The new and the old. The top disc on the 3D print has a separate circular collar glued to it. When the impeller is installed into the blower, the collar fits within a slightly larger diameter sized hole in the blower housing. A circular jig was printed to align the hole in the top disc and the hole in the collar during gluing. Care had to be taken as not to accidentally glue the jig in place!
The motor shaft is a brass fitting with a reverse-screw thread, over which the plastic impeller shaft is installed.
My original impeller plastic shaft design had a screw thread, but it was not possible to match the pitch of the brass thread. Instead, my final plastic shaft was designed as a jam-fit, where the inside of the shaft was a slightly smaller diameter (0.4mm) than the brass shaft it was to fit over.
Fitting the impeller to the motor required a small amount of heat from a butane torch to be applied to the brass shaft; the plastic impeller shaft slid easily over the hot brass motor shaft. Don’t know how I’ll ever get it off if it needs replacing… maybe more butane-fired heat!
Although the impeller collar and the corresponding circular part of the blower housing are separated by a small gap to ensure there won’t be any friction by rubbing, just to be on the safe side a small amount of high temperature bearing grease was applied to both the impeller collar and housing.
So far, after a couple of month’s use, the 3D printed impeller is performing well with no sign of rubbing against its housing, and no tell-tale warning smells of melting plastic!