robot coupe SPINDLE SANDER shaft too short (food processor)

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tomasg

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Hello there i recently salvaged a broken robot coupe
for those who dont know what this is .....
its a heavy duty food processer thats got a 250w motor in it
and around 2 inches long of a 1/2" stainless hex shaft

I plan to turn it into a spindle sander
(ive heard that at this rpm burns the paper but this doesnt matter because its
only for very final sanding exactly square ) guitar bending forms

Ive bought a sanding drum for chucking up to a drill press
thinking their was some kind of ingenious sandpaper locking device , their wasn't
Also ,from the pictures I thought from the picture it had a coupling to fit
the hex shaft on my motor .... it was round
Anyway
I managed to bodge a sleeve of cut pipe tight over the hex shaft and onto the drums coupling
turned it on only to find out its totally wobbley......
Basically i need a longer shaft for an axle at the top of the drum for stability

Ive looked EVERYWHERE for a 3" deep socket ,extension or coupling so i could mount it on the shaft
and fit a sleeve over that to make a shaft extension

The only other options i can see is to get some specialist to weld another extension on
or turn this project into a big one by attaching a pulley to the shaft and gettin more parts exc
any suggestions folks ?
thanks in advance
tomas
 
I forgot to mention could i just replace the motor shaft completely ?
It was not immediately obvious to my eyes but then again i had a bad headache that day
thanks again
 
Sounds like a bit of a tall order - getting a shaft extension to run true at full motor speed, and withstand the side forces associated with sanding is a bit of an engineering challenge - even if the motor bearings are up to it. sounds like you need to find some sort of shaft/bearing setup to support the sanding drum and transfer the drive from the motor by some sort of flexy coupling or belt drive. If your sanding drum is chuck mounted then it may be easier to buy a cheapo drill and rig up a bracket to hold the drill steady and keep the motor for other things. It's often the case now that supermarket cheapo power tools are absurdly under priced - but still remarkably good. Even better if you watch the discount bins eg wickes detail sander and jigsaw - in a toolbag £15, and plenty of sub£20 drills....

Just checked - cheapest corded drill in homebase 550Watt for £9.99!

Dee
 
Not sure I've visualised this properly, but I think you are saying you want to connect a 1/2" hexagonal motor shaft to a sanding bobbin of (guessing) about 2" diameter and 4" long.

Could you start with a rough cylinder of wood (ideally turned on a lathe, but planed octagonal would do) with a hole along its axis a bit less than 1/2" diameter. Force the wood onto the motor shaft - nice tight fit. (May need chiselling out or wedging or filling with gripfil style adhesive if loose). Then turn the motor on, and use a static file or coarse sandpaper on a block to make the rough cylinder into an accurate one. By doing this on your salvaged motor, it would automatically be true. Then fix the sandpaper onto the bobbin in whatever way you want. (I'm thinking of a slot into which one end will tuck, with top and bottom held tidy with a wide elastic band / piece of bicycle inner tube.)
 
Thanks for the replys guys
after looking everywhere for a "hexigonal tubing" coupling it seems like its
cheaper to get/buy/find other parts than get it in usa

It seems im gonna go the full hog and make up a seperate shaft
thats belt driven from my motors shaft attached to a frame by
2 "pillow blocks" the same as on a drum sander (thickness sander for luthiers)
with the pulley in between them

The only thing ive got to find out is what kind of bearing to get to mount the vertical
shafts weight on .
Say for ease... could something like this work?

So far .the diameter of the new shaft is depending on this bearing if i definatly need one
ive got a broken garden mucher also
and i presume that it has a vertical shaft bearing
ill report back when i get a better idea on the new parts im trying to source
any suggestions appreicated though
espically on the pulley sizes as ive never done this stuff before
Thanks again
tomas
 
Tomas,

sorry can't help with the "engineering" but here is an idea I have used for wedging a strip of sandpaper on a home-made bobbin:

Using a Tenon saw cut two angled slots longitudinally along the bobbin, such that the cuts will form a "dovetail" shape, then chisel out the waste. Fit the sandpaper around the bobbin and into the bottom of the wedge slot. Now make a longitudinal wedge from hardwood. It is important that the wedge is a firm but not tight fit and that the "sharp" end of the dovetail slot is just wide enough for the two layers of sand paper. See sketch:

HTH

Dave
 

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