adapting a part to fit?

[cooldan]

greets pinheads



i have been nagging people for help for ages now with trying to get my R&B Nell log assembly together, when i realised the parts weren't available i improvised and have now *almost* reached the last lap of my journey.



i have the motor, a gear that correctly engages the gear rack to move the log along, a spring to pull the gear back home after it's finished, a pulley to move the belt, and the belt to spin the circular saw for effect. trouble is that the shaft of the motor is slightly too small for the gear, and slightly too big for the pulley. is there a recommended way to make these things fit, or do i have to get creative with a drillbit (to enlarge the pulley hole) and some glue or something?



here's a pic of my stuff, on a photo of how it should look (thanks Ian!) - that's Ian's gnarly looking fingernail in the photo, by the way.



[attachment=1413:all the parts ready, almost.JPG]



thanks for input fellas



p.s. motor shaft width is approx 7mm, pulley hole approx 6.5mm, gear hole approx 11.5mm. i accept that the too-small hole will need drilling bigger, i only hope i have the right drill bit and the skill to do it. the problem is more the too-big hole in the (plastic) gear rattling loosely on the (metal) motor shaft. ideas so far to enlarge the shaft (oo-er missus)-

1 coke can metal shim wound round shaft?

2 single thin wire wrapped round shaft enough times?

3 heat-shrink tubing?

all finally bound with superglue....

 

[Calimori]

To increases it's girth, you could use PTFE tape or some electrical tape wound around the shaft. This may work and grip the gears enough, if not then it is none destructive and can all be removed and a shim/collar of some sort made up.

The pulley is metal though so opening it up a smidgen might be a little harder. It looks as though there will be a grub screw in the end to bite into the shaft, maybe you can flatten off the shaft on one side to slightly reduce the girth but also give the grub screw a flat surface to bite into.



We really are into the realms of the good old fashion bodge here.

 

[cooldan]

can't beat a good bodge job



the shaft already has a flat bit on it, and i have the grub screw for the pulley. will i need a vice or a special clever drillbit or something?

 

[Judge Dreads]

Here's me thinking that you were adapting that ciggy' to fit between them butt cheeks

 

[BigIan]

The collar on the pulley looks like it would nearly fit in the centre of the gear.

Could they fit together ? Maybe filing the center of the gear or sanding the collar etc to fit.



The pulley can be moved about as long as its within the confines of the nell assembly it should be able to drive the saw ok, so if you could mount the pulley on the shaft collar side out and fix it with the grub screw you could then stick the gear over the collar and epoxy it on (although this is kind of unreversable)



Drilling the hole of the pulley should be easy enough, all you need is a 7mm drill bit. nail or screw the pulley onto a largish piece of wood with 2 or 3 screws/nails so that you have a decent base. then drill slowly (preferably with a drill stand or bench drill)



The hard bit as such will be mounting the gear, depending on how close to fitting over the pulley collar.



You could get another meccano collar and have the pulley and gear as two separate units.



By the way the knarly thumb nail if the result of some microsurgery. My brother cut my thumb off with a hatchet when I was about 2 and a half (he was 4) We where cutting wood out the back at the time, as you do....

 

[cooldan]

Nearly there, I'm on the last lap and approaching the final straight.



The gear fits snugly on the shaft (lots of shrink-tubing and a bit of tape) and is in line with the gear bracket which it engages and moves. The pulley fits snugly next to it and is held tight by the grub screw. It's a bit smaller than the original pulley so the belt is a tad loose but I'll be fine to improvise that with a rubber band or something.



Last piece of the puzzle is the spring. So after the gear turns half a revolution to move the log all the way along the track, is this spring supposed to pull the gear back against the motor direction? Sounds like an odd design if so. I drilled loads of tiny holes in the gear so I hope to be able to find one that works but I first need to get hold of a suitable spring to do the job - strong enough to pull the gear back round but not so strong as to impede its original movement. Can anyone identify a spring like that？



When I finally get this Nell log moving (and the DMD working) it will be a relief.