How to fit a round thing (sprocket / pulley) in the middle of another thing ?

[gentlegreen]

So ... I have loads of spare bike parts and realistically I could do with an exercise machine - if only as a health evaluator as I move into my 60s ...
I am also faced with having to haul a load of materials upstairs, so could do with an electric winch - though I will be mounting a block and tackle ...

For over 30 years I've been sitting on a couple of large DC motors that came from a computer tape drive - and somehow managed not to lose one of the tape reel hubs.
It will be interesting to see what I can usefully do with maybe 100 watts when used as a dynamo ... my first thought was some sort of rave machine to wheel onto the path to amuse the neighbours on Thursday nights ...

I thought I'd fallen at the first hurdle because the teeny American grub screws weren't metric - but it'll do for now...



Luckily the only sprocket size I have with sufficiently close mounting holes is just big enough for the chain to clear the sides.
But before I start drilling holes in it, I need to accurately centralise it ....

 

[Saul Goodman]

Draw two or more chords across the top of the aluminium block (the more the merrier). Draw lines perpendicular to the chords toward the centre of the block from the middle of the chord. Where the perpendicular lines intersect is the centre of the circle. Draw a line through the centre of the circle. Draw another line through the centre at 90 deg to the first. Line up the holes in the sprocket with the newly created lines, or measure the distance between centres of the holes in the sprocket, measure half that distance along each line from the centre and centre punch.

 

[a_chap]

This will end well...

 

[gentlegreen]

This will end well...

I have for some time had very definite plans to hook a static bike up to a washing machine drum ...
This current unexpected crisis is changing everything ... and I'm about to retire and need to replace the daily hour of cycling ... hopefully I will get out for an average of 20 miles every couple of days, but for 33 years I had no choice but to do it whatever the weather ... including a decent hill ...

Even if I wanted to pay money for a proper spinning machine, i bet they're difficult to come by at the moment ...

 

[gentlegreen]

The main issue to start with is how wide a base I will need for stability since I have no concrete available ... though I have no issues with screwing things to the floor ...

 

[Saul Goodman]

The main issue to start with is how wide a base I will need for stability since I have no concrete available ... though I have no issues with screwing things to the floor ...

Can you not just remove the wheels from your stabilisers and screw the stabilisers to a couple of blocks of wood?

 

[gentlegreen]

actually that's given me a clue about spacing - and I'm less wobbly than a toddler ...

 

[Saul Goodman]

actually that's given me a clue about spacing - and I'm less wobbly than a toddler ...

You'll also be able to exert a lot more pressure on each pedal than a toddler would. But I reckon if you measure the distance from the spindle to the floor, add a couple of inches if you're going to be leaving the wheel on, cut a length of bar to approximately twice that length, bend it at 90 deg in the middle and weld in a 45 deg gusset, it'll be fine.

But back to the washing machine thing. I think most washing machine motors will be in the region of 300W - 400W. You'd need to be a proper cheating tour de France rider to achieve that sort of power.

 

[gentlegreen]

You'll also be able to exert a lot more pressure on each pedal than a toddler would. But I reckon if you measure the distance from the spindle to the floor, add a couple of inches if you're going to be leaving the wheel on, cut a length of bar to approximately twice that length, bend it at 90 deg in the middle and weld in a 45 deg gusset, it'll be fine.

But back to the washing machine thing. I think most washing machine motors will be in the region of 300W - 400W. You'd need to be a proper cheating tour de France rider to achieve that sort of power.

I'm only talking about doing me smalls

I was a mere 53 then - albeit 4 BMI points heavier, but I can still manage a couple of hundred watts for 45 minutes if I'm in the mood ...

 

[gentlegreen]

I don't currently have access to a welder or the skills, so this is all going to be assembled from lumber and coach screws - and glue if I'm happy with it
I have a nice chop saw.

 

[teuchter]

Draw two or more chords across the top of the aluminium block (the more the merrier). Draw lines perpendicular to the chords toward the centre of the block from the middle of the chord. Where the perpendicular lines intersect is the centre of the circle. Draw a line through the centre of the circle. Draw another line through the centre at 90 deg to the first. Line up the holes in the sprocket with the newly created lines, or measure the distance between centres of the holes in the sprocket, measure half that distance along each line from the centre and centre punch.

Nah, overcomplicated. Won't be any more accurate than eyeballing it.

 

[Saul Goodman]

Nah, overcomplicated. Won't be any more accurate than eyeballing it.

You have to try to imagine doing it with something sharper and more accurate than crayons.
But if measuring aint your thing, you can easily find the centre using a compass (the pointy type, not the magnetic type).

 

[teuchter]

You have to try to imagine doing it with something sharper and more accurate than crayons.
But if measuring aint your thing, you can easily find the centre using a compass (the pointy type, not the magnetic type).

All of your suggestions are technically correct; I'm guessing you have recently graduated in mechanical engineering or something. Once you have a bit more real world experience you'll understand better about how to do things like this in practice.

Anyway, you don't want the centre of the the bit of metal, you want the actual centre of rotation, which may not be the same. I would find the diameter of the circle that the four fixings need to sit on, and roughly mark that on the bit of the metal. Then I'd set it rotating and use my crayon to make a circle, hold it steady and let it go round a few times to cancel out small errors. Doesn't matter if the resulting line is a few mm wide. Then by eye sit the sprocket on, with the holes centred on that line. Could even tape it down in position, and rotate again at which point you would see visually if the outside of the sprocket was concentric.

 

[Saul Goodman]

All of your suggestions are technically correct; I'm guessing you have recently graduated in mechanical engineering or something. Once you have a bit more real world experience you'll understand better about how to do things like this in practice.

Anyway, you don't want the centre of the the bit of metal, you want the actual centre of rotation, which may not be the same. I would find the diameter of the circle that the four fixings need to sit on, and roughly mark that on the bit of the metal. Then I'd set it rotating and use my crayon to make a circle, hold it steady and let it go round a few times to cancel out small errors. Doesn't matter if the resulting line is a few mm wide. Then by eye sit the sprocket on, with the holes centred on that line. Could even tape it down in position, and rotate again at which point you would see visually if the outside of the sprocket was concentric.

It's the hub from a tape drive, not a rusty old wheelbarrow wheel he found on the tip, so I'll hazard a guess that the centre of rotation and the actual centre are in exactly the same place, because in the real world, this is how things are machined.

 

[gentlegreen]

I realised that drilling holes without a pillar drill might be an issue, so I thought I would see what was inside the thing ...
Luckily the three hex screws holding the hub together were close enough to metric ...
the two halves are keyed with a tapered nylon core - I'm damned if I can figure out how it worked ...

The sprocket is tantalisingly close to lining up with one of the screw holes !
And fortuitously I bought a shedload of superglue in Poundland recently

 

[Saul Goodman]

I realised that drilling holes without a pillar drill might be an issue, so I thought I would see what was inside the thing ...
Luckily the three hex screws holding the hub together were close enough to metric ...
the two halves are keyed with a tapered nylon core - I'm damned if I can figure out how it worked ...

The sprocket is tantalisingly close to lining up with one of the screw holes !
And fortuitously I bought a shedload of superglue in Poundland recently

View attachment 205982

View attachment 205981

Remove the tapered nylon bush, wrap tape around the piece we now see as the top, until it's a tight fit in the hole. Turn it over and insert it from the sprocket side. The taper will centre the sprocket.

 

[gentlegreen]

Who'd've thunk it ...
Shims needed 0.4mm
Neighbour with mahoosive Dr. pepper habit.
(I washed them down with strong detergent - catching the boomerflu this way would be too ironic to bear)
No doubt things will shift a little, but I reckon it'll still be more precise than any pushbike transmission.

It's looking dangerously like I have to do this thing
Research suggests pedalling machines are approx 2 feet wide so I will begin on that basis - I can always add "stabilisers"

 

[mauvais]

Yeah, everyone on this thread is going on a watchlist.

 

[beesonthewhatnow]

Something tells me the results of this are going to be spectacular.

 

[weltweit]

I would have used Araldite rather than superglue.

 

[gentlegreen]

It's ended up 1.5 metres long because the 2x2 was 3 metres.
And 2 foot wide, because that's the minimum ergonomic gap for things and roughly the width of my handlebar.
There's actually room for an improvised washing machine drum - I own one of those silly "jobber" cement mixer things ...

I was well into the project when I remembered that the pedals needed space to turn.
So I'm going to run a third beam the full length of the bike.

If nothing else I'm getting practice on my chop saw and impact driver ...

 

[beesonthewhatnow]

This has got the weekly GCN “hack or bodge” segment sewn up

 

[gentlegreen]

I would have used Araldite rather than superglue.

I haven't used any glue so far, but if I need to, you're probably right - I'm hoping the clamping force and shimming will be adequate - otherwise I might even have to start drilling things ...

 

[gentlegreen]

I'm glad my beloved frame of 19 years / 40,000 miles may yet see me clock some more miles on it

 

[The39thStep]

This thread reminds me of this

 

[weltweit]

gentlegreen what are you trying to build? Is it a stationary exercise bike? or is it a way to use pedal power to do your washing?

If it is a pedal powered washing machine I expect you will be able to power the wash cycle because that is relatively low speed and probably low power, but the spin cycle is I think where more power is required, and in your case - gearing would be critical - I wonder if you will be able to achieve a decent spin cycle!!

 

[gentlegreen]

gentlegreen what are you trying to build? Is it a stationary exercise bike? or is it a way to use pedal power to do your washing?

If it is a pedal powered washing machine I expect you will be able to power the wash cycle because that is relatively low speed and probably low power, but the spin cycle is I think where more power is required, and in your case - gearing would be critical - I wonder if you will be able to achieve a decent spin cycle!!

I'm not too fussed about the spin cycle - jut getting me smalls properly agitated will do me - I imagine I may insert some sort of balls to add to the friction
I reckon I'm going to have a shelf for a laptop - or I'll go nuts exercising for the sake of it - perhaps I'll investigate syncing up some scenery ... I have an old data projector in my back room - though I need to order a lamp for it ...

 

[teuchter]

This is lining up to be a good thread.

 

[gentlegreen]

Necessity is the mother of invention
Whether I can actually bear to sit on it and pedal for half an hour at a time remains to be seen ...
I've been googling around and no one else is doing it this way

 

[weltweit]

I am confused because at the start you were saying you had a couple of DC motors, do you plan to use them at all?

If it is a washing machine, how do you plan to add and remove water soap, rinsing water etc, will you stop cycling and use a hose / bucket?