Hi, just a small thread demonstrating some of the uses of epoxy putty and where a more substantial solution is needed.

Things have been quiet lately so I've been getting round to those jobs that should've been done a long time ago but things got in the way.

One of them was repairing 2 broken 5" cast iron step pulleys, it's an accident on my machine that happened a long time ago when i first got it, since i've changed the motor and shes been hobbling along on a single large aluminium pulley from machine mart.

Not that there's anything wrong with an aluminium pulley, just that i'd rather have the steps back for lower speeds and the cast iron. They weren't badly damaged to the point of "bin them", but badly enough that it couldn't be ignored without tearing the belts to shreds on the sharp corners and possibly jumping off on the worse of the two.

Now it didn't have to look pretty, it just had to be sound again. My first solution, on the first, worked alot more neatly than i thought it might. I reached for the epoxy putty, put some on and waited a day for it to fully cure, i came back to it and filed it flat to the Vee form by spinning it in the machine.

As you can see, it's totally flush with the body, and its a very strong bond. It's appropriate to use this on it with a single chip, as theres enough land around the breakage to support the bond.

Now for the second, that just wasn't the case, this was battered and beaten to the point of no return for the front vee. I didn't take a picture with the damage but i can show you a photo of the piece i sawed off, to give you an idea.

The "wheel" form had been so badly damaged, that putting putty around it just wouldn't be appropriate, i've tried this with repairs in the past, and it just breaks off if you're having to form a large area with it.

I thought about bolting a piece of plate metal to the front. But it would be a little on the flimsy side at 1 or so mm thick and wouldn't create a vee. So i noticed a little, not much, 2.5mm of land on the pulley after cutting off, so i created an aluminium "half form" on the lathe, i measured the angle to be around 13.5 degrees. And loctited a push fit onto the pulley.

Hopefully this will help those of you who frequently need to repair things like myself!

Michael W

Hi Michael G,

I don't think i'm quite seen as a pillar of the forum community so i'm hoping i will get away with brand naming here but it's the closest thing i can get to a grade.

**LINK**

The only thing i can list as pre-treatment would be to wipe away any grease with a tissue and only apply on a dry surface, would probably be a sensible idea.

And to make sure it's a reasonably tight fit to begin with, where you know the part will be under a certain load.  

Michael W

Edited By Michael Walters on 15/08/2016 20:02:17

Thanks john, it sounds like your thinking came to a similar solution, as i was thinking about bolting something onto it. I have used your method before for repairing broken shafts by machining the other end to suit after the bond is made, to ensure a proper match.

I like to create posts like this, because you don't necessarily always want to read about the projects that go right, as inspiring though they may be. You want to read about what you look for when things don't go right, so that you may put them right.

There have been quite a few occasions where i've gone wrong and i haven't a clue how to approach it once it does. I would like to think that a voice of experience, would mean not only be good at making wonderful things, but also have the answers to these problems.

I guess when it comes down to it, breaking and then fixings things, has just as much a place in engineering as making the things themselves. 

Michael W

Edited By Michael Walters on 15/08/2016 21:05:00

Well Ian, i think i may actually take you up on that idea, it sounds like it could only help in the long term what with a tensioned belt going round it everyday.

I'm just waiting for some new screws, the stainless ones i used to buy break without much force being put on them. So i'm taking a new approach and going with high tensile bolts, and counter sunk rather than round head for greater pressure i suppose.

Thanks

Michael W

Edited By Michael Walters on 16/08/2016 19:58:17

Can't believe i forgot about them john, well i am a lucky bugger, the hole size is 38mm which i happen to have.

Little job for tomorrow then.

Michael W

So i got round to finishing these repairs, by first adding the steel plate, as recommended: I tried to rotate them but the formatting hasn't transferred over to here this time round so everything is sideways.

It looks alot neater than looking at the epoxy i have to admit. I tried to use countersunk screws but unfortunately without having a "punch" to press the shape into the metal first, the threads were too fine at M4 so the threads just stripped out under the pressure. So i used some nuts as spacers and fastened with some proud HT socket screws. Even so it got the job done. The middle was treppanned out on the lathe with a grooving tool, the lathe has to go alot slower than you might expect when you do this operation i found like 100-200rpm. It obviously bent in slightly once it was cut, so to clean up the rags i just used a very sharp knife tool to clean it up. Never trepanned thin material on the lathe before now so it was a new experience for me.

The last job to do with this pulley was to drill or bore a larger hole into the pulley to fit the slightly bigger 3 phase motor from 14 to 19mm shaft. I would have to say, retrospectively i shouldve bored it but i was worried about breaking the tool on an interupted cut from cast iron on the keyway. So i used a 3/4" drill. The only problem with this is without using a "core" drill, which is like a 3 or 4 flute finishing drill, it would create a lobed hole, so it runs a little off centre but not enough to be a cause for worry. But thats the proper way to enlarge the bore with a drill.

The keyway was interesting because i don't like creating them on the lathe because i cant lock the spindle. So i mainly use broaches, only trouble was i needed a 6 and i've only got a 5 as my biggest one. I don't have the money to spare on a new one so i managed to create a "stepped key" by milling away the last mm on a half and half key of different sizes! it does work, you just have to be sure of your measurements on the height of the key so it fits perfectly and not able to move inside it.

So this is the setup on the inside now, back to its original state. I'm very happy with how it went and learnt a few new skills along the way, it sounds like a very dull job but there were moments where i needed to think about it a bit more. I'm glad to now have a variable speed motor with 6 positions at full torque! from 150rpm to 1600rpm.

By the way i measured the RPM myself, i was lucky enough to obtain a smiths gauge from a farm that was chucking out it's old workshop gear. Good hint;it pays to collect tat and junk in this pursuit, you shall be goodly vindicated when it comes in handy!

I created a chart to note all the new speeds, i'll get it laminated and stuck on the inside of the machine, hopefully if anyone ever takes over this machine from me, they wont need to do this themselves then. As the manual will no longer be correct for this.

Edit: The machine is much quieter now, but i'm not really sure why. I only switched an aluminium pulley for an iron one! Maybe someone can tell me this. 

In the first photo it looks like the steel is slightly bent, but if you look closer it's actually my forehead in the reflection!

Michael W

Edited By Michael Walters on 23/08/2016 20:31:43