A number of bells have been cast in brass. The castings are somewhat rough, and the outside needs polishing. I don't see how to do this on a lathe. The castings are not perfectly round and would need too much metal taken off. There is a hole in the middle, andI I propose putting a bolt through and spiinnng the bells slowly in a drill press while using a flappy wheel on an angle grinder to polish them. Unless anyone has a better idea!
well cast them again properly!
Do it right second time. If you want a proper tone, they need to be trued up.
The original bell is 100 years old. I don't want them to look modern, just polished.
They sound fine already.
Then leave them alone. You might be able to get some help from the Whitechapel Bell Foundry but I suspect their advice will be the same as mine. Bells are tuned before they leave the foundry. If you try to mess around with them at best you are likely to detune them and at worse fubar requiring them to be scrapped and recast.
They are not musical instruments - they just make a ding ding noise and llook shiny. Any pitch will do.It's better if they all make different noises, then the driver will know which bell is which!
Here's one that somebody else polished:
Your hand will 'follow' the eccentricity if you use low spindle speeds.
If you want to do it by machine, rather than by hand, the correct equipment is a spindle polishing machine with a calico mop and brass polishing compound. A flap wheel is far too aggressive for polishing brass.
Colin Bignell
Have a word with this lot...
I suspect that using a smaller diameter flap wheel and not too coarse grit will take time but produce the result you need prior to proper polishing with a proper buffing machine. Remember that pre-buffing finish should be as fine as you can get with whatever method you use as finish buffing will take longer otherwise. Also the finishing produces quite a bit of heat, so working the full set of bells in rotation should give you time to let them cool. even wearing gloves you'll get hot hands...
Obviously you could hand polish them but it is a very laborious process, so perhaps finishing off with their polishing kits on
You can make a simple mandrel for the polishing mops and mount in your lathe so as to make a substitute polishing machine. Using the right soaps and the right mops and you'll produce a good finish.
When finished you might like to have them sealed with a clear coat of lacquer
I'd say you are probably more experienced at this than the rest of us, but, as it is brass, then I would start off with a brass brush wheel (a good thick, but fine wired one: not one of the typical 'shed' things, and definitely not one that is just brass plated!). Then move on to the proper polishing mops and 'soaps'.
At a pinch - and depending on the bell size - you might be able to make a reciprocal sander, that can take some of the pain out of hand polishing the tricky bits. I once made one of these from a 'side to side' type electric razor, with a half a wooden clothes peg stuck on where the shaver part used to be. Stuck strips of different grades of emery on the peg with double sided tape, and used it to get all the casting marks out of a pair of carbeuretters (never can spell that!) before the final buff up. (Riffler files are handy too.)
S
The bells have been cast in sand, so I need to take a lot of metal off before using the spindle polishing machine. They are plenty thick enough. I could take 1mm off if necessary. That will alter the pitch for sure!
about Bells, as in Church Bells?!?
You're also in NZ Matty (by the look of it), so "local" uk.d-i-y advice ain't a lot of use to you!
Personally -- seeing the "here's one we did earlier" -- I'd just get the Brasso out, along with the old tooth brushes.
J.
On Oct 25, 5:56 am, "R" > round and would need too much metal taken off.
on
I'm not after an extremely high polish, although that's easy enough. The main problem is to get rid of the sand casting finish first. I just realised that there's a collet chuck that will fit the big drill press, and that will hold the bolt that I will put through the bell. With a three jaw chuck I would have to sand the bell from underneath so that the pressure of sanding doesn't make it fall out of the chuck. With the collet chuck I can sand the bell from the top. I propose running the drill at about 60 rpm. The inside of the bell doesn't need polishing.
You seriously misunderestimate him.
He has been posting here for quite some time and has impressed us with his talents and ingenuity.
Dave
Chuck them in the lathe, using a woooden jam chuck turned up to fit securely inside. Ideal jams chucks are turned to be a perfect fit for each bell, but you won't do this. Gluing neoprene foam on can make one jam chuck work for multiple bells, although it does reduce the clamping force. Another way is to coat the jam chuck with a spiral of hot-melt glue before shoving it in the casting.
Then use the lathe to rotate them slowly. Use your favourite angle grinder and flap wheel to then polish them. Foam backed flap wheels are even better (foam between the flaps - more conformal). Don't use a hard disk! Do put a sheet over the lathe, or else use your dedicated grinding lathe (with the worn bedways). A gentle action with the grinder and a slow lathe speed will cope with an oval bell. Finish with a Garryflex block by hand (still rotating in the lathe) to make neat circular brushmarks.
Plain brass isn't a good bell alloy (goes clunk, not ting!) and you really want a bit of tin (or modern pewter) in there.
Since there's a hole in the middle of the bell, it would be easy to bolt it to the wood.
The chief engineer won't let anyone grind on the new lathe, so I think that's out. However I think the drill press with a collet check will do the job. Another way is to put the bell in a portable drill and rotate it against the saggy part of a linisher. But I can't fit a collet chuck to a portable drill, and the linisher is a huge dangerous thing! I'd probably sand a hole in the bell.
Well, I call them brass but they are bound to be the right alloy. They do make a nice ringing sound. I suspect the foundry does them at mates rates.
I made these knockers for the bells to match the old one that's been hitting bells for a hundred years and has got a bit flattened.
This is the first time I've cut a diagonal on the lathe. Nobody told me to start the diagonal cut near the middle instead of the outside. So one is not so good. Never mind, it's inside a hole where nobody will see it!
Not if you've read most of Matty's posts :-)
Why not? I'm in the US these days (coming up on three years now) and this ng's by far the best when it comes to asking/learning about the proper tricks and techniques to do various things - it's surprising how little "UK-specific" traffic there is, and most stuff is relevant no matter where you are in the world.
cheers
Jules
It is perfectly possible to produce a polished sand finish but, if you want a smooth polished finish, then you do need to take material off. I would still do that on a spindle polisher myself, but using a more aggressive mop and compound combination to start with. However, we are then getting into the field of which equipment each of us feels most comfortable with.
Colin Bignell
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If you follow your earlier suggestion of using a pillar drill you could probably get a bit of extra support by fixing some kind of flat bearing to the drill table and bringing it up to contact the through-bolt to which the bell is attached. This would help reduce the possibility of 'wobble' due to the ovality in the castings.
As far as the grinding/polishing is concerned, I think you might get a satisfactory result by using a static (rather than rotating) abrasive; a slightly flexible flat backing pad covered with emery cloth would be easy to use and probably safer than having two rotating items (bell + flap disk) working against each other.
Cic.
I'd still use a jam chuck. It avoids the cantilever aspect and inevitable wobbliness of clamping through a bolt at one end.
Wise. That's why you need a grinding lathe. They're cheap, because you can use the clapped out old clunker that the S/H machinery dealer wants rid of for just the scrap price of the copper in the motor.
tinypic.com/wa537t.jpg
I think that's important - from what I gather the best way to crack the bell is to hit it with something that's not free to rebound afterwards. Talking to the chap at the Whitechapel foundry I gather that bell metal is a copper/tin alloy, though it has more tin than the more common bronzes, which is why it looks yellow like brass rather than the normal kind of reddish colour. It's a bit of a compromise - it needs to be fairly hard to ring properly, but if you put a bit too much tin in it becomes too brittle and cracks Mike
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