06-03-2012, 12:18 PM
There's always going to be problems of cost versus quality with the making of repro knobs. Some slight shrinkage is practically unavoidable, too. Wim Jaegers uses RTV mouldings and 'proper' casting resins. Plus he has access to a lathe, so the knobs he makes, with a filler included to give the right 'feel' are always going to be better than ones made using the simple method I outlined. But expensive to make and therefore to buy.
I've used other moulding compounds in the past, notably Gelflex, but there are problems with air entrapment - as in truth there always is, no matter what moulding and casting method you choose, which is why industrially they use a vacuum chamber for degassing before the compounds set.
The beauty of making knobs the way I've suggested, using Alginate, is the speed and low cost. One poured the mould is ready in minutes, rather than hours. Casting using resin - with a filler such as a small amount of dry powder plaster (I do mean a SMALL amount) to give a better feel to the finished control - will give you an at-a-glance accurate control knob.
I do not suggest by any means that the Alginate method is the best, but it seems to me to be the cheapest and the moulds are very accurate and detailed.
Loads of other ways: a search on U Tube will bring up a host of examples and some of the supplying firms (the American ones at least) offer explanatory videos.
You pays yer money and takes yer choice, folks!
Gary, it must be rather galling to have paid out for good control knobs only to find they fade. I don't see why that should be inevitable: quality colours should be lightfast, surely.
Mark, sure! I'm pleased you think it important enough.
Finally: in the past I've drilled and fitted brass tubing into cast knobs to take the grub screw thread, also used a mini-tool to clear a slot in the back of a casting to take a 4BA nut. These were when the repro knob was of a type where there was too little thickness of resin to take a secure tapping. The more you get into it the more avenues open up to you. As the old saying goes, there's more than one way to skin a cat - not that I have any personal experience of doing so, you understand. I like cats, generally!
I'm very pleased at the positive response to this quick summary video. My thanks to Lawrence, Paula and Robert for their replies.
-Tony
I've used other moulding compounds in the past, notably Gelflex, but there are problems with air entrapment - as in truth there always is, no matter what moulding and casting method you choose, which is why industrially they use a vacuum chamber for degassing before the compounds set.
The beauty of making knobs the way I've suggested, using Alginate, is the speed and low cost. One poured the mould is ready in minutes, rather than hours. Casting using resin - with a filler such as a small amount of dry powder plaster (I do mean a SMALL amount) to give a better feel to the finished control - will give you an at-a-glance accurate control knob.
I do not suggest by any means that the Alginate method is the best, but it seems to me to be the cheapest and the moulds are very accurate and detailed.
Loads of other ways: a search on U Tube will bring up a host of examples and some of the supplying firms (the American ones at least) offer explanatory videos.
You pays yer money and takes yer choice, folks!
Gary, it must be rather galling to have paid out for good control knobs only to find they fade. I don't see why that should be inevitable: quality colours should be lightfast, surely.
Mark, sure! I'm pleased you think it important enough.
Finally: in the past I've drilled and fitted brass tubing into cast knobs to take the grub screw thread, also used a mini-tool to clear a slot in the back of a casting to take a 4BA nut. These were when the repro knob was of a type where there was too little thickness of resin to take a secure tapping. The more you get into it the more avenues open up to you. As the old saying goes, there's more than one way to skin a cat - not that I have any personal experience of doing so, you understand. I like cats, generally!
I'm very pleased at the positive response to this quick summary video. My thanks to Lawrence, Paula and Robert for their replies.
-Tony
