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Post by Bob Killip on Oct 24, 2022 17:00:17 GMT 12
As we all know, Bell Colt short-shaft push-on knobs are near impossible to find so I'm asking if anyone has attempted, or succeeded, in fabricating them, or found an after-market source? We have a 3D printer here & just weighing up the pros & cons of making some but it would take some time & effort to design and build, not knowing if it would ever actually work. We don't want to "re-invent the wheel" as it were.
Cheers, Bob
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Post by Bob Killip on Oct 27, 2022 18:34:16 GMT 12
A kind member has forwarded me an existing 'stl' (3d print) file modelling the knob we need which definately saves time & effort so that's great progress, with big thanks go to them. A dummy run on my budget 3D printer proved suitability but is not granular enough to be of any quality. I'm persuing having it fabricated professionally and will update on progress.
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Steve
Society Members
vintageradio.co.nz
Posts: 724
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Post by Steve on Oct 28, 2022 10:40:07 GMT 12
I have played with 3D printing of knobs before, and found even good quality FDM printers - the standard 3D printers most people are used to seeing - will give a rough finish. The finished product will also be weak, particularly between layers. FDM stands for Fused Deposition Modelling. We have Ultimaker FDM printers at work - quite expensive, but still incapable of producing an acceptable finished product. A better method is DLP (Digital Light Processing) - better known as resin 3D printing. The finish is much (much much!) better, as is the overall strength of the part. The hard thing is getting the colour correct, and there are still some concerns around the cocktails of chemicals in the resins (often unknown and undisclosed). That aside I would expect that resin-printed white slide-on knobs would do the trick - and the quality, even from a cheap one, would probably be acceptable for the job - but I have not tried one. We do have a small resin printer at work, and I did make one repro early 30's Marquis test knob with it once - the finish and strength were both good, the colour was weird though, and I never ended up using it. I can't make any promises as to when - although I do have a bit of time coming up where the workload will get lighter - but if you wanted to send the file through I could try printing it and see how it comes out. The other way to make them is something I think RestoreOldRadios on YouTube did a while back - moulding the original and then using a 2-part epoxy resin to make reproductions. Whichever way you go, keep us posted
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Post by Bob Killip on Oct 30, 2022 9:49:57 GMT 12
Thanks Steve... the quote below is from a local 3D print company. They have printed these knobs before and I understand the quality is almost perfect. A little pricey though I think. I may go ahead but waiting for more feedback from others, such as you. The stl file is over 3 meg so too large to send from this forum but I could email it to you if you wish.
Thanks, Bob
"we print them via SLA which has the best resolution available from a printer. The material is an ABS-Like white epoxy resin, it can easily be painted, nothing special is required but for the best and most durable finish I recommend using a primer, then base coat (colour) and clear coat. Spray cans from Bunnings or alike are perfectly fine.
I'll offer some quick pricing here, if you'd like to proceed then please let me know the name to go on the invoice and a delivery address for courier.
SLA printer, 0.07mm layer steps, ABS-Like epoxy: $14.30 each ex gst. Minimum order amount of $25 plus gst."
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Post by Radiotech on Nov 1, 2022 19:22:22 GMT 12
As already mentioned, 3D printing isn't the best when it comes to professional looking knobs. Whenever this subject comes up, I think of this video on Youtube: www.youtube.com/watch?v=aNBHtlhlHF4The results are truly impressive and it's difficult to tell the clones from the originals. Given that the Colts come in different colours, the trick would be to find the right coloured casting resin. It looks like white and ultra-black are the most common, but from a quick Google search it seems pigments to give other colours may be available. There's a distributor here in NZ - have a look here: www.resincraft.co.nz/products/smooth-cast-onyx-polyurethaneMay be worthwhile inquiring with them to see what the colour options are.
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Post by Bob Killip on Nov 19, 2022 15:59:36 GMT 12
Update... I decided to go-ahead with having 3 knobs 3D printed professionally and the outcome was very good. As per the original they need the spring-steel collar and are a snug fit (they won't fall off & can be removed with just a little effort). Understand that they are in white so need primer, colour coat and clearcoat. I will update once that's done. Quite expensive but as the red Colt was given to me and the cabinet is 'mint' I felt it was worth persuing. Pics below: Point of note... before throwing a broken knob in the bin make sure to keep the spring-steel collar as they are now quite rare.
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Post by Bob Killip on Dec 15, 2022 13:11:15 GMT 12
Finally got there... Here are pics of the completed 3D printed knobs after spraying. Colour match wasn't too bad and everything turned out quite good really. Attachments:
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Steve
Society Members
vintageradio.co.nz
Posts: 724
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Post by Steve on Dec 15, 2022 14:21:20 GMT 12
That looks fantastic, well done.
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