AWGB Woodturning Forum
General Category => Tool tips & reviews => Topic started by: Les Symonds on September 23, 2013, 08:48:19 PM
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I'm going to be turning some craggy lumps of wood over the next few weeks and fancy having a go at filling a few splits and cracks with brass powder. I buy glass-fibre supplies from a company called CFS, and they stock metal powders (brass, copper, bronze etc) at quite reasonable prices. What I'm not clear on is how to fix the powders. Do you guys use polyester resin, or do you pack the crack with powder and trickle ca glue in to it....if you do use ca glue, what grade do you use, please? Is it better to use a thin glue to get deeper saturation, or a thicker glue to bind the surface better. Then of course, there's the issue of cutting the brass back....what abrasives do you use for that?
Sorry that it's so many questions, but I've no idea where else to get such info!
Cheers...Les
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I use brass, aluminium and copper powder a fair bit when I make green oak goblets. I trickle the powder into the crack then thin ca glue on top and stir it up and push into crack quickly. It sets rapidly an I find the thicker glues go off faster than I can fill the crack. Make sure you put some sealer or something to protect the surrounding wood first though as the CA glue will stain the wood especially lighter colours. Not the best of pictures but the two on the right
have splits filled with the powder.
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Thanks, Pete, that helps. I've tried using ca with coffee grounds and with sawdust and have had some success with it, but I find it difficult to cut back and and down. I guess that I'm overfilling, so might invest in some of those tools that ceramicists use for fine modelling and texturing the surface of clay....they're basically fine pallet-knives.
Les
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I use dental tools as they can get into the finer cracks and they are dirt cheap on flea bay. I scrape excess off as best I can efore it totally hardens then cut back to the wood with 180 grit locally before finishing off with the lathe spinning. Make sure it is really dry though and watch out for the dust as it isn't just wood dust but the CA dust as well. I tried using the dust with epoxy glue but it never looked as good or clean, maybe I got the mix wrong. With CA glue it looks like solid metal filling.
Pete
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I use dental tools as they can get into the finer cracks and they are dirt cheap on flea bay. I scrape excess off as best I can efore it totally hardens then cut back to the wood with 180 grit locally before finishing off with the lathe spinning. Make sure it is really dry though and watch out for the dust as it isn't just wood dust but the CA dust as well. I tried using the dust with epoxy glue but it never looked as good or clean, maybe I got the mix wrong. With CA glue it looks like solid metal filling.
Coffee grounds are very coarse but if you mash them uip with a mortar and pestle ort something first you can get them pretty fine. Wood dust tends to soak the glue up very fast and dries off so quickly I find it easy to put the glue into the spluit and then shove the sawdust in with the dental tool. Sometimes needs a 2nd layer if the crack is deep.
Pete
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Thanks again, Pete...will definitely give that a go.
Les
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For large cracks I use Aradite with the powder mixed before the hardner agent goes in, again hard to sand down if you overfill.
Cheers Martin
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I trim down after filling with a high speed flexydrive motor with a barrel trimmer,then just the last bit with abrasive wrapped round a piece of hardwood,cork blocks move to much for detail working,just shape the block to the contour you need,regards,
Eric.
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Thanks Martin & Eric...this is all helping!
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I spent a few years working with glassfibre , and I think the best thing to use for filling cracks as you describe would be Clear gel coat, with catalyst ( hardener ) and your chosen powder , brass .copper . aluminium , etc all mixed to a thick'ish paste for bigger cracks, and thinner for narrow cracks , you can seal one side of the crack with sellotape to prevent it running through and going to waste , with small quantities great care will be needed to get the correct ratio of catalyst to gel . Try to fill the cracks as flush to the surface as possible and this should reduce the need for excessive sanding , or as some one else has already mentioned , before it fully hardens , when it is a firm toffee consistency it can be trimmed with a sharp blade flush to the surface of the crack , and it should sand easily . CFS ( Redruth ) should understand if you chat to them .
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Hi there, TWiG....I know CFS well, and actually had a delivery from them today. I've bought their brass powder, plus some polyester resin and catalyst. I've also got a few measuring/dispensing bottles and syringes, so I'm now set up to experiment with ca, epoxy and polyester as a medium for the brass.
Cheers....Les
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I have used a fair bit of powered metals, mainly brass. I use the thinnest CA you can get and do it in layers allowing plenty of time for it to dry, usually over night. Fine lines or cracks look the best, heavy and or large voids etc dont come out that good they look very chunky.
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Thanks, Hughie...that was very timely. I've just cut up a big slab of yew and was about to start using the brass powder that I bought a few months back. I'll keep your advise in mind.
Les
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Hi there, TWiG....I know CFS well, and actually had a delivery from them today. I've bought their brass powder, plus some polyester resin and catalyst. I've also got a few measuring/dispensing bottles and syringes, so I'm now set up to experiment with ca, epoxy and polyester as a medium for the brass.
Cheers....Les
Hi Les, I would go for the polyester/epoxy resins, as I find CA too brittle when cured, and that it goes off too quickly.
An old trick to get polyester/epoxy resins to flow more easily, once they are in place, is to warm them up. They will go quite runny and flow into the smallest crevice. It also gets rid of any air bubbles introduced whilst mixing. I use a hairdryer or heat gun on relatively low settings, less than 100 deg.C. This also helps the curing process.
If you do use this tip, I recommend another tip from an earlier posting - put a piece of sellotape on the back side of the crack or the liquid will just run through.
And remember at this time of year, thermosetting resins don't like the cold. I bring glued items into the house to fully cure.
One other tip, clean out the area you are filling with acetone (nail polish remover) to get rid of any oiliness in the wood. Improves adhesion, but some woods are almost impossible to stick to. e.g. Lignum vitae.
I will be interested to hear how you get on.
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Thanks, Paul....looks like there were several useful tips in that post.
Les
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Thanks, Hughie...that was very timely. I've just cut up a big slab of yew and was about to start using the brass powder that I bought a few months back. I'll keep your advise in mind.
Les
I have a few slabs of red gum that are prone to splitting . What I do is using epoxy glass coat I tint it with a spirit based tint usually a burgundy colour and fill the crack with this. It turns ok and blend in with most species of timber.