overmodulated Posted January 30, 2010 Share Posted January 30, 2010 Folks: what do you all do to ensure a solid epoxy bond between wooden scales and the steel? You'd think a good scuffing of a perfectly clean surface with coarse paper (100 grit) would do. But not always. It's pretty frustrating when a scale falls off before peening the pins, as happened to me tonight. (I usually epoxy first, then insert the pins.) Any magic trick here? Thanks! Quote Link to comment Share on other sites More sharing options...
pkrankow Posted January 30, 2010 Share Posted January 30, 2010 Did you degrease with acetone or denatured alcohol with a clean rag that was not washed with fabric softener? Fabric softener is an oil, and add contamination for gluing. Phil Quote Link to comment Share on other sites More sharing options...
overmodulated Posted January 30, 2010 Author Share Posted January 30, 2010 no, but I thoroughly cleaned the surface with soap & water and dried it. I should mention I'm dealing with JB Weld. supposed to be one of the better epoxies, correct? Quote Link to comment Share on other sites More sharing options...
reefera4m Posted January 30, 2010 Share Posted January 30, 2010 I've found the best way to insure a great epoxy bond is to sandblast the tang and then wipe down with denatured alcohol. If you have access to an air compressor then with a bucket of silica sand and a $19 siphon sandblasting gun makes it real simple. JB Weld is definitely not something I would use. I've tried it and it doesn't bond wood to metal all that well. Loctite Hysol, 'E' series epoxies are excellant. In a glue/epoxy comparison on another forum, JB Weld came in near the bottom and specifically not recommended for attaching slabs to handles - too bad for me I didn't find it before I tried JB Weld.. The sandblast tip came from the same forum and was credited with being the best means of prepping the tang - over sanding, grinding, or anything else. Quote Link to comment Share on other sites More sharing options...
bigfootnampa Posted January 30, 2010 Share Posted January 30, 2010 Sandblasting that way could get you into a lot of trouble! Silicosis is SCARY! At the least wear a really good dust mask... better yet get a sandblasting booth. The booths are not all terribly expensive and they are quite well suited for knifemakers uses (I have seen them on Craig's List for a hundred or two). I have personally found that Loctite "professional extra time epoxy" from Lowe's serves me well. You can tint it with standard painters tinters (glycol type). Use small amounts of tinters... I often just use raw umber. I don't get into any special prep before gluing but my blades are forged and then I hot brush the scale. The natural scale pitting and forge marks leave a helpful "tooth" to bond to. If you do stock removal only, you'll have to add some work to get the needed "tooth". Further, since the epoxies tend to grab the wood rather well but sometimes have trouble holding onto the metal, try drilling an extra hole or two so that your epoxy can self rivet to the metal (this in addition to your riveted pins). I've not needed to do this so far, but I think it would work well in case I do have problems. A similar technique is to file or grind notches out of the tang edge so that the epoxy makes a through join there. An under sized or hidden tang can also be used allowing for the edges of the scales to glue directly together. One further note on the use of epoxies in general. The mfr's don't often make this clear but epoxies produce a waxy "blush" as they cure (called Amine Blush). This must be removed with a damp cloth or by sanding or both, before subsequent coats or other finishes will stick to the epoxy surfaces. Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted January 30, 2010 Share Posted January 30, 2010 reefera4m nailed it! You definitely need tooth, sand blast or scratch the steel AND scratch the wood ( I mean scratch with the corner of the file to leave grooves!). Always clean the wood with denatured alcohol and acetone. I use both because it has become a habit after having Teak and Ebony joints fail. Nobody has mentioned this yet but epoxy needs the glue joint to form the bond, if you squeeze all the glue out of a properly fitted joint, there won't be enough epoxy to actually hold. JB Weld? never touch the stuff..... Quote Link to comment Share on other sites More sharing options...
CBrann Posted January 30, 2010 Share Posted January 30, 2010 I may be simple... but 15 minute 2 ton epoxy works for me... I spend a lot of time fitting my scales.. drilling "glue rivet holes" throught the tang... I file/grind my tangs so they are parallell on the scale sides, but leave as much tooth as I can.. I also use brass pins that I rough with coarse sand paper on the belt sander... and I use plenty of glue... its relatively cheap.. .. and scrub with acetone after fitting before!! gluing!! .. both tang and scales.. unless the acetone will bleach the wood.. glue.. peen rivets a bit.. wipe up squeezed out glue... and leave somewhere warm for a day.. then go to town finishing the handle.. Quote Link to comment Share on other sites More sharing options...
overmodulated Posted January 30, 2010 Author Share Posted January 30, 2010 Thanks much for the great tips. I don't happen to have acetone or denatured alcohol, but would mineral spirits do? The glue holes is something I've done a lot, and it does help! But it lightens the handle end considerably (if a few holes are drilled) and I didn't want to do that for the balance on this particular knife. So it sounds like it's wrong for me to clamp down hard on the scales, with multiple clamps, because it squeezes out virtually all the epoxy. I hadn't considered this. Does that mean that some of you intentionally clamp the pieces together lightly instead? This could be the problem Quote Link to comment Share on other sites More sharing options...
pkrankow Posted January 30, 2010 Share Posted January 30, 2010 Rubbing alcohol would be better than mineral spirits. Mineral spirits leaves a residue. I'll let more experience weigh in on clamping. Phil Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted January 30, 2010 Share Posted January 30, 2010 Don't use mineral spirits or lacquer thinner, they both leave a residue. Mineral spirits leaves the worst. If you have a spray can of brake or carburetor cleaner that works well to remove the oils too. I use tape (blue painters tape). If you are looking for a "perfect" looking fit up, I use 2 methods. One is to hollow out the scales just a bit around 1/32" or so, leave a "rim" of tight fitting wood to meet the edge of the tang, a 1/16" or so is good. The other is to add pigment or finely ground saw dust (sanding dust) to the epoxy to act as a colored filler (use the same wood and 100 grit hand sand paper to generate this dust). This works best on dark colored woods. You will be able to see a seem however because the epoxy and wood reflects light a little differently. On somethings that are critical, I have gone so far as to use shims to get a uniform glue joint. Then remove the shims and fill with same recipe of epoxy. If done right you can't tell there was a seem break. I will usually do this before full cure of the epoxy, when its in that rubbery / leather state. I hope we get to see some pictures :D Quote Link to comment Share on other sites More sharing options...
overmodulated Posted January 31, 2010 Author Share Posted January 31, 2010 I use tape (blue painters tape). ... Fe-Wood: can you please clarify that part about the painter's tape? Do you use this as spacer material for glueing? Quote Link to comment Share on other sites More sharing options...
mcraigl Posted January 31, 2010 Share Posted January 31, 2010 In the same post on another forum mentioned previously a fairly good effort was put into trying to objectively test various glues and prep processes. I believe one of our forum members here (KBA) was involved. Among the tests conducted were shear tests, and dishwasher followed by shear tests. Sandblasting did outperform the other prep tests. Scratching with a new 36 grit belt worked well, jut not quite as good as the sandblast treatment. On the glue front, there were a couple of interesting results. The most surprising was that Gorilla Glue was very near the top. One thing you have to understand about gorilla glue is that even though it "expands" and foams up as it cures. That foamy xxxx has no strength. It is useless as a gap filing adhesive like for a stick/partial tang. But for scales on a full tang, its very good. The best glue in the test was Brownell's Acraglass epoxy. It is formulated specifically for bonding metal to wood. I broke down and bought a quart size kit of the resin/hardner mix. Those are the two glues I use. All the various Devcon epoxies failed early in their testing. I've had a couple of failures with the 5 minute and 2 ton type epoxies, and so they're not worth using to me for these applications. Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted January 31, 2010 Share Posted January 31, 2010 Fe-Wood: can you please clarify that part about the painter's tape? Do you use this as spacer material for glueing? No, I use it to hold the pieces in position while the epoxy hardens. Another trick I have used is Crazy Glue. I use it as a fillet, also to hold the pieces in position while the epoxy hardens. Quote Link to comment Share on other sites More sharing options...
markb Posted January 31, 2010 Share Posted January 31, 2010 Here's a link to the testing http://www.bladeforums.com/forums/showthread.php?t=337504 Quote Link to comment Share on other sites More sharing options...
bigfootnampa Posted January 31, 2010 Share Posted January 31, 2010 So it sounds like it's wrong for me to clamp down hard on the scales, with multiple clamps, because it squeezes out virtually all the epoxy. I hadn't considered this. Does that mean that some of you intentionally clamp the pieces together lightly instead? This could be the problem Some types of glue (titebond, elmer's or gorilla glue for instance) like to be clamped tight... epoxy suffers from that same treatment. Because the epoxy has less penetration and is very strong as a gap filler... it is actually better if you leave a bit of gap when using it. Quote Link to comment Share on other sites More sharing options...
overmodulated Posted January 31, 2010 Author Share Posted January 31, 2010 all good to know. BTW I am familiar with the epoxy & glue shootout on the other post - what a great experiment that was. I forgot that several prep work experiments were also part of that. One thing I don't like about the Gorilla glue is the foam it leaves around all seams. If there were a way to clean that mess up before it dries then I'd try it on a knife Quote Link to comment Share on other sites More sharing options...
reefera4m Posted February 1, 2010 Share Posted February 1, 2010 Sandblasting that way could get you into a lot of trouble! Silicosis is SCARY! At the least wear a really good dust mask... better yet get a sandblasting booth. The booths are not all terribly expensive and they are quite well suited for knifemakers uses (I have seen them on Craig's List for a hundred or two). I have personally found that Loctite "professional extra time epoxy" from Lowe's serves me well. You can tint it with standard painters tinters (glycol type). Use small amounts of tinters... I often just use raw umber. I don't get into any special prep before gluing but my blades are forged and then I hot brush the scale. The natural scale pitting and forge marks leave a helpful "tooth" to bond to. If you do stock removal only, you'll have to add some work to get the needed "tooth". Further, since the epoxies tend to grab the wood rather well but sometimes have trouble holding onto the metal, try drilling an extra hole or two so that your epoxy can self rivet to the metal (this in addition to your riveted pins). I've not needed to do this so far, but I think it would work well in case I do have problems. A similar technique is to file or grind notches out of the tang edge so that the epoxy makes a through join there. An under sized or hidden tang can also be used allowing for the edges of the scales to glue directly together. One further note on the use of epoxies in general. The mfr's don't often make this clear but epoxies produce a waxy "blush" as they cure (called Amine Blush). This must be removed with a damp cloth or by sanding or both, before subsequent coats or other finishes will stick to the epoxy surfaces. When I use the siphon sandblast gun I do it outdoors and use a dust mask, indoors I use my sandblast cabinet. However, most small, inexpensive sand blast cabinets specifically advise against using sand (silica sand). Even without a mask (though well advised) sandblasting one tang outdoors doesn't create much of a serious risk of silicosis. And using a siphon gun is by far the least expensive method to get the best results. Quote Link to comment Share on other sites More sharing options...
reefera4m Posted February 1, 2010 Share Posted February 1, 2010 As for clamping slabs to tang while using epoxy - tight is relative. You certainly don't want to use an 8" 'C' clamp and really screw it down. On the other hand using a couple of small spring clamps works well as does several strong rubber bands. I like to use rubber bands as they allow for easy positioning of the slabs and can easily be adjusted looser or tighter just by adding or subtracting a wrap or two. Regardless of the glue you use, pins are alway a good idea. I've had two knives that I've used the Home Depot 2 ton epoxy on whose handles have come off in normal usage but they didn't have pins. After I added pins they seemed to hold a lot better, thought not as well as the high performance Hysol epoxies from Loctitie. Once epoxied in, you couldn't remove the pins without destroying the entire handle - whether you peen the pins or not. I stopped peeding small pins (1/8" or less) altogether - less chance of damaging the handle for little or no benefit. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted February 1, 2010 Share Posted February 1, 2010 Many of the woods used by knifemakers are oily by nature and so you have to clean the wood as well as the steel to get a good bond. Acetone is a common method---but only on the surface being glued! Probably a bigger danger than silicosis is becoming sensitized to the various tropical hardwoods we commonly use. Their sawdust *IS* toxic! Quote Link to comment Share on other sites More sharing options...
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