mjshp Posted March 20, 2013 Report Share Posted March 20, 2013 The mothership has a laminated oak tiller that has suffered from minor separation issues issues all of it's 30 year life because the hardware is attached and the tiller is mounted with holes that had no epoxy bushing. In building the S10N I learned about creating epoxy bushings, so I thought AH HA! I can fix the mothership's tiller-separation issues. I I borrowed a set of forstner bits and a drillpressan drilled out the misshapen holes with a generous margin. My plan is to fill the holes thickened epoxy and then drill new holes for the mounting and hardware bolts. As I contemplated my generously oversized holes, I began thinking about the volume of thickened epoxy I will use to fill the holes and realized there would be a whole bunch of heat coming from that much epoxy. The question is: What is the best way to fill the holes with thickened epoxy? One big pour per hole? Multiple pours per hole? All the holes at once? One at a time? Relevant factors: The holes for are 2.5-3 inches deep and 5/8" to 1-1/8 across--see the attached photos. I'm a hair below 60N, it was 8F outside this morning, so I could make the pours outside in the cold to offset the heat from the thickened epoxy. I'm finishing the S10N off in a heated workshop Any guidance the epoxy gurus can provide would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted March 20, 2013 Report Share Posted March 20, 2013 Many have poured bigger epoxy holes than that with no problems and I don't think you will have any. Just use slow hardener and make the pour before the larger bit exotherms in the cup . I use holes as large as 1 1/4" by 2 1/4" deep for outboard mounting on transoms in the summertime. Quote Link to comment Share on other sites More sharing options...
Howard Posted March 20, 2013 Report Share Posted March 20, 2013 If you are concerned about it, turn a 2 x 4 on edge, drill a similar sized hole, pour a test batch and see what happens. Slow hardener would be a big help, even in colder weather. If this is to be a load bearing bushing, I'd go about thick enough to barely pour and let it mound up on top. It will shrink a lot as it cures. You may have to do a 2nd pour to bring it up flush. If this proves to be too fast and it gets hot, you could pour it in half batches. Epoxy will still chemically bind to itself for a day or two after it hardens, but you would only have to wait until it started to kick to make the 2nd pour. Lastly, I finally learned to mark the lines that form my centers well outside the hole I'm drilling. That way, when the holes have been back filled, I can still go back and remark the centers to drill a hole for my fastner centered in the bushing. A drill press gives you the best shot at drilling the holes square. If you are using screws that will not pass through the stock, you can wax up your screws (machine or wood) and set them in the hole and pour with them in place. Instant bushing with threads. Quote Link to comment Share on other sites More sharing options...
Dale Niemann Posted March 21, 2013 Report Share Posted March 21, 2013 I may be wrong here but I thought you were supposed to us un-thickened epoxy for bushings like this. Thickened will not soak into the wood as well and or be as strong? Quote Link to comment Share on other sites More sharing options...
Dale Niemann Posted March 21, 2013 Report Share Posted March 21, 2013 Sorry, I also have a question. Is there a formula for the bushing diameter relationship to the bolt or screw diameter? Quote Link to comment Share on other sites More sharing options...
Brent Posted March 21, 2013 Report Share Posted March 21, 2013 I use thickened epoxy with the diameter of the epoxy filled bore about 50% bigger than the bolt hole diameter. Keep the epoxy thin enough to flow into the hole and be careful to avoid entertaining air into the pour that result in voids. Quote Link to comment Share on other sites More sharing options...
Boatguy30 Posted March 21, 2013 Report Share Posted March 21, 2013 The best way is to use something like milled glass fibers as a filler. Coat the holes with unthickened resin. Ideal to do several coast wet on wet and then fill with tick resin. Also when doing this fairly large it is best to glass over the "bushing" as the resin will shrink over time and allow water to enter the created cracks. Quote Link to comment Share on other sites More sharing options...
Hirilonde Posted March 21, 2013 Report Share Posted March 21, 2013 I may be wrong here but I thought you were supposed to us un-thickened epoxy for bushings like this. Thickened will not soak into the wood as well and or be as strong? First, I don't think soaking in is all that important. Epoxy bonds so well to wood that it does not need to soak in much at all. Second, fillers add different characteristics to epoxy, so to say use them or not in general doesn't mean a lot. Cabosil thickens epoxy while keeping it a good bonding material. So in small amounts it makes epoxy into a great glue. Too much and the result is brittle. As a bushing it just needs to resist compression, so fillers that make is softer like for fillers aren't the best idea. I used a little cabosil only when I made bushings for my Spindrift. I suppose you could add chopped glass fibers, but not sure that it is really necessary unless a lot of material will be left after drilling it out. Quote Link to comment Share on other sites More sharing options...
hokeyhydro Posted March 21, 2013 Report Share Posted March 21, 2013 If the bushing is for a rotating joint, such as a CB or rudder tilt pin, I mix graphite powder in as a filler. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 21, 2013 Report Share Posted March 21, 2013 The technique I use is to wet the holes out with unthickened epoxy first, which prevents a glue starved bushing, then pour thickened epoxy in. Pour is a relative term with thickened epoxy, as it's easier to just apply dollop after dollop with a putty knife, until full (slightly proud as suggested). Filled fiber can be pretty abrasive, but it is a favorite of mine. Any of the typical filleting mixtures (cotton flock, silica, wood flour, etc.) will work. Do the pour(s) all at once, you'll not have any problems. With a little prep, you can cast a pilot hole for the fastener, by gluing an appropriate size dowel to the backer you'll be doing this over and pouring epoxy around it. The mix doesn't have to be especially thick and it's better if it isn't, just reinforced with something tough. I recently made some similar holes with bronze dust. I made a very thick mixture, because I wanted it to look the part. I'll bet these bushings out live the boat. Quote Link to comment Share on other sites More sharing options...
Howard Posted March 21, 2013 Report Share Posted March 21, 2013 I think most of us are using variations of the same thing, which is outlined in the West System manual on the subject: http://www.westsystem.com/ss/boat-repair/ Download the repair and restoration manual referenced at the top of the page. What that doesn't really address is how big these bushings can be. 5/8" would not be a problem. Not sure about a 3" hole that was 1 1/4" in diameter. That is probably on the verge of flaming out, depending on the epoxy and hardener used. Quote Link to comment Share on other sites More sharing options...
PAR Posted March 21, 2013 Report Share Posted March 21, 2013 A 3" x 1 1/4" hole isn't a lot of volume (about 12 cubic inches), so I wouldn't be very worried. Most of the heat will will dissipate into the surrounding wood, especially with nearly 8 sq. inches of surface area to "vent off" on each end. I would use more than tape to seal the one side of the hole, probably a piece of plywood, covered with plastic packaging tape, clamped into place. Quote Link to comment Share on other sites More sharing options...
ecgossett Posted March 25, 2013 Report Share Posted March 25, 2013 I've used the trick of putting a pencil through for small holes, or a cheap piece of cut out wood sanded and waxed for larger holes.. It makes drilling through easier, and saves on epoxy. The pencil trick is one of my favorites. Sears makes a nice precision drill guide (poor man's press). http://www.sears.com/promax-79251-precision-drill-guide-tool-for-portable/p-SPM6308615907?prdNo=4&blockNo=4&blockType=G4 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.