Drill Tap Epoxy?

[Mark Raine]

Has anyone had any experience drilling and tapping epoxy in this instance for 5/16 machine screw? I have searched the thread and found little. WestSystem doesnt talk about it in their book although they come very close. MY application involves remounting a 10' jibtrack onto a caprail would be very difficult to hold down and in place for all 30 screws. I planned on oversizing the hole, introducing CPES,then microfiber reinforced epoxy, then drill,then tap for 5/16. I can wet out the screw with epoxy before I put it in. (I can not back plate, simply no access).

[JimConlin]

You're headed in the right direction.
The Gougeon book describes a slightly different way to get to the same result.
Their process is one of casting the plug of filled epoxy around the bolt rather than drilling & tapping the bolt into the plug. The key is to use bolts somewhat longer than the depth of the cast plug, extending into a tight hole in something, thus positioning the bolt and supplying a little tension. I've had cases where it worked fine.
Read the book and invent away!

[NormMessinger]

But, why the CPES?

--Norm

[Don Maurer]

Epoxy will soften when heated. You would probably get better holding power using wood screws and a tapered fuller bit of the correct size. Screw in the wood screw to cut the threads. Remove the screw and saturate the hole with CPES. If you really want a permanent fastening, you can put a little epoxy in the hole before inserting the screw for the final time. Otherwise, wax the screw threads or you may never get it out again.

[TCrisp]

Go to the hardware store. Buy the correct epoxy for the job. Don't try and make your own. They have a 5 minute epoxy with metal shavings in it for just this purpose.

[Ed Harrow]

As Jim says the Googe Bros discuss this at some length. I can attest to repairing the bottom bracket threads of a very expensive bicycle using this technique (cleaned well, smeared with plastic steel, filed off the high points, reamed it to size, then rethreaded) Worked quite well in a relatively low-stress application.

[Ross Faneuf]

I've had good success with an alternate scheme. I get SS connectors from Jamestown Distributors. These are threaded pieces of hex, much like a nut about 4 times as thick as a regular nut, designed to join two pieces of threaded rod.

I then embed these in an oversize hole with epoxy, and screw into them. If there's plenty of material, you can put a stub of threaded rod in the other end, drill both nominal size (5/16) and a clearance hole for the connector, and epoxy the whole thing in. I like to bury the top of the connector a bit below the surface.

I do installation by making up the connector & rod locked in with LocTite bearing mount. I then spray a bolt with WD40 and thread it into the top. Put some epoxy in the hole, and possibly dip your connector/stub assembly. Use that bolt to handle it and (if necessary) tap it into its hole. When the epoxy sets, remove the bolt. This avoid the hassles if you get some epoxy into the trheads.

Ceol Mor's genoa track is mounted this way with 5/16 bolts. In some cases, I was able to go clean through toe rail and sheer clamp with long bolts; in others, I used the system described with a stub piece of threaded rod 4-5" long (there's LOTS of meat in Ceol Mor's structure at this point). I now wish I'd done all of them with this system - the bolts were a paint.

I also did mooring bits (3/8) this way.

I consider this far, far stronger than attempting to tap into epoxy, or cast into it, and you can remove the bolts as many times as you like without the threads deteriorating.

I've also tapped into expoxy and set HeliCoil inserts into it, which again I think is going to work better than threads in epoxy.

[Terry Etapa]

I've never done it. In the aircraft biz, they make inserts that are meant to be bonded into composite/honeycomb panels. We actually use an epoxy goo to bond in the inserts. They are not very strong in tension. It's a shear connection with some capability in tension.

[JimConlin]

Ross- that's elegant! The connector serves as a threaded socket to which the hardware can be easily bolted/unbolted, and the whole works is anchored in tension by the threaded rod beneath and in sheer by the bulk of the connector. Nice.

If Hodgdon Bros. will use potted fastenings like this to bear the forestay loads of their mega boats, such lesser stuff as we might do is a piece of cake. I'm intending to use potted studs in some form to anchor the crossbeams of a 28' trimaran.

One question. Is the length of the connector enough to bear the rated strength of the two studs which go into it? For example, the 3/8" item fron JD is 7/8" long, Is 3/8" of 'bury' (1 diameter) enough? Is there an engineer out there?

Jim

[Ross Faneuf]

You get more bury with a connector than with a plain nut - And we all feel comfortable with those taking a tension load. You do have to be careful that the stub uses just 1/2 of the connector, and that any bolt/screw you use buries enough threads. I remember a rule of thumb with nuts being that you had to engage 3 full threads to develop the full holding power of the nut. Anyway, I've seen no sign of any problems.

[Mark Raine]

Thanks very much for the replies. Ross, I considered doing what you describe using 1/2" allthread that was drilled and tapped for 1/4-20. I needed 70 of them and at $10 a peice it got way too spendy for me ( I got bids from 5 machine shops ) The other issue ( I felt ) was After I buried these anchor bolts, how lucky would I be that they would line up with all 35 ( on one side ) holes for the track. Mainly it was the extra cost. I havent priced out these connecting rods yet. I agree that burying a threaded big hunkofanything in the epoxy would be closely approximating the ideal of backplating.

[Wiley Baggins]

Got Helicoils?

http://www.emhart.com/products/helicoil/default.htm

[Ross Faneuf]

The connectors from Jamestown Distributors aren't cheap, but they are a lot less than $10 apiece.

The alignment issue is not trivial, and I should have mentioned what I did for Ceol Mor. I made a hole pattern for the track by making up a piece of hardwood stock as wide as the track x about 1/2" thick. I clipped it to the track, then drilled through all the holes in the track on the drill press to make a pattern. I then bent the pattern around the toe rail, with temporary fastenings, and drilled through it to get my holes. I know this sounds elaborate, but you're going to have to do something like this if you want a good job no matter how you fasten the track. I didn't want to take the chance of gouging any material out of the track by drilling in place with it. This whole process was quicker than you might imagine; making the pattern took, at the outside 1/2 hour.

[Nicholas Carey]

Originally posted by Don Maurer:
Epoxy will soften when heated. You would probably get better holding power using wood screws and a tapered fuller bit of the correct size. Screw in the wood screw to cut the threads. Actually, I seem to remember reading some studies that show that machine screws have higher holding power in hardwoods than do woodscrews, for the simple reason that the machine screw threads offer more surface area than does a wood screw of comparable size.

The drawback of, course is that you have to drill and tap the hole for the machine screw.

And an epoxy-bonded machine screw has higher holding power yet because the silica/epoxy casting in the oversize hole dramatically increases the area of the interface with the wood compared to a screw fastened directly into the wood.