Post By maweis
Temporary Wood Glue?
Would like to glue some blocks of mahogany together for machining. Some get turned in a lathe, others get milled. After machining I'd like to be able to cleanly break the two halves apart again. I'm making both halves of a casting pattern. Any ideas on this?
glue with Hide Glue. Use paper in between the parts
typical wood turner trick. Split at joint, paper will separate
Hide glue will either sand off
or can be removed with hot water
why not just leave waste on either end and screw together?
Always just use regular wood glue with a brown trash bag between the parts. leave a little extra wood on one end and tap with a chisel at the parting line (extra is to take care of the small chisel dimple) You can even go at it fairly aggressively, but I've only ever done this with handheld tools. Not sure if you'd run into a problem with tooling mounted in a holder if you got too aggressive.
The idea to screw it together through some extra is a sound idea, as long as you're careful to note where the screws are. Perhaps spin it up and touch it with a lumber crayon to give you a bright yellow mark to avoid. Hitting a screw with a handheld chisel could be quite painful.
Put a sheet of paper in between the glue joint. A good smack will break it loose. DO SOME TEST PIECES TO GET A FEEL FOR ITS STRENGTH. It might not be good for turning. Start with yellow wood glue. If its too strong try white glue or gorilla glue.
I'd stick with a non-polyurethane glue. Elmers white or yellow or one of the non-poly Tite-Bond variety. With mahogany being a finer grain, you may get away with a poly (like Gorilla) but it's going to be a hell of a lot tougher either way, since it's not supposed to part. Yes, I understand that the paper as a parting agent doesn't wet through, but the poly is going to hold stronger and be more of a pain to remove if you do get it parted.
Originally Posted by Coppa5
i like the idea of screwing the halves together. Sometimes the paper trick doesn't quite work out as expected
If the pieces are long, you can screw them in the middle also, just so long as you counter bore them far enuf to not hit the screws. If you're turning by hand you can plug the hole to avoid having that void. Then after you separate them, plug the holes and fair the plugs in by hand. Since it's a pattern you're not concerned about appearance.
I use the paper trick but I have had the glue joint fail on some small pieces and I have also over done the glue and had it soak through enough that I could not get the pieces apart. Lots of thin wedges are your friend when taking it apart. I usually dowel pieces together before turning or machining as it is easier than trying to line them up later to dowel and if possible I throw some screws in as well as the glue. Having a big pattern or corebox come apart while turning can be very dangerous. A patternmaker at a nearby shop was hospitalized for a few days after a large pattern came apart on the lathe. I have never had a problem turning over the counterbore hole for a screw either with a carriage or turning by hand. I have also hit the screws with hand held scraper tools without too much drama apart from having to resharpen the tool and put in a shorter screw.
White or yellow glues can be softened with isopropyl alcohol, the 99% variety. Wrap the glue joint with a rag saturated with alcohol and put in a plastic bag overnight. I have had very good luck with smaller joints, coupled with the paper spacer it might even work on larger ones.
Here is one that is not going to get away, even though there is no glue between the core box halves. The box halves are lag screwed together and clamped at front and the four jaws are clamping the back. Thru studs with nuts below face are screwed into tee nuts in tee slots in the chuck.
I don't think you mentioned how large the blanks will be, but I've used the paper and glue method lots of times with no failures on some fairly large blanks. Just don't get crazy with the rpm's. Mahogany turns and machines so easy, I think you'll be fine.
Rather than screws, why not leave an extra half inch of wood at each end past the paper for a wood-glue-wood bond. This can then be cut off, or split with a chisel to part the pieces. I have glued four 2-1/2" square blanks that were 8" long together with only glue at each end, making a 5" square blank. No paper and no glue on the center portion! Again, sharp tools and lower rpms. After turning the outside, these were taken apart, and the turned portion put in the center, glued back together and turned some more! These were Christmas ornaments when finished.
I have used hot hide glue for this.Always worked for me,never yet had a failure.
When you separate the pieces ,just use a heat gun on the seam.The glue becomes liquid again and the pieces slide apart.Another advantage is no clamps are required to glue up.
Although I usually clamp the work til the glue solidifies.This usually takes 10 minutes or less,then you are ready to machine.
As far as the hot hide glue in a bottle that does not use any heat to make the glue,I have never used it,just used the hot hide glue granules or flakes.I heat the glue in a weighted glass jar that sits in a crockpot filled with water.The reason for the weight is too keep the jar from floating .The glass jar means no clean up when done. The crockpot stays clean,got one at a yard sale for $5.00.
How about a small dab of hot glue ? the same type used by arts and crafts folks. You could experment and see, vary the amount depending on the temporary bond strenght you require. Its cheap and easily removed with putty knife agmented with heat gun if needed.