Threading Purpleheart

I am in the process of turning some bottle stoppers out of purpleheart. The end grain will not take a thread, no matter what I try. I've tried CA to shore up the inside of the hole, to no avail. I tried hot glueing the blank to the mandrel with no success. My next move is a knurled insert with epoxy to rectify this.
I suppose I could make a mandrel with a wooden dowel and have a pressure fit to finish turning, or wait until the inserts arrive. Patience is not one of my best features.
Any suggestions from the experts?

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Originally Posted by Steve Eure

I am in the process of turning some bottle stoppers out of purpleheart. The end grain will not take a thread, no matter what I try. I've tried CA to shore up the inside of the hole, to no avail. I tried hot glueing the blank to the mandrel with no success. My next move is a knurled insert with epoxy to rectify this.
I suppose I could make a mandrel with a wooden dowel and have a pressure fit to finish turning, or wait until the inserts arrive. Patience is not one of my best features.
Any suggestions from the experts?

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I've used multiple applications of thin CA, let dry cure wel without accelerator, tap with a 60% bottom tap part way, apply more CA and let cure and tap again, then apply more CA and tap again.

I like the threaded brass inserts but I've only used them on bigger things, not a bottle stopper.

Another thing that works very well in problem woods is to drill a larger hole and glue in some strong fine-grained wood, then drill and tap that. For example, using soft ceder to make a finger chuck to turn the ends of wooden eggs I glued a cylinder of dogwood (any strong fine-grained wood would work), then drilled and tapped that.

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JKJ

Are you hand chasing, or using one of the powered cutters, like Baxter or Klein jigs? Hand chasing works in some woods, but not others. The powered set ups can be made to work with just about any wood. That may involve chasing the threads as you cut them with thin CA glue, or I used to use the walnut oil to lube the cut.

robo hippy

Reed, I'm fust using a standard 3/8-16 tap. I've used this method many times with no ill effects. I usually put it in my vise and use the hand tool, but with this purpleheart, I've tried that and on the lathe using the tail stock to help align but with little pressure. No joy either way. CA glue didn't do much either. It would start and then the threads would crumble even with the CA. All is not lost though and I won't give up. I will put knurled inserts in when they arrive.

Hi Steve, try cutting a 5/8” - 3/4” plug with a hole cutter in a 1” board and insert this in the bottle stopper. Now you have a No Cost insert that will take a thread with the 3/8” x 16tpi tap.

Hmm, I would think a direct tap like that would cause problems with a lot of woods as in just trying to take a bigger bite than the wood would take. With one of the thread cutters on the headstock, it would be fairly simple, I would think anyway...

robo hippy

The problem with threading end grain is the tap is cutting the lengthwise grain. Imagine running a tap through a bundle of soda straws. Tapping into face or side grain will be much stronger. I remember reading that using a screw chuck in end grain doesn't work real well.

I would think that if you drilled a clearance hole for the threaded stopper, and then just epoxied it in, that it would hold okay. I'm wondering if there is a purpose why the wood end of the stopper needs to be unscrewed from the metal part. Maybe it is okay that they just stay together with epoxy ??

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Originally Posted by Brice Rogers

The problem with threading end grain is the tap is cutting the lengthwise grain. Imagine running a tap through a bundle of soda straws. Tapping into face or side grain will be much stronger. I remember reading that using a screw chuck in end grain doesn't work real well.

I would think that if you drilled a clearance hole for the threaded stopper, and then just epoxied it in, that it would hold okay. I'm wondering if there is a purpose why the wood end of the stopper needs to be unscrewed from the metal part. Maybe it is okay that they just stay together with epoxy ??

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I often do just that - epoxy the metal into the wood, whether threaded or not.

For something that needs to be unthreaded, for example sharing the two meat tenderizers that Ruth Niles sells with a single handle, rather than tap into the wood I epoxy in a threaded brass insert, knurled on the outside to grip the glue.

But that said, I've tapped the end grain on MANY bottle stoppers with no problems. However, I use hard, fine-grained wood, either hard domestics like dogwood or persimmon or more often exotics like ebony, olive, bloodwood, etc. These take fine threads well.

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