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So, I got the 3/16OD 5/32ID Steel tubing which Tyler suggested, and attempted to practice with it on an oak rod which I drilled out a 3/16. All was well, the drilling was perfect, and it was so tight that it was all I could do to get the steel tubing through the rod. I had to lock down my tail stock and clench the tubing in my jacobs chuck, pushing it one grinding mm at a time into the airway, one crank of the tailstock wheel at a time.

Sadly, all this torque bent my steel tubing a bit near where the tenon should be... nobody likes a bent tenon. Should I be drilling the hole slightly oversize and epoxying? Maybe I should be drilling at 7/32s not 3/16?

Thoughts?

Did you mic the tubing? Sounds a couple of thousandths over on the OD, chuck a bit of it up and clean it up with sandpaper. If it's still too tight, repeat until it fits.

I think the rule for pipe-sized objects is that if you have to choose between forcing something or going up a size and epoxy-ing, go up a size. I've seen a few pipes broken after a few years of service because tolerances were too tight.

Epoxy is hellacious stuff, and if you bother to groove or even rough up the metal you are bonding, it's there forever.

I would go with jhowell and check the diameter. After that I would spend a couple dollars and buy a wire, letter or metric bit that is just slightly over (a couple thou if possible) and adjust your bit from there (nick the edges and whatnot). There are some metals dealers that specialize in small quantity sales. Most of the guys who sell really nice hypo tubing sell in bulk, but a few will sell small quantities. You want the fit snug, but if its too tight you will squeeze out your expoxy at the very least (dry joints are bad in this case) or you'll bend it like you did.

Sas is right, chances are it will break if its too tight. One solid knock on a table during a dry winter could do it in....

Another option, is the size is decently close, is to use pin gauges in incremental steps to enlarge the hole. This will also compress the wood giving you a stronger joint.

You might also try a few different 3/16" drill bits. They're not all created equal.

Rad

There are a number of ways you can adjust. Just use the next size number drill. Test out a few of them to make sure. Sand or cut the tubing diameter down. Or you can enlarge the hole by sanding if you do not have a numbered drill set.

And off to the hardware store I go.

When I fit 9mm filter tenons (being so large it is hard to get just the right fit using only a drill bit) i take the next drill bit size down, wrap a piece of 320 grit around the shank of it and while the stummel is still spinning on the lathe i run the paper in and out for a couple of seconds applying hardly any pressure, then test the fit, I keep doing this until the fit feels right.

RadDavis wrote:You might also try a few different 3/16" drill bits. They're not all created equal.

Rad

I'm finding that is more and more true. I bought a short 5/16" bit so as to reduce drift (listening to you guys). Unfortunately, it is not the same as the delrin I purchased, just a it too large. Now the dewalt 5/16" regular length I was using before, perfect, delrin fits tightly, just perfectly. I now try the drill bit out on a piece of hardwood, make sure it is actually the size that will work.

JHowell wrote:Did you mic the tubing?

If you did, did the tubing have anything interesting to say?

Sorry, ex-sound engineer here.

UberHuberMan wrote: Sorry, ex-sound engineer here.

that's no excuse.

sam a wrote:

UberHuberMan wrote: Sorry, ex-sound engineer here.

that's no excuse.

Your mom is no excuse.

UberHuberMan wrote:

sam a wrote:

UberHuberMan wrote: Sorry, ex-sound engineer here.

that's no excuse.

Your mom is no excuse.

that's right... she's a lady, and a classy one at that.

sam a wrote:

UberHuberMan wrote:Your mom is no excuse.

that's right... she's a lady, and a classy one at that.

Nice parry, old chap!

or - after you drill the hole and extract the drill bit ... run it through a second time
Might even take the bit out, rotate 90 degrees, re-chuck it and run it through on the second pass

Even if the second pass does nothing more than burnish the surface, it may be just enough.