tapping

[prkaye]

For the tie-down bar on the -9, we have to tap it. The plans say "tap 3/8x16x1 deep". The tap that I picked up is labelled as "3/8-16 NC". Is this suitable?

[Will Womack]

Make sure you go 1.5 inches deep. One inch is not enough if you are using the Vans tie downs.

[mdoyle]

That'sthe correct one. Remember, quarter turn forward,half turn back to break the chip. Kerosene is a good lubricant for hand tapping aluminum. Starting the tap straight is the most important part.

[mlw450802]

Originally Posted by prkaye

For the tie-down bar on the -9, we have to tap it. The plans say "tap 3/8x16x1 deep". The tap that I picked up is labelled as "3/8-16 NC". Is this suitable?

Probably. The 3/8-16 is a coarse thread and the NC is the indicator that that is so.
You just need to make sure you tap deep enough to get complete threads for a full inch. The depth that the tap goes in will be more than one inch and to what extent depends on whether it is a starting tap (tapered more than the others), a plug tap or bottoming tap. All will have the correct threadform but where on the tap the full threads start will vary.

-mike

[robertahegy]

When I tapped mine, I removed the tap often and cleaned debris out about every other turn or more. Lots of cutting oil and blow it out with air. I have not tapped much AL and found it trickier than steel. I actually broke a tap off in one and had to reorder. I needed to remove the tank, as this was a QB, and I broke the tap in one of the wing hold downs.

In retrospect, I would remove them from the wing of a QB for tapping. It can get really messy.

Roberta

[Mel]

A word of caution about tapping aluminum; Never use lubricants made for steel. They will cause aluminum to gaul and break the tap. Use only lubricants specifically made for aluminum.

[Les Dial]

You may also want to make sure that the hole is the correct "Tap Drill" size for a 3/8-16 which is 5/16. I actually did this last night and the holes were somewhat undersize.

[sportpilot]

We just did that same thing today. The plans show 3/8-16 UNC which stands for Universal National Coarse I think. Cleve and I went to our local machine shop and had the tap done by a professional machinest. His charge was less than the cost of a tap drill. That was soooo easy.

[captainron]

I think I would go straight to Heli-Coil, for a permanent stainless-steel threaded part.

[G-force]

Originally Posted by captainron

I think I would go straight to Heli-Coil, for a permanent stainless-steel threaded part.

I dont know about the -9, but the tie down extrusions for the -8 are too thin to helicoil. It possabley could be done, but would leave very little material on the sides.