What's new
What's new

tap gone bad

johnfin

Plastic
Joined
Oct 23, 2012
Location
florida
So I have a chunk of aluminum on my car that cant be removed. It has a M20 x 2.5 threaded hole, open end. the starter threads were botched so I used a tap but....the tap drifted and started to go on the wrong angle, it stopped when it hit a lip. So my question is do you think I could straighten the hole and use helicoils to repair it.
 

Attachments

  • hole.jpg
    hole.jpg
    9.5 KB · Views: 376
How are you planning on straightening the hole? A hand drill? You might end up with a "kind of straight" hole but chances are it'll be a little wallowed out and not be perpendicular the the surface.

If you want to do it right, and the car is worth it, I'd pull the motor/transmission (I'm assuming the starter bolts to the transmission), throw it up on a mill and make a proper/perpendicular hole to start your repair with.

JMHO (anal retentive as it might be :D)

-Ron
 
Is it possible? Sure. Is it possible for a guy who botched chasing an already threaded hole with a hand tap? Possibly.

Sorry, had to give you some crap. But realistically, yes, as long as you are careful, and there's enough meat in the piece of aluminum for a larger hole and a helicoil, it should be fine. Just make sure you use the proper drill size for a helicoil, and the proper tap for the helicoil, you should be fine.
 
So I have a chunk of aluminum on my car that cant be removed. It has a M20 x 2.5 threaded hole, open end. the starter threads were botched so I used a tap but....the tap drifted and started to go on the wrong angle, it stopped when it hit a lip. So my question is do you think I could straighten the hole and use helicoils to repair it.

We have no idea what tools & abilities you posses.
 
Sounds like you cross threaded the tap at the start. The gapa on the tap threads allow it to mate up with the existing threads at an angle.

Yes, the hole can be straightened and Helicoiled, but you're going to have to be a hell of a lot more careful than you were the first time. Guides for drilling and tapping would be a good idea.
 
So I have a chunk of aluminum on my car that cant be removed. It has a M20 x 2.5 threaded hole, open end. the starter threads were botched so I used a tap but....the tap drifted and started to go on the wrong angle, it stopped when it hit a lip. So my question is do you think I could straighten the hole and use helicoils to repair it.

No. If you can't chase an existing thread there is no chance of you cutting new threads for your helicoil.
 
hole

Its part of the frame, cant be removed and cant get tap from back although thats a good idea. Not sure what would happen if I were to tap from the back into the new hole. Is there such thing as a stubby tap, like 1/2"-3/4" long? So yes it would be man handling a power hand drill. I was thinking of using a smaller drill to guide it into the good threads in the bottom part (part not screwed up). and then work up drill sizes, creating a semi screwed up pilot hole. Even on a drill press, there will be a void somewhere in the path.
 
Its part of the frame, cant be removed and cant get tap from back although thats a good idea. Not sure what would happen if I were to tap from the back into the new hole. Is there such thing as a stubby tap, like 1/2"-3/4" long? So yes it would be man handling a power hand drill. I was thinking of using a smaller drill to guide it into the good threads in the bottom part (part not screwed up). and then work up drill sizes, creating a semi screwed up pilot hole. Even on a drill press, there will be a void somewhere in the path.



Don't do this. Get a drill guide for the proper sized drill. Mount it to the piece somehow, a clamp, super glue, double sided tape, whatever. Drill the proper sized hole in one shot, and make it STRAIGHT. Use a proper sized tap guide to tap the hole with an STI (Screw Thread Insert, AKA helicoil) tap. Install the helicoil.

Serious statement without recrimination: If you managed to drive a hand tap crooked while chasing an existing thread, your odds of drilling a straight hole into a hole that already exists without a guide of some sort are almost nil. And if you screw this up a second time, you're looking at either big bucks for a machinist/shop to fix it, or replacing the part. Do it right the second time, or pay someone to do it right, because it will cost less than paying someone to fix it if you get it wrong again.
 
find this, bolt steel plate to said part and flat, mount mag drill and drill it out or endmill it out. slim chance other then removing said bolt, welding the hole closed and redrilling it.
 








 
Back
Top