Tapping a hole

[Bill B]

I'm working on a Baja Special and a screw broke off flush with the frame....been doing the 50/50, heat and cold, ground a slot for a flat screw driver, but it looks like I'm gonna have to drill and tap,  Should I try to drill and tap the same size or go up a size.  It's a 40tpi frame screw.......Bill

[RowdyW]

Bill try drilling slightly smaller then the tap drill size first. The hole has to be dead center, which goes without saying. After the pilot hole is through then use the tap drill size. You should then be able to work the tap into the hole.              Rudy

[Three se7ens]

If you are very careful, you can salvage the threads by drilling undersize, and running the proper tap through the hole.  Its a bit of an offball size though, #5-40.  

If you go that route, I would use a 3/32" drill bit.  Make sure its very well centered when you drill, otherwise you may cut into the threads.  That should only leave the threads of the original screw, and running the tap through afterwards will remove whats left of the original screw.  Be careful when starting it to line up with the original threads, otherwise you will cross thread it and ruin the threads.

If you are not successful in that, you would likely be better served drilling and tapping a new hole in another location, instead of going to a bigger size.

[mikeysm]

Helicoil is the best way.

Mike

[oldmanjoe]

  I personalty would try to drill a hole in the screw all the way through , and hit it with penetrating oil again  .     Use a easy out or believe it or not hex key .    Hammering a hex key in the hole usually shocks the screw enough to back it out.     joe

[Cortez_Conversions]

Lots of options here Bill.
Do what ever you have the best suited tools for, and you feel most comfortable with.

[mikeysm]

Drilling it out is the best way. If that fails then helicoil will allow you to use a stock screw.

Mike

[Bill B]

So drill and tap it is..McMaster Carr has a 5-40 tap and recommend .1015 drill bit, figure I will get the shorter bit for less flex....next question......which tap starting or blind hole?

Bill

[oldmanjoe]

  Starter , blind hole is a bottom tap no leed .      Be careful ,to easy to brake a tap  due to chunking ...     joe

[Three se7ens]

So drill and tap it is..McMaster Carr has a 5-40 tap and recommend .1015 drill bit, figure I will get the shorter bit for less flex....next question......which tap starting or blind hole?

Bill

http://alantani.com/index.php?topic=17892.0

Read that before ordering anything. 

You will want a taper tap.  I would still recommend starting with a 3/32" drill bit though.  It is only a few thousandths under the minor diameter of the threads, so you are less likely to damage the threads in the handle with that size.  You are only chasing existing threads, not cutting new ones.  No need to use typical drill sizes, the requirements are different when cutting fresh threads.

[oldmanjoe]

 Here is one that came out of a 155 surf master bar  5-40 .    Hole rite down broadway , removed with hex key.   I do this first , if it dose not move than i redrill and chase with a tap .   joe

[Midway Tommy]

I use the smallest easy out they make on smaller bolts and use a 1/16" bit first rather than the bigger size they recommend. That gives a little margin for error and oval movement. Never had one not come out that way and have never had to retap a hole. Most of the time, if there's nothing on the back side, the bolt turns out the back side with only the drill bit friction. If there's something on the back side it doesn't take much to get that little easy out to grab a hold and back it out. 

[PacRat]

If you have not placed your order yet, get a left handed drill (better yet, get two). This will help to loosen the screw as you drill. Be very carefull to center that drill...they always take the path of least resistance. Buy two taps, 1 starter and one bottoming.
Good luck!
Mike

[oc1]

Start with the smallest bit you can find.  It's much easier to center.  If you get a good dimple in the exact center, it will all go smoothly from there.  The micro bits are handy.

I didn't know they make left-handed bits Mike.  Very clever.
-steve

[ReelClean]

I have a set of these.

http://www.aldn.com/Pages/grabitMicro.php

Most expensive save was a Stella rotor that "the other guy" handed back in bits to the customer with a "s#*t happens" attitude.

cheers
Steve