Drilling a pin out of a blind hole

[H Wally]

As the title says, I'm looking to drill out a pin in a blind hole in a rather delicate/close tolerances part.

I've always had problems with gauging where the pin ends and new metal begins. In this case I have no idea how deep the hole goes, so can't set the drill for depth.

Any advice or tips? Usually if I'm doing this it isn't so vital I only drill out the pin with little overlap

 

[tiriaq]

If you don't know how deep the hole is, or what the length of the pin is, it could be pretty hard to tell when the pin ends and the part starts.
If the pin isn't bottomed, you might be able to tell when you break through.

 

[Striker]

my only suggestion is a bit at a time. Can you use a drill press for the job?

 

[achtanelion]

Can you drill into the pin and use an expander to grip the pin inside the new hole you made, then draw it out?

 

[trevj]

How big is the pin? What material? Hard? Soft? What is it? The job, that is. It could make a difference in the ways and means used. Do you have the replacement pin in hand?

If it's big enough, and soft enough, drill it, tap it, and use a bolt threaded into it, along with a nut and some washers, to pull the pin. If it's really small, run a small drill into it, then progressively larger drills, until the pin is cut away.

Really need more info to give good advice, though.

Cheers
Trev

 

[jethunter]

Good advice from trevj. Best bet is to drill and tap then pull the pin if there's enough metal to do so. In some circumstances welding a nut or an extesion onto the pin works and allows you to work the pin loose.

If you're drilling blind go very very very slowly. There is quite a risk of damage. You may not be able to tell where the pin ends and it might be a judgement call - how deep is deep enough?

Start with a smaller bit and work up in stages unless you pin is too small for that. Dull bit or too much force on it increase the chance of side tracking. Carefully use a light centrepunch dead centre of the pin to ensure you start in the right place and prevent bit wandering. An occasional squirt of lube keeps the bit from overheating and dulling.

This assumes you're using a drill press, fgs don't attempt it with a handheld drill.

 

[big boar]

I've had to drill out screws/pins before, not a lot of fun but not to difficult either. Rule #1 use a drill press or milling machine, no hand drills.(Actually I've used hand drills but you have to have another person to help guide the drill from the side. You make sure from the top it's square to the hole and the other person verifies parallel from the side.) 1-measure for pin dia.(eg 1/8") and make a bushing with an o.d. about 1/2-3/4" and a 1/8"I.D. Ideally the bushing should be hardened but for 1offs I just use whatever is avail. 2-Mix a small amount of epoxy and carefully glue the bushing over the hole(to act as a guide)and let set. 3-Drill in small steps using small amount of cutting oil. I can usually feel when I've cut through if you go slow. 4-Heat the bushing sslloooowly using either a heat gun or a bit of flame from lighter of SMALL amount of propane torch just to release the epoxy. Using the bushing can allow you to do the job with a hand drill but you have to be RREEAAALLLLY careful as mentioned above. If you screw up the setting of the bushing off square you'll really mess up the job, but by using epoxy you have time to make sure you're setup ok. Good luck.

 

[H Wally]

Yep, not an issue technique wise, just never had to worry about the depth, usually I've known about how deep to drill or it hasn't mattered. Going to rig it up in the drill press and go slow.

The pin is almost literally a pin... it's miniscule. Runs parallel to a big bolt and interupts the threading to lock the bolt in place. The pin enters from the opposite side of the piece as the bolt. Going to just have to drill and check every few mm's. Plus I'm pretty sure the bolt is seized so it'll be fun figuring out if it's rust or a tiny bit of pin stoping it from turning. It has been soaking in penetrating oil for several days so that'll hopefully help.

After I'm thinking I'll tap the pin hole for a small screw so I won't have to deal with this again

 

[trevj]

This the pin on the Colt over in Antiques and Black Powder?

If so, figure out what tap size you plan on using, set up the drill stop to prevent punching past the skin on the other side, and go to town on it in a drill press.
With some care, you may be able to drill out the pin without scarring up the hole too badly. You gotta watch for the pin rotating with the drill, and lift it out slowly, if it does. Sometimes it works.

Undoing a permanent install that was really meant to be permanent, is a PITA. Blind pins are for sure in that category.

What is the diameter of the pin, more or less?

I've dealt with taper pins from tractor parts down to a bit bigger than a raspberry thorn on watches. Big ones are easier to deal with!

Modifying original parts in non-original ways kinda sucks, but ya gotta do what ya gotta do. Best thing is to stick to an approriate change, if you cannot avoid making changes.

Cheers
Trev