Best technique for drilling through a bolt?

[creia]

Does anybody have any technical tips on the best way to drill a bolt? I am fabricating a clutch band brake set up and need to drill a hole through a 5/16" bolt that the band brake pivots on for the brake cable to pass through. How best to center punch and drill it w/o having the punch and bit wander/drift off center? I do have a small drill press and a vice.
Thanks you gents,
Michael

 

[Bill Ellerby]

I like taking a jewelers file and make a small flat spot first then strike with a punch. Make sure you hold bolt firmly so it will drill straight.

 

[Neck]

Drill a piece of 5/16 key stock with the desired hole diameter first, then clamp the the key stock on top of the bolt in the vice, with the hole over the area you want the hole in the bolt. The key stock will act as a drill bushing, and keep the drill bit from walking.

 

[KustomKartKid]

Drill a piece of 5/16 key stock with the desired hole diameter first, then clamp the the key stock on top of the bolt in the vice, with the hole over the area you want the hole in the bolt. The key stock will act as a drill bushing, and keep the drill bit from walking.

:thumbsup:

I know your drilling the shoulder in this case but if you were drilling the threaded end for a cotter pin or similar you can double nut it and drill through the flat on the nut at the desired location...

 

[ScooterBoy]

I always enjoy reading this stuff.....

I have a full machine shop available at all times so my immediate thought was put it in the mill and drill it on center. Pretty easy if you have the machines.

Some of these ideas that you guys come up with to do these tasks truly impress me. Both the ideas that Neck and KK had were great !!:thumbsup:

 

[Oldsalt]

The problem, I have found, when drilling through a small diameter rod is that the drill 'drifts' off the radius. Even when a deep center punch mark is used it will still usually happen when using regular drills. So pop for a couple of "90 degree Spotting Drills". The narrow sharp point [in comparison to a regular drill] will not tend to wander so badly. Even if the rod is put in a mill and properly centered a regular drill, being too long a willowy and having a relatively blunt flute angle, will often still be a problem. The spotting drill is very short and rigid, and with it's sharper point will minimize the problem. They were extensively used in Automatic Screw Machines. All that you will probably ever need is a 1/8" and a 1/4"; they are dirt cheap and ENCO [enco.com] has them. All you do is "spot" with them. After a shallow hole is made a regular drill will follow it.

The pic shows a std. 1/4" twist drill and a couple of 1/4" 90 degree spotting and a 1/8" 90 degree spotting drill. I cannot imagine not having them; even on a flat surface using only a regular drill almost always drifts a little and is OK for rough work but not for close work.

 

[bigrob]

I do it similarly to Old Salt but I use a centre drill to make my pilot hole
it is much rigider than a standard drill bit.
Rob

 

[waltsuz]

If its a size I will frequently do I make a drill jig. I use aluminum round cause I find it easier to drill without the bit walking off center. I drill 1/2 way through then turn the bolt and jig around and drill the other 1/2..Best way I have figured this task here..Tap magic works miracles for bit life. My red bike has a cable adjuster made this way for the throttle cable. Walt

 

[creia]

Thanks for the replies guys- all good stuff, duly noted and APPRECIATED!:thumbsup:
As you all know, this will be a very small hole (only large enough for a brake cable, and part of the problem is that drill bits of this size, also BEND so easily which only adds to the drift/walking problem. Are any of the "special" drill bits mentioned in the replies readily available at a "walk-in" store, or are they all an order item only?
Regards,
Michael

 

[Oldsalt]

Thanks for the replies guys- all good stuff, duly noted and APPRECIATED!:thumbsup:
As you all know, this will be a very small hole (only large enough for a brake cable, and part of the problem is that drill bits of this size, also BEND so easily which only adds to the drift/walking problem. Are any of the "special" drill bits mentioned in the replies readily available at a "walk-in" store, or are they all an order item only?
Regards,
Michael

You won't find 90 degree spotting drills at the local hardware store. If you live in a big city some industrial supply companies will have them in stock. They will also carry 118/135 degree spotting drills which will be an improvement over a regular drill but 90 degree works far better.

 

[george3]

Keep the bit short in the drill press. minimal pressure high quality sharp bit works fine. centering drill bit is better to start it of coarse but I have done this alot of times with out it.

 

[jeep2003]

thanks for that tip oldsalt. i have some of those from my grandfather and wondered why they had such short twist. obviously percision drills though. I usually just grind a little flat spot to get it started. when you grind it it also leaves a scratched surface and that also helps keep your bit where you want it

 

[creia]

Thanks guys- duly noted.:drinkup:
Michael