Suggestions for drilling a hole in a grade 8 bolt?

[ichthos]

I am going to need to drill a hole in two 9/16-18 grade 8 bolt for the castlenut cotter pin. Can someone tell me how to do this, or is this something I would be better off to have a machine shop do? Thanks,
Kevin

 

[kodanja]

center punch,

then drill press if ya have one!
use oil to keep it lubed

 

[liljohnTR250]

you will deffitely need a drill press

 

[liljohnTR250]

a vise and drill would work but you have to watch crushing the treads.


So drill press is your best option

 

[tomshobby]

Use either a spot drill or a center drill to start it. The following is for a HS steel drill with the diameter measured in inch units, not metric. Sharpen the drill to a 118 to 135 degree point angle, closer to 130 would be better. A cutting speed between 60 to 90 feet per minute would probably work. Spindle speed equals 12 times the fpm divided by 3.14 times the diameter of the drill. Use cutting oil, not engine oil, and do not let the drill turn in the hole while not cutting.

 

[ichthos]

Will a regular drill bit work? Is there a rating for drill bits like there are for bolts? If so, what would I be looking for? I have had problems even drilling through a grade 5 bolt before. I will try the suggestions that were given. What would you think of putting on the old castle nut where I want it and using it for a guide in drilling the hole?

Kevin

 

[liljohnTR250]

go to the hardware store and get a bit for drilling metal. Tell the guy what you are doing and he should be able to hook you up with what you need

 

[liljohnTR250]

you may also need to rethread the bolt so that the nut will go on smoothly

 

[DNK]

Kevin. Run a die down the bolt to the end before you drill. that way when your finished the die will start the thread clean up.

 

[liljohnTR250]

very good idea indeed don never tried that will have to do next time

 

[DougF]

You will need a better quality drill. Preferrably a 135 degree split point drill. These will allow you to drill without a press if you don't have one. They allow you to drill on a curve without walking. Cheaper drills may not complete the hole before dulling. Many are only hardened at the tip and won't hold a resharpened edge. The punch will help get past the threads. Keep your drill speed down. This allows the cutting edge to work and keeps the heat down. Heat is a cutting tool's worst enemy.
If you are having trouble, put your nut in position. It will act as a guide and help to keep you going straight.

 

[Twosheds]

Someone makes a drill jig for doing this. You put the bolt into a hole in an aluminum bar. The bar holds the bolt firmly. Then you put a drill bushing into a hole that guides your bit straight through the bolt. It comes with two bits. If the bit is too small for the cotter pin, you could step the hole up with the right size bit, using the first hole as a pilot. Of course, you can't use the drill bushing for this.

There are holes for several size bolts, but I don't remember if it goes as large as 9/16". Mine is lent out now so I can't look at it.

I got it from Racer Wholesale or Pegasus, I think.

Oops, never mind. It's for a safety wire hole in the head, not a cotter pin hole in the threads. I thought for sure it drilled the shank.

What's happening to me?

 

[dklawson]

Twosheds beat me to my suggestion. I was going to suggest taking a mating nut and splitting it (half way through) using a hacksaw. Thread it onto the bolt and squeeze the nut in a vice to close the nut securely to hold the bolt. Leave the "point" of the nut above the vice up so you can file a small flat spot on it. Use a center punch on the flat spot to mark where you want to drill.

If you have regular 118 degree drill bits but they are of a decent quality high speed steel you'll be OK. However, you really need to run the bit at low speed, use a drill press, keep the drill bit well oiled, and pull the bit out frequently to break and clear any chips. I would not try this without a drill press.

 

[GreenOne]

You can buy them pre-drilled from Aircraft Spruce and save a whole lot of aggravation.

https://www.aircraftspruce.com/menus/ha/bolts.html

 

[TR3driver]

What I do is to run a regular nut down the threads first, so it gets turned over the hole after drilling. Doesn't seem to me that you would need to do that if you were using a die to clean up the threads, as the hole will not be at the very end and the die will easily pick up the original threads.

I've done "Grade 8" with just ordinary "cheap Chinese" drill bits, and they seem to cut fine. But I do always use a drill press, with a vice, and a good cutting oil, so YMMV without those things. Gonna be hard to do freehand and keep the hole well enough centered that it will match the slots in the castellated nut, IMO.

What works for me is to take a Dremel with a small round grinding stone mounted, and touch the threads where I want the hole. Gives a nice, smooth place for the drill bit to bite in and not wander. Also makes it easier to line the hole up in the center of the bolt by eye.

But usually, I just buy a matching Nyloc or similar "prevailing torque" nut and don't worry about a hole. Those "deformed thread" nuts work quite well.

 

[heliguy]

You can buy them pre-drilled from Aircraft Spruce and save a whole lot of aggravation.

https://www.aircraftspruce.com/menus/ha/bolts.html

And save your drill bits and cutting fluid too!

 

[TR3driver]

If you guys see a part number on the AS site for a 9/16-18 by 4-1/2" bolt, please post it. I couldn't find one. Their "bolt selector" doesn't even go that large; and the only AN9 I see listed is only a -33, which is only 3-3/8" long.

 

[TruCraft]

What I do is to run a regular nut down the threads first, so it gets turned over the hole after drilling. Doesn't seem to me that you would need to do that if you were using a die to clean up the threads, as the hole will not be at the very end and the die will easily pick up the original threads.

I've done "Grade 8" with just ordinary "cheap Chinese" drill bits, and they seem to cut fine. But I do always use a drill press, with a vice, and a good cutting oil, so YMMV without those things. Gonna be hard to do freehand and keep the hole well enough centered that it will match the slots in the castellated nut, IMO.

What works for me is to take a Dremel with a small round grinding stone mounted, and touch the threads where I want the hole. Gives a nice, smooth place for the drill bit to bite in and not wander. Also makes it easier to line the hole up in the center of the bolt by eye.

But usually, I just buy a matching Nyloc or similar "prevailing torque" nut and don't worry about a hole. Those "deformed thread" nuts work quite well.

Lots of good ideas!
A grade 5 bolt is about 25 to 35 Rockwell, pretty soft. A grade 8 bolt is a medium carbon tool steel heat treated to under 40 Rockwell, so a HSS drill about which is about 65 Rockwell will work fine.
Any carbon steel can be work hardened with heat or pressure.
So like everyone said, slow RPM, steady heavy feed, with no dwell.
Cutting oil, or a water based fluid helps keep the bolt/drill cool.
Randalls idea with a nut and dremel are good, why buy a die?
Using the castle nut as a guide will work great also.
It will be easier than you think.
Lyle

 

[heliguy]

Randall, for a 4 1/2 " AN9 bolt, you will need a dash 44. The only place i can think that this is used on a TR would be in the front suspension. I measured my old one, and it came out to be 4 7/16", so this would be a dash 43. Might want to go with the 44 as you can always use washers to take up the extra.
I found some on the "3 R" aircraft sales site, but any online aircraft hardware supply place should have them. I bet they are pricey in that diameter.

 

[trfourtune]

i like carbide drill bits for that.
Rob