"Best" way to drill and coutnerbore for a 1/2-20 bolt?

[LVLAaron]

Working on this D1-5 backplate. I need to drill clearance holes and counterbore for the bolt head. For either 3/8-24 or 1/2-20 (haven't decided yet) machine bolts.

What's the "best" process for this? is this a two step op, clearance hole with one tool, counterbore with another? or is there a specific tool for the job? If not, what tool to drill the counterbore? HSS end mill?

Backplate is cast iron fwiw

 

[ttabbal]

I know they make counterbore tools for socket head screws. I would imagine there would be something for standard hex head if that's what you're after. I usually just use an end mill though.

 

[benmychree]

Two drills.

 

[brino]

Counterbore sets are readily available. I have no direct experience with these sets but here's a few listings:

https://www.amazon.com/Accusize-Ind...eywords=counterbore+set&qid=1647448087&sr=8-3

https://www.amazon.com/AccusizeTool...eywords=counterbore+set&qid=1647448087&sr=8-5

I like to do it in this order:
1) drill the guide hole for the counterbore pilot
2) do the counterbore to depth required
3) drill final thru-hole

Brian

 

[LVLAaron]

Counterbore sets are readily available. I have no direct experience with these sets but here's a few listings:

https://www.amazon.com/Accusize-Ind...eywords=counterbore+set&qid=1647448087&sr=8-3

https://www.amazon.com/AccusizeTool...eywords=counterbore+set&qid=1647448087&sr=8-5

I like to do it in this order:
1) drill the guide hole for the counterbore pilot
2) do the counterbore to depth required
3) drill final thru-hole

Brian

Nice. That's what I figured. I found some USA made tools on MSC direct. Wish me luck!

 

[RJSakowski]

My counterbores all have a pilot bushing the diameter of a standard clearance hole and cut a bore for a socket head cap screw. I am not aware of any that will cut a counterbore for a hex head cap screw.

 

[benmychree]

Counterbore sets are readily available. I have no direct experience with these sets but here's a few listings:

https://www.amazon.com/Accusize-Ind...eywords=counterbore+set&qid=1647448087&sr=8-3

https://www.amazon.com/AccusizeTool...eywords=counterbore+set&qid=1647448087&sr=8-5

I like to do it in this order:
1) drill the guide hole for the counterbore pilot
2) do the counterbore to depth required
3) drill final thru-hole

Brian

Good advice! I guess I missed the part about counterboring for the (presumably) Allen capscrew.

 

[Mitch Alsup]

Abomb79 uses center cutting end mills to counterbore his recessed cap-head screws.

But since you are working on D1-x fitment, you should use the D1-x threads.
But, also note: you should "index' the start of the thread so that after x turns each D1-x attachment is equally deep in its hole.
That is you want each thread to start at the same relative angle.

 

[Parlo]

My counterbores all have a pilot bushing the diameter of a standard clearance hole and cut a bore for a socket head cap screw. I am not aware of any that will cut a counterbore for a hex head cap screw.

There is no such thing as a hex head cap screw. It's either a cap head screw or a hex head.
It's not common practice to counterbore for hex head screws as a spanner won't have access and no standard for square drive socket diameters.

 

[RJSakowski]

There is no such thing as a hex head cap screw. It's either a cap head screw or a hex head.

https://www.grainger.com/category/fasteners/bolts/hex-head-bolts/standard-hex-head-cap-screws