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Creating Recessed Hole for a Bolt

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CapsFanBen

Plastic
Joined
Nov 26, 2021
I am hoping to get advice on creating a recessed screw hole so an 8mm wafer head is flush with an aluminum surface. I drilled the hole for the screw (4mm) and now I just need to make it recessed. Would this be a good bit to use?

Offline page | RS Components
 
If it matches the od of your screw, yes it will work. It's known as a counterbore, usually used for sinking socket head cap screws (shcs). What are you using to drill and sink the holes?
 
They are also made with a removable pilot. You can make/buy another pilot so the same bore can be used. with slightly different sized screws.
No idea about your tools and tooling. If making a lot of these counterbores on manual machines considerer getting an aircraft countersink cage.
Bill D
 
I was using someone's drill press, but I kind of want to do it on my own with a hand drill. Are there any hand drill guides that are actually any good? I don't really want to invest in a press, but it would be good to have a hand drill guide if they actually are any good. Thoughts?
 
Thank you. I only need about 1.3mm of depth, so I think the cage would work! I need a threaded counterbore bit though to use the cage, so that first bit I linked to would not work?
 
CapsFanBen said:
I was using someone's drill press, but I kind of want to do it on my own with a hand drill. Are there any hand drill guides that are actually any good? I don't really want to invest in a press, but it would be good to have a hand drill guide if they actually are any good. Thoughts?
Click to expand...

I have an old General hand drill guide that I occasionally use when I need dead straight holes away from the drill press. Works OK but base is too small and the extra height makes you lose some of the feel you get with drill alone.

Solutions? A good dry lube on the posts and I swapped out the keyed chuck for a Makita keyless I had on hand. Also a good idea to make an oversize base plate and screw it on for more stability.

I regret giving away my old drill stand, which was actually a lightweight drill press used with portable drills. By enlarging the hole in the aluminum baseplate and clamping it to the work it became a poor man's mag drill.
 
Scottl said:
I have an old General hand drill guide that I occasionally use when I need dead straight holes away from the drill press. Works OK but base is too small and the extra height makes you lose some of the feel you get with drill alone.

Solutions? A good dry lube on the posts and I swapped out the keyed chuck for a Makita keyless I had on hand. Also a good idea to make an oversize base plate and screw it on for more stability.

I regret giving away my old drill stand, which was actually a lightweight drill press used with portable drills. By enlarging the hole in the aluminum baseplate and clamping it to the work it became a poor man's mag drill.
Click to expand...
That is really just an overgrown version of a countersink cage. Or they are related to a woodworking plunge router.
 
did you see the 4.5 mm pilot?

these countersinks if made to din specs are pretty much useless for precision work, as the pilot is quite a bit bigger than the nominal hole. the idea is to make larger holes so (big) components fit. so for a nominal 4mm screw you make a 4.5 mm hole.

the combination sets usually are the same. i managed to get a set that has pilots with nominal sizes a while ago, but its not very good quality. anyway, go slow when countersinking.
 
CapsFanBen said:
I am hoping to get advice on creating a recessed screw hole so an 8mm wafer head is flush with an aluminum surface. I drilled the hole for the screw (4mm) and now I just need to make it recessed. Would this be a good bit to use?

Offline page | RS Components
Click to expand...

It will be OK on thicker material but not on Sheetmetal because of the recess between the pilot and the cutting portion. What is the material thickness you are working with?
 
The pilot should be perfect as the screw size is 4mm. The material is 3mm thick aluminum. I am a little concerned about cracking it, but a 1.2-1.3mm sink should be okay, right?
 
Bill D said:
An aircraft countersink cage would work well for you then. You can use a threaded drill bit to drill the hole and it will keep it normal to the work face. The counterbore will be accurate to about.001".
Only issue is the stroke length is probably 1/2" or so.
Bill D.
I have a few used ones bought from the bay.

6 Piece Countersink Cage & Cutter Kit | Brown Aviation & Aircraft Tools

29/64" Threaded Counterbore w/ 1/8" Pilot Hole | Brown Aviation & Aircraft Tools
Click to expand...

Any ideas on where I could find the counterbore size I need that is threaded, so I can use the countersink cage? Or is there some kind of adapter so I can use the non-threaded counterbore I already identified?
 
With a hand drill, you're guaranteed to get a seat that is not parallel to the mating surface. I assume you have very loose requirements for fit and finish and function.
 
That is why someone recommended the countersink cage...

But I guess I could still suffer some side to side imperfections.
 
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