[ChuckM]

I purchased some custom pistol grips from an eBay merchant to replace the plastic grips. The problem is the counterbored hole for the screws that attach the grips to the pistol is not deep enough for the screws to screw securely to the pistol. The diameter of the counterbored hole is about 8 mm (the diameter of the screw head is 7 mm). I need suggestions about how to deepen the counterbored hole about 1.5 mm without changing the coaxial hole. Thanks.

 

[yomanbill]

The checkreing in the bottom of the counter bore is an interesting touch. I think that before modifying the hole I would try to find some longer screws. If that doesn't work, get a forstner bit of the proper size and set it up on a drill press. I'm assuming the screw hole is perpendicular to the surface of the back of the grip. If not, you will have to shim it on the drill press so the counter bore will remain in proper alignment. Of course, if you do it this way, you will lose the checkeing in the counter bore.
Further thinking; could you use a small chisel and carefully shave off the tops of the checkering at the bottom of the hole. Would that be enough?

 

[Steve Neul]

I think I would be inclined to purchase longer screws. If you start trying to re-bore the hole the bit is likely to hit the sides of the hole and make an ugly mark. Then even with a drill press what happens if you drill it too deep, the grips could easily break off.

 

[woodnthings]

I've never seen checkering in the bottom of a screw hole! That's seems weird since it wouldn't show once the screw is in place.
Chisel it off OR use the same size Forstner bit that was use to counter bore the hole as suggested.
Should be a pretty easy "fix".

 

[John Smith_inFL]

I think the grips were checkered before the hole then a high pressure press punched in the holes. (I've never seen one either).
what model is the gun ?

 

[Half Fast Eddie]

8 mm = 5/16”. Try this, reverse the pilot bit so the smooth shank is exposed, not the flutes. Simce you are not drilling the full hole, just trimming it, you might want to consider a hand drill.

 

[ChuckM]

I think the grips were checkered before the hole then a high pressure press punched in the holes. (I've never seen one either).
what model is the gun ?

Sig Sauer P238. I'm not sure how the grips were made. Maybe the checker was done with a laser? I have no idea.

 

[ChuckM]

The checkreing in the bottom of the counter bore is an interesting touch. I think that before modifying the hole I would try to find some longer screws. If that doesn't work, get a forstner bit of the proper size and set it up on a drill press. I'm assuming the screw hole is perpendicular to the surface of the back of the grip. If not, you will have to shim it on the drill press so the counter bore will remain in proper alignment. Of course, if you do it this way, you will lose the checkeing in the counter bore.
Further thinking; could you use a small chisel and carefully shave off the tops of the checkering at the bottom of the hole. Would that be enough?

It never even occurred to me to find longer screws until you suggested it. I just assumed these particular screws were custom for the pistol, but I probably can find some longer screws. I just need to figure out the threads per inch and thread diameter. Thanks for the idea. And thanks to everyone for the ideas and for taking the time to reply.

 

[calabrese55]

Take it to a gun smith chances are a decent gunsmith would have a collection of fasteners kicking around or have the ways and mens to modify the counter bore depth without any trouble at all.
Possibly a place like BasPro could recommend a compentent gun smith in your area.
calabrese55

 

[woodnthings]

Longer screws will indeed fasten the grips to the firearm, but they will not fit flush in the bottom of the hole because of the weird checkering there.
There will be small gaps around the screws that will trap crud and become unsightly. A proper solution would be to remove the checking leaving a flush bottom hole with no means to collect dirt or other contaminants.

 

[shoot summ]

You will need a counter bore bit. Has a pilot that guides the bit from the through hole.

Counter bore:

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McMaster-Carr

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Longer screws would be cheaper and easier.

 

[woodnthings]

You will need a counter bore bit. Has a pilot that guides the bit from the through hole.

A same size Forstner bit would "self-center" in the existing hole, more common and cheaper if not already owned by the OP.
It can NOT be a saw tooth type bit, must be flush cutting on the bottom.

 

[Rebelwork]

Take it to a gun smith chances are a decent gunsmith would have a collection of fasteners kicking around or have the ways and mens to modify the counter bore depth without any trouble at all.
Possibly a place like BasPro could recommend a compentent gun smith in your area.
calabrese55

Agree. Less chance of running his purchase...

 

[shoot summ]

A same size Forstner bit would "self-center" in the existing hole, more common and cheaper if not already owned by the OP.
It can NOT be a saw tooth type bit, must be flush cutting on the bottom.

8mm(5/16") is not a common size in Forstner sets, who knows if the OP even has a typical set, let alone an atypical size?

A 5/16" straight cut router bit is an option as well.

All of this is assuming the OP has a drill press.

 

[Rebelwork]

8mm(5/16") is not a common size in Forstner sets, who knows if the OP even has a typical set, let alone an atypical size?

A 5/16" straight cut router bit is an option as well.

All of this is assuming the OP has a drill press.

I thinks if the OP had a drill press, he wouldn't have had to ask.

 

[shoot summ]

I thinks if the OP had a drill press, he wouldn't have had to ask.

I thinks we really have no idea if he does or doesn't, people ask a lot of questions, some have equipment, some don't, the question in no way is a clue to what they have.

Suggesting cutters that require a drill press would require the OP to have one, or access to one.

Buying longer screws wouldn't require any of that, but would require getting the right length, too long and they can interfere with the mag.

Regardless it looks like the OP is headed to longer screws.

 

[John Smith_inFL]

if the grips were for a 1911, several of us here could provide more accurate options. But, for a Sig-P, I have no clue what would work and what wouldn't.

 

[Rebelwork]

I would take it to a gun shop...

 

[knothead1]

Don't know what tools/facilities/skills OP has on hand but I've done a few of these kind of mods. Success has best come from using a piloted counterbore, preferably with a pilot that can be changed to suit the diameter of the screw hole. This tool can be used in a hand drill so a press, while desirable, isn't a deal breaker. Since it sounds like a one time use I don't suppose investing big $ on a counterbore is a good idea but maybe throwing a few dollars at something like

Amazon.com: 5pcs Counterbore Drill Bits Set,High-Speed Steel M3-M8 4 Flutes HSS-AL Straight Shank Counterbore End Mills for Copper Aluminum Steel Cast Iron : Industrial & Scientific

Buy 5pcs Counterbore Drill Bits Set,High-Speed Steel M3-M8 4 Flutes HSS-AL Straight Shank Counterbore End Mills for Copper Aluminum Steel Cast Iron: Counterbores - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

might be OK?

 

[ChuckM]

I think I would be inclined to purchase longer screws. If you start trying to re-bore the hole the bit is likely to hit the sides of the hole and make an ugly mark. Then even with a drill press what happens if you drill it too deep, the grips could easily break off.

Well.. I called the manufacturer to ask for the screw specs, and found out they sell longer screws for wood grips. I had no idea. So thanks again for the suggestion. Glad I didn't spend money on tools to modify the holes and possibly mess up the grips!