Making screw holes smaller?

[Jib]

So I’m looking to see if anyone knows a way to make a screw hole that has already been drilled and tapped smaller to accommodate a smaller sized screw.

In my 1/8 model, for some aesthetic bits they bolted them on with M3 hex screws. I think it would look better if they used M2 hex screws, but the holes are already there.

I was wondering if anyone had any idea of a way to do this? The only thing that came to mind was filling the holes with body fill and re-drilling and re-tapping them, but I don’t know if this would work or not. Moving the items and drilling new holes in a different position is not an option for most of the things I want to do this with.

[jarndice]

In larger engineering work if a hole has to be reduced it is possible to resleeve it, An example is when a garage botches the removal/replacement of a sump plug, the hole is retapped with a reverse thread and a new threaded sleeve (Called a Helicoil )coated in loctite or similar is put in, Being reverse threaded the new bolt as it is tightened in the sleeve actualy tightens the sleeve at the same time,
The original hole is now reduced but functional,
That is with much larger machinery I doubt it is possible with 1/8th but it might be worth checking with model engineering suppliers.

[HERMAN BIX]

Could drill a clearance hole into the post or mounting point.
Fill the hole with a plastic spruce section securely set in with a glue or suchlike then refill the smaller required hole & away you go.

[Jib]

Could drill a clearance hole into the post or mounting point.
Fill the hole with a plastic spruce section securely set in with a glue or suchlike then refill the smaller required hole & away you go.

So you’re saying drill the hole bigger, fill it with a sprue or some solid plastic of size equal to the hole, glue it in, then re drill a smaller hole through the sprue after the glue is set and secure?

I wonder if I could 3D print a cylinder with a 1.5 mm hole down the center of it and then all I’d have to do is just tap the hole with an M2 tap.

I wonder if I could do that with an 3mm cylinder and then use a 3mm die on it and just screw it in there and the tap the hole inside that. Make my own thread adapter if you will. I’d be using PETG, which I think it supposed to be on the sturdier side.

[Jib]

Ha, so, I think what I’m going to do, is print some M2.5 (which I found out is the actual hole size) rods that look like scale bolts on the outside, then use a die to add the thread.

[Meter rat]

I do not know if this is of any use to you.
https://www.ebay.co.uk/itm/122660153011
Used a 4mm version, to repair a thread on a suspension arm.

[HERMAN BIX]

Could drill a clearance hole into the post or mounting point.
Fill the hole with a plastic spruce section securely set in with a glue or suchlike then refill the smaller required hole & away you go.

So you’re saying drill the hole bigger, fill it with a sprue or some solid plastic of size equal to the hole, glue it in, then re drill a smaller hole through the sprue after the glue is set and secure?

I wonder if I could 3D print a cylinder with a 1.5 mm hole down the center of it and then all I’d have to do is just tap the hole with an M2 tap.

I wonder if I could do that with an 3mm cylinder and then use a 3mm die on it and just screw it in there and the tap the hole inside that. Make my own thread adapter if you will. I’d be using PETG, which I think it supposed to be on the sturdier side.

Yes Sir, thats how I'd do it

[Jib]

Great success!

Going to do a little tweaking so the bolt head fits in my M3.5 socket, then it should be good to go.

[John Glover]

This may be of help.Look at Ebay or AliExpress and search for brass insert nuts. These are for a stripped bolt hole .I have used these before and work great.