How do you screw into fiberglass/gelcoat without chipping?

[guy48065]

Yup, this is the way to do it.

He's drilling 9/16 holes for bolts, not for small self-tapping wood screws.
In my case the drilling itself didn't cause any damage so going in reverse wouldn't help. It's the teeth of the screws lifting the gel before they 'bite' and pull in that was the issue.

 

[Texasmark]

When in industry, people who worked certain substances used a peculiar bit. It may be referred to as a "sheet metal" bit. Rather than having a chisel point where the cutting edge starts at the center and as it penetrates the material the bit is slanted and works its way out to the final diameter.

The bits had a small center cutter to maintain position on the material and above that and on out to the OD, the blade was basically flat out to the outer edge where the circumference of the bit was pointed from the mid section to the outer diameter that sloped out to a sharp edge with the OD being inline with the rest of the OD of the bit. The result was that other than the centering point, the OD cut first which kept the circumference from chipping the material and as the bit penetrated, the cut material increased from the OD to the center.

A picture would help....a lot fewer words trying to get the idea across!

 

[Horigan]

He's drilling 9/16 holes for bolts, not for small self-tapping wood screws.
In my case the drilling itself didn't cause any damage so going in reverse wouldn't help. It's the teeth of the screws lifting the gel before they 'bite' and pull in that was the issue.

You need the bevel from a counter sink bit to be deep enough so the OD of the screw threads initially contacts fiberglass and not the gel coat above it.

 

[guy48065]

You need the bevel from a counter sink bit to be deep enough so the OD of the screw threads initially contacts fiberglass and not the gel coat above it.

Agreed.

 

[Jeff J]

Has anyone ever tried the drill bits for putting holes in plexiglass and the like?

 

[froggy1150]

Try the above mentioned bevel/chamfer but before attaching whatever hardware take a screw, add a touch of lube and install just the screw going back and forth to cut threads just like a tap. That way your not cutting and pulling at the same time.

 

[Texasmark]

Has anyone ever tried the drill bits for putting holes in plexiglass and the like?

I have done that and I think this is the type bit I was trying to describe above.

 

[Jeff J]

I had to look it up. General purpose drill bits like most of us have laying around are 118 degrees. The angle will likely be 135 degrees if you drill a lot of steel. The bits for cutting plexiglass are 90 degrees. I haven’t tried it on fiberglass or gelcoat but it makes a huge difference drilling plexiglass, lexan and pvc.

 

[dingbat]

The bits had a small center cutter to maintain position on the material and above that and on out to the OD, the blade was basically flat out to the outer edge where the circumference of the bit was pointed from the mid section to the outer diameter that sloped out to a sharp edge with the OD being inline with the rest of the OD of the bit. The result was that other than the centering point, the OD cut first which kept the circumference from chipping the material and as the bit penetrated, the cut material increased from the OD to the center.

They are called "brad Points"......used to grind our own for drilling sheet metal and "gummy" aluminum