Drilling deep holes query.

Talulah

Talulah

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What would you use to drill a 76mm hole through 100mm of fibreglass?
A standard hole cutter can't used due to lack of depth.
(Hole is needed to mount a rudder bearing.)
 
I suspect with solid fibreglass it would be difficult to break out. Not sure though.
Can you get fortsner bits that size? In addition I doubt you would end up with a straight hole.
 
Thanks for the responses so far.
Here is the actual problem.

rudderport_zpsa7e5da58.jpg

I want to replace this rudder bearing with a modern one.
The replacement requires a 76mm diameter hole.
The rudder stock is 35mm.
So I could take a length of 35mm bar, drill a guide hole in the end and insert it in to the bearing. This would give me a guide for a hole cutter which would also give me a good alignment.
Easy enough to cut the existing bearing flush so a hole cutter would go over it but that only gives me 40mm. I need to cut 100mm in total removing the existing bearing in the process..
 
Talulah said:
Thanks for the responses so far.
Here is the actual problem.
I want to replace this rudder bearing with a modern one.
The replacement requires a 76mm diameter hole.
The rudder stock is 35mm.
So I could take a length of 35mm bar, drill a guide hole in the end and insert it in to the bearing. This would give me a guide for a hole cutter which would also give me a good alignment.
Easy enough to cut the existing bearing flush so a hole cutter would go over it but that only gives me 40mm. I need to cut 100mm in total removing the existing bearing in the process..
Click to expand...

Do what you propose and use a multi tool to dissect and remove the "core" debris to allow you to get the depth. I've done similar to make 90mm dia blind holes in an oak beam.
 
Hadenough said:
Do what you propose and use a multi tool to dissect and remove the "core" debris to allow you to get the depth. I've done similar to make 90mm dia blind holes in an oak beam.
Click to expand...

Agree with Hadenough, use a 10mm blade in the multi tool and cut from both sides. Once you have dissected the core a sharp wood chisel will remove the pieces.
 
Talulah said:
Thanks for the responses so far.
Here is the actual problem.

I want to replace this rudder bearing with a modern one.
The replacement requires a 76mm diameter hole.
The rudder stock is 35mm.
So I could take a length of 35mm bar, drill a guide hole in the end and insert it in to the bearing. This would give me a guide for a hole cutter which would also give me a good alignment.
Easy enough to cut the existing bearing flush so a hole cutter would go over it but that only gives me 40mm. I need to cut 100mm in total removing the existing bearing in the process..
Click to expand...

Seems like a good plan, you can use a wood peg with a guide hole.
If the hole saw is to short (after cutting from two sides) I would have perforated the "disk" inside the circle with lots of 10mm holes before breaking out enough material to complete the cut.

A good quality HSS hole saw should be good for this job.
 
I would use a good quality hole saw and have a water hose or puddle and running quite slowly to cool the saw teeth, electric safety n all that accepted.
A 6mm woodchisel/hammer and a smaller drillbit will make short work of the middle 'waste' bit as you progress but take care not to 'lever' the chisel against the pristine outer sides of the new hole.

When the saws central bit breaks through to the open air, finish off by coming in from outside, to prevent ragged gelcoat edge.

Try a plumbers shop/Screwfix etc for large dia holesaws, but keep it cool, don't cook the blade ( GRP is a lousy heat dissipator)! Especially as you start to immerse the whole saw deeper into the grp
 
Reference the doubts about using a diamond hole-saw on GRP. It is common to trim polyester / glass mouldings with a diamond blade in an angle-grinder so if the other tool geometry is OK then the abrasive should be fine. The dust will not be pleasant however.................

cheers
Rum Run
 
alahol2 said:
Anything like this any good? http://www.amazon.co.uk/Faithfull-CDHD76TC-Core-Drill-K-Taper/dp/B000C753SA
Click to expand...

Thanks for finding that. I don't think I would have come across it otherwise.
That looks the business. Anyone any thoughts on its suitability?

I have some 35mm aluminium bar. Now how best to drill a central hole down the axis to act as a guide for the above?
I don't have access to any laith or pillar drill.

I've now ordered one of the above from Amazon.
Interestingley they had 3 available. The price was £33.73. After I ordered it the number available went to 2 as expected but the price shot up to £72.80.
 
Last edited:
If I was doing that job I would use a selection (perhaps three) hole cutters of various diameters. Start with the outer one and take it to about 1" depth, then use one of about 2" diameter followed by a 1" one. You will find that it is then quite easy to use a wood chisel to remove the 1" deep rings. You will find that the GRP will split away in layers relatively easily.
Then progressively repeat in further steps of about 1" depth.
As soon as the pilot hole has penetrated to the full depth of the hull then cut a complete circular ring using the largest hole cutter from the outside of the hull. Then return to cutting from the inside. This will help to give a tidy edge to the hole on the outside.

I do have a large range of cutters which helps for this type of job. Also wear gloves and a face mask.

I would use a wooden dowel to replace the existing metal central fitting, drilling a pilot then becomes relatively easy.
 
Last edited:
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