Drilling deep holes query.

Go to your local hire shop and get a deep diamond hole saw, as used to cut plumbing holes through walls.

Insert a bored bar as a guide as you suggest. Also use an extension on the cutter so that you have as long a distance between it and the drill as possible to help you align the hole with the intended rudder stock angle. If possible I'd go so far as to clamp guide(s) two or three feet away from the hull to help to achieve this.
 
Talulah said:
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?
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Never tried this tool, have used HSS hole saw for similar jobs before.

Talulah said:
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.
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Using a hole saw you only need to center the drill bit the first mm's until the hole saw starts to cut.

Have successfully used two different techniques.
For smaller holes we used gaffer tape wound around the center bit to fit the existing ID of the hole.
For larger hole we have use a hole saw with the correct ID to cut a plug out of a 5 cm plank (or slightly over sized and sanded it down to size attaching to a drill)

You could of course combine theses two
Use the hole saw to cut a plug out of a plank, add gaffer tape until you get a tight fit.
 
Talulah said:
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.
Click to expand...

You will also need a taper to straight shank adapter as the one you ordered has a taper shank and will not fit a standard drill chuck.
 
Just a general word of caution. If anyone is considering using a diamond core drill bit. Some of these can clog up in soft materials and may be damaged. If you have hired it, the company will charge you the full monty price for replacement and you will still have to pay for the hire.
 
A core drill would be the best bet. Just out of interest what have you got that is fibreglass 100mm thick? Even minesweeper hulls are only about half that thickness.
 
cryan said:
A core drill would be the best bet. Just out of interest what have you got that is fibreglass 100mm thick? Even minesweeper hulls are only about half that thickness.
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The following picture is the rudder port off a sister boat.

rudderportside_zps11aba387.jpg


The existing bearing is buried in about 3.5" off fibreglass.
As the new bearinging has a much bigger flange (6") I have to build the current shelf up by an inch so the back edge of the flange can clear the hull.
https://www.tidesmarine.com/tides-marine/rudder-portbearing-c
I also have a stainless steel ring drilled and tapped to fibreglass in for the bearing to bolt in to.
The depth of the new bearing is 4".
I have a bit of leeway so the top of the bearing is a couple of inches higher then the top of the old bearing but a recess in the rudder stock for a woodruff key prevents me from going any higher.
The boat isn't coming out until the beginning of March so I'm just lining everything up in advance. I'll post photos when I actually do it.
 
DanTribe said:
Something like this, not cheap though.
http://www.blackdiamondinternational.co.uk/p/w076c-76mm-10554.php
I'm not convinced that diamond tipped bits are suitable for GRP, but might be worth checking.
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Diamond tipped cutting discs are normal for GRP

I have a series of hole cutters for masonry that lock into a mandril plate with a centre drill. For 100mm I would weld the right size onto an extension tube of the same diameter so as to avoid cleaning out the core until finished. The cutting edge is carburundam fragments and cuts a bit bigger than the OD & ID of the tube, so should not stick if removed to clear the dust frequently.
I have drilled holes in 60cm walls with such kit, way cheaper than Hilti core drills (but not as fast)
DW

Sorry all, missed the second two pages...DUH!
 
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Wrong! The core bit he has bought is for drilling holes in masonry with a Kango. It works by chiselling rather than cutting so probably unsuitable for the task in hand. Without the impacting action the teeth will not cut.
 
myquest said:
Wrong! The core bit he has bought is for drilling holes in masonry with a Kango. It works by chiselling rather than cutting so probably unsuitable for the task in hand. Without the impacting action the teeth will not cut.
Click to expand...

Yes.

A glance at the image of the core bit will show that the teeth have negative rake and they are never particularly sharp. It might be possible to grind an undercut with an angle grinder fitted with a diamond blade but it would be very much of an experiment.
OTOH a diamond core drill has very little clearance and would, I think, very quickly seize in the hot and sticky residue (they are bad enough in concrete). It might give a few mms of cut which could perhaps be chiselled out before you went any further but again it would be a matter of experiment. ( I have never tried water cooled core drills but I believe they can come with a man attached so they might at least know whether or not your project is feasible).
 
What you need is one of these;
http://www.directindustry.com/prod/sutton-tools/bimetal-hole-saws-built-in-arbor-30553-908103.html

I have one of these with two of the hole saw holders. On one you fit a hole saw of the size you need to drill and on the other you fit a hole saw that fits in the existing hole. If you go in from inside and outside you may meet in the middle. You can get longer hole saws and tungsten tipped ones might be better for grp, so one of those would be best for the actual hole cutter. The holders slide up and down the shaft of the mandrel so that will allow you to get the smaller hole saw deep into the old rudder gland and then start drilling. It's rather difficult to explain it but I have increased the size of existing holes in thick wood on a number of occasions and it works very well.
 
When you decide which type of hole saw or core drill you intend to tackle the job with ( I would use a decent quality HSS hole saw from both sides) if you still need a bush to centralise the centre of the existing 35mm hole let me know, I am not far from Shamrock Quay and would happily either pop your piece of aluminum in a lathe and put a centre pilot hole through it or make one up for you in acetal.
 
Scarron said:
When you decide which type of hole saw or core drill you intend to tackle the job with ( I would use a decent quality HSS hole saw from both sides) if you still need a bush to centralise the centre of the existing 35mm hole let me know, I am not far from Shamrock Quay and would happily either pop your piece of aluminum in a lathe and put a centre pilot hole through it or make one up for you in acetal.
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Many thanks indeed. I think the thing with the aluminium bar is to have two pilot holes. One end for the core cutter pilot drill and one the other end for the Bosch holesaws pilot drill. (Different diameter pilot drills.) I'm sure I would succeed with the Bosch holesaw cuter but would continually have to cut the middle waste out otherwise I reckon it would only cut about 15mm deep before it would jam up. I could also use a holesaw once size smaller to help clean out the waste.
Has anyone used a Duragrit Carbide cutter?
http://www.axminster.co.uk/dura-grit-carbide-cutting-wheel?gclid=CLDRxpD5p7wCFYUIwwodLB8Aqw
I'm thinking of one of these on a Dremel to cut the centre out as I go down. (Bear in mind that means cutting through the existing bronze bearing.)
 
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I think you would be suprised how easily the job will go with a good sharp holesaw correctly bushed to centralise it. Just run it in till it decks down then cut the core out with a good sharp chisel, in my experience the layers of mat are not always as well wetted out perfectly and you will be able to pop good sized chunks out at a time, a bit like you would going through plywood only a bit tougher. Messy job though - make sure you have a hoover running the whole time.
 
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