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Catalina/Capri 25/250 Sailor's Forums

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Drilling the swing keel

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Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Initially Posted - 11/12/2006 : 15:42:51

Couldn't find the thread with the question.

I just finished drilling for zincs, it took about an hour and a half. I used titanium nitride coated bits (hardest) - 1/8 for pilot holes and 13/64 finals. I broke two 1/8 bits (not hard to do with firm pressure and small bits) and a tap ( #10 is the bit size for 1/4 in tap, but I changed to a 13/64 and the few hundredths larger size made subsequent tapping uneventful. The screws are not heavily loaded, so slightly less tooth on the threads won't matter) and plenty of oil. When tapping, I periodically removed the tap and inserted the spout of the oil can deep into the hole to flush chips. Much easier than I expected

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

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jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 11/22/2006 : 21:01:35

Dave,
Did you put zincs on both sides?

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sweetcraft
Admiral

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USA
816 Posts

Response Posted - 11/22/2006 : 22:53:19

Drilling cast iron does require pressure but also slow speed. I drilled my keel on each side for the 1/4 inch bolts for the zincs and also had to cut part of the keel to make room for the upgrade from CD for the cable attachment. I used a course metal cutting blade in a receprocating saw. I have used Permatex #2 on the threads of all the bolts in the keel without any problems. My C25 is a 1979 #1490

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Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 11/23/2006 : 12:15:15

Yes, two zincs just below and aft of the pivot assembly

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 11/23/2006 : 12:23:25

For those who might be doing this in the future... Here's a link to a simple table with recommended drill (spindle) rpms for different materials.

Side note: 1/8" is approx 3mm... so you should be turning about 3100 rpm for that particular bit in cast iron. For 1/4" drill, step down to about 1500 rpm.

http://www.diracdelta.co.uk/science/source/d/r/drill%20bits/source.html

"...and plenty of oil." (dave)

What kind of oil? 'Regular' lubricating oil will wreak havoc when machining. If you use oil, be sure to use special purpose machining/threadcutting oil. (I use 'RapidTap' for tapping).

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Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 11/23/2006 : 21:06:51

Since I can't dial a speed on my 3/8 variable speed drill, I just increase speed until it cuts smoothly. I'm sure it was nowhere near 3000 rpm - that is higher than my drill's no load speed. Cutting at a higher spped saves time of course, but too fast will only burn the bit.
That is why I stay near the lowest speed that bites smoothly. Once you crosss the threshold,
time is the only disadvantage and it takes less than 5 minutes to drill each hole. I might save a minute; I might burn a three dollar bit.

As for oil, I really don't think it matters in this material. I use cutting oils in harder material, and it is superior. I didn't have any so I used 3in1 - water would have been just as good for the drilling since it is there to wash away the sludge and cool the bit. But if I had made a hardware store run, my tap may not have jammed. The broken 1/8 bits were due to the difficulty in staying perpendicular with the drill in an awkward position and the boat on the trailer.

Dave

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Jay Schkloven
1st Mate

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USA
84 Posts

Response Posted - 11/25/2006 : 08:54:24

I thought this might be a place for asking about the best coating for my keel. The material I used 8 years ago is not coming off. It was a tar like epoxy that came in two cans. I can grind down the flaking area, but what is the best material to use as a patch. I really do not want to grind all the old material off the keel?

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 11/25/2006 : 10:33:12

>"The material I used 8 years ago is not coming off. "
I'm assuming you meant to say "is now coming off" ???

Sounds like you used VC-Tar. (Now replaced by VC-Tar 2)

Here's the stuff.
http://www.boatersworld.com/product/377381652.htm

I'd suggest using the same product again so it will match the remainder of the keel. If you want the patch job to last treat any exposed metal with Ospho to 'convert' any active rust and coat with an appropriate paint before applying the epoxy coating.

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