I need to drill 4 holes thru the transom for the ext steering mounts. I have pre-drilled backing plates.
What's the best way to ensure the holes don't deviate more than 1/8" when they exit in the bilge?
Only way I can think of is to build a drilling guide. Any other way?

http://www.harborfreight.com/angle-d...ide-95622.html

Use a drill press and drill a 4x4 wood or a aluminum block. Should work good for a few holes.

I just used a simple construction square when drilling for kplanes. Good eyes, square, and pay attention. Maybe lucky but works for me. Having two people helps.

This is exactly what I used for my K Planes and transom assembly holes. Worked perfect.

I have an aluminum block that I drilled,works perfect.do like the HF set up.

if it doesnt have to be dead on balls straight you can get real good results with a cheap DIY drill guide.....piece of threaded pipe with collar and whala

I've used this for years and works like a charm. Hold it on the transom and you'll have a perfectly straight with the transom hole.

http://m.ebay.com/itm/Big-Gator-Tool...287?nav=SEARCH

They also have one that goes to 1/2" here.

http://m.ebay.com/itm/BIG-GATOR-TOOL...977?nav=SEARCH

I'll be drilling 1" holes for the hyd thru fittings and 5/8" holes for the bolts.
The brad point bits I ordered aren't super long so going thru a 4x4 and a transom will be a stretch I'm afraid.
The block of alum sounds good. Probably get by with a 1-1.5" thick piece? Maybe??

I'm now envisioning a rectangular shaped drill guide with different size holes bored in each corner.
(This is due to drilling holes oversize, filling with epoxy, then re-drilling normal size = 4 sizes)
I may wind up drilling fairly close to the trim tab mount. Having holes in the corners should help with getting in close.

Thx for all the tips!!

Looks like I have the perfect excuse to pick-up a drill press.

You are going to need to use a hole saw to go through the transom. So you get a drill guide and use a long 1/4" bit for your pilot holes. Then you use a 1/4" drill blank or piece of pencil rod as the guide in the hole saw, anything long enough to follow your pilot holes and keep your hole saw straight. Hole saw, run it in reverse until you get through the glass, nice clean hole.

Personally I feel like drilling the holes to size, then coating with epoxy is sufficient. By the time you add sealer on both inside and outside you are good to go and only have to drill once.