Drill & tap question

[Tony]

What size bit should I buy to drill my prop shaft to accept a 5/16" bolt? I know this sounds stoopid but, as witnessed by yours truly, there are some "not-very-mechanical" Donzi owners, too. THANKS!

http://detnews.com/pix/2001/04/25/spowings.jpg

[boldts]

Tony,
I did this to my prop shaft so I could run a right hand prop on my Volvo 250. I used a 5/8 - 16 tap (Fine thread) and it looks like a 1/4 or a 9/32 drill bit. Sorry, the drill bit is not marked with a size. You want to be sure the drill bit is smaller than the tap so that there is metal to put the tap threads into. I went to a tool supplier to get my tap and drill bit. If you check with someone who deals in these tools, they'll know what you should use.

Scott Boldt

[Tony]

Thanks, Scott. I found this chart (http://www.americanfastener.com/techref/tapdrill.htm) but do not know what size an "F" drill bit is? I want to stick to a 5/16" bolt, coarse thread, it fits nicely through the prop cone.

[pmreed]

Tony,

You're into "letter" size drills which follow the "number" size drills.

Number size drills start at a number 80 (.0135") and go to number 1 (.2280"), then go to letter sizes A through Z. An "F" size drill is .2570" and is the correct tap drill for a 5/16-18 thread. Forget the decimal equivalent, just go to your local home improvement store and ask for an F size drill.

Phil

[RickSE]

5/16-18 UNC (Course) Tap requires a .261 ("G")Drill Bit

5/16-24 UNF (Fine) Tap requires a .272 ("I") Drill Bit

[boldts]

Tony,
I used the 5/16 - 16 and the F drill bit. Looks like from the other post, to use the 5/16 - 18, you need the G drill bit.

Scott Boldt

[Tony]

Thanks a ton, everyone! Forecast for Michigan says 75 to 80 degrees this weekend...Yee-haaa!!! Drill the propshaft, flush out the antifreeze, coat of wax, and try out my new 14 x 24 Volvo Ultra!

[Rob]

I had to do this a while back when I bought a Volvo Ultra from Madpoodle for my 16. You have to buy the new style propshaft cone, a stainless 5/16" socket head bolt and the nylon spacer/washer that goes with the new cone.

I used the cone as a guide, and drilled the propshaft very slowly with lots of oil. I bought a special cobalt tipped bit for the job. I don't recall what size I used, my tap set has a table that gives the correct size.

Once you have drilled the hole deep enough, tap very carefully using a high quality tap with lots of oil. I would run the tap about 1/4 turn or less, back off to break the chips and go another 1/4 turn. Be very careful not to put any sideways load on the tap. Also be careful as you get to the bottom of the drilled hole. Taps are very hard and brittle, and you do not want to have one of them broken off inside the hole.

Be sure to put Loctite on the bolt before you install.

[Peter Beck]

Well Tony since everyone has told you the correct size for the drill I only can remark that I feel the same way as Kurk Maltby does about the season except I am sure he is hurting more inside. Next year right????