I am about to nervously drill in a Tel-Tru 2-1/2" stem (BQ300) temperature gauge with a Unibit #4 step drill directly across from the vent on my precious Weber lid. After looking through the thorough drilling modification instruction page, I could not determine if the hole I drill (thinking 1/16") would be at the gauge of the stem or should it be at a gauge wide enough to seat the gauge all the way though the NPT so that I'm able to fasten a ½ bolt from the underside. I also plan to widen a washer as depicted on the site for the top to give it a more secure fit. Is the drill bit sufficient or do I need to get a punch as well to cut a ½” hole?

Sorry for asking such a basic question but either I read it wrong in the instructions or I just didn't see how this is done.

Thanks,

Mike

The drilled hole must be wide enough to allow passage of the threads so that the nut can be used for securing the thermometer.

And use these washers from GARDNER SPRING:

Website: http://www.gardnerspring.com/mbline.htm

Part number: MB1750-057

For further info, checkout this thread on why use a step drill:

http://tvwbb.infopop.cc/eve/forums/a/tpc/f/8680069052/m/2350096964/p/1

Mike,
I used a UniBit to enlarge the hole in a washer when I added my TeTrue thermo to the dome of my WSM.
Adfter I drilled the hole in the dome, I sprayed the hole and the enlarged washer with hi-temp paint before assembling it all. I also used a large washer on the inside of the dome to add support to the mounting. On top of that, I used a couple of sockets and a hammer to put some shape to the washers so they matched the contour of the dome a little better.

Thanks for all the help. I now have the bit and I'm waiting for the tel-tru temp gauge which I ordered along with the installation kit (washer and lock nut) to come in the mail. I actually practiced a bit (no pun) on scrap sheet metal and it works great. I like the idea of doubling up on the washers and shaping them.

Thanks,

Mike

I used two stainless steel fender washers (on inside and outside of the top).

Drilling the dome for the gauge was easy. Drilling the fender washers was a real pain. In retrospect it was overkill. I thought I would never get them drilled out with the uni-bit step drill. The stainless flakes and the little chips want to collect in the corner of the step bit constantly stopping the cutting action. I suspect those uni-bits were never designed to cut through thick stainless fender washers like that. Not to mention you have to find a way to clamp those washers down and still have clearance for the bit.

Like I said, the dome top of the smoker was a breeze.

Unibits are meant for drilling into THIN METAL ONLY. For drilling the thick stuff use a regular drill bit.

TJ, did you ever get your thero installed? How did it work out? John.

Yeah, the procedure worked out fine and the curved washers match very well with the curvature of the domed lid.