Drilling out a Grizzly banjo for 1" tool post

[Jeff Walters]

Now that I have the new lathe, I need to adapt the banjo for my existing tool tool rest however I am concerned the being it is made from cast iron which is soft that the drill will grab and dig in. Looking for advice or other ideas before proceeding.

Jeff

[daryl moses]

most people have just used a 1" twist drill at a very slow speed. I didn't have a 1" drill bit so I turned a hardwood dowel a little shy of 1" cut a slot in the end and wrapped 80 grit sandpaper until I got a tight fit. Took awhile but it did the job.

[Belton Garvin]

It's simpler than most people think. You are only taking .4mm off the banjo. As has been said before the most critical part is making sure your banjo is clamped in place so it doesn't move. I did mine on a drill press but I've heard of others doing with a hand drill. just oil and take it easy. I actually had to ream mine slightly because after drilling....it was still too tight on the 1" post. It's not a critical measurement. Your 25mm post will still work in the banjo when it is drilled out.

[Bill Boehme]

The rule on drilling/milling/grinding cast iron is that it is done dry. Sometimes a flood coolant is used in shops when the volume of iron being removed generates significant heat. Do the drilling on a drill press and have the piece clamped down to the table so that it can't move. Drilling by hand invites bell mouthing the opening. Finally, back the drill out frequently to clear the swarf.

Don't forget to wear safety glasses. It's better than picking pieces of cast iron dust out of your eyes.

[Roger Chandler]

I did my G0698 with a hand drill with twist bit, using a squirt of oil, and my G0766 on my drill press, with the speed on slow, and the banjo clamped to the drill press table, again with a squirt of oil to lubricate the cut. If you find the fit is still too tight, know that not all posts are the exact diameter......even the best may be over a few thousandth's.....I had one that was .005 over 1 inch!. In that case a hand drill with some side pressure can open up the hole just a little if you are careful to circle the opening on all sides, but be judicious on this!

[Don Bunce]

As mentioned, cast iron is usually milled dry, but generates lot of nasty dust. Using oil, wd40, etc, will help keep the dust to a minimum, if nothing else.

Wouldn't hurt to wear a dust mask.

[Brian Myers]

Don't sweat it ,drilling cast iron is easy. Use a drill press when ever possible. Like others have said , clamp the banjo securely to the drill press table and make sure to have the banjo perpendicular to the drill bit (as best you can). You can place some shims under it before clamping it down if needed. As Bill said , you need to clear out the swarf so drill in a short distance,retract the bit to clear out the metal shavings and then drill a bit deeper .... repeat until you are through. You are removing such a small amount in a soft metal that it should be a piece of cake. As Don said wearing a dust mask is a good idea , personally I hate the metallic taste the dust can leave in your mouth and surely your lungs would be a lot happier without it. If afterwards the hole is too tight for your tool posts you could use Daryl's idea of sandpaper around a dowel to slightly ream it out unless you have or know someone with an adjustable 1" reamer which would make it easy.

[Ralph Lindberg]

I just used a brake hone to ease the hole slightly larger

[Bill Boehme]

One other thought. This isn't precision machining. The next-to-last thing that you would possibly want is a too tight fit. And, the last thing that you would want is a stuck tool post. Fortunately, cast iron is somewhat self lubricating. Unfortunately, it likes to rust.