help grinding a drill pilot

I have a barrel that has a bore that a .311" gauge pin will fall thru but a .312" pin will not. I'd like to drill this out to .5" using a piloted drill. I plan to grind the pilot on the surface grinder using a motorized spin fixture and resharpen the ground ends on the T&C grinder.Questions include:
1. How to hold the 6" drill for grinding. Four inches of drill out in front of the collet makes me nervous. Would it be best to drill out a brass 5c collet and hold the drill by it's flutes or hold it by it's shank and support the tip? Or?
2. Is there a general rule regarding pilot length? In drilling a bore that measures .3115 with the piloted drill would it be best to use a .311",.312" or ? diameter pilot.
Thank you for any help in answering these questions.
Otto

I plan to grind the pilot on the surface grinder using a motorized spin fixture and resharpen the ground ends on the T&C grinder.

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Any chance of turning the pilot and resharpening with the same setup?

Drill Pilot

Both the spin fixture and sharpening fixture will use the 5-C collet but I'm not sure how to do this job with one setup. Any and all suggestions would be welcome and appreciated.
Otto

Otto
I would make a thin flexible bushing to fit a larger size collet
and hold the drill by its flutes.
Gene

I would go a couple tenths under bore size use the 5c collet and chuck it up short.

Is this drill expected to provide a finish size, or are you going to ream it to size?

I've always wondered what the best way to center your whirlygig under the wheel would be, other than just eyeballing it. Is there a way ???

Use a core drill and hold it in a collet. Holding on four flutes is better than two. How are you going to handle the runout between the drill and the pilot? I haven't seen a collet spin perfect yet?

I would seriously consider using a piloted reamer. You can hold them between centers and grind the pilot to the body. (I know that is a lot to ask of a reamer but you could do it in a couple of steps.)

Rockfish: It only has to be close. I was holding .0003 yesterday by eyeballing center of the wheel. If you have to get closer us a square, same as you would on a wheel cutter.

rockfish said:

I've always wondered what the best way to center your whirlygig under the wheel would be, other than just eyeballing it. Is there a way ???

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First thing to do is make sure your spinner axis is square to the long travel of the table. Indicate it if necessary.

Have a round piece running fairly true in the spinner, or use a round part of the spinner spindle if it has one.

With the wheel OFF, slowly move the table back and forth under the wheel while bringing the wheel down in small increments until it just touches. Lock the table. Set a stop. This will get you fairly close.

If you want a little better, after doing the above procedure, grind a spot on your part enough to have it running true, and basically do the same procedure as above while watching the sparking.

I do that with mine and never have a problem. The only way to get it closer is to indicate one spindle to the other, which I've never found necessary.

OTN,
I think your question was related to the holding of the drill for spinning the pilot rather than the grinding itself. You are correct in thinking that holding the shank while spinning the end under a wheel would be a disaster.

My point as to whether you were using the same fixture was badly worded but the question was more to the point that you wouldn't hold the shank when resharpening the flutes, so you wouldn't hold the shank to spin the end either.

Insert the drill into the collet and snug it down with an inch sticking out front. Set up an indicator touching the flute in the back next to the collet and rotate the drill under the indicator (counterclockwise so you're not spinning into the indicator point) and see that the indicator moves to the same spot at the peak of each flute. Now do the same at the front of the drill. Tap the drill with something until you get the same indicator reading on the high points front and back, then tighten the collet down all the way and recheck.
Spin away! -Mike

Drill Pilot

Thank you all for your helpfull advise.
Your reply's raised a few questions
Arnie: I'm glad that I asked the question regarding pilot size to bore size as I would had guessed the opposite. Any recommendation regarding pilot length?
Huntingguy:I'll use the core drill and reamer on the next barrels as I really wanted to see how this method works.I was considering holding the drill in a fixture with a collet at the shank end and a female revolving center at the other but it doesn't sound as if I'll need to do this.
RJNewbould:The drill should bring me to finish size if the barrel drilling follows the same course as a test piece done without pilot. If not, I'll probbly ream it to final diameter.
Holescreek:Is there any utility in wraping the drill flutes with a layer of shim stock before tighting to protect the flutes and facilite centering ?
New questions same topic
I have .5" steel collets which would work but will have to drill a blank collet if I want to use Brass or plastic. Any votes for Brass or Plastic? Any tricks for drilling the collet? What diameter should I drill/ream for a .5" drill ?
Thank you
Otto

Otto, If you do wrap the drill with shim you may not need to go to brass or plastic collets. However, you must not overlap the shim or risk introducing runout to the setup. Personally, I have done this with a steel collet and no shim. If you do decide to go the other way, size your reamer to the drill. .5" drill =.5 reamer. My opinion on pilot length is a standard Length = 1.5 X diameter. If you are going into a gun barrel there are other things to consider.

Are you drilling the barrel out for a sleeve or is the .5 drill going to a certain depth which will leave a step? If you are leaving a step, and have a good setup (rigid and aligned) I would use a shorter, tapered pilot which only reaches .311 just ahead of the drill flute so as to not marr the rifling ahead of the c'bore. FWIW. -Mike

Drill Pilot

I plan to drill the whole barrel .5" for a liner. The breach end will be threaded to accept a short .75" section and all the parts held together with loctite.
Thanks again for your help.
Otto