Deep hole drilling?
Tried the search function, but it really didn't give me the info I was looking for. Maybe I should have said deep STRAIGHT hole drilling. I need to drill a 1/4" hole approx. 6" deep, and I need to know how to keep the drill from wandering. Is it a special drill, special technique? Any help here would be much appreciated, thanks.
A regular drill you can expect it to wander about .0010 - .0015" or more per inch of depth. Gun Drills are a special breed they are .0005 or less/1.0 depth.
First I would be sure the bit is sharp and the point is very well centered. Easy and steady pressure while cutting, relieve the pressure every .050-.100 keep the chips out of the hole.
I didn't stop for chip cleaning quite that often, but I was able to drill a 3/8" hole from each end to the middle of a camshaft out of a V8 engine. The holes met with just a hint of mismatch.
I had welded a newish standard drill bit to the end of a rod, nad ground the joint smooth. The camshaft was held in the 3-jaw with the other end in the steady rest. The steady had been adjusted on a piece of scrap turned to the size of the journal and still in the chuck.
Maybe first-timer's luck, but it went very well for me.
Now you've done it, winchman. Why did you drill the camshaft??
One trick is to use progressively longer drills.
Start with a good 60 degree spot drill (not a center drill if possible).
Then a regular length drill, about 1 inch deep.
Then a 3 inch drill, if possible.
Then a long drill to finish.
And use shallow pecks.
Allow the drill to cut, DON'T FORCE THE DRILL, which causes it to flex.
Just be patient.
The best way is to use a Parabolic flute drill. They are made for deep holes with a lot of extra flute clearance to move the chips out of the hole. They don't start well on their own. Best to use a spot drill out to the finished hole size, then the Parabolic drill will do the rest.
Someone wanted to make a lamp for their son who was interested in cars. The base was a disc brake rotor. Probably similar to this:
Appreciate the info. I just stumbled across a site last night with parabolic flute drills, was wondering what they were for, now I know :-). Apparently NOT the sort of thing you'll find at your local Big Box. Later.
My thread shows how I solved my problem.
Start with a 4.00 mm ball ended milling cutter, then use a standard drill. This is so that the long series parabolic fluted drill is stable in the hole. This setup at 2,500 rpm needs very little pressure to drill and only 3 or 4 retractions to clear the swarf.
Drill in the lathe, and use an "Aircraft" bit..... meaning one with a long shank, and short flutes. They are findable at some hardware stores.
A possible substitute is the long drill with a standard length of flute on it, but I'd suggest the aircraft bit, since the flutes are too flexible.
The issue is obviously keeping the hole straight.
Drilling in the lathe, with the work spinning tends to do that. The use of a bit with minimal flutes and a long round shank for the least flexibility and best guidance along with using the lathe should get you the least runout possible.
A gundrill is nice, but how many people have one laying around? You can MAKE a solid shank gundrill, but it seems extreme. They are also available commercially, I have a few short 6" or 8" solid shank gundrills, and they do work nicely.
With any long drill that does not have an oil passage to flush chips, you have to pull out the drill and clear chips regularly, or you will either jam up, or go off the proper line.
Drill about 1 diameter, no more than 1.5 diameters, then clear chips and drill again (peck drilling).
Use lots of oil.
Solid shank gundrill end view
side view of tip