Lathe Question - How do I get a perfectly centered hole all the way through?

[Pepe_Silvia]

I've tried drilling from the tailstock once the piece is done and that result was not so great - it did not drill down the center.

The next piece I did I drilled the hole first, then used a dead-center on the headstock and a live-center on the tailstock.  That worked well enough to keep the piece centered around the hole, and I was able to get it done, but it slipped a lot.  Is there some kind of a spur-drive/dead-center combination I should be using?

[Dan_Shade]

Are you drilling into end grain? 

[Dan_Shade]

Are you using a chuck? 

Pen turners use mandrels sometimes. 

[Pepe_Silvia]

When I tried drilling it on the lathe I was using a 4-jaw chuck.  That was for a replacement handle for a rolling pin through end-grain.  It did not end up straight.

When I drilled off the lathe and then tried using the dead and live centers I was also drilling end-grain.  That was for a knob for a planer crank handle and it turned out straight. 

A mandrel is a good idea, but I'd need one for every size hole I'd possibly use.

[ESFted]

You might try reversing the piece in the lathe and drilling from each end.  The bit may wander a little so the center isn't a perfect match, but at each end the hole will be centered.

Assuming you are using a drill chuck in the tail stock, you can also purchase a cheap installer bit from the big box and regrind the point like this guy did.

Those bits come in many different lengths, so you can find one that matches your project.

regrind the point.  

[Old Greenhorn]

There aren't a lot of details here. I think you are drilling wood, but not sure what the outside shape is you are holding on. Also not sure what kind of wood. You say 4 jaw chuck so I am assuming those are independent jaws, which means you have to have the piece centered in the chuck both at the front and the rear of the piece, in other words it must be dead straight. Assuming you have that, you have to consider hard spots, not sure how to deal with that. Finally, the cutting too, and here is where I might be of some help. Wood and steel are not all that different from the perspective of cutting tool behavior except that wood might be a bit more forgiving, but the physics cannot be denied, they still exist. So tell us about the drill you are using and how deep you are going? Do you notice a lot of heat on the drill? What do the chips look like and do you have an even amount of chips coming out of each flute? What is the diameter of the drill? Are you using a center drill to spot the hole before you use the drill? What kind of point is on the drill? Is it a 'split point' or just a standard jobbers drill point? Are you using any lubricant? All of these details matter in one way or another in getting you a good hole. I am guessing you are using a relatively small drill to do a deep hole, but that is just a guess. I spent 50 years learning how to get straight holes of various sizes through various depths, in various materials from aluminum to  hasteloy, plastics, stainless, cast iron, carbon, fiberglass, and other stuff. It's a simple question with a complex answer. Give me some of those details and we'll see if we can figure this out.

[Larry]

Drilling long accurate holes on a wood lathe is near impossible with conventional drill bits. 

There are three ways that work.

The first way is to drill the hole with a gouge.  Just push the gouge straight in and it will self center.  Takes a little practice and is the least accurate way of the three.  I sometimes do it with holes no longer than about 6".  It's a fast way to drill.  I like a spindle or detail gouge but others will work.

The second way is with a "D" drill.  The point is in the shape of a D.  I don't think you can buy one, you will have to make your own.  I used O-1 and hardened the end.  Extremely accurate and extremely slow as you can only drill maybe an 1/8" before having to back the drill out to clear chips.  Than you have to keep the drill cool by dipping in water.

Third way is a gun drill.  Gun drills are used in metal working (drilling gun barrels).  They have a carbide tip and high pressure oil goes through a hole in the drill to lubricate and force the chips out.  Extremely expensive new and they might ask a question or two if you try to buy one.  They can be found on ebay used and resharpened all the time for maybe $30.  They have a funky screw thread on one end.  I drill it out and fit a 1/4" plumbing fit so I can run air through it to eject the chips.  I've drilled holes 18" deep with less than a 1/16" variance from end to end.  Making flute bodies.  The drill is just pushed in and self centers.  Really fast, accurate, and a pleasure to use.  The air keeps both the drill and the wood cool so you don't run the risk of the wood checking.  I use mind a lot.

Can't remember, but probably drilling somewhere between 8 to 12" with the drill in the picture.

[21incher]

One thing you may want  to double check is that the tail stock is centered on the chuck. I would check it with the drill in place but no workpiece.  Some  wood lathes need tweaking  on the tail stock for perfect alignment of the 2 centers.. 

[Old Greenhorn]

WOW Larry, that is cool, never heard of anyone using a gun drill on wood or even thought of it. Neat application of the tool and your brain!
 In recent years there have been some major changes in cutting tool design. In fact I would say there has been more radical progress in drilling technology in the last 5 years than there was in the previous 45 that I was paying attention. When I retired back in June we had a job on a machine where we had been drilling 4340 tool steel castings with 3/8" holes 5" deep in about 3.5 minutes a hole. On the day I retired I watched that same machine popping in the same holes in about 45 seconds (yeah, 5" deep in tool steel) and those drills were running over 200 holes before they began to degrade. So there are some new options besides the good old rock solid gun drill now. Of course, they come at a price none of us guys can pay to play with. (Those drills I just referred to are about $195. a pop.) However there is a lot to learn from the way these drills are pointed and sharpened, and this little detail I have been able to replicate to my own advantage on even cheap drills. True, you really need to have some good grinding experience and hands that can follow the wheel and there is plenty of trial and error, but you know when you hit it, for sure. Drills come down to a few different basics, thinning the web, relieving the pressure on the center, balancing the load on the lips, lip angle, chip clearing, etc. If these are observed and corrected, things improve. Not something I would expect the average skilled guy to pick up without a rabbi helping him/her along the path. Cutter grinding is a black art in many ways. ;D

[low_48]

Perfection is rarely achieved when boring an end grain hole. Well really rarely achieved at anything in life!

[Phenoix66]

What kind of wood are you drilling into?

[Joe Hillmann]

If the hole is a big enough diameter you can drill it underside then use some type of boring bar to open the hole up to the size you want.

[mike_belben]

Bore the hole first, then turn the OD using an expanding arbor in the chuck and a center in the tailstock.  


The bigger the bore diameter the easier to get straight, especially if you can get away from deep flutes.  A 2 flute twist drill is flexy and walks around hard spots if it can.   A 4 flute endmill or reamer is much more rigid because it has a thicker cross section with more even dispersal of the material north south east and west, not just in 2 directions.  It would help a lot to pilot the hole by pecking with center drill or a spot drill.  They have very little flute to hold chips and will be a pain to continually clear out but theyll walk in pretty straight thanks to a solid shank that resists deflection.

Then you come in behind that with a pilot tipped reamer or a pilot tip drill or even end mill to bore final size.  If the hole is too deep you make extensions from drillrod with a setscrew biting into the turned down shank of your finish drill, or pressfit and brazed if its too thin for a setscrew.   If the finish drill is .500" the extension should be like .490" OD for example.  

[SwampDonkey]

Is it that you can't find centre of a round? If so, use a center gauge. I use 7/16" forstner bits to drill holes for pulleys on drill press. They slip on 3/8" rod.

Center gauge