Drilling dowels center on a lathe

[Andrew Stenvall]

Hi all,

I am currently having some issues getting my new grizzy G0462 lathe centered. I have a 4 claw square chuck on the headstock, and a chuck with my 7/32" drill bit. My dowels are 1/2" OD (drilling 2" into the dowel and whenever I chuck up my piece of wood and turn the wheel on the tailstock to slide the drill bit, my holes are always inconsistent. I have experimented for days with a drill press and a pen centering jig but have not had success with that either. Is there something I am missing where with the lathe or is there a way to correctly calibrate the wooden dowel so that it meets dead center on the bit? I have read about parabolic bits, but unfortunately they do not make 7/32" like I need. Any advice would be much appreciated!

Thanks,
Andrew

[John Aperahama]

How accurate do you really need to be? What type drill bit? I always use forstner.
I do this a lot 3/8 in 5/8 always seems to be minor wander. To prevent jaw marking on stock dowel i split a piece of sch 40 and found it did help some. Have you checked actual centering on your 4 jaw chuck?

[Mike Henderson]

You might post this in the turning forum - you'll probably get better suggestions.

Mike

[Sid Matheny]

You will get much better results if you start with a center drill so to give it a better center place to start drilling.

335278

[Shawn Pachlhofer]

use a collet chuck to hold the dowel

far more accurate than a 4-jaw chuck

[Brice Rogers]

I think that you have already received some good advice from several people. Here are a few things to add:

Right now you don't seem to know the source of your error/problem. It could be an imprecise chuck, misalignment of your tailstock, a bent or wandering drill bit, etc. Some things I'd do:

1. Use a pencil to mark the dowel. If the circle or point isn't dead-on and concentric with the OD, your chuck is imprecise. A collet (which another poster mentioned) would also solve this issue.
2. I sometimes make a dimple with a center punch to help start the drill in the dead center. If you make a dimple and the drill doesn't line up right or wobbles in the dimple, your tailstock isn't lined up
3. Brad point bits tend to wander less than regular drillbits. Forstner bits (like another poster mentioned) are also pretty good.

Check those things out and if you are still having problems, come back with more info.

[Al Launier]

Have you tried using a dial indicator to confirm that when the lathe chuck is tightened on the dowel that the dowle is rotating concentric with the lathe spindle? Same with the tail stock by running the indicator around the dowel to confirm they are concentric with each other.

If both ends are concentric to one another, check the travlel of the tail stock to be sure it's moving parallel with the C/L of the lathe spindle. If it isn't you probably you may have to adjust the gibs on the tail stock or shim them.

Finally, since the problem appears to be common for both the lathe & the drill press. It's possible the the drill was sharpened incorrectly. If one cutting edge of the bit is longer than the other that would cause the bit to cut oversize.

[John K Jordan]

First, be sure to use a good Jacobs chuck to hold the drill bit. Some cheaper chucks are not so good. You can check it by mounting it in the headstock and check the runout on a length of drill rod held in the chuck.

A dril bit can easily get started a little off, often due to the irregular grain on the end. If it gets started wrong it just gets worse as you drill deeper.

I get far better holes if the bit gets started exactly in the center. One way is to use a parting tool or use a skew chisel as a scraper and turn a small conical depression in the end, then drill.

Another way works well: drill a starting hole with a machinist's center drill bit. These bits are short and can't flex like a long drill bit. They are cheap, too: http://www.amazon.com/Triton-Industrial-Premium-Combined-Countersink/dp/B004MOJVKU

Make sure your tailstock quill is not over extended which can allow play. To minimize errors due to play in the quill, I lock the tailstock and drill a little bit. Then back off the quill, unlock and slide the tailstock forward, lock and drill some more.

Another thing I keep in certain sizes for drilling are taper shank drill bits. These have a morse taper that fits directly into the lathe eliminating the Jacobs chuck completely.

A completely different way to get a perfectly concentric hole that works for some situations: start with a piece of wood with a larger diameter, drill a hole, then mount the piece on a sturdy steel mandrel or pin chuck and turn it to the desired diameter.

JKJ

[robert baccus]

Most 4 jaw chucks have an inner set of jaws for smaller items. Usually overlooked.

[Dick Strauss]

Make sure your headstock drive spur and tailstock livecenter points line up before you do anything else. If they don't align, fix this issue first (which could be caused by a lathe twisting/leveling issue).

Assuming the points line up, mark the center using a center finder making at least 3-4 lines with a fine pencil. Use an awl or similar...push and wiggle it to make a center dimple of a decent size. Have the end of the wood dowel with the dimple that will be drilled as close to the chuck face as possible. In other words, put most of it into the headstock spindle MT so that most of the dowel is not visible (the further out from the chuck you are the more likely you are to get runout!). If you have a dowel 2" long, this shouldn't be a problem. If it is 12" long you need to choose a different method than what I suggest. Use split PVC pipe as already suggested for a cheap collet substitution (the pvc will distribute the load to more surface area of the dowel and keep the dowel from being crushed and wandering/flexing off center when you tighten the 4 jaw chuck). Use a center drill in a drill chuck that has a draw bar tightened to the tailstock to get started as previously stated. If you've got them, start with a smaller center drill and step up to a larger one drilling deep enough in a pulsing fashion to engage the angled cutting surface of each to guide the next largest bit. Finally finish with the shortest drill possible (so that it has less flex) that is an appropriate size for your needs (also done in a pulsing fashion). It will never be perfect (DBO) because we are talking about a wood lathe but should get you pretty close to center with this method.

If this is somthing you need to do often, you might consider making (or having made) a jig to hold the dowels centered on the lathe. It could be a block of wood with jaw index marks and a 1/2" hole drilled in the center. The wood should be as stable as possible and finished on all sides to help prevent seasonal movement. It could be a faceplate with a heavy steel tube stepped into and welded/bolted to the face to hold the dowel centered...

If you need something perfectly centered, you need to start with a larger dowel and turn it down to size to account for a center that may not be perfect. This obviously has its own set of challenges.

Good luck!

[Marvin Hasenak]

I drill and tap a block of wood and then make a collet like chuck that screws on to my spindle. I drill a hole the size of my dowels and cut 2 slots and use a hose clamp to clamp the dowel in place. I keep the "chucks", because I use a lot of 3/4", 1" and 1.5" dowels to make game calls. For the drilling process I start with a center bit as described above, then a stubby bit, finally the longer bits. All of the holes must be centered, with the other size drill bits, I start with a 9/32 all the way through, then drill with a 3/8 for 1/2", then reverse the dowel in the "chuck" and final drill with a 5/8" bit for 2".

In my case the drilled holes must be centered with the others or they stick out like a bleeding thumb. In most cases out of 48, I will have about 45 or 47 that are good, and a few rejects. Not a perfect method, but the homemade "collet chuck" gets me pretty close or at least with a 90% success rate.

[Stan Calow]

I had a similar problem and posted question in the Turning forum, and got a lot of good tips, like starting with a drive center. My head and tail stocks lined up just fine, but when I put a drill bit in the chuck, I could see there was a bit of dangle at the tip of the bit which caused enough wobble to make the hole oversize. I corrected with shims under the tailstock, but still requires a bit of fussing to keep drilling straight.