Drill bit wobbles while drilling on the lathe

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jasonmac73

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Has anyone experienced their drill bit wobbling while drilling on the lathe. It appears my quill has a slight movement to it. Is there anyway to tighten the quill in the tailstock so that there is no play without locking it down. I lock it down and no play but obviously I can't drill then.

I have a Nova Comet II
 
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My suspicion is that there is some hysteresis in your tailstock, with the result that the bit isn't absolutely centered when you start drilling. When that happens, you will see some wobbling and/or flexing of the drill bit.

The best was to address this problem is to first create a small dimple exactly on center in the turning. Then, before starting to drill, make sure that the tailstock quill has extended just a bit - just enough to make make sure that the jacobs chuck taper is fully inserted into the quill and is locked in place. Finally, make sure that the drill bit is centered exactly in that dimple before locking down the tailstock.
 
Roll your drill bit across your work bench or table saw table to see if it's bent. That's usually been the cause of bit wobble when I've experienced it, especially if you are using a 7mm bit, although I did have a 10mm bit with a bend in it.
 
I suspect that my Jacobs chuck has a little runout, I have found that I can rotate the chuck until the bit is more accurately centered for better drilling. I rotate about 10 or 20 degrees and recheck until I get the best result. Obviously I have something out of alignment, but this added step gets me close enough. Might be worth a try...
 
Thanks for the ideas. I've had the jacob chuck for a long while and use it for mounting 2" sanding disk, to buffing wheels, to drilling. It may be that. The drill bit is rather new and straight because it turns perfect on my drill press. Drill press only has 2" plung so not working to drill holes in blanks.
 
I just re-adjust the pen blank further up on the drill bit and that allows me to drill deep enough for what I want. Just make sure you have the blank marked so it goes in your clamp in the same direction. This works for me.
Tim.
 
Jason; This is an alignment routine I wrote up some time ago. It can be used to check the alignment of the head stock to tail stock. As others have said, the problem may be the drill bit or jacobs chuck. Put the jacobs chuck in the head stock, position the tool rest very close to, but not touching the rest and turn the lathe BY HAND. Watch the spacing between the tool rest and bit. If it changes, investigate to figure out what is causing it. Lastly, inspect the tapers on the head stock, tail stock, chuck and jacobs chuck for any bumps or uneven-ness or crud. It takes very little to throw off the alignment.

Hope this helps.
 
randyrls said:
Jason; This is an alignment routine I wrote up some time ago. It can be used to check the alignment of the head stock to tail stock. As others have said, the problem may be the drill bit or jacobs chuck. Put the jacobs chuck in the head stock, position the tool rest very close to, but not touching the rest and turn the lathe BY HAND. Watch the spacing between the tool rest and bit. If it changes, investigate to figure out what is causing it. Lastly, inspect the tapers on the head stock, tail stock, chuck and jacobs chuck for any bumps or uneven-ness or crud. It takes very little to throw off the alignment.

Hope this helps.
Click to expand...

Thanks for the advise. I just took the quill apart and cleaned but still does this. The Nova chuck screws on so no issue with debris in the taper on the head stock. I'll check the jacobs chuck. It's not a real expensive one or anything. It could be off.
 
monophoto said:
My suspicion is that there is some hysteresis in your tailstock,
Click to expand...

This is a fairly common issue with less expensive lathes. What frequently happens is that the extension on the bottom of the tailstock casting that aligns the tailstock to the bedways of the lathe is very slightly narrower than the spacing between the ways. As a result, the tailstock can rotate very slightly about a vertical axis - perhaps only a degree or two. But that means that the alignment between the headstock and the tailstock in the horizontal plane can vary depending on where the tailstock is in that very narrow angle of rotation.

If you are drilling, and the headstock and tailstock axes are not bang-on aligned, the drill bit will enter the piece at a very slight angle. If you are drilling very slowly with a fairly robust bit, you will get a hole that is very slightly conical rather than a pure cylinder - an error so small that in most cases you won't notice it. But if you are using a small bit (which will be more flexible), you may see visible wobble in the bit. And in extreme cases (such as drilling a deep, small hole when redressing BIC pens), the bit can wander off axis ending up with a hole through the side of the blank (DAMHIKT).

I suppose it might be possible for a good machinist to add shims on the bottom of the tailstock to correct this problem, but I'm not a good machinist. Instead, I've found that making sure that the tailstock jacobs chuck is firmly seated in the taper in the ram, and also making sure that the bit is centered in a center dimple in the workpiece before locking down the tailstock, will essentially eliminate the problem.
 
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I use a center drill bit to create the starting dimple in the end of blanks, got mine from HarborFright link

These bits are very resistant to bending -- even if they don't hit the exact center of the spinning blank, they'll cut using one edge and you end up with a perfectly centered (but slightly larger) starting dimple. Of course, that also gives you advance warning that your drill bit is not going to hit center so you should be on the lookout for reasons why things are out of alignment.
 
Center drill is good idea. When putting the tail stock in place, you may want to try pushing it against the way, or pulling it against the way then lock and see if either way makes a difference. Wood lathes are not presicion machines for drill dead on.
 
monophoto said:
monophoto said:
My suspicion is that there is some hysteresis in your tailstock,
Click to expand...

This is a fairly common issue with less expensive lathes. What frequently happens is that the extension on the bottom of the tailstock casting that aligns the tailstock to the bedways of the lathe is very slightly narrower than the spacing between the ways. As a result, the tailstock can rotate very slightly about a vertical axis - perhaps only a degree or two. But that means that the alignment between the headstock and the tailstock in the horizontal plane can vary depending on where the tailstock is in that very narrow angle of rotation.
Click to expand...

I never realized it but it does pivot left and right ever so slightly. Really sucks when a $500 tool is considered cheap. I have my eyes on a Laguna revo 18/36. I know that is overkill but I turn other stuff as well. I only got into penturning because my wife wanted one and they are so easy to sell. Pens support my bowl habit. LOL
 
Paul in OKC said:
Center drill is good idea. When putting the tail stock in place, you may want to try pushing it against the way, or pulling it against the way then lock and see if either way makes a difference. Wood lathes are not presicion machines for drill dead on.
Click to expand...

The bits I use for drilling my blanks are brad point bits. They are nice.
 
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I had a somewhat similar issue with my Comet II. The main issue was with the fit of the tailstock to the lathe bed, or so I thought. Finally, I noticed that the hole, through which the tailstock tightening bolt goes, was oversized and mostly egg shaped to one side. That caused the tailstock to misalign as it gets tightened into place.

I got a 1/2"x3/8" flanged bushing and drilled it out to 25/64" ID and inserted that into the egg shaped hole. Now, my tailstock does not move sideways when tightening down and I get arrow straight drilling every time.

Check the hole in your tailstock and, if necessary, true it up with an appropriately sized bushing.



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Most of the alignment issues have been addressed and agree with the use of a center drill. Another thought, don't allow the spindle tightener on the tailstock to be too loose or the spindle will wobble. Just loose enough to allow the spindle to travel as you drill.
Gordon


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A good way to check alignment between stocks, use a center in each end and lightly clamp a small metal rule between them. The rule will exaggerate the misalignment both side to side and up and down. Testing will help you know if you should push or pull the tailstock to get better alignment when you clamp it down. Also test with tail stock in and extended to see if there is a difference implying the tail stock is twisting with respect to the headstock.

"Really sucks when a $500 tool is considered cheap."

I have a mini metal lathe that cost $400 and is very accurate and adjustable to keep it there. But it's only a 7" x 10" lathe. Wood lathes aren't meant for turning consistently to 0.001" precision along the length of what your turning. You paid for a bigger frame and stronger motor with a solid rest to point sharp things at turning wood.

You could also have a bent drill bit or one sharpened unevenly. I also have better luck with a conventional drill bit designed for drilling metal than a brad style bit for wobble and crooked holes.

Danny
 
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