Tired of not being able to drill accurately with lathe

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Fish30114

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OK Gang, I have posted about a variety of issues with my lathe all presumably leading to out of center drilling. Even though I find it ridiculous to need to do it, I have gone as far as to order a set of center drills to help get my bits started in the wrong direction. So let me say that the first few blanks I drilled, I drilled all the way through and the hole was pretty accurately centered. But within about 2 weeks time my blanks were being drilled far enough off center that it was borderline if I would have enough meat on the tube to produce a successful turning. So....I have tracked down that I had the wrong insert in my chuck, changed that, and it helped slightly.

At this point I think it is something with my lathe--How would ya'll go about checking that the Headstock and Tailstock were aligned properly? I have simply put a spur drive in the Headstock, and a live center in that tailstock and the points in them seem to line up pretty precisely.

I'm really stumped, and the whole reason for drilling on the lathe, was supposedly--to get better accuracy. Color me frustrated!!

Any feedback/advice welcomed.


Thanks--Don
 
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I use a PSI drill chuck but you have to make sure that your blanks are square on the ends so that they seat tight on the chuck. Also very sharp bits
are necessary.
Hope this helps.
 
How are you drillilng? In general, the best way is to have the blank in a chuck on the headstock (rotating), and the drill bit in a Jacobs chuck in the tailstock (stationary). Its a good idea to also hold the Jacobs chuck with your left hand as you drill - to minimize wobble - and this is essential as you are backing the bit out of the blank to avoid pulling the Jacobs chuck off the taper mount.

How big is the blank? Are you drilling through the side of the blank? If so, the first thing I would suspect is that the blank is shifting laterally as you drill. You can grip a square blank in a scroll chuck, but if the blank is not perfectly square, it will be held on only two faces, and that means that it can shift laterally (or to be more exact, pivot on the two jaws in contact with the blank) as the bit starts to enter the wood. The result of that is that the hole will go through the side of the blank.

One way to avoid that problem is to use special-purpose pen-drilling jaws on your chuck. While those are nice to have, I have found that I can get straight holes without them by putting a tenon on the end of the blank and then mounting the tenon in standard jaws in a scroll chuck. If you have a round tenon, it will be in contact with all four jaws of the chuck, and won't be able to shift.

Another thing that I've found is that you have to find the sweet spot for drilling. What I mean by that is that you have to advance the bit into the blank slowly while allowing the bit to smoothly cut the wood - if you force the bit into the wood, it will attempt to follow the grain of the wood leading to an off-axis hole. On my lathe, I advance the tailstock crank in steps of about 1/2 revolution, with about 2-3 seconds between steps. Also, you don't want the lathe spinning so fast that you build up a lot of heat, but it has to be rotating fast enough to actually cut the wood. I tend to drill at about 400-500 r/min. The bit must be sharp. Putting a little paraffin on the bit helps (but is not a good idea if you are going to glue a tube into the hole).

I also find that using multiple bits helps. I start with a center bit, and then move to a standard jobber-length bit that I mount as far into the Jacobs chuck as it will go leaving a minimum extension. After drilling to that depth, I remount the bit to expose more flute and drill to that depth. Finally, I shift to a longer bit and drill the full depth.

Drill in short bites - in my experience, drilling about 3/4" deep, and backing the bit out of the wood to clear the swarf, is more successful than trying to drill a hole the full depth that the bit can go in one pass.

Finally, drilling straight grain wood is much easier than drilling wood that has some kind of crazy grain that switches direction several times along the length of the blank. Of course, it's those timbers that are most dramatic and make the best looking pens.
 
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Fish30114 said:
OK Gang, I have posted about a variety of issues with my lathe all presumably leading to out of center drilling. Even though I find it ridiculous to need to do it, I have gone as far as to order a set of center drills to help get my bits started in the wrong direction. So let me say that the first few blanks I drilled, I drilled all the way through and the hole was pretty accurately centered. But within about 2 weeks time my blanks were being drilled far enough off center that it was borderline if I would have enough meat on the tube to produce a successful turning. So....I have tracked down that I had the wrong insert in my chuck, changed that, and it helped slightly.

At this point I think it is something with my lathe--How would ya'll go about checking that the Headstock and Tailstock were aligned properly? I have simply put a spur drive in the Headstock, and a live center in that tailstock and the points in them seem to line up pretty precisely.

I'm really stumped, and the whole reason for drilling on the lathe, was supposedly--to get better accuracy. Color me frustrated!!

Any feedback/advice welcomed.


Thanks--Don
Click to expand...

Don to properly help you it would be a good idea to list your steps in the drilling process and include a description of the chuck, drill bits, and methods you are using. You do not drill some perfect and some off center for no reason. The use of a center drill is a step in the right direction but it is only the beginning. Maybe you could post a photo of your set up also. I would highly recommend the PSI drill chuck for drilling blanks. You can put any shape blank in there and it will always drill on center. They have 2 sizes.

Dedicated Pen Blank Drilling Chuck at Penn State Industries
 
Monophoto and Jtheclockman, thanks for the advice, I'll try to take some pics tomorrow, coming down with a bug or the flu, so I'm a pretty weak mess right now.

My method is as following though: I mark center on both ends of my blank--just because--I then use one of two chucks with the same results, a Supernova 2 with Pen jaws, or the Easy wood chuck with the small spigot jaws. Both sets of jaws see to be gripping-and leave marks-on all four sides of the blank--then I put my drill in a keyless Jacobs chuck in the tailstock, I am using Fisch super penmaker bits-mostly--but I have the same results with either type of bits, the other bits I use are whichever ones Ernie at Beartooth Woods or Ed at Exotic blanks sell for the occasional kit I build which I don't have a Fisch bit for. I never drill out the side of the blank, but it is enough off center that it is quite obvious that it is off center, and measurable as well. If it was just a fraction off it wouldn't bother me, but it is quite a bit off center on the far side-the side opposite from the side I start on. I usually take about 3/4" bites as I drill and then clear the flutes. I am pretty diligent about not letting the Jacobs chuck get pushed out of the Morse taper it's in, although I do not drill with my hand on the chuck, but certainly am willing to! I hope this tells enough about my process, it seems rather straight forward-just not centered!!! Oh and one other detail, I drill at 450 to 500 RPM's.
 
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Have you checked to see if the jacobs chuck is running true.Also check to see if the chuck is hold the bit straight.
 
If your drill bit does not 'wonder' at the start and goes pretty straight, the problem could be in the chuck. I am just trying to picture things that happen when drilling on th lathe (which I do not do for pens, but do it almost daily at work in metal). If the bit starts to wonder and wobble at the start, it is not lining up true to the axis. You could make sure that you put a little pressure on the tail stock, either towards the back or pull towards the front so you have a repeatable process. You might also just snug the quill lock screw just a tad to help prevent that from wobbling as you drill. Just my .02 (I almost always use a center drill to start holes in metal, may be the key here)
 
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you said you are "marking the center" - then chucking blank

have you checked that the center that you marked is actually spinning at the centerline of the lathe?

If your blank is not perfectly square and you are only marking the center 2 ways - you aren't actually marking the center - you'd be close, but off just a bit
 
Stick the drill chuck in the headstock with a short piece of drill rod. or a 1/4" transfer punch in the jaws, turn the lathe on slow speed. Is the rod turning true?

Try the same with your Nova and Easy Wood chucks, with these chucks you will need a 3/4 or larger steel rod, or something that doesn't crush under the pressure of the jaws. Does it turn pretty close to true, since these are chucks for wood lathes, close is good enough.
 
It is possible (it was in my case) that the tailstock is the biggest part of the problem.

You can put the drill chuck in the tail stock with a fairly long (12" or more) piece of drill rod, put a 60 degree center in the headstock and see if the end of the drill rod is aligning perfectly with the tip of the 60 degree center.

The drill rod mounted that way will serve to magnify any out-of-alignment problems there might be with the tailstock.
 
Try Dan's method, just because the points of two centers touch doesn't mean the tailstock is "in line" with the headstock. You need to imagine a long straight line going through the center of both the headstock and tailstock.
 
A few notes I found for myself when I noticed off center drilling.

I have a oneway lathe, but i noticed that the farther out I turned the quill in the tailstock, the looser it seemed to be. When I'm drilling, i continually tighten the tailstock lock knob to take up the slack. This drasticly reduced wander.

I was using a keyless chuck, but i noticed one day, that the bits were not sitting quite square in the chuck. When i loosened the bit in the chuck and retigtened, the bit shifted. Only sligtly, but even a little off is a lot at the other end of a blank. I have a spare 5/8" keyed chuck from my drill press wih a #2 morse. I started using that and the bits tigten down the same every time.

I don't know whays wrong with my keyless, one day when time permits, i will examine it closer to see whats wrong.

Another effect I found was drill sharpness. Even if it is only a little dull, depending on material, I have found bits to wander dramaticly. I have gotten into the habit of giving my bits a quick two turns on th drill doctor whenever i use them. Quite often, people don't realize that some of the woods we use are a lot harder on the bits than some of the exotic materials.

The last point, is drilling speed. Not only the rpm, while i do try to keep those low, but more importantly the feed speed. This is a hard one, because the feed speed has to match turning speed. To much rpm and you can heat the bit which can cause the metal and the material to react pulling the bit off center. To fast feeding for the rpms used and you end up pushing harder than the drill can cut which will send the bit of center.

While I personally far prefer drilling on the lathe to my drillpress, i have found it took me some time to get down all the nuances for each material. Sometimes being off a little bit isn't a big deal, but if you just spent a few hours doing up a nice segmented blank, being off center even a few thounsandths can be a disaster.

A little long winded, but I've received so much help here, I have to try and give some back. If you can pull any help from my experiences, I'll gladly share.

Merry Christmas everyone and Happy Holidays
 
I see alot of people have already offered up some advice as to your problem and each has its valid points. These are all things to look at. You do not mention if you do between center turning of your blanks. The reason I point this out is you would have OOR turnings if your lathe is not turning true. Assuming the lathe is fine I would look at a few things and one being those chucks. I never did like pin nose jaws on chucks for holding blanks. If the blank is not square it sits oddly in a chuck like that and surface contact to hold the blank is not true all around the blank so the blank can shift when torque is applied. The chuck I linked to is ideal for what we do.

As mentioned sharp bits are a must. Drilling timber can be tricky at times because of the unknown grain directions and using dull bits can lead them astray as you drill. Holding the drill bit steady especially when starting is a good thing to develop. As I mentioned getting some of those center bits will help. They are short and stubby and will eliminate bit wander when starting.

keeping the quill short as you advance the drill bit will take some of the slop out of that end also. I too like to just snug the holding screw to help there. Keep the bit cool and to do this I always use DNA. Keep extracting the drilling scraps from the hole often. Drill around 500rpm and advance the bit slowly.

I would chuck a blank in the chuck you are using and do not apply the tailstock. Run the lathe and see if the blank turns true. Just because you put the point of the drill bit on the center mark you made does not mean it will drill straight down the blank in the same spot especially if the blank is not square and sitting in the pin jaws squarely. square is the key word here. Again that is why that chuck I linked to is the perfect chuck because it makes up for that because it is touching 2 opposite sides of the blank and that is the center of those 2 points is what you are drilling through.

I am sure there are enough good points given in this and each others responses for you to start correcting your problem. Good luck.
 
monophoto said:
How are you drillilng? In general, the best way is to have the blank in a chuck on the headstock (rotating), and the drill bit in a Jacobs chuck in the tailstock (stationary). Its a good idea to also hold the Jacobs chuck with your left hand as you drill - to minimize wobble - and this is essential as you are backing the bit out of the blank to avoid pulling the Jacobs chuck off the taper mount.

How big is the blank? Are you drilling through the side of the blank? If so, the first thing I would suspect is that the blank is shifting laterally as you drill. You can grip a square blank in a scroll chuck, but if the blank is not perfectly square, it will be held on only two faces, and that means that it can shift laterally (or to be more exact, pivot on the two jaws in contact with the blank) as the bit starts to enter the wood. The result of that is that the hole will go through the side of the blank.

One way to avoid that problem is to use special-purpose pen-drilling jaws on your chuck. While those are nice to have, I have found that I can get straight holes without them by putting a tenon on the end of the blank and then mounting the tenon in standard jaws in a scroll chuck. If you have a round tenon, it will be in contact with all four jaws of the chuck, and won't be able to shift.

Another thing that I've found is that you have to find the sweet spot for drilling. What I mean by that is that you have to advance the bit into the blank slowly while allowing the bit to smoothly cut the wood - if you force the bit into the wood, it will attempt to follow the grain of the wood leading to an off-axis hole. On my lathe, I advance the tailstock crank in steps of about 1/2 revolution, with about 2-3 seconds between steps. Also, you don't want the lathe spinning so fast that you build up a lot of heat, but it has to be rotating fast enough to actually cut the wood. I tend to drill at about 400-500 r/min. The bit must be sharp. Putting a little paraffin on the bit helps (but is not a good idea if you are going to glue a tube into the hole).

I also find that using multiple bits helps. I start with a center bit, and then move to a standard jobber-length bit that I mount as far into the Jacobs chuck as it will go leaving a minimum extension. After drilling to that depth, I remount the bit to expose more flute and drill to that depth. Finally, I shift to a longer bit and drill the full depth.

Drill in short bites - in my experience, drilling about 3/4" deep, and backing the bit out of the wood to clear the swarf, is more successful than trying to drill a hole the full depth that the bit can go in one pass.

Finally, drilling straight grain wood is much easier than drilling wood that has some kind of crazy grain that switches direction several times along the length of the blank. Of course, it's those timbers that are most dramatic and make the best looking pens.
Click to expand...

Ah feel yo pain.. I had a similar problem. The quote above gives very valuable tips. I also use the PSI blank chuck. We have a tendency to look for a single problem and solution when there can be multiple issues. The problems I had were:

1. Blank was not totally square and you had to do a double take to see it. The blank must be square.

2. Stopped using a brad point bit and found some good quality 7mm short center bits on line.

3. Got a better quality no key drill chuck (South Bend brand). It cost twice what the cheaper wobbily one cost, but worth the price. You have to hold it while drilling to steady it some though.
 
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