Tailstock Upgrade

[iclark]

Johnathan,

I've been reading about pen turning but have not tried it yet. so maybe I don't understand. if I am off-base, I would like to learn.

that said, if I understand the process correctly, you are
1) taking a (relatively speaking) long slender piece of wood that has not been turned yet,
2) chucking it up on one end,
3) spinning it,
4) extending the quill to drill a hole down the center of the slender piece of wood.

it seems to me that whatever the end of the slender piece touches first is going to try to act like a dead center
and flex the piece so that it revolves about that point.
with a brad point bit, it seems that one of the spurs will almost always touch first (even if the blank is perfectly balanced and not whipping as it spins) and you will get that funnel shape at least until both spurs are engaged and cutting. this would happen no matter how stiff the lathe system is.

if I got the problem right (and whipping isn't too bad), you could get what you want by starting with a small regular drill where the distance across the tip flutes is smaller than your required tolerance. drill a short pilot hole. use regular drills to reach your desired hole diameter (going to larger sizes where the tip flutes fit inside the existing hole so that it doesn't try to walk by flexing the blank). once you have the shallow hole the same diameter as your desired through hole, switch to the brad point and finish the job.

if I have it right, the part that bothers me is - how do you get the blank balanced enough that it doesn't whip when you just have it chucked at one end? I thought that was the whole point of using the pen mandrel.

Ivan

[RobertTaylor]

the fastest and easiest method would be to (A)cut the blank long enough to trim the end after drilling. (B)more precise drill can be accomplished by using a center drill on both ends of the blank then mounting the blank between centers, turn it round, then mount in a scroll chuck, then drill and glue in the tubes. square the blank to the tubes, mount on the mandrel or between 60 degree centers and turn the blank. having done over 200 pens with plan A, plan B seems like a lot of extra work.

[JPG]

IS YOUR BIT BENT?????

[grauenwolf]

I just don't know why the entry point of a drilled out tube would become larger than the end point. I have no explanation for this at all. Not even a guess.

Like I said in my original post, it is due to the flex in the tailstock. Instead of being perfectly horizontal, the tip of the drill bit sags ever so slightly.

Once it start drilling, it centers itself. That's why it looks like a funnel, complete with a long, perfectly straight segment throughout most of the length.

Jonathan

[grauenwolf]

IS YOUR BIT BENT?????

Nope. But all metal is flexible, which is why shorter drill bits are preferred when doing this kind of work.

Even when I'm spinning round stock 1 1/2" thick, having it hang out 4" without a center to support it will cause it to bend.

[charlese]

Like I said in my original post, it is due to the flex in the tailstock. Instead of being perfectly horizontal, the tip of the drill bit sags ever so slightly.

Once it start drilling, it centers itself. That's why it looks like a funnel, complete with a long, perfectly straight segment throughout most of the length.

Jonathan

Well, Jonathan - This is a first for me! After making sure your tailstock is tight in the base arm - secured with the Sleeve and Insert assembly - the tailstock should only wiggle a very small amount. After inserting your chuck arbor and setting it firmly into the tail stock, there should be no wobble at all on this part, nor on the chuck, nor with a tightened drill bit.

I fail to envision how there would be a sag of the drill bit (forward movement of the tail stock) enough to cause a drill bit to shift from a lower position to a high one upon moving the wood into the bit. If there is that much play in your tightened tail stock - it's time to check out the hole diameters in your Base Arm (part# 518381 $51.40) Elongated/ out-of round holes could possibly cause this problem, but they would have to be way out of round.

If your tail stock wobbles after tightening it in place - call Shopsmith for assistance after measuring the diameter of the tailstock legs, and the inside diameter of the mounting holes in the Base Arm.

[charlese]

Nope. But all metal is flexible, which is why shorter drill bits are preferred when doing this kind of work.

Even when I'm spinning round stock 1 1/2" thick, having it hang out 4" without a center to support it will cause it to bend.

How much bend are you talking about? .000001"?

[dusty]

Nope. But all metal is flexible, which is why shorter drill bits are preferred when doing this kind of work.

Even when I'm spinning round stock 1 1/2" thick, having it hang out 4" without a center to support it will cause it to bend.

Machine tolerances may allow it to shift position an unacceptable amount but I have a hard time accepting that it bends that much.

[a1gutterman]

Machine tolerances may allow it to shift position an unacceptable amount but I have a hard time accepting that it bends that much.

And also the implication that it flexes back. Once bent, why wood it flex back? It sounds more like something is loose, or as Chuck was suggesting, the holes in the base are enlarged.

[grauenwolf]

Machine tolerances may allow it to shift position an unacceptable amount but I have a hard time accepting that it bends that much.

A 16th of an inch, maybe just a 32nd. It isn't much, but when you need a tight fit it ever bit counts. And of course any flex in the tailstock is multiplied by the length of the bit and chuck.