Lamp boring bit guide difficulties

[MacG]

Greetings All,

I have a lamp base to bore that is about 14" tall. I noticed that the tailstock bore/knockout hole has a bit of play with a 3/8 bit in it. So I decided to make a bushing to guide the bit shaft while the lamp base spins. I made a morse taper between centers out of white oak to fit the tailstock. After fitting the tailstock with the plug I made, I used a drill chuck in the head stock with a 3/8" Forstner to drill clear through the plug leaving a nice tight straight hole through the plug, right? Well it seems straight through but it is off center in the plug. I repeated this three more times with slight variances like making not a true taper but a tight at the ends only as it it not holding anything spinning but the same offset hole every time. Varied the length and type of drill bits. The results are consistently off center.

I checked alignment with a dead center and a spur drive and I get point to point alignment on my Nova Comet II.

Any Ideas? I mean germane to this

 

[Charlie_W]

Hi Mac,
A several thoughts come to mind here. I think the answer could also be a combination of factors.
First, you say the spur and tailstock drive point match up. This would be with the tailstock slid towards the headstock. If your lathe is bolted down, the surface to which it is attached may not be all on the same plane. Perhaps the tailstock end of the lathe is ever so slightly twisted in relation to the headstock. When you slide the tailstock away from the headstock, it's axis may change.

You are using oak which has an open grain and the drill bit may be following softer grain. Using a forstner bit, you would not have used a starter bit as with a twist bit. The forstner bit may have simply followed the softer grain.

Make sure he Morse tapers are clean of debris.

You may try using a piece of maple for your sleeve. After turning the Morse taper, mount this new piece in the headstock, put your drill chuck in the tailstock and drill. See how this does. Make sure the end of your newly turned Morse taper is turned square. In re reading your post, you turned the Morse taper between centers.....without squaring the end to be drilled, your forstner bit may have had some play where it's point fit into the recess left from your spur or live center point allowing it to drift off. If the end was not square, that can push the bit also. Square the end before drilling.

Your drill bit may not be true. The length of the drill chuck plus the bit will increase any error in the alignment between the head and tail stock.

Also, the tail stock usually has some play where it mounts to the bed/rails of the lathe. There can also be play in the quill when it is not locked down...such as when drilling.

With all these chances of error, you can see how you could have a stacking effect of more than one item combined with others can cause your off center issues.

A little detective work and a change in wood may help get you on the straight and narrow!

Good luck with your lamp drilling!

 

[KenV]

Charlie missed the runout on the drill chuck and taper. Some of the "value" units can have 25 thousands runout. Precision comes with a price.

You did not comment on if your live center will support the dril bit. The robust live center is built to fit 3/8 through the center. The Nova live center with interchangable will also support a drill bit (do not recall the size but used it several years ago.)

Last -- I drill the other way using the headstock to hold the mt taper, truing the face, and creating a starting hole with either a small gouge or a center bit before drilling.

Drill smaller and redrill. I commonly hand hold the chuck as the bit wants to drill straight.

 

[Charlie_W]

Charlie missed the runout on the drill chuck and taper. Some of the "value" units can have 25 thousands runout. Precision comes with a price.

You did not comment on if your live center will support the dril bit. The robust live center is built to fit 3/8 through the center. The Nova live center with interchangable will also support a drill bit (do not recall the size but used it several years ago.)

Last -- I drill the other way using the headstock to hold the mt taper, truing the face, and creating a starting hole with either a small gouge or a center bit before drilling.

Drill smaller and redrill. I commonly hand hold the chuck as the bit wants to drill straight.

Thanks Ken!
The drill chuck variables did cross my mind but didn't make it out my fingertips!
Yup, agree with wood to be drilled being in the headstock....maybe I didn't make that clear....a centering divot for sure with twist bits!

 

[MacG]

Hi Mac,
A several thoughts come to mind here. I think the answer could also be a combination of factors.
First, you say the spur and tailstock drive point match up. This would be with the tailstock slid towards the headstock. If your lathe is bolted down, the surface to which it is attached may not be all on the same plane. Perhaps the tailstock end of the lathe is ever so slightly twisted in relation to the headstock. When you slide the tailstock away from the headstock, it's axis may change.

You are using oak which has an open grain and the drill bit may be following softer grain. Using a forstner bit, you would not have used a starter bit as with a twist bit. The forstner bit may have simply followed the softer grain.

Make sure he Morse tapers are clean of debris.

You may try using a piece of maple for your sleeve. After turning the Morse taper, mount this new piece in the headstock, put your drill chuck in the tailstock and drill. See how this does. Make sure the end of your newly turned Morse taper is turned square. In re reading your post, you turned the Morse taper between centers.....without squaring the end to be drilled, your forstner bit may have had some play where it's point fit into the recess left from your spur or live center point allowing it to drift off. If the end was not square, that can push the bit also. Square the end before drilling.

Your drill bit may not be true. The length of the drill chuck plus the bit will increase any error in the alignment between the head and tail stock.

Also, the tail stock usually has some play where it mounts to the bed/rails of the lathe. There can also be play in the quill when it is not locked down...such as when drilling.

With all these chances of error, you can see how you could have a stacking effect of more than one item combined with others can cause your off center issues.

A little detective work and a change in wood may help get you on the straight and narrow!

Good luck with your lamp drilling!

All good points. As for truing the face, given the light pressure it takes to turn something like this, I parted it off but that left a bit of a stem to drill through...I suppose it could have coerced the bit to travel. I like the idea of putting it into the head stock to true it up and will give that a go as well as using a small stick of maple. The odd thing is that the hole is off center in the large end of the taper without the tell tale sloped opening of a wandering bit and the hole on the small end is out by the same amount adding the distance of the taper, so it it drilling straight just off center. My results were consistent for all four pieces. I, of course, did not mark the position of the undrilled wood in the tailstock - you know, just to make it interesting...yeah, yeah, that's it.

Now I am leaning towards the alignment. There is slop in the ways and when I was checking with various centers I found that when I pull he tail stock tight to the operator's side of the ways every thing lined up. BUT that is when, like mentioned, they are close together. Not sure how to check them for alignment once far apart? Pin point laser? More over, this head stock has the left feet of the assembled lathe resting on the bench and is bolted perpendicular to the ways/bed. Something could be very well twisted. Maybe the bed machining is not true 90 degrees where it mates to the headstock...

I could do a double taper like the metal ones used for the lathes with the rotating heads and see how they slide together.

The lamp base is an unfinished redwood burl that my Grandfather made but never completed. I only get one shot at this drilling. I am going to get some 2x2 or 4x4 to practice with :glasses-cool:

Thanks for your input,

 

[MacG]

Charlie missed the runout on the drill chuck and taper. Some of the "value" units can have 25 thousands runout. Precision comes with a price.

You did not comment on if your live center will support the dril bit. The robust live center is built to fit 3/8 through the center. The Nova live center with interchangable will also support a drill bit (do not recall the size but used it several years ago.)

Last -- I drill the other way using the headstock to hold the mt taper, truing the face, and creating a starting hole with either a small gouge or a center bit before drilling.

Drill smaller and redrill. I commonly hand hold the chuck as the bit wants to drill straight.

Live center. Hmmm. Have to check that. There is a recess in the bottom of the lamp base that I was going to use to support it. Not sure why I did not think to drill it the 'normal' way that one does on a lathe...probably because it is the normal way

My plan was to support the lamp at the headstock, pinch it between the center and use my power drill to run the bit in and out that way the lamp base does not have to spin on hte wood tenon that I had conceived of using. This still method also vastly reduces the chances of the thing coming loose of the running lathe

Thanks for your input too!

 

[KenV]

There is sold a mt hollow taper for drilling. I have an MT1 from years back. They are dead centers and are lots less expensive than a a live center but work well at slow speeds with a bit of Johnsons Wax. The shell bits sold for drilling straight holes are spendy.


Look at packard or CUSA for costs. Some one here might have one in a drawer if you are not in a hurry. I will give my MT1 away to some one who will use it.


Robust live center is nice, but they are quite proud of it.

 

[Skie_M]

You may also find that using a chunk of vinyl (check the big box stores for their vinyl window stock) may be a better choice than using wood ... might even get some for free from a contractor who is tossing out cutoffs of the stuff.


Making sure you use a sharp bit is also a good idea. If you have a Drill Doctor, use it to touch up your bits and try to ensure that the cutting edges are matched up so that one side is not cutting more than the other, as that side will tend to "pull" the bit in that direction.