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Problem with center boring

John Torchick

John Torchick

Joined
Jan 24, 2010
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Cleveland, Tennessee
I have attempted to make some small parts for a winding check for a flyrod. That's the part in front of the grip where the butt wrap threads start. I bore the hole but when I turn it down, the hole is off center. It is me? Lathe not level or what? Thanks in advance for your help.
 
Exactly what he said. I can never get a drill to follow the exact center. boring the hole first and then mounting it on a wooden mandrel to turn the outside works great.
The only way I know to get a hole perfectly centered would be to do the reverse. Turn the outside and then put that in a chuck or collet and then turn the inside. Of course that means that you have to protect the outside while you turn the inside. Much easier to do then inside first.
 
john lucas said:
Exactly what he said. I can never get a drill to follow the exact center. boring the hole first and then mounting it on a wooden mandrel to turn the outside works great.
The only way I know to get a hole perfectly centered would be to do the reverse. Turn the outside and then put that in a chuck or collet and then turn the inside. Of course that means that you have to protect the outside while you turn the inside. Much easier to do then inside first.
Click to expand...

Same here, I rough my tool handles turning between centers then mount the handle in the chuck. I mark the center of the end of the tool handle facing the tail stock and use the tail stock to help align the handle in the chuck. After the hole is drilled, I true the outside of the handle and finish it.
 
The reason for your problem is your lathe and not you. There is an angular misalignment between the tailstock centerline and the spindle centerline. Unfortunately, there is no easy fix nor for that matter any easy way to determine how much angular misalignment exists.

It appears that most turners mistakenly assume that if the points match on a drive center and tailstock center that everything is hunky-dory. However, that check only tells you how much radial misalignment exists. It does not give you any clue about the amount of angular misalignment.

For lots of things, angular misalignment doesn't matter, but for a few things such as drilling on the lathe in which the drill chuck is rigidly mounted in either the headstock or tailstock, the angular misalignment can be an issue.

One other bit of machining advice regarding drilling on the lathe -- even though you see turners sometimes drilling from the tailstock with the work piece rotating, it is always better to drill from the headstock. The reason is that angular misalignment will cause binding due to side loading of the drill which leads to the hole being wallowed out larger than the drill diameter when the work piece is rotating and the drill is stationary. On the other hand, when drilling from the headstock and the work piece fixed, the hole size will be true and circular even though angular misalignment might mean that it is not always concentric with the exterior diameter.

The best solution in your case sounds like the earlier suggestion of drilling the hole and then mounting the workpiece on a mandrel that runs between centers.
 
Does anyone know how to check or measure angular misalignment. I've had this discussion with a machinist but I don't actually know how to measure it. I am especially interested in how to measure the headstock vs the Bed alignment but would also like to know about the tailstock.
 
Thanks to all. The hole I was drilling was about 7/16; don't have a mandrel that size. I'll see what is available in drill rod. I'll do some experimenting and see what works best. Or........talk the Better Half into a new lathe?
 
don't need mandrel

You don't need a mandrel per se. Use tapers on both ends, one held in the chuck and one butted against the live center. This is the same method I use when turning kaleidoscope barrels and such.

Vernon
 
john lucas said:
Does anyone know how to check or measure angular misalignment. I've had this discussion with a machinist but I don't actually know how to measure it. I am especially interested in how to measure the headstock vs the Bed alignment but would also like to know about the tailstock.
Click to expand...

I'm not sure hoe to check for it but I have a ornamental turning system from tecknatool and to allighment it up you have to put in a dual mt2 bar into the head stock and OT system but be careful they offer a nut to eject it from the OT system to pop it out but refused to pay +$50 for it so I just got a 1 1/4 nut with a wash between the alignment tool and nut to eject it out. check it out at https://www.teknatool.com/old/spare_ordering_page.htm
it's called 2 Morse Taper Acruline System
This double ended morse taper acruline system can be fitted onto your lathes existing Tailstock. This product is used to check the alignment of your lathe
 
You can sometimes use the drill bit as the mandrel. I have done this several times. You may have to put some tissue paper or tape on the bit to make it hold the wood well enough. don't put a lot of pressure on the wood when turning this way. Drill bits were not designed for side loading.
I use a chuck with jaws that go down this small to hold the drill bit. What you could do is simply drill a hole in a waste block attached to a faceplate. Then simply loosen the drill chuck and leave the bit in the wasteblock. Insert your wood on the drill bit shank and turn it.
Another option would be to glue a piece of 5/16 all thread into the wasteblock. Then you could use nuts to tighten up on both sides of the wood to hold it in place. turning up to the nuts would be kind of tricky but doable if you just approach the nut very slowly. Ideally I would center drill the loose end of the rod and bring up my tailstock.
Wooden mandrels are easy to make. I do it all the time. They have the advantage of being able to taper the far end just a hair so it holds the piece better. Just put a piece of wood with the grain running parallel to the bed on a faceplate. turn down the front to 7/16. test fit the piece periodically until you get a snug fit. Then push the wood on and turn it.
 
John Torchick said:
Thanks to all. The hole I was drilling was about 7/16; don't have a mandrel that size. I'll see what is available in drill rod. I'll do some experimenting and see what works best. Or........talk the Better Half into a new lathe?
Click to expand...
John
You can put some of that polyethylene on the mandrel you normally use, then taper it down to less than 7/16 or cut a 7/16 tenon on one end to make a pair of bushings. That's what I use. Or drill out some pecan and do the same. I fyou need more of the plastic let me know.
Dean
 
John, measuring the angular misalignment would probably require some expensive lab equipment such as a theodolite.

The double ended Morse taper gives me the willies. If your spindle and tailstock bores do not line up wthin a couple ten thousandths of an inch (and it is a dead certainty that they won't) then there will be binding in these high precision machined tapered surfaces. This would be analogous to using a skew as a pry bar ... uh, wait, bad analogy. :D
 
In John's original post he used the term "bore" but all subsequent references were to drilling.

Drilling a deep hole that is centered, even on a precisely aligned metal lathe, is an iffy proposition -- especially with a twist drill.

The only way to make a deep straight hole is to use a boring bar: tough to do freehand on a wood lathe!

So the most practical solution is the advise to drill it first and them mount it on a mandrel or between centers and turn the OD true.

I would not bother trying to realign your lathe, even if it is dead straight varying density in the wood (among other things) will make a drill wander off center on deep holes.
 
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