Drill is 12.5mm but the hole is 12.8mm....why?

[rodtod11]

Hello,
Thanks for all the help earlier, but now a new question. I had off center holes using my drill press. I went to the Blank Holder from Penn State and am drilling the holes perfectly on the lathe now...with one exception. The holes are always a little too large. I had a 12.5 mm drill from Penn State for the Bolt action pen. Using my drill press the diameter was perfect. But the hole was off center and by the time it got all the way through to the other end of then blank it was so far off center is twas unusable.
So now, with that same bit on my lathe , the hole is perfect as far as centering goes, but .3mm too large. Just enough to make me wonder if I will be able to glue the brass in place.
Any ideas whats going on???

 

[maxwell_smart007]

with the drill press, you're getting deflection (From pressing too hard, or a dull bit)....

I'd say you're getting runout on the lathe - but have you checked the points of a livestock and deadstock in the tail and head stock of the lathe to see if they come to the same point?

 

[ChrisN]

Do you have a calipers? If you do, measure the bit. It is possible that the drill bit is actually too large.

 

[rodtod11]

I did measure with calipers. But the runout on the lathe, how would you suggest I check it? What I do is to place the drill bit against the blank, then slowly rotate the adjustment knob to move the bit out.

 

[edstreet]

If you follow the thread HERE you can easily see how/why this happens. Though the thread talks about bushings, mandrels and shafts the same exact things applies to everything on the lathe. Head to tail of the lathe, every tooling you put on the lathe, how BENT the drill bit is, how NON-ROUND the drill bit is, how much pressure you apply to the drill bit be it on the lathe or drill press, hard/soft spots in the blank material, how sharp the drill bit is. All comes into play the exact same way.

 

[Fatdawg]

Hello,
Thanks for all the help earlier, but now a new question. I had off center holes using my drill press. I went to the Blank Holder from Penn State and am drilling the holes perfectly on the lathe now...with one exception. The holes are always a little too large. I had a 12.5 mm drill from Penn State for the Bolt action pen. Using my drill press the diameter was perfect. But the hole was off center and by the time it got all the way through to the other end of then blank it was so far off center is twas unusable.
So now, with that same bit on my lathe , the hole is perfect as far as centering goes, but .3mm too large. Just enough to make me wonder if I will be able to glue the brass in place.
Any ideas whats going on???

Why are you using a 12.5mm drill? If I remember correctly the PSI Bolt Action pens use a 3/8" drill and tube and the Magnum version is 10mm.

 

[nava1uni]

If you are moving the tail stock quill in and out while drilling you are enlarging the hole because of the movement. On the drill press there is no sideways movement.

 

[edstreet]

If you are moving the tail stock quill in and out while drilling you are enlarging the hole because of the movement. On the drill press there is no sideways movement.

Are you saying that vertical movement is superior to horizontal movement?

I do know for a fact that you can and will have side movement on any drill press so can you please elaborate on your statement as I may have misunderstood your post.

 

[jyreene]

Why are you using a 12.5mm drill? If I remember correctly the PSI Bolt Action pens use a 3/8" drill and tube and the Magnum version is 10mm.

This. The mini and regular bolt action use a 3/8s drill bit and the Magnum uses a 10mm. 12.5 would be way too large unless you've stumbled on a new bolt action no one has seen yet (which is entirely possible in the pen world).

 

[HamTurns]

I had a 12.5 mm drill from Penn State for the Bolt action pen.

Hi Rodtod11 - I wonder what kit you are using? I just went out to Penn State's website and looked at every one of their bolt action pen kits and none of them use a 12.5mm drill, they are either 3/8" or 10mm.

Another question, if you are supposed to be using a 12.5mm drill for the kit you have and you're getting a 12.8mm hole after drilling, you are only talking about a difference of 0.011". Not enough to matter. If you use CA to glue your tubes use a thicker one, epoxy would fill that area.

Happy turning
Tom

 

[edstreet]

that would depend if it is 'GAP FILLING' or not. Not all glue will qualify to be gap filling and more often than not gaps like that will structurally weaken the glue bond.

 

[KenV]

When I see that problem -- usually means that I have not been cleaning the morse taper in the tail stock with enough care. One wood shaving will throw the alignment off enough to provide oversized holes.

Amazing how those chips get into all kinds of places -- including the headstock tapers. Drilling on the lathe means extra care to clean shavings out of the headstock tapers before mounting a MT therein.

 

[Smitty37]

Hello,
Thanks for all the help earlier, but now a new question. I had off center holes using my drill press. I went to the Blank Holder from Penn State and am drilling the holes perfectly on the lathe now...with one exception. The holes are always a little too large. I had a 12.5 mm drill from Penn State for the Bolt action pen. Using my drill press the diameter was perfect. But the hole was off center and by the time it got all the way through to the other end of then blank it was so far off center is twas unusable.
So now, with that same bit on my lathe , the hole is perfect as far as centering goes, but .3mm too large. Just enough to make me wonder if I will be able to glue the brass in place.
Any ideas whats going on???

I think I'd check that the drill table is level and square to the bit a perfectly sized hole eliminates any number of possibilities but the table just a tad out of square with the bit could cause exactly what you are seeing.

Personally I have yet to drill a blank on the lathe that was not at least a bit large - sometimes on only one end. I have always attributed it to slight movement on the tail stock as I advance the drill - but that could easily be related to the make and model lathe I'm using (low cost lathe).

 

[mredburn]

IF the hole is .011 larger that would mean that what ever is effecting it is only .005 off. This could be a lot of things. Slop in your quill, dirt in the mt, alignment of the tailstock, the drill could be the problem. If your drilling it on a wood lathe you may not have the accuracy built into the lathe to correct it. You could get a smaller drill bit.

 

[Paul in OKC]

This is one of the few times I will agree with head stock/tail stock alignment. Normally a bit off is a non issue, IMO. If they are not aligned there will be a rubbing of the bit as you drill. The fact that the tail stock has some front to back play between the bed rails on most lathes is something to consider as well. I drill on a drill press. If the table is not perpendicular to bit, you will have the issue you are describing. Aligning can be as easy as using a bent coat hanger and 'sweeping' it around the table (put one end in the chuck, bend out to the edge of table). Use only a piece long enough to reach the edge.

 

[jcm71]

Also keep in mind your lathe setup needs to be aligned in all three axises. It is not enough to check for point to point alignment. That only verifies two axises, the "x" (as you are looking at it) and the "y" (looking from above). The longitudinal axises of both the dead center and live center, when tip to tip, should be a straight line. After checking for tip to tip alignment, advance a drill bit or a dead center through your empty morse taper. You can easily see if you have a "z" axis alignment problem. Think of it this way. Out of round turnings when using a mandrel are essentially a "z" axis alignment issue. I know you are talking about drill hole sizes, but the principle is the same. Good luck.

 

[Paul in OKC]

Not sure what you mean by 'Z' alignment. From a point to point issue it is no different than the side to side. If you are talking about run out, that is a bit different. Head stock run out will cause out of concentric parts.

 

[Dale Allen]

The 'Z' axis huh? I had not thought of it that way but I understand the concept.
Image there is an extremely small hole all the way through lathe assembly by going through the center of the MT fittings. That imaginary hole would be that axis. In a perfect setup, it is absolutely straight and would pass through the points of 60 degree centers when they are present. It would be possible to have the points of the centers meet exactly but have the Z axis bent at that point. Such a condition would be most problematic when drilling on the lathe. It is also somewhat problematic when turning between centers.

 

[Dan Hintz]

Also keep in mind your lathe setup needs to be aligned in all three axises. It is not enough to check for point to point alignment. That only verifies two axises, the "x" (as you are looking at it) and the "y" (looking from above). The longitudinal axises of both the dead center and live center, when tip to tip, should be a straight line. After checking for tip to tip alignment, advance a drill bit or a dead center through your empty morse taper. You can easily see if you have a "z" axis alignment problem. Think of it this way. Out of round turnings when using a mandrel are essentially a "z" axis alignment issue. I know you are talking about drill hole sizes, but the principle is the same. Good luck.

Not everyone will have this, but I used a laser center finder / alignment tool chucked up into both the headstock and the tailstock. Showed me my Robust was off by a couple of mm's over roughly 1', which explained my wobbling bits. Once I did some light filing on the headstock, everything is beautiful now.