HELP-Lathe drilling for an Omega

[webby962]

OK, I hope some one here can help!
I have just tried to drill the cap blank for an OMEGA pen.

I started with a 7mm, and then went up the drills until I had done the 25/64". At that point everything is fine. The bottom tube fits a treat, nice and snug and straight.
So I move on with a 10mm drill, 11mm drill and again it all looks good.
The problem arises when I then use the 15/32". For some reason the size in the blank becomes too big!
The first blank was oversize throughout.
The second blank was oversize for about half the length (right hand pic), then ok on the exit side (left hand pic), as per the pics.

Does anyone know what is happening? Or how to overcome it?

 

[Woody]

Sounds like your headstock chuck was loose so the end not in the chuck could move sideways but the other end stayed where it should be or your drill bit wasn't centred in the jacob chuck but I would be inclined to think the first one was the problem

 

[webby962]

Looks like I might have to try pen jaws then, to support the blank further along. Oh well, live and learn :-)

 

[Terry Q]

I have no solution but wonder why are you using smaller bits first? If you were drilling steel that would make sense. It seems like wasted effort with wood.

 

[edlea]

I have no solution but wonder why are you using smaller bits first? If you were drilling steel that would make sense. It seems like wasted effort with wood.

I'm with Terry, provided your drill bits are sharp go straight in with the size your after, it never fails for me....I see a probable cock up on my next drilling session now that I've said that..

 

[Woody]

Looks like I might have to try pen jaws then, to support the blank further along. Oh well, live and learn :-)

You dont need pen jaws all I ever use is step jaws or use ordinary dovetail jaws turn the blank so that the corners fit between the jaws and tighten up a bit then bring up the tailstock then centre the end of the blank on the drill bit and then fully tighten the jaws holding the blank

 

[Phil Dart]

Well, the tube IS designed for a 15/32 hole, so your problem is down to pilot error somewhere along the way. Just to give you an alternative view though, unless I'm using Colt bits, I always drill out first for the larger tubes with something smaller, but generally just once is enough with something like a 7mm, just to remove the core and ensure a straight hole with the proper sized bit. (which appears to be a nice little irony in your case)

As Woody has said, check all your alignments, and a roll test on the drill bit itself wouldn't be a bad idea either. Good luck.

 

[fortress]

Oh that's a shame Adie, I normally just pilot with a 7mm when drilling large holes, once you've found out why things happen, you can take steps to prevent it from happening again, as you yourself know.

 

[pittswood]

Hi Adie,

Look at your drill point. The two lands on the cutting face should be of equal length. If not, it will drill larger. Measure from the base to one side of the land edge, then do the same to the other. Both should measure the same. I not grind the drill point true and back on centre.
Kelvin

 

[21William]

Some modern wood turning lathes don't have very good tail stock alignment with the head. If your tailstock is out, any bit you put in the chuck can act a bit like a boring tool and cut an over size hole. Using a smaller than recommended drill bit may solve the problem though. It's also a good idea to start the hole with a nice rigid centre drill or spot drill.

 

[Penpal]

I like the right sized drill only also check the right sized ? drill you have maybe and often they are not the size they say. Stop when its wrong after the first loose hole and reexamine methods and drills.

Peter.

 

[wm460]

Is your drill bit straight I have a few from PSI that are as shonky as your P, I mean wonky.

 

[silver]

quite a good few pointers there and agree with them all.

Drilling is down to your own personal preference. ?I know some that always pilot drill with 7mm first then drill out with the size they need and also some that drill out with the actual drill size they need an =d don't bother with piloting.

Its all down to what works for you, I guess what you are doing is not working for you.

As per woody, I don't use pen jaws either, just another gimmick. It still won't guarantee a perfect parallel drilled hole.

It could be your tail stock not aligned, do the kiss test to see if they are OK. if not then you have found the problem.

It could be the original pilot drill, if its not drilling dead center and causes the drill to "wobble" then it will be out of alignment on entry but correct on the exit.

What I do is drill with a center drill first so that the hole is centered then drill with the finished size drill. always worked for me so that is what I always do. HTH

 

[AllenN]

I agree with Eamonn' comments. Do check that your drill bit is straight, I have found some that most certainly are not. One other point, if the shank on the drill is damaged it is possible to misalign the drill in the Jacobs chuck, although you might notice this in a rotating chuck you may not in the stationary lathe chuck.

 

[Winemaker]

Just a thought has the drill been resharpened at any time, it may be sharpened out of line, so it cutting one side making it drill wrong

 

[Dalboy]

With refence to jaws for the chuck like some I did not buy the pen jaws but did however get the pin jaws for my chuck as I had other jobs that I can use them on, including reverse chucking hollow forms with small holes to remove the foot

 

[Penpal]

Still with all the solutions how is it going for you Adie I reckon all your original questions have been addressed , using these as a guide what comments do you have as you eliminated the possibilities mate. Follow up from you could also assist another person in the future. Good luck. From the 13th what news?

Peter.

 

[webby962]

Thanks for all the advice. Just a few follow up points form me.
First the drills are brand new from UK Drills, and do not appear to be damaged or bent and have not been resharpened.

Second, I drilled a small piece in the chuck that was only protruding by a few mm, to remove the extended wobble bias. The hole size was still over even though I only went in a few mm.

The tail stock does have some play in it, so I need to work out where that sits (what exactly is the kiss test?), even through there is no play when tightened up.

I only drilled the pilot holes and moved up the sizes to see what was going wrong where, as the first time I drilled the hole, it was oversized.
I have ordered a smaller drill bit, and will see if that drills to size or not (11.5mm).
I think it might be the tail stock, but no other hole size is oversize, which I would have expected to be a problem at all sizes.

Adie

 

[Bammer]

Make sure you don't tighten your chuck onto the thread of the drill bit, this can add wobble and therefore your hole won't be true

 

[21William]

I've reamed holes on my metal work lathe into steel and noticed it cuts a very slightly larger hole if the tailstock is locked and the reamer is advanced into the work with the hand wheel. If the tail stock is left unlocked and the reamer is advanced by slowly moving the complete tail stock the reamer follows the prepared hole more closely and cuts to size. The tail stock appears to be spot on with the headstock but is perhaps very slightly off. The tail stock is adjustable on my MW lathe but the error is so small attempting to adjust it is likely to make things worse.