Bad .492 drill bit?

[picnic42]

I made a nice pen with an Over/Under kit from PSI.. I think it came out pretty good... However the blank bored with the .492 drill bit, the hole came out grossly over sized! I had to use gel CA and wait for it to dry, then use thin CA to fill in the spaces between the tube and blank. This worked, but this should not happen. I called PSI and they are going to "Mic" a .492 drill bit for me and send out a QA checked bit.

This is what I found upon further tests and measuring:
Over Under tube is .481 (12.22mm)
Drilled hole in blank is .509 (12.93mm)

The brass tube actually rattles inside the blank hole.

I checked the drill press and it is as straight as I can get it... very near perfect top to bottom on drill bit. I use a pen blank centering vise on the drill press.

Taking another scrap piece of wood... I found a problem. Using the same drill bit, I bore another hole and found something I cannot figure how this happens.

the entry hole is
.5195 (13.19mm)
the exit hole is
.4960 (12.61mm)

(length of scrap wood... is 1.15 in.)

I checked the next pen blank I had previously drilled for another Over/Under pen and found the same thing... very oversized on one end and a fairly decent fit on the other end.
What is causing this? I am not having any other problems with the slim lines, .30 cal cartridge pens and European pens. I have done a few other pens with varying drill bit sizes, and found no other problems.
I assume this drill bit is faulty... but I am puzzled how the entry and exit hole is so different in size!!!!

Anyone have any ideas?

Ralph

 

[walshjp17]

I learned a lesson with PSI bits from China: do not trust the dimensions they quote. You must measure them to be sure. Ruined my share of blanks due to faulty-sized bits for PSI.

 

[mredburn]

Are you drilling a pilot hole first or just going right
to the .492 drill bit?

 

[mredburn]

If your not using a pilot hole the front of the bit is wandering around a little bit and then is held straighter as the drilled hole guides it. You could take and roll the drill bit on a piece of mirror or glass and see if the drill has a bend to to it. It will lump as it rolls or at certain places you will see light between it and the glass and at other places not at all

 

[picnic42]

I just tested the 9/16 drill bit sent in the kit along with the .492. The 9/16 bit works fine and bores a hole very straight and no variance between the entry and exit holes!

I have not used a pilot hole and will probably start using them on these larger bits.

I will keep an eye on these bits from now on!

Ralph

 

[1080Wayne]

When you turn the drill press on , does the bit appear to wobble ? If so , it may be slightly bent , or have slipped in the chuck at some other time , scarring the shaft , so that it isn`t held concentric with the drill axis .

 

[gbpens]

The drill bit is not properly sharpened. Wait for the replacement bit and test it on scrap before using it on a good blank.

 

[picnic42]

When you turn the drill press on , does the bit appear to wobble ? If so , it may be slightly bent , or have slipped in the chuck at some other time , scarring the shaft , so that it isn`t held concentric with the drill axis .

It just might have a bit of a wobble... will check that later today!

 

[Smitty37]

When you turn the drill press on , does the bit appear to wobble ? If so , it may be slightly bent , or have slipped in the chuck at some other time , scarring the shaft , so that it isn`t held concentric with the drill axis .

It just might have a bit of a wobble... will check that later today!

I have had a similar experience when drilling on the lathe -- when you back the bit out to clear chips and it is not perfectly aligned when you reinsert it that is exactly what will happen.