Drilling Holes

[montmill]

I'm drill my blanks on the lathe and using jobber bits. I just drilled a 12.5 mm hole after starting the hole with a starting bits. I turn with my lathe down slow (Jet mini VS) and take my time advancing the bit, stopping and backing out, cleaning the bit about every 8 - 10 turns. When I'm done I find the hole won't take the brass in the middle of the blank. It doesn't seem to help to redrill the blank, it's always tight in the middle. wondering if that has happened to anyone else and if so what's the fix?

 

[walshjp17]

Resin or wood blank? If resin, it could be that the heat of the drilling may have deformed the blank. However, take a round file (rat-tail file) and see if you can work the deformity down.

 

[jttheclockman]

It could be a few things. One is maybe not the right size bit for the job. Check to see if bit is bent by rolling on a flat metal surface. if you say you redrill and it does not correct problem then it can also be either the blank is not spinning true or the lathe is not. This would explain the larger hole at the start but the back end is a puzzle.

 

[Mike]

I have been drilling blanks (wood and acrylic) on the lathe too, using brad point and twist bits. I have had this happen with both type of bits. When this has happened I moved to the drill press, clamped the blank in a small bar clamp to hold it (I am old and have weak hands) and re drill by running blank on and off drill bit a couple times. So far this has worked every time. Not sure of the cause.

I also noticed that the tube is difficult to pass through the blank if it is still warm from drilling. After it cools a minute or two it goes through. Blanks are only warm, not hot.

I have a Jet Midi and it is not VS. I run on slowest speed when drilling, I think it is 540 RPM.

Have you discovered the problem?

Mike

 

[Todd in PA]

I back out every 4 turns to keep things cool and easy. Might be the shavings clogging the flutes causing the bit to drift off center.

 

[ed4copies]

If it is oily or wet wood, it will swell after drilling. Drill again with the next larger size bit or use a round file if
you don't have a large assortment of bits.

 

[dogcatcher]

When you are drilling in wood you release stress inside of the the wood. The change in the wood along with exposure to change in humidity, the heat from the drilling process etc., causes weird things to happen in wood. You CANNOT control the movement or the reactions that wood does naturally.

One option and the easiest is to drill one size under and then the next day use a reamer to get the correct size.