Center Drill prior to larger Drill

[brownsfn2]

I have read many places that you can get a more accurate hole in your stock if you use a center drill first followed by the larger drill bit you are using for the tube.

I have a 60 degree center bit that is 5/16" in diameter and a norseman magnum series drill bit that is 135 degree split point drill bit. I am using the 12.5 mm for the cap of a Jr Gent II. The drill chuck I am using is the keyless chuck from PSI. Lathe speed is 1000 RPM.

I can use the center drill just fine and I drill in to just before the end of the flute on the center drill. Then I chuck up the drill bit and when I try to start drilling it shudders horribly and will not cut straight in. The hole at the beginning of the blank is larger than at the end.

I need to master this since I eventually want to do kitless and I know I need to drill accurate holes.

I have only used the drill bit 3 times so I know it is sharp and the wood I am drilling is olive wood so it is not too hard.

Am I drilling with too large of a center bit? Maybe my chuck is not accurate? I am just not sure. I am hoping someone else has had thsi problem in the past or maybe I am doing something wrong.

Thanks for any help!

 

[flyitfast]

I totally agree with drilling on the lathe.

Center drills come in different sizes. Harbor Freight has a set for about $5 that includes 5 different sizes. I think there is a HF in Dublin. If the hole opening is too big, maybe a smaller center drill would fit the size drill you are using for the hole for the tube.
Lathe speed varies with the material being drilled. You may be a little fast for drilling, particularly for acrylics.
Also, don't forget to back the drill out every so often to clear the chips. If the chips backup then it will really make the drill hot and too much for the material. I cool mine with a spray bottle of water. Some people use Pam.
Water and Pam are not the best for wood, especially if you are using CA to glue the tubes in. If you give the blank a good chance to dry it is probably OK.
gordon

 

[Curly]

If you can, slow down your lathe to a couple hundred rpm. The centre drills are designed to drill the proper cone for a lathe centre to mate with. Even though they are used by many people to start holes, a better tool is a Spotting Drill bit. They are designed to match the cutting angle of your drill bit so that when you start to drill it engages the entire cutting edge of the bit which will reduce or eliminate the chatter. Here is an example.

Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

 

[Whaler]

I drill on the lathe at 500 rpm and use a center drilling bit for starters but for larger holes, over 10 mm, I drill through with a bit 1/2 the size of the final hole prior to using the larger bit. I also use nothing but Norsman bits.

 

[frank123]

Complete center drill sets are available fairly cheaply, it doesn't hurt to have a whole set of the common ones.

For some reason, no one ever seems to consider using those short stubby little spotting drills for starting high accuracy holes, but that is what they are intended for.

A reference to them here Spotting Drill, Centering Drill for Pre Dilling holes on many materials, not anything I'm promoting, just the first reference I grabbed off of an internet search. Most suppliers should have them available, I would think.

 

[brownsfn2]

I just found a whole bunch of discussions on the spotting drills and what angle to use prior to the larger drill. very interesting. I finally found this PDF file and I think I am going to go with its advice.

Catalogue - Hole Making Catalog - Ingersoll Cutting Tools - (Version JPG) - page 93

 

[soligen]

You want to face the end of the blank to true it up before using the center drill. If the face is not trued up, then the bit will catch on one side.

Another thing is to try is a larger center drill. 5/16 is pretty small for that size bit.

Another way I often do it to save time is to make a "dimple" in the end of the blank with a lathe tool instead of a center bit. Since i'm truing up teh end of the blank anyway, its pretty quick to just make the starter dimple then - I eyeball it to approximately the size & angle of the bit

 

[Gregf]

I was having a similar problem. I had neglected to check the alignment of my headstock to tailstock.

 

[Wood Butcher]

Another thing that helps, get a green (PSI) morse taper cleaner. Debris in the taper will miss align the whole shootin match.
WB

 

[Rich L]

I vote also with:

RPM too fast for the big bit
Face off your piece carefully

How long is the drill? The shorter the better. Have you got the tailstock screw backed up all the way?

Some of the problem might be technique. If your center hole is good or if you have drilled a pilot hole then when going for gold with the big bit don't hesitate at entry. You could sneak up on it and let the tip act as a mill for a few thou but once it's engaged be firm and deliberate in cranking it in. Once you get past the tip you should be good.

You say the bit is sharp but maybe you got a bad grind - uneven. Take a look at that split point - is it dead center and does the grind end up at the flutes the same distance back? Does it look precisely centered when you approach the part? Have you checked alignment and parallelism?

Good luck!

Cheers,
Rich