[ant17]

hi guys i am trying to build a coupler for x2 mill for a powerfeed but i need to drill a hole in the center but i am drilling a 8 mm hole through a 20mm 100mm long pice of aluminium stock the trouble i get the hole started in the center but by the time its gone to the 100mm depth its off by about by 5mm i tried it on a piece about 1 inch and it was dead on so i don't know what to do i have a 3 inch boring head but it only goes to 10mm any suggestion also i have know acess to a lathe

[Torsten]

hi guys i am trying to build a coupler for x2 mill for a powerfeed but i need to drill a hole in the center but i am drilling a 8 mm hole through a 20mm 100mm long pice of aluminium stock the trouble i get the hole started in the center but by the time its gone to the 100mm depth its off by about by 5mm i tried it on a piece about 1 inch and it was dead on so i don't know what to do i have a 3 inch boring head but it only goes to 10mm any suggestion also i have know acess to a lathe

If you drill it from both sides your only off half as much!:-)
Make sure you start out your hole as perfect as possible.
You only have controll over the first inch or so of depth, make sure it is perfectly centered.
Ensure the Drill is ground correctly use light pressure feeding it down.
Drill half the depth through, then repeat from the other side.

Once a Drill gets off center it gets progressively worse.
Run the drill all the way down from the second side.

Now pick best of the two sides and finish the hole through.

[ant17]

can you buy 8mm boring bars of decent length

[handlewanker]

Hi I've drilled 9mm diam holes 4 feet deep through a drive shaft for grease lubrication, and we used the same method of drilling from both sides to meet in the centre.

The drills were regular twist drills welded onto mild steel rods.

First we marked out and the drilled the holes using a normal drill bit to get started, then the "extension drill" was used to peck it's way down the shaft, 1/2" at a time, to about centre and then from the other side 'till the two met up.

We drilled the shaft (4" diam) on a radial arm drill press, taking great care to make the shaft dead vertical.....and only drilled in short 1/2" deep steps withdrawing the drill bit and removing the swarf with a magnet on a piece of wire..... never had a failure.
Ian.