What's the best way to drill deep holes on a 7x12 mini-lathe?

[digits]

Hi guys, I hope you can help me - I am having trouble drilling deep holes in aluminium on my mini-lathe. I get about 30mm deep with no issues, but after that, I just can't seem to get the chips to eject cleanly, and the motor tends to stall. I have a mini-mill, so I am used to driling holes in stages and using various smaller diamteter drills, and peck drilling a few mm at a time, but I am still managing to stall the lathe, despite having twice as much power as on my mill!

I have tried squirting in a little WD40, but it's hard to get it into the hole when it's full of chips and drill bit. Any tips would be greatly appreciated!

Cheers.

[lerman]

Tell us more:

drill diameter
drill type
speed

You might try a high helix drill made for aluminum.

Ken

[digits]

Originally Posted by lerman Tell us more: drill diameter drill type speed You might try a high helix drill made for aluminum. Ken

Hi Ken, I want to drill a 12mm hole so that I can get going with a boring bar. I started the hole off with a centre drill, and then a 6mm HSS twist drill, followed by an 8mm and then a 12mm. The speeds were pretty low - below 500 rpm, but I think that's the sort of speed I'm using on my mill - I don't have tachos on either, so it's all a bit vague, I'm afraid.

Do people use special drills to drill on a lathe - I had assumed that what works for a drill-press/mill in aluminium would be fine in my lathe?

Cheers.

[LeeWay]

I use cobalt bits and crank it up all the way in high gear in brass. Does a good job with that. Higher speed makes smaller chips that are easier to eject. I think if you are getting long curls, you are going too slow. You may have to manually peck at it some as well. Some aluminum is pretty gummy stuff. Using an uncoated bit might help too.

[pastera]

Aluminum wants speed - 350-400 feet/min, so for a 12mm drill that works out to ~2800 RPM. Obviously this is higher than you would want to go for most work but crank up the RPM to help out if possible.

Have you checked your tailstock alignment? It could be binding in the hole if it is misaligned.

Make sure your drills are properly sharpened - they may have a very aggressive grind causing them to dig in. Look into 4 facet drill sharpening. Can be done off hand on the grinder with a little practice and gives much better performance.

Also, I tend to step drill such that the drill's web is slightly larger than the hole left in the previous operation. If the drill is cutting only on the outer edges it will get very grabby and digg in badly.

I have never had an issue drilling to 1/2" on my 7x12 even in steel - the only metal I don't like to drill is brass because it does grab and dig in so badly (use a slightly dulled bit for brass)

Aaron

[KOS]

how deep are you going? I also crank up the speed when I am drilling. use some oil,WD40 or what have you and your lathe should not have any problems. The slow RPMs are a killer for this lathe when drilling into AL. However your part will be nice and "warm" when you are finished.

[Geof]

Have you tried omitting any pilot hole and just going straight in with the 12 mm bit. Sometimes stalling is partly due to the drill cutting right on size so the lands rub a lot. This is made worse if the drill has been well used because the lands near the tip are worn to a smaller diameter than further back.

When the drill goes in directly without a pilot it tends to cut a bit bigger so you don't get the rubbing. You can deliberately make it cut a bit oversize by grinding the cuttings edges slightly unequal.

[handlewanker]

Hi Digits, a lever feed tailstock feed is the way to go for deep hole drilling, and for that matter any small drilling jobs where sensitivity is required.

The Myford lathe brigade are famous for adapting their lathes in this way.

You remove the tailstock handwheel and screw and make up a lever feed ( something like a pump action) to push the tailstock spindle in and out, takes more to describe it than actually make it.
Ian.

[digits]

Thanks for all the replys guys - I guess I was running my lathe way too slow -I had a 4" square lump of ally in a 4-jaw chuck and TBH I was just petrified about it coming away and removing my head/midsection!

I have also bought some cobalt (well 5% cobalt) drills which arrived today, so I will try out your suggestions at the weekend when I drill and then bore out some pulleys.

Cheers.