Is There A Faster Way To Bore A Hole On A Lathe?

JeepsAndGuns

JeepsAndGuns

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I have a custom little project I am working on. I have a 5-1/4 dia, 1 inch thick aluminum disc I am needing to bore a hole in. I have chucked it up, faced it and drilled a small center hole and started going up till I got to my largest drill bit (3/4). Now I have switched to a boring bar. I went at it for a bit and have gotten it up to about a inch right now. However I need the hole to be 2.75 inches. At the rate I am going with this boring bar, it will take all week to enlarge this hole.
So I was wondering if there is a faster way to bore a large hole on a solid piece of work, on a lathe?
I thought about trying to mark roughly where the hole would be with a marker, leaving my self some wiggle room, then take a regular carbide tipped tool bit, then start at the current center hole and basically make face cuts stopping at the mark I made and then keep doing that over and over till I reach the other side, then finish the the hole with the boring bar. Could that work? I figure I can take slightly larger cuts with a standard tool bit than I can with a boring bar, since the boring bar flexes some if you take too heavy of a cut. Would this be recommended/safe? Or is there a better way?
 
That's about a ten minute job on my 13" Sheldon Sebastian lathe!!!

What size lathe are you using? Since you are cutting aluminum, you may be able to use a hole saw and cut out a slug. Run in a sloe RPM spindle speed and use a cutting fluid to aid in cutting and not dulling the hole saw.
 
A totally different approach, which I did over the weekend, would be to put the part on a rotary table on your mill, chuck up a 3/4 4 flute end mill, and start cutting circles.

The reason I was doing this on the mill last weekend, is the part with the hole (hole in this case for a bearing), is too large to chuck up... the bearing is about 5" from one edge, and about a foot from the other edge.... my lathe (which is not here yet), will not swing 24".

Granted... it took about an hour and some change to cut out the hole (was not all the way through, rather about .750 deep).
 
Yes indeed!! It's called trepanning. You need to make a tool to cut straight in from the face of the plate. As the plate turns, you cut out a narrow slot in until you go straight through the plate. In fact, if you were to simply run the tool straight on in from where you are in the picture, you will cut out a disk of aluminum-material you don't have to reduce to shavings.
 
A more robust boring bar maybe? To me, doesn’t sound like a weekend job, just a few minutes to bore it out. Making all those chips is a waste of good metal though. Trepanning as suggested would let you repurpose the center metal. ALSO, I would stuff paper into the all the areas behind the disc in the chuck tracks and chuck center hole. This keeps chips/crap out of your chuck and lengthens your chuck PM housekeeping interval. As your cut reaches the backside of the boring the chips can really get inside you’re chuck if you don’t protect it. And just use like newspaper, don’t use anything that has strength to it, you don’t want the paper to fight back if you happen to catch it with the boring bar or stringy chip, be safe…Good Luck, Dave.
 
I guess I would start out with a hole saw if I had one, get it as close to on size as you can that way.

Failing that, it is time to see what your lathe will really do. You might be surprised at what depth of cut and feed rate your lathe will take. Try 1/8 inch depth of cut (1/4 inch off the ID) and feed by hand. See if the lathe is happy cutting at that depth, if it doesn't like it, your lathe will tell you, if it's happy at that depth try a bit more. Remember you are hand feeding, you can stop and back out any time. If it starts to chatter too much, try increasing the feed pressure. Your taking roughing cuts here, they don't have to look pretty, just remove material. Once you find a feed rate and depth of cut the lathe likes, then you can power feed at rate that is the same as you were hand feeding.

Play with the speed, in aluminum you can turn pretty fast, especially while the hole diameter is still small, once it gets bigger, you may have to slow down a bit. Use WD-40 as a cutting fluid, keeps the aluminum from building up on the edge of the tool.
 
If your lathe use's the half nuts for power feed, remember to keep the lead screew well lubed as thats how I managed to wear out my 9x20 half nuts pritty quickly. Opps.

Stuart
 
All good methods above. Another way for large holes is to pre-drill a number of nearly intersecting holes inside your desired diameter. Go to a slightly larger diameter or use an end mill on a mill to complete the separation. If drilling, make sure to clamp the part securely. I do it for large holes to save wear and tear on my more expensive end mills.
 
Trepanning works for me. Especially in a soft metal like aluminum.
 
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