Removing large amounts of material?

[AZHTR]

I’m an avid reader on this forum, but don’t contribute too much from my lack of experience. I have a Logan Powermatic 11x 24 lathe (2 hp motor and VFD) and occasionally get requests to machine aluminum round plate stock.

Example - 1” thick, 6” diameter round plate stock and needs a 4” inner diameter machined through.

My question - What is the best technique for removing all of that material? I have drilled a 1” hole through and then I used a boring bar to remove the rest of the material. Takes quite a few passes to get there. Has anyone used any type of groove tool and just cored-out the majority of the stock?

Just looking for the forum’s expertise. Any suggestions are appreciated!

Thanks, Rob

[RB211]

How about a trepanning bit? Custom ground on the bench grinder, looks sort of like a crescent moon except the cutting edge is flat. Basically cutting a slot at near the finished diameter of the hole, saving the big chunk in the middle for the scrap bin.

[RB140]

Maybe a core bit or hole saw in the tail stock just to get close to the 4" I'd

[AZHTR]

Thank you two! I’m “Googling” trepan and hole saws........

[JoeLee]

Maybe a core bit or hole saw in the tail stock just to get close to the 4" I'd

I'm with the hole saw as well.

Quickest way to make a big hole. Get it within 1/4" or so of the finished dim. and then finish up with the boring bar.

JL..........

[The Metal Butcher]

Yes. Curved groove tool. Takes a lot of power. Difficult on an 11" lathe that deep.

[jimsehr]

If you trepan you have have to stop just before you cut thru part or it can be dangerous as tool can break and part can fly out of machine. Be safe. I have trepanned thousands of parts in production.

[BCRider]

Maybe a core bit or hole saw in the tail stock just to get close to the 4" I'd

That would be one helluva cut even with a metal rated hole saw. I'm pretty sure it would have the Logan dancing around the shop.

The trepanning tool bit RB211 is suggesting would need to be shaped fairly long and sort of like a boring bar due to the thickness of material you're describing. I'd say it would be cut from some 1/4 x 1/2 HSS up on edge.

Using your example for the 4" inner diameter here's what I see. The arcs of the blue were done in CAD in real size to be 4" on the outer diameter with the tool in the cut being 1/2 inch tall by about 3/16 wide. The length of the tip with the sort of cross section shown would probably be about 1.1" so you clear the back of the block before it



Notice it's a touch narrower than the groove. To avoid binding I'd plunge in about 1/8" at your outer diameter than move the cross slide in about .06 and plunge that away along with another 1/8". Then cross slide out to the original setting and plunge the small waste away and another 1/8. By jogging back and forth like this it should aid a lot for preventing the tool bit from binding in the cut and snapping off.

Also to avoid working with an extremely deep groove I'd make the portion shaped as shown in the sketch only about 5/8 long. Then cut half way in on the first face using the in and out step plunges. Once half way or just over turn the disc around and trepan in from the other side. You'd do this about .02 to .03 smaller than the desired final dimension and a regular boring bar to finish things up and remove any nasty chatter marks that might occur.

Hope that helps. Or at least gives you some ideas.

[BCRider]

If you trepan you have have to stop just before you cut thru part or it can be dangerous as tool can break and part can fly out of machine. Be safe. I have trepanned thousands of parts in production.

Good point. Working with aluminium means a somewhat higher speed. But at 3.9" diameter I'm thinking you'll be in the slowest direct speed anyway. And more likely in one of the back gear speeds. I would say that if you're in the slow direct drive then stop and switch to the slow back gear speed for the last .03 to .06 before the center comes free. The slow RPM will avoid any issues I'm thinking.

[AZHTR]

Thank you all for your quick response and suggestions! This is EXACTLY why I read and learn on this forum. Always so helpful!

[oxford]

If you are going to use a normal hole saw it works way better if you drill a hole for the chips to escape out of. If not once the gullets get buried into the work piece you will have to back out quite often to clear the chips. The difference in drilling speed is pretty substantial.

If I had a 4” hole saw, I would lay it out so I drilled a hole 1.750” off the center. I would then use a 31/64” drill bit for the hole. I found that this was enough for the chips to get out and not have that hole break into the finished hole from the saw.

I might drill 2 “chip” holes for 4”, under would only get 1 and over would definitely get 2.

edit: Hole saws also work way better if you can get the saw tight on the arbor. If using a standard hole saw and arbor that means either skipping the drive pins and running the saw up tight to the shoulder or shimming the saw so it’s tight against the shoulder and the pins still line up.

[DR]

When you come right down to it, by the time you set up for trepanning you'd have it done by boring after the 1" drilling.

Speaking of trepanning.. a friend made cylindrical, deep ocean data collection devices of titanium. Titanium tube wasn't available in sizes near what he needed. So he had to buy solid bar. A shop in California trepanned the solid bar making tube for free, their payment was the core. This was at least 25 years ago and I recall him saying the solid bars were something like $25K. Now that I think about it those trepanned pieces were a couple feet long. I have no idea how they did it, maybe something like an annular cutter.

[oxford]

Speaking of trepanning.. a friend made cylindrical, deep ocean data collection devices of titanium. Titanium tube wasn't available in sizes near what he needed. So he had to buy solid bar. A shop in California trepanned the solid bar making tube for free, their payment was the core. This was at least 25 years ago and I recall him saying the solid bars were something like $25K. Now that I think about it those trepanned pieces were a couple feet long. I have no idea how they did it, maybe something like an annular cutter.

I don’t know the name but there is a channel on YouTube doing this. They were using homemade “cutters” and used indexable inserts iirc. I believe they were also doing “exotics”.

I’ll try and to ask a look to see if I can find them.

edit: Here you go. He had a bunch of videos up, this is just one.

https://youtu.be/pAactI93w6U

[deltap]

Take to someone with a plasma table then finish in lathe. Chain drill then finish in lathe.

[The Metal Butcher]

When you come right down to it, by the time you set up for trepanning you'd have it done by boring after the 1" drilling.

Speaking of trepanning.. a friend made cylindrical, deep ocean data collection devices of titanium. Titanium tube wasn't available in sizes near what he needed. So he had to buy solid bar. A shop in California trepanned the solid bar making tube for free, their payment was the core. This was at least 25 years ago and I recall him saying the solid bars were something like $25K. Now that I think about it those trepanned pieces were a couple feet long. I have no idea how they did it, maybe something like an annular cutter.

They trepanned it with a true trepan cutter. As David Wilks (linked above) will say, what we are talking about is face-grooving. A true trepan cutter supports the slug and go nearly infinetly deep. They use trigon cutters using two of the 6 edges.

Relevant:







Extremely relevant: https://bbs.homeshopmachinist.net/fo...-for-a-backhoe