Best/fastest/least risky way to remove center slug on lathe blank

I will have a task to make some lens cells from MIC-6, 1.125 thk x 8.5 OD, with a center bore about 6.22 ID. I would like to be able to remove the center slug as a chuck rather than turning it into chips. Trepanning through is always high-rish in my experience, but just wondered if anyone has better suggestions. Rotabroach as hole saw crossed my mind, but I imagine that's an expensive tool, and may not be efficient on a BPort mill. Any suggestions welcome.

I recall a similar thread a few months back and if I remember correctly, the most common advice was to leave a bit of material on it, then remove the center by some other means (either on the lathe, or removing it form the chuck and putting it back on with the slug out of it). Might depend on how many you need to make if it's worth taking out and re-chucking it.

In any case, leave some beef on the ID so you can bore it true once you take care of the slug.

Edit to add: Best, Fastest, and Least Risky are almost certainly three different methods

there's nothing risky about trepanning. Check out some youtube videos on it and what your looking at is a piece of cake.

You can also have them circle sawn. and no, i'm not kidding.

You say lathe blank, then mention a b-port. Which one you plan on using to get the slug? If it is on the b-port, I would drill a hole on center for a bolt to mount the slug to table (optional depending on your comfort level) then trepan it out so it can't break free and jam.

specfab said:

I will have a task to make some lens cells from MIC-6, 1.125 thk x 8.5 OD, with a center bore about 6.22 ID. I would like to be able to remove the center slug as a chuck rather than turning it into chips. Trepanning through is always high-rish in my experience, but just wondered if anyone has better suggestions. Rotabroach as hole saw crossed my mind, but I imagine that's an expensive tool, and may not be efficient on a BPort mill. Any suggestions welcome.

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I trepan a lot of stuff myself on the manual lathe, but just how much money do you think you are saving by trepanning a 6" diameter x 1.125" thick aluminum slug vs blasting it into chips? The effort put into getting the slug vs reward is pretty low.

Philabuster said:

I trepan a lot of stuff myself on the manual lathe, but just how much money do you think you are saving by trepanning a 6" diameter x 1.125" thick aluminum slug vs blasting it into chips? The effort put into getting the slug vs reward is pretty low.

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x2 on this. At the current price for scrap aluminum, much cheaper to turn into chips. If you are saving the center slugs to use for something else, my saved pieces lay around for a year or so, then get sold for scrap. Just sayin'

A good quality hole saw 6" would do the trick cheaply.
bore to final size.
easy peazy

I don't think specfab is looking to save money. Time is more important, I'd imagine. I use a Val-Cut on the lathe and mill. To minimize the risk, I know my thickness and touch off. Go the depth minus a few thou and knock it out with a rawhide or other type hammer/mallet.
And to add: Mic 6 will crack away quite easily, so keep a whisker more material....at least for starters. Before you know it, you'll have her in power feed with kickout adjusted while you're eatin' a cheeseburger.

Thanks, all, for the inputs. As Ray Behner notes, the money-saving or salvage value isn't my interest, it's doing the task with minimum time investment. The parts will have a lot of work, and this part of it is just prep to get to the real work.

I think my view of trepanning is based on the idea of the slug getting free while on the lathe, smacking somebody in the nuts, breaking the tool, etc. I'll look at the ValCut tool. Seen their ads and info, never tried it.

Regarding the hole saw, I have tried that on 4" diameter holes. Pretty worthless if you don't have the correct tooth and gullet geometry; I haven't researched the ideal hole saw for sure. I imagine something like a brazed carbide-tooth saw, maybe .090 kerf width on a relieved body, and maybe 20 teeth or so(?) I used a variable tooth pitch standard bi-metal Milwaukee hole saw, probably ~12TPI, on some 1/2" plate out of desperation a while back, and thought I'd never get through the part, with the chip compaction and stalling the 2HP BPort spindle... 1-1/8" plate at 6" would be far worse, although in concept, it seems "easy". If you have a specific source in mind, I'm open to info.

This job is a manual lathe job as it stands right now, so time is going to be key for me.

This is where a good carriage stop comes in handy. You can set the depth of cut just shy of all the way through and go off and do something else. Set your carriage feed rate really slow so nothing gets gummed up and you don't really need to watch it. Hand feed after that until the tool just starts to break through and stop. There will probably be some points at the end of the cut that will still hold the disc together enough so you can safely take it off the lathe and whack it with something to break the "web" holding the disc on.

specfab said:

I think my view of trepanning is based on the idea of the slug getting free while on the lathe, smacking somebody in the nuts, breaking the tool, etc. I'll look at the ValCut tool. Seen their ads and info, never tried it.
.

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We use a piloted trepan tool. You drill a small hole in the center, then you can run the trepan in a BP or a drill press. The pilot holds the cutout from coming loose.

You know, what if you used a (for example) 3 morse taper Val-Cut in the tail stock of your lathe. The pilot would keep the slug in place. If you weren't so damn far away, you could use mine.

Note that the material here is MIC6 -- generally only available in plate. As such, someone has to cut rounds out from plate, or turn squares into rounds. Either way, whoever does that, can take out the inside at the same time. Waterjet, router, VMC, something like that.

Regards.

Mike

Waterjet a possibility?

specfab said:

Regarding the hole saw, I have tried that on 4" diameter holes. Pretty worthless if you don't have the correct tooth and gullet geometry; I haven't researched the ideal hole saw for sure. I imagine something like a brazed carbide-tooth saw, maybe .090 kerf width on a relieved body, and maybe 20 teeth or so(?) I used a variable tooth pitch standard bi-metal Milwaukee hole saw, probably ~12TPI, on some 1/2" plate out of desperation a while back, and thought I'd never get through the part, with the chip compaction and stalling the 2HP BPort spindle... 1-1/8" plate at 6" would be far worse, although in concept, it seems "easy". If you have a specific source in mind, I'm open to info.

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It helps tremendously if you drill a couple holes (~1/2") in the workpiece that intersect the kerf taken out by the hole saw for chip evacuation. Of course, this only works if you have a designated waste piece...not so much if you're trying to save a round slug out of your plate.