Amateur Question - Is "coring" possible instead of "boring"?

[JAndrew]

HMEM,

Here's the question:

When you bore a piece to expensive stock, the cylindrical section of stock in the center gets turned into chips that are longer as stock...

So...is it at all possible to remove the center section in one useful piece by coring with some type of custom cutting tool that would look similar to a hole saw? It would obviously have to have some relief to it's internal and external diameters after it's cutting teeth to prevent the tool from rubbing against the surfaces.

Or maybe less like a hole saw and more like a cutting tool that would be used to machine an o-ring groove onto a flat surface...?

A lot of good metal stock is going to waste with convential drilling and boring. I suppose that's why sand casting is so appealing as you can cast a core into your stock.

Thanks in advance for taking the time to explain why this is a silly idea!:wall:

-J.Andrew

P.S. I should have mentioned I am thinking in terms of lathe operation.

 

[Rivergypsy]

Hi,

No reason at all why this shouldn't be done, either by a hole saw as you say, or by a trepanning tool. I would work from each side too. Length can be an issue, but custom deeper hole saws can be made by brazing a strip of bandsaw blade around the lip of a cup shaped tool.

One thought if you trepan the centre out is to drill a small hole in the centre of the part, and then catch the centre on a length of rod in the tailstock - far less messy than it dropping or catching the tool

Dave

 

[Swifty]

A core drill is a good idea, the only problem would be with chip removal, especially on longer pieces.

Paul.

 

[Tin Falcon]

Core drills are common in steel fabrication shops.
So it can be done.
you are limited to depth and you will still need to bore the hole as drilling a roughing operation.
Tin

 

[OrangeAlpine]

I have cut a lot of "cores" with hole saws on drill presses. The saw cuts like gangbusters until the cut is deeper than tooth depth and the gullets fill with chips. Things then progress at a snails pace. That is especially true on a drill press, as chips do not clear when the saw is retracted. Add a little cutting oil and it becomes a nightmare. I drill a couple of holes in the waste portion and on the periphery of the cut, usually about 3/8" diameter, allowing chips to drop out of the kerf. The saw will then cut at the speed of a band saw.

I have also used a vertical mill. They of course allow good chip clearance and are ridged enough you do not need a pilot hole.

I have never attempted this on a lathe and have no idea how well the chips will clear. They may clear quite well simply by retracting the saw. Maybe a little compressed air directed into the kerf would help. I'm not talking massive pressure, something like a bandsaw chip blower. I do think the lathe would be steady enough a pilot hole would not be necessary.

Bill

 

[JAndrew]

Hi,

No reason at all why this shouldn't be done, either by a hole saw as you say, or by a trepanning tool.

Rivergypsy,

I made the mistake of googling the term "trepanning". Picture of people drilling into human heads abound! Yeck! I recommend anyone else interested instead googles the phrase "trepanning tool". The results are much more palatable and pertinent!

Thank you for this post! A trepanning tool is exactly what I was envisioning in my head (not drilling into my head! ha!). It seems to happen quite often that I invent some incredible new gadget only to find it was already invented centuries ago. I guess I missed my era.

-J.Andrew

 

[JAndrew]

OrangeAlpine, Tin and Swifty,

Thanks for the replies. the chip clearance was my primary concern also so I was thinking of a tool shaped something like this:

OrangeAlpine's idea of retracting frequently and clearing chips with compressed air would do the trick too.

Thanks again all.

-J.Andrew

 

[dman]

OrangeAlpine, Tin and Swifty,

Thanks for the replies. the chip clearance was my primary concern also so I was thinking of a tool shaped something like this:

i've actually done it with a hole saw on the lathe. you need to be gentle with the feed untill you get a groove going. then you can start making a chip once the saw follows it's own groove. then you have to retract the tool and clear the chips frequently. you probably wouldn't want to core a very long part with a hole saw.

at work we use face grooving tools frequently. the tool above on the left is an example of one. they have a range they are designed for. a tool like the second shown above would not be suited for different sizes. many of the face grooving tools available would have depth limitations. that all said, the last place i worked at was the manufacturer of a carbon material and we used diamond tools. there wasn't much of a market for these tools and for special applications we would braze the inserts to tools we would make to do the job. i didn't work in the manual shop but they had some large turret lathes that seemed to be setup for coring. they had pieces of pipe that would have the end ground to a spiral for relief and an insert brazed at the end to do the cutting. you could probably do this with a carbide insert.

 

[ShopShoe]

I have done this with a tool I ground that was similar to a grooving tool. I did cut grooves (trepan cuts?) about three times the width of the tool for extra clearance and I used compressed air to help clear the chips (less than ten psi, probably about 5psi). I did this while cutting a 3-inch hole in a 4-inch square piece of 1.25-inch thick aluminum that was held in the 4-jaw chuck on my 7x mini-lathe. I also went about 3/4 of the way through on one side, then came through the rest of the way after flipping the stock over as I was also cutting a step in the hole.

The "cored" area was very rough and the piece cut out was also very rough. Additional machining was required to clean up the bored area and bring it to final size. I did, as you asked originally, save a good chuck of aluminum for future use in some project instead of turning it into chips. I saved a lot of time, too.

Not something I would always do, but useful to remember in similar situations.

Good luck,

--ShopShoe

 

[JAndrew]

Dman and ShopShoe,

Thanks for the replies. Good to know that this could work.

-J.Andrew