# How To Turn A Shoulder Or Hollow Out An End



## little_sparky (Jan 3, 2016)

Hello all,

Very simple and basic question here.
I was just wondering what the easiest or most effective way to turn a shoulder or hollow out the end of part to look something like either of the following pictures.




take note, material is either aluminium or mild steel and the maximum OD is 2 inches, so the part is small. The first image has a diameter of .900" on the inside of the shoulder.

thanks, little_sparky


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## mikey (Jan 3, 2016)

I would bore either piece, especially the second one. The first one can also be done with a turning tool if inner bore is large enough to get the tool in there.


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## pineyfolks (Jan 3, 2016)

I don't know what tooling you have to work with but I would just use a 2 flute center cutting endmill in a boring bar holder. Set it on center, bore to depth step over and repeat. The cutting edge will have to be on center of course.


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## DSaul (Jan 3, 2016)

Boring bar with the carriage stop set at the desired depth, manual feed.


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## T Bredehoft (Jan 3, 2016)

Turn a shoulder. On a lathe, either a form tool, (needs heavy lathe and lots of power) or just file it round and polish with sand paper.


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## dave2176 (Jan 3, 2016)

Since they are fairly small I would use a round HSS toolbit. Grind half off one end so it looks like a D. Grind it back 10 degrees so the most pointed part is to the outside. Mount the bit in a tool holder and plunge it in so it takes maybe .020" at a time to the desired depth. Run the bit towards the center to clean up the bottom. On the blind hole in the second picture predrill it to just shy of the finished depth so you have a starting point. 
Dave


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## ChipsAlloy! (Jan 3, 2016)

Hi, a HSS tool like this would work for at least the part on your first pic.


For the second one I think you could make it with the same tool, others will chime in and correct me if im wrong. I would center drill, drill a diameter large enough for the Hss tool to fit in. Making sure my drill bit tip does not reach the final depth. Then bore to diameter with the Hss and finish depth at the same time.

Of course there are carbide insert boring bars, but you mentioned you had basic stuff so maybe its not available right now for the job.


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## joshua43214 (Jan 3, 2016)

That little shoulder at the top is best formed with a conventional left hand turning tool, though a boring bar will also work - a turning tool is just a bit more rigid.

Your tool should have a bit under 80* at the tip, though for a lip that small an 80* tool might work just fine.
For best results, the final finishing cut for the inside diameter and the face should be cut in one go. Either bore to final depth and face, or face to final depth/diameter (from the center out) and bore to the right. Both methods work fine, I chose based on which cutting edge on my tool leaves a better finish when run "backwards."

Here is a step by step of how I do this sort of thing.
I align my tool so that when the point goes into a corner, the relief is split between both faces. In other words, the front and side angles should each be 5* from the work (assuming an 80* tool).
I set the carriage stop to the final finished depth, then paste 2 PostIt notes on the carriage were the stop hits. PostIts are ~0.003" thick, this will let me machine the depth to about 5 or 6 thou shy of final depth. If you do not have a carriage stop, just mount a dial indicator to the bed and use that.
I then bore to the rough depth til I am about 0.005" from final diameter.
Remove the Postits, bore at final diameter right into the corner, then face to final depth while hold the carriage up against the stop.
You want to try to make the transition from boring to facing in a nice smooth motion otherwise the tip will start to drag in the corner and cause chatter. You should be able to practice the technique enough during the roughing to have it down by the time to get to the finish cut.


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## little_sparky (Jan 3, 2016)

Thanks heaps guys these replies are awesome, im going to get some stock tonight and give a few methods a go and post them on here within the next day or so.

little_sparky


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## Paul in OKC (Jan 3, 2016)

Small holes I drill a hole close to depth, then use an end mill in a drill chuck to flatten the center, then boring bar. A small HSS or brazen on carbide tool used for turning can have a bit of extra clearance ground underneath and used to bore out the pocket.


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## sanddan (Jan 4, 2016)

I've also had a bit of trouble with the second version you show. If you have a through hole a boring bar works great but not so much for a blind hole with a flat bottom. I've used a center cutting end mill to get the flat bottom but without a tailstock DRO scale it was hard to get an accurate depth as the markings on my tailstock aren't very good. On larger diameter holes you can use the boring bar to get the bottom flat as you will then have clearance for the bar to cut from the centerline out to the final diameter.


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## mikey (Jan 4, 2016)

sanddan said:


> I've also had a bit of trouble with the second version you show. If you have a through hole a boring bar works great but not so much for a blind hole with a flat bottom. I've used a center cutting end mill to get the flat bottom but without a tailstock DRO scale it was hard to get an accurate depth as the markings on my tailstock aren't very good. On larger diameter holes you can use the boring bar to get the bottom flat as you will then have clearance for the bar to cut from the centerline out to the final diameter.



Both of these bores are simple, routine bores. Sandan, if you have trouble with boring a blind bottom I would guess you were using a zero lead boring bar. This type of bar tends to chatter at the bottom of a blind bore. A positive lead bar is far more useful for these jobs because only the tip cuts. Typically, you would use a depth stop to rough out the bore to a thou or two less than final depth. On the final pass, the stop is removed and the cut is taken to final depth and ID. The bar is then fed in toward the centerline to produce a cleanly faced bottom before it is withdrawn.


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## sanddan (Jan 4, 2016)

Not to highjack the thread but what is the difference between a zero lead and positive lead bar? A picture would be worth a thousand words here.

The blind hole I was trying to do recently was for a set of machinist jacks and the hole dia was less than 1". I bored the hole as I wanted a snug fit to the mating part.


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## mikey (Jan 4, 2016)

A zero lead bar is square across the front and tends to drag in a flat bottomed bore. A positive lead bar typically has a 5 degree lead angle so that only the tip of the insert or tip cuts. Here are some examples, with the positive lead bar on the right:




Most solid bars - HSS, brazed, cobalt - tend to have zero lead geometry so they are flat across the tip. Higher end bars like Bokum and Criterion can have zero, positive or negative leads. Inserted tip bars like those above are usually zero or positive lead. The former is better for through bores or when roughing heavy; the latter is better for precision boring and in blind bores.


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