Basic Lathework: Turning into a Corner

[Antman]

Hi Guys,
Another one of my infernal questions, this is quite basic lathe technique again. I'm hoping to reach a level where I don't have to ask so much. I really do appreciate all the help from HMEM members and I wouldn't have made half the progress without you guys.
Say you want to turn a shaft with 2 diameters, or a cup to retain a bearing shell, where a face meets a diameter, externally or internally. How do you get the face to meet up with the diameter? I've seen something about an undercut but not the "how to." Also a radiused corner, well that I can understand by looking at a motor crankshaft. Does one use the same tool for finishing the face, the diameter or bore and the undercut? What is the sequence of operations?
Thanks so much for all your help (again), maybe you'll all still make a model engineer of me.
Ant

 

[lensman57]

Hi,

Use an HSS tool with a very sharp nose or one with a very small tip radius. Turn the large diameter first to correct size, then turn the small diameter to correct size and length, on the last pass once you have reached the required length, lock the saddle in position and bring the tool outward as you were facing but in the opposite direction, this will clean up the cuts and makes sure that you have a uniform and true face for the bearing or any thing else to contact the shoulder.

For the other question, use either a chamfering tool or use a metal file to radius the end of the shaft. If you are going to use a file then ONLY USE ONE WITH A PROPER HANDLE AND GENTLY FILE IN THE OPPOSITE DIRECTION OF THE ROTATION, KEEP THE FILE WELL AWAY FROM THE CHUCK JAWS. THIS OPERATION IS VERY DANGEROUS IF THE FILE HITS THE CHUCK, IT COULD DO SERIOUS DAMAGE TO YOU. YOU HAVE BEEN WARNED.

Good luck, and be safe.

A.G

 

[Tin Falcon]

ANT: a very basic skill indeed . but none of use were born with a micrometer in hand.

If you have not already done so download and read US army TC 9-524 IIRC unlimited distribution.

here is the way I learned
1) set up a tool that will turn and face.
2) set up you work
3) mark the end of cut on the diameter with hemamphordite calipers
set up a micrometer lathe stop if you have one.
4) turn to diameter leaving allowance for finish cut
5) measure how much to take off for finish shoulder.
6) dial in for finish diameter
7) set mic stop for finish shoulder.
8) take your finish cut on the diameter take a plunge cut at the shoulder to get your relief groove then back out the tool taking your finish shoulder cut.
9) measure your part repeat step 8 if needed . if the shoulder is too deep just take a light cut off the end face if you can.

A bore can be don pretty much the same way. just a little inside and backwards.
Tin

 

[rkepler]

I use a triangular insert for most of my turning (TPMG), so when I need a square corner I simply dwell when the tip of the tool is buried in the corner and roll in the tip radius on the cross slide - that creates an undercut on the part where the 2 cuts join (I try and setup the last cut so I can withdraw the tool using the cross slide and finish the face cut). Since I'm usually using a 1/64 radius tip there's very little meat lost unless the part is very small.

 

[Antman]

Thanks again A.G., Tin and RK. I've actually done this a few times, but blanked on this present workpiece. I have so much effort and only enough stock for its pair in this workpiece that I needed to do it right the first (and second ) time. I'm working this bearing recess quite deep and using my home made carriage stop.
Ant

 

[Antman]

One boo boo I made was having my compound slide set to 14.5 degrees (.01mm off diameter per division) and working to a stop, I forgot that a small radial feed would also move the tool forward by 8X that amount. Lucky for me I discovered my mistake while still 0.5mm off target so no damage. Whew!
Ant

 

[rkepler]

You're going to make a few mistakes while you're learning things. The important thing to keep in mind is that if you're not making mistakes you're likely not making anything at all.

 

[Antman]

Thanks RK, for your encouragement to make more mistakes I got the one bearing cup finished, too stressed to begin on its pair so went for something easier for now. What a hobby! Are we doing this for fun? Beats sitting in front of the TV though.
Chow,
Ant

 

[rkepler]

Thanks RK, for your encouragement to make more mistakes

The point is that mistakes are going to happen. I once read a depth mic the wrong way - the scales are backwards from a regular mic - and took .100 (exactly!) more than I should have, this on a $125 casting. Not much to do after than than pop a beer and mumble under your breath. If I'd taken a bit more care I might have avoided that, but I'd been out of the shop for a while and had gotten out of practice. You should see my "spare parts" bucket - castings with inclusions, parts that slipped in milling, etc. You're going to make those along with all the right parts.

In the end my advice is "don't sweat it". I was running my loco at a friends a few weeks ago and something broke because of a fault in the track. The friend was apologetic but all I said was "I made it before, I'll make another - a little bit stronger". That's the nice thing about all this - if it doesn't work you can always make another.