[How do I?] Turning To A Shoulder- Shoulder Ends Up Tapered

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Skeet_Man

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Just picked up a Sieg C3 @ Grizzly a couple weeks ago.

Working on my first project now. I'm turning a 7/16 mild steel rod to .164 for a 8-32 thread. Length of smaller diameter is approx 1/2"

When I get near the end of the shoulder, the tool starts squealing, so instead of going all the way to where I want to end up, I'm a little shy, more so with each pass.

In the end, I end up with a pretty decent taper at the shoulder, instead of it being perfectly square.

I can to back and take plunge cuts to get rid of this taper, but that's kind of a pain.

I guess next step is to just try powering through the squeal and bring the tool where I want it to end up instead of where it wants to.

Am I on the right track, or is there something else I should try?
 
If I am understanding you right, I will use my cutoff tool and square it up with the piece and squre up the shoulder. Hope this helps.
 
Skeet_Man said:
When I get near the end of the shoulder, the tool starts squealing, so instead of going all the way to where I want to end up, I'm a little shy, more so with each pass.
Click to expand...

How is your cutting tool angled? It sounds like the side cutting edge is contacting the work, producing the tapered shoulder. Try angling the tool so the side cutting edge clears the intended shoulder by about 5 degrees or so and you should be able to cut all the way up to the shoulder and then face out without anything rubbing.
 
Like the others said, it sounds like you do not have enough side cutting angle. That said, there are other things that can cause this on a small lathe.
These lathes lack rigidity and can get really touchy at times.
Cheap carbide tooling can cause this because it is not ground well and is not sharp.
Make sure you are not machining with the compound over hanging the top slide - ideally you want the entire tool post over the cross slide, not hanging over the edge because the compound is extended too far (this is probably the most common mistake with people new to lathes).
Make sure the gibs are all properly adjusted.
This is an HF lathes, they are regarded by hobbyists as being "lathes kits." Most of them need a fair amount of work done to them to get them to perform well.

Lastly, this is a tiny lathe, and you have to sometimes just do extra steps to get good results. If you have to back out the tool and plunge back across the face to clean it up, then this is just what you have to do. Just leave a few though for clean up. Normally you would need to pull the tool out across the face to clean it up.
 
In my experience, turning tools don't do well cutting on two faces at once. I will turn down the diameter, stopping short as you do and occasionally go back and make a facing cut on the shoulder to keep it fairly close to the finished dimension. As I get close to the finished diameter, I will run a finishing pass on the face followed by the finishing pass on the diameter. This gives me a sharp corner with a shoulder perpendicular to the axis.
 
Skeetman, it might help to post a pic on your setup. After re-reading your OP, I wonder if you're not taking each pass to full length. If not, then even if your lead angle is correct you are running up against a lot of metal as you come into the shoulder and the tool is chattering. A picture would help clarify.

The other thing you can try is to skim cut the work piece and take an accurate OD reading. Then determine what the minor diameter of your intended screw is and use a parting tool to cut in to that depth at the length you need. This does two things: it creates a shoulder for you and it also creates a thread relief, both at the same time. If you feel the need you can then take your turning tool and face out the shoulder when you're done to get a truly flat face.
 
check your cutter height too. It might be a tad too high above part centerline.
 
Your description helps, but without a pic or two, you will get nothing but guesses on your problem, sorry...Dave.
 
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