Problem getting a good finish on stainless

This always polarises opinion but I'll reiterate what Mike, Shaun etc said above. If you take a fine (and / or slow) finishing cut you'll most likely end up with a worse finish. Ideally you'll take nice deep cuts and run your machine near max speed. You don't always need a lot of power - my Bantam is only 1.5HP and manages quite happily. I use power feed on both axes where possible and increase the speed as the tool approaches the centre line.

This is what I manage using carbide inserts. The 2 disks are 4140 carbon steel (rather like silver steel) and the shaft is some sort of mystery stainless steel I recovered years ago from the Ark. Not a touch of emery paper in sight. With experience, frequent measuring as I go and careful use of the micrometer dials I can get the final dimensions within a thou or so despite taking a decent final cut. If I undercut it, I take a shallower finishing cut and get out the emery paper but I try to avoid that.

It's a good idea to sacrifice a piece of material for some experimentation, rather than learning the hard way on something that matters. Discovering that increasing speeds and feeds improves the finish significantly with indexable tools is a major step forward. Same goes for indexable parting tools, which I also used for parting off those disks with power feed. Stuff takes a lot less time to do this way....

Murray

Thanks Allan you may be right I will try some mild steel and see how it goes. I have several shop bought expanders for the price they charge I thought it would be more economic to make my own.

Having done much the same thing when making reloading gear as Al. I agree with his choices. Get near to size and then polish with what are called, 'Buff sticks', much used by watchmakers to polish spindles. They come in several grades 00, to 3 grit. Can be ordered and bought from watchmaker sites. If you are seriously worried about wear on the sizing die then case harden it and re-polish. Non of the commercial ones I have seen have any really fine finish at all. They look as if they have been finished off with a fairly coarse diamond paste by lapping. You have to get the size right as if the int. size is too loose then the bullets will move on recoil if in a magazine.

Clive

How did you cut the splines on the gear wheel. How do you set the lathe up to use power feed as opposed to thread cutting.

Thanks Clive I will have a look for buff sticks. You learn some thing new every day.

Dave the charts on the front of your machine will show the gear setup for a fine feed, the small one at the top is feed rates and looking at the spec on SPG you should be able to get down to 0.08mm (0.002" ) per rev which will be far better than hand feeding if that is what you have been using

Edited By JasonB on 23/02/2014 18:27:09

I never even thought of using the power feed what a dummy I am.

All I need to do now is make sense of the numbers they don't mean any thing to me.

Post a larger picture of the chart and we will sort you out.

J

See this thread **LINK** for a discussion, and results, for turning 303 stainless and silver steel, both soft and hardened.

Contrary to popular opinion 303 stainless is one of the easier materials on which to get a good finish. Finishing cuts work fine too. Subsequent to writing the above I've turned a lot of 316 stainless and that gives a beautiful finish too. However, 304 stainless is a real pig, and I've still haven't got to grips with it.

If I was turning stainless now, I'd use higher feedrates than I used in the above trials.

Regards,

Andrew

Dave if you take the end cover off the lathe and then look at the gears from the front you will need to swap some about so that they look like this.

The fixed 40T on the spindle drives an 84T which has a 30T on the same stub. That 30T drives an 80T which has a 20T on thesame stub and finally that 20T drives another 80T on the feed screw, you will also need to add a spacer to keep the 80T gear to the left, spacers are shown as "H" on the charts

Its quite likely that the lathe came to you with the mid range 0.138mm feed set up so you will only need to change the 33T for a 20T

J

Edited By JasonB on 24/02/2014 10:19:26

When posting photos to a album, I had major difficulties when I started, then I found that if I rt clicked on the photo on my hard drive I could reduce with one lft click to 640 x 480 which seems ideal.

As for turning stainless, I have made a hot cap for a Stirling Engine from a 2 1/2" dia x 3" long bit of 316, the bloke at the steel merchants said that he didn't envy him the job. Apart from miles of swarf, it machined well, the bottom end is .015" thick, and the open end has a thread cut in it to 32 TPI. X 1 3/4" dia. All done with HSS tools.

Ian S C

Hi al,

Has anyone tried using a vertical shear bit to improve the finish on difficult materials ?

Ian.

Thanks for that Jason.

How to turn to size without emery paper.

Assuming that your tool and setup are robust, divide the amount of material to be removed into equal parts.

For example, after roughing if 2mm is left on then plan to take 4 equal cuts of .5 mm.

take a cut and check that you have the finish and parallel accuracy you are aiming for.

Take measurement and adjust your next cut to give an accurate size exactly 1mm above your

finished size. After this you should be able to trust your tool and set-up. Take another .5mm

cut and re-check your size. Your next cut will take you to your finished size. (Obviously the depth of cut

will depend on job). The point is that the tool will only behave the same if the depth of cut and conditions

are the same, if it goes pear-shaped towards the final cut, you can recover the situation by dividing the remaining

amount into workable cuts.

I would keep emery paper/ cloth well away from your lathe .
Nobby

Am I right in thinking that to use the threading and feeding table I posted the picture of.

If my lathe is metric I should use the columns on the left of the table.

If my Lathe is Imperial then I should use the columns on the right.

Is this correct.

Yep, you need to use the correct chart as the feed screw will have a different pitch one metric/imperial machine and the ratios are calculated on how far the carrage moves relative to the rotation of the screw.

Edit having said that it does not say on your chart which is for which, does it on the lathe front plate? But they usually only have one of the two charts on the machine which will make the decision easy

J

Edited By JasonB on 25/02/2014 19:51:34

Edited By JasonB on 25/02/2014 19:53:08

The insert thing is starting to make more sense to me now. I have ordered some inserts that are for finishing. I think the ones I have are for general roughing etc. Any way we will see. One of the tool makers at work is going to give me a teach in so hope fully that will help.