Problem getting a good finish on stainless

[Dave Harding 1Participant @daveharding1]

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

[JasonBModerator @jasonb]

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

[Dave Harding 1Participant @daveharding1]

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

[Dave Harding 1Participant @daveharding1]

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

[JasonBModerator @jasonb]

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

J

[Dave Harding 1Participant @daveharding1]

[Anonymous]

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

[JasonBModerator @jasonb]

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

[Ian S CParticipant @iansc]

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

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi al,

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

Ian.

[Dave Harding 1Participant @daveharding1]

Thanks for that Jason.

[Roy MParticipant @roym]

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.

[NobbyParticipant @nobby]

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

[Dave Harding 1Participant @daveharding1]

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.

[JasonBModerator @jasonb]

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

[Dave Harding 1Participant @daveharding1]

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.

[jonathan heppelParticipant @jonathanheppel43280]

As Alan implies, if you're not hardening the expander then silver steel isn't the best choice. For similar jobs I've used a normal HT bolt or (better) a socket cap as stock, which is half hard and cheap even new. The ideal material is probably case hardened mild steel.

High speed and deep enough cut is generally the key to finish. You must generate enough heat to take you out of the built up edge zone, or work below it as suggested on this forum not long ago.

Small machines always benefit from higher rake angles and dead sharp tools, and like Douglas Johnstone I've achieved good results on gummy materials with ground tips for aluminium, but only for finishing to close limits cos I'm tight.

[Dave Harding 1Participant @daveharding1]

The material does not need to be hardened the expanders are used on thin walled Brass.

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