Problem getting a good finish on stainless

What type of insert should I be using to get a good finish on Stainless steel and Silver steel bar stock.

Use high speed steel, it' can be a lot sharper than carbide. Tool life isn't really an issue for model engineers. I get really good results with am tangential tooling setup.

I use high speed as well but hone the tool to a smooth finish with an oil stone & use bags coolant
Nobby

inserts were initially made for nc and cnc tooling, they were manufactured for high speed work on different materials that's why there are different grades of inserts .secondly they are power flooded with special coolants that cost the earth some £750 + per 50 gallons and more . For our purpose hss is more than sufficient if, like nobby said you keep it honed ,and keep the speed down ,even on none free machining stainless. you wont have any problems providing you stick to the rules of the materials your machining and you decrease the cuts as you near the end size or diameter, finishing cuts should be no more than a couple of thou. This applies to milling as well ,if your machine does not come down to a slow enough speed just take finer cuts the same with drilling ease of the pressure and slow down if you have no coolant facilities use a washing up squeasy bottle. ian c

Dave, given your previous post about shattering parting inserts I wonder if there is a fundamental problem with your setup rather than the inserts, either your lathe is not rigid enough or there is play in the spindle.

I'll ask the same question from the other thread as this will help people give more selective advice rather than general points about carbide for example if you have a mini lathe then feeds and speeds used on an ex industrial machine are of little use to you.

".........and also tell us what the lathe is, what speed and feed you used, dry or cutting fluid, how much sticking out of the chuck, grade of stainless, etc and we may be able to see where things went wrong"

J

Edited By JasonB on 23/02/2014 10:17:11

Jason I was thinking the same, I find when machining stainless with insets that its better to use high relative feed rates and run dry, I've watched friends try these insets and invariably they are far too timid with them, resulting in what looks and feels like a torn surface, I have a ton of HSS tooling but very rarely use it now, apart from for form tools, as stated in other posts you need to know your machine and develop a feel for the metal, on inch 316 stainless I will never take less than 0.5mm doc, at 900rpm, I have Harrison with 3hp, but as I said you must know your machine when taking cuts this deap or you will cut under or over on final pass, the finish I get is like Chrome, the above probably doesn't help Dave, however the offer is still open for you to visit and see for your self, or I can pop round and try and point you in the right direction...

HTH

Shaun

Hi Dave,

As has been said before HSS is more than adequate, use cutting oil and use two tools, one for roughing and one for the finishing cuts.

Tony

I have used both HSS and carbide over many years and both have served me well. HSS tends to be more forgiving and cuts well when sharp and thus has a lot going for it. Having said that, I rarely use HSS these days for a number of reasons. Modern carbide ( not the old stuff that many have complained about ) is so convenient to use and keeps sharp for much longer. I use a lot of ground and polished inserts with high positive rake, which are designed for aluminium, but work a treat on steel and freecutting stainless and can give a beautiful finish.

Doug

I think a seriouse point has been made the word experience, we also have our own preferences from them as to how we tackle a job so somewhere along the line dave and others with less experience will hope fully get the right answeres lets hope we don't get to technical and confuse them ian c

I am definitely not an expert on these matters, but rifle builders who profile stainless barrels tell me that they use carbide tips and, for a good finish, like to take a deep cut. Apparently a final finishing cut of, say, 5 thou, is a recipe for disaster. Can't tell you which grade of stainless is used for barrels, but modern manufacturing methods suggest it is considerably hardened by cold working.

I was going to post some pictures but I give up its to much of a chew on trying to work it out.

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Dave,

It is a bit of a performance, but not really difficult:

• Create an Album [or several]
• Add photos to Album[s]
• When creating a post, use the camera icon
• Select photo from those in your Album[s]

go on ... give it a try !!

MichaelG.

I gave it a try I gave up I created a album and tried putting pictures in it. Did not work.

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Albums only accept jpg/jpeg files

... might that be the problem ?

MichaelG.

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Edit:  evidently not, because you have a picture in your Album

Edited By Michael Gilligan on 23/02/2014 16:29:00

I think I have got it. I posted a picture of my lathe in my Album. Here it is.

Edited By Dave Harding 1 on 23/02/2014 16:30:53

I am trying to make small parts they are called case neck expanders used for opening up brass cases to precise dimensions. The work needs to be about 1" long and .313 along the length with a collar stepping up to .317 at the chuck end. The measurements need to be precise and I need a smooth ripple free finish. The finish is proving to be a challenge. I am using 1/2" silver steel bar taking approx. 5 though cuts at about 600rpm until I get some were near the required size .317 then I am slowing the work and taking very small cuts to get to my required dimensions a portion of the bar is left at 1/2" diameter I just part it of to the required length .(Now I have mastered parting off) up to now I have wasted a lot of silver steel bar. But its all a learning curve.

The parting off problem was mainly due I think to the tool post not being rigid enough I was using a not very good quick change tool post I changed back to the original tool post and set it up with a parting tool holder and blade and some good quality carbide inserts and the problem went away.

.

Dave,

It might be worth honing, or lapping, the final couple of thou'

I think there was an article in MEW a while back, about external lapping.

MichaelG.

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Edit: It was Issue 200, and it was about building an External Hone Kit from Polly Models.

Edited By Michael Gilligan on 23/02/2014 17:13:15

You want to be taking bigger cuts and running the lathe faster, don't slow it down for the last few cuts, speed it up if anything as you are removing less material.

It may also be that the feeds on te lathe just don't go low enough to get a super smooth finish in which case honing as Michael suggests may be the answer, Bit of Emery cloth backed with some MDF works well for that final sizing operation.

J