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Finishing 303 Stainless

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Kroll

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#1
Guys I know there is so many variables when it comes to a question like this but maybe an answer will help. I am running the lathe at 250 then tried 400 rpms but just didn't help any.After each pass the finish looks like a pinwheel finish.I am hand feeding at a slow rate and very small cut maybe .002 you know just enough to clean up.My cutting tool is made for SS but wondering about rpms if that is where my problem is.Guy when I cut these these disk which is 1.5dia I am getting a better finish when cutting on the bandsaw.Thanks for any guidance IMG_0506.jpg IMG_0507.jpg
 

tjb

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#2
I think a little more info would be helpful. What kind/size lathe are you using? Is this a new problem or have you had it since you've been using the lathe? 250 - 400 sounds slow to me, but I defer to the more experienced experts on that one.

Regards,
Terry
 

mikey

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#3
Kroll, that looks like a CCMT insert. What is the nose radius on it?

The issue is that the tool is deflecting and not cutting. These inserts have to take enough of a bite in order to cut and a 0.002" depth of cut just ain't getting it. I suggest you take a depth of cut at least the nose radius plus 0.003 - 0.005" and speed the lathe up to about 1400 rpm or so.
 

BaronJ

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#4
It also looks as if it could be work hardening.
 

Kroll

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#5
It's a 14"SB,this is first time I ever tried 303,and really only have maybe 4hrs of experience on this lathe.Mike I don't know the radius but its not the one for finish.So like ya'll saying its for removing a bigger cut,I check see if I have one with a smaller radius.I just was trying to take a finish cut to get a smooth finish.Would taking a finish cut with HSS be better? I have some blanks but never grind before
 

Kroll

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#6
Guys ya'll got me looking into the way I have my part mounted which is on an arbor.Which is a 1/2-20 threaded bolt with a nut then a washer which I screw on my part.So guessing its not supported enough to keep it from deflecting,dang Mike I crank up my rpms which is for the first time at 1400 rpm.
So my new game plan is chuck up a piece of 1.5 dia stock the drill tap a hole for a piece of threaded stud so that I can screw the disk on then face it off.
 

P. Waller

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#7
303 is a stainless made for ease of machining.
It turns, drills and taps easier then 304 but costs a bit more and gives up some attributes that one would specify SS for in the first place, also it chips far better then 304/316

It is not possible for anyone to make a cutting speed suggestion without knowing the diameter of the part, RPM settings mean nothing without this data.
Being a hobbyist I am going to guess that the part is less then 6" in diameter and that the operation is facing.
Using the tool pictured which appears to be right handed are you facing from the inside out or the outside in?

If you hold the tool that way and face from the outside in you are dragging this tool backwards through the part, this will cause problems.

A conservative cutting speed for such a tool in 303 would be 400 SFM, at 3" diameter the spindle rpm would be around 500 RPM's, I would not run such an operation at less then .005" DOC and .005" IPR feed. Trying to dust off a part with a tool with that large of a nose radius will often prove itself difficult, try a sharper tool.
 

Kroll

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#8
Good questions I wish I would have put that info in my first post,kinda shows I'm new.Its 1.5 dia and I am facing from the inside out.Not using the power feed just doing it by hand so maybe thats also part of my problem.Yes it is facing, I drill and tap the hole 1/2-20 few days ago then today I just wanted to face it just to get good finish which means just removing enough to clean it up better than what band saw cut leaves.The 1.5 dia disk which is 3/8 thick I was screwing it on a threaded bolt then chuck up the bolt and put the disk up against the jaws then face it off just tad
 

mikey

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#9
Would taking a finish cut with HSS be better?
Stainless likes to work harden so I prefer to use a sharp HSS tool that cuts readily and gets the chips out fast. Stainless tends to hang on to heat so coolant is a good idea, too.

One option is to try a CCGT insert instead of the CCMT. Unlike the CCMT insert, the CCGT has a sharp ground edge that might work better for you. Look up the speed from your insert maker and try it.
 

P. Waller

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#10
Good questions I wish I would have put that info in my first post,kinda shows I'm new.Its 1.5 dia and I am facing from the inside out.Not using the power feed just doing it by hand so maybe thats also part of my problem.Yes it is facing, I drill and tap the hole 1/2-20 few days ago then today I just wanted to face it just to get good finish which means just removing enough to clean it up better than what band saw cut leaves.The 1.5 dia disk which is 3/8 thick I was screwing it on a threaded bolt then chuck up the bolt and put the disk up against the jaws then face it off just tad
Chatter, holding a 1 1/2" Dia. part for a facing operation on a 1/4" threaded fastener is sure to end in tears.
Doing this with the tool insert you are using will likely never result in the finish that you want regardless of speed, feed and DOC.

This is unstable work holding at its best.

That is a large nose radius tool, your results would be greatly improved using the same holder with an insert having the smallest nose radius that is available. If a small number of parts are required a HSS steel tool is an option.
 

benmychree

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#11
A positive rake tool would do much better, 303 does not tend to work harden to my experience, have made hundreds of pounds of chips with it; call it screw machine stainless. I use TPG inserts with it in 3/8 and 1/2 I.C. sizes in C-2 grade.
 

P. Waller

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#12
As an example of unstable work holding.
I did this last year, 28" diameter burnout in 304 stainless, face, drill a center hole then bore a 8+" diameter counter bore about 1/2" deep.

The stock is only 3/4" thick.
34" aluminum disk bolted to a 24" faceplate, gap removed from lathe, boring bar held upside down with the spindle ran in reverse in order to span the gap.
This is EXTREMELY DODGY work holding. This lathe does not support CSS which made it virtually impossible to achieve a uniform finish across such a large facing operation as can be seen. It did not even come close to the flatness requirement on the drawing but was not red tagged by the customer.

Dodged a bullet on this one.
It took over 18 hours from start to finish including set up.
 

Kroll

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#13
Thanks guys for the help,I do want to kinda get setup with the correct tooling for making parts out of 303 so I will give other inserts a try with a smaller nose radius.Maybe I also need to come up with a different way of making these disk which are for fine adjustments for DP.What I did is take 12" 1.5 rod cut into disk on band saw,then I chuck up the disk and drill,tap for the threaded rod.Next I chuck up a 1/2-20 bolt with rod coupling so that the jaws had something solid.The bolt would only protrude just enough out past jaws to allow me to screw on the disk.Maybe my plan is wrong on how to make these.
But from these suggestions I need to better support the part,use/try different insert smaller radius or HSS. Here's few pics of my setup so if ya'll see any problems or know better way to support please let me know.Thanks for all the help IMG_0508.jpg IMG_0509.jpg IMG_0510.jpg
 

BaronJ

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#14
A positive rake tool would do much better, 303 does not tend to work harden to my experience, have made hundreds of pounds of chips with it; call it screw machine stainless. I use TPG inserts with it in 3/8 and 1/2 I.C. sizes in C-2 grade.
In my experience the dealer doesn't always know what he is supplying !
 

BaronJ

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#15
Hi Kroll,

I don't think that there is much wrong in the way that you are doing that job, just the cutting tool and feeds / speeds need getting right !
 

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#16
Off topic but what kind of chuck is that Kroll?
 

Kroll

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#17
Guys looking in my Shars catalog I see that the insert I am using is for medium finish on SS so I am going to order 424-1051 which is for finishing and has a 7* positive rake which has a nose radius of 1/64.So maybe this will help out some but I know I still need to take a bigger cut,well its to late for this part but I have 3 more that I would like to take a finish cut to where be easier to put little polish on them.If anything that I learn is having the right insert can make a big difference plus speed/feed so no more hand feeding for me
 

P. Waller

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#18
Guys looking in my Shars catalog I see that the insert I am using is for medium finish on SS so I am going to order 424-1051 which is for finishing and has a 7* positive rake which has a nose radius of 1/64.So maybe this will help out some but I know I still need to take a bigger cut,well its to late for this part but I have 3 more that I would like to take a finish cut to where be easier to put little polish on them.If anything that I learn is having the right insert can make a big difference plus speed/feed so no more hand feeding for me
A 1/64" nose radius is rather large for such an unstable operation, try a .008" NR tool.
 

P. Waller

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#19
A positive rake tool would do much better, 303 does not tend to work harden to my experience, have made hundreds of pounds of chips with it; call it screw machine stainless. I use TPG inserts with it in 3/8 and 1/2 I.C. sizes in C-2 grade.
That is a positive rake insert.
 

Kroll

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#20
Off topic but what kind of chuck is that Kroll?
Sorry for not getting back sooner,I look for a name on it but found nothing.The tag that is seen on front just says Make In China with their symbol.Name may be on back side,when I take chuck off when start cleaning up lathe little bit I will see if names on back side.
 
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