Round insert tool not cutting

[wongster]

Hi folks,

After reading quite a bit on the nice surface finish using round insert tool, I ordered one 6mm dia from CTC Tools. It was sitting on my bench for many month till I decided to do some testing.

I started with some spare SS 304 left over from one small job that I did for my dad. Lots of chatter encountered and I can hardly see the tool cutting into the stock. Thinking it may not be a good idea with start off with SS, I put a piece of alu into the chuck. Again, lots of chatter and I sense more rubbing than cutting.

Anyone has any idea what may be wrong?

I'm using a Proxxon PD400 lathe. The tool is the one in the pic:



I've yet to set it up in a flycutter as I don't have one for the Wabeco mill yet. Thinking of making one than to buy. Had some experience making one for my Sherline with 1/4" tool.

Any advice is very much appreciated.

Wong

 

[sssfox]

Wong,

You might try putting a small spacer under the right side so the edge is angled slightly in relation to the work. If that works, regrind the seat.

These things work really well with wood.

Steve Fox

 

[t_ottoboni]

Take a look in those insert cutting edge: If the cutting edge is a little "rounded", these inserts would work better in high power and rigidity machines and would have a longer tool life. They are better for shearing the workpiece rather then cutting it apart.

For lower HP machines and less rigidity (like most hobby lathes and mills) a razor sharp edge in the tool requires less cutting power, so the chatter and vibration are reduced.

Also, the larger the radius in the tool, you will have a better finish, but the larger the surface lenght in contact with the workpiece, that requires much more HP and rigity from the machine!

I don't mean to discourage you, but a HSS toll bit ground with a rounded tip may work better for your lathe, as long as the tool tip is razor sharp edge (honing after grinding).

I've had done many attempts with "round edges" carbide inserts in my lathe (Sieg C6), following the manufacturer specification (Depth of cut, surface speed and feed rate), and found out that the lathe doesn't have enought rigidity or HP to supply these rpm, feed and deep of cut requirements. I've also found out that carbide inserts doens't like to work at slower rates (booth rpm and feed)!

 

[wongster]

Thanks guys.

I'll try to up the RPM before calling it quit with this tool. Need to get back into the hobby as I just found rust on some of the tools!

Regards,
Wong

 

[rcfreak177]

I've had done many attempts with "round edges" carbide inserts in my lathe (Sieg C6), following the manufacturer specification (Depth of cut, surface speed and feed rate), and found out that the lathe doesn't have enought rigidity or HP to supply these rpm, feed and deep of cut requirements. I've also found out that carbide inserts doens't like to work at slower rates (booth rpm and feed)!

I agree with the above, this type of tool needs a very rigid machine and also high HP to match, Running the lathe faster will only make matters worse.

I would try and adjust the gib-strip to take out any slop, run the tool just below center and slow rpm. As you probably know carbide inserts are not sharp as such so they need a positive cut.

If you made a HSS tool 3mm radius with a negative rake then honed sharp on a stone I would almost guarantee it will work, obviously to get a full 3mm radius you still would still need to step it out to prevent chatter.

I have used the 12mm button tool on large lathes a lot in the past, even they are a bugger but when it all comes together they are a great tool.

Baz.

 

[wongster]

Hi Baz,

I'm now wondering if they sell HSS version of the same type of insert. I bought the HSS version of the other inserts I'm using from AR Warner. I'll check with them. The reason for buying this round insert tool is to have nice looking finish I've seen on this board and others. Even when using autofeed, I got very fine "screw" like lines when turning, which I have to finish off with sandpaper.

Thanks for your sharing.

Regards,
Wong

 

[t_ottoboni]

You can also give it a try with contrary ground tool bits:
how-to-grind-and-use-the-contrary-finishing-tool

 

[narrowgauger]

Hi there

have you cheched the tool height ?? I have found that these should be set slightly low when used on the Proxxon 230 and believe that the same would apply to the 340.

if set correctly you will get a perfect cut. if set too high they will not cut and create a surface that looks like chatter.

hope this helps
Bernard

 

[wongster]

Hi Bernard,

I'll confirm that again when I get home tonight. It's a PD 400. But I think doesn't make a different as compared to a 340.

Regards,
Wong

 

[wongster]

Hi guys,

Reached home passed midnight and therefore no time to test if lowering the insert a little helps.

This is some info on the insert. Its 10mm instead of 6mm I mentioned earlier. There are some data on the right which I don't understand. Anyone can shed some light?

Regards,
Wong

 

[cncjunior]

As regards the cutting info on the Right it is the proverbial "Speeds and Feeds" that is essential when machining on CNC. The vc (m/min) is the surface speed and the fn (mm/rev) is the feed and the ap (mm) is the depth of cut per pass all are the recommended range.

The formula for the rpm to turn the work is: RPM =SFx320/diam.
were SF is surface meters per minute and diam. is work piece diameter in millimeters

Using the above info RPM =115x320/40 eg. a 40 mm shaft
RPM then equals 930 rpm.

The above is a starting point. It is what the insert can handle. It doesn't mean that the machine can handle it. The above info would be for a ridged machine. When cutting with carbide, you need more cutting pressure to get into the material where HSS needs less.

Your cutter needs to be at center height or perhaps a bit lower as was mentioned above.

 

[MachineTom]

As already posted speed and feed are normal for carbide inserts, But the doc is .4 to 2.0mm> can a mini lathe take a .4mm cut in SS 304 I doubt it. With all that radius there needs to be a good load on the bit to prevent chatter, your asking too much from your machine.

 

[wongster]

Thanks for your input, guys. I lowered the bit a hair and it started cutting aluminium. Still no joy on steel, but I'm happy enough; at least it cuts something...

Regards,
Wong

 

[V. Lehtonen]

I'm still greenhorn in these things but what if you'd take a small Ap/ high feedrate approach? Keep the depth of cut small but increase the feed, achieving the similar load than the normal Ap/slow feed combination? It could help against chatter

 

[cncjunior]

There is a common saying in the trade schools teaching machining that if there is chatter and everything is secured properly then reduce speed and increase feed. This would go along with what V. Lehtonen is saying.

Out of curiosity, wongster, are you using the radius insert just to machine a groove or radius on an inside corner? If you are using the radius cutter for general machining as in OD turning or facing then you might want to use a different insert style like a CNMG 332 or (?) depending on what profile you need. The reason being is that your 10mm round insert is one of the more challenging tools to use with the frustration level on the high side. There are other inserts that are easier to use and cause less frustration.
http://www.homemodelenginemachinist.com/members/v.+lehtonen

 

[wongster]

Hello guys,

I tried increasing the feed as well as reducing the speed with no joy. Read that from Joe Martin's book.

As in the use of the profile tool, it is merely experimental. Read about the good finishes it can produced and therefore bought one to try it out. It did work well on aluminium after lowering the tool height a hair.

If its not meant to be used on my machines for SS, I'll leave it just for aluminium. Maybe make a flycutter to go with it.

I really need to get back into the shop to start working on something. The last job I did was a simple job for a foreign student who is making a micromouse for a school project.

Regards,
Wong

 

[gus]

Hi Baz,

I'm now wondering if they sell HSS version of the same type of insert. I bought the HSS version of the other inserts I'm using from AR Warner. I'll check with them. The reason for buying this round insert tool is to have nice looking finish I've seen on this board and others. Even when using autofeed, I got very fine "screw" like lines when turning, which I have to finish off with sandpaper.

Thanks for your sharing.

Regards,
Wong

Hi Wong,

Try using Tapmatic Tapping Fluid when cutting with HSS cutters.
Use a small brush to apply dobs of fluid. Works well on steel and aluminium.
Gives good finish.

Recently tried boring with Warner Boring Bar with HSS bit.Very happy with the finish when boring aluminium. Again with some dobs of Tapmatic,I got smooth finishing.

When parting off,I used very thin parting tool from LMS with Tapping Fluid.
I have not broken parting tools for a long time.

For my Mini Sakai Lathe,I have given up with carbide tools.

I am looking at buying a PD400 which is a bit pricy.Are you happy with yours.

Gus Teng.

 

[wongster]

Hello Gus,

Tapmatic gives me a headache whenever I use it. So I bought a small fan for better ventilation. As for thin parting tool, I gave up after having it jammed midway. So I use the insert parting tool from Glanze or the thicker one (HSS) that I bought as a set from Proxxon.

I'm able to use carbide turning tools on the PD400 despite its size. So far the lathe has done its job well though I've had problem in the pass. They were all the user (me) and not the machine, I would like to think. I would sometimes wish I had bought a SIEG and be able to follow some of the modds found online. But as a newbie to the hobby, I don't think I'm able to set it up right to begin with. That's the same reason why I bought the Wabeco mill after careful consideration, drawing from the experience with the PD400. I wish now that I bought the Wabeco lathe instead...

You're welcome to contact me offlist to arrange to try out the PD400 at my place. I'm available most Saturday, at least for now.

Regards,
Wong

 

[chrsbrbnk]

In general the larger the radius of a tool tip the more rigid the machine must be. So if your cutting tough material stainless for example the smaller the tip radius on your tool the better. another factor is to look how the cutting forces are being resolved . a large radius is pushing the work heavily side ways causing the work to flex away from the cutter a tool the pushes more towards the head stock push the work in a column mode much stiffer than a bending mode try to picture where the cutting forces are going and how large the cutting surface is the smaller the forces the easier and many times more accurate the cutting

 

[wongster]

Thanks Chrsbrbnk. Would putting the stock between centre helps?