Carbide insert

I am new to this type of tooling and having used HSS I tried carbide both on facing and turning for the first time. I was reducing a 22 mm round aluminium bar to around 19 mm. Everything was tight and in order, the only difference is now I'm using a carbide tip instead of HSS. RPM was around 600, works supported by the tailstock. There was a screeching noise during the cut. I reduce the RPM to as low as 300 and it still produce the noise. The tip is ok and I even counter check this on a magnifying lens. The torque screw is tight, the holder is a 8mm square bar to fit the MS-7 tool post. I'm not experiencing this with HSS am I missing something? The overhang is around 15 to 20 mm and I understand carbide will be efficient at higher RPM cutting mild steel is this different with aluminium? Thanks for the replies.

Cheers,

Raphael

Edited By RAPHAEL VAL GOLEZ 1 on 11/10/2018 19:40:46

Apologies for asking, but are you using an insert suitable for aluminium?

Regards

I suspect you're rubbing more than cutting. My chart for ally cutting speed suggests for 25mm diameter 2000RPM with HSS and 4x that with carbide. - Not that most hobby lathes could run 8000RPM.

Type of carbide insert and depth of cut make a huge difference.. for ally the ground tips are sharper and I'd have taken that 2mm depth of cut in one hit (my lathe is bigger than your myford).

I've just been turning some gash unknown hot roll. At 0.5mm depth of cut I get long whispy bits. At 1mm depth of cut I get horrid long long strands of swarf but the finish improves. At 2mm depth of cut the finish is like glass and 1/2in curly bits.- partly 'cos I'm cutting it slower than ideal because they are small parts and I need to be able to catch the autofeed.

pgk

Hi FMES, I have no idea if this insert is intended for aluminium solely. It came with the holder that was given to me.

pgk, I will try to increase RPM although my lathe won't go as high as 8000 as suggested. The tip is likely a CCMT though I'm not 100% sure about this. I'm not also sure if its intended for aluminium. Its cutting as it make a long annoying strands of aluminium instead of chips with a DOC around 10 to 15 thou.

Hi Raphael, as FMES asks, what style of insert are you using?

You are running very slow for aluminium alloy unless you are using a sharp-edged uncoated insert.

Neil

The polished insert on the right is specifically for alumimium alloys:

Carbide inserts will cut at much higher surface speeds than HSS, but it's not necessarily a requirement. It depends upon the material. However inserts do not like wimpy feedrates. I'd agree with pgk squared that you're probably using too fine a feedrate and rubbing rather than cutting. I use 4 thou/rev as a minimum for finishing cuts. If the 15 to 20mm overhang is on the tool shank that's one hell of an overhang. It should be less than half that.

Good luck, but with an unknown insert in a holder someone gave you you're probably on a hiding to nothing. There was a reason they gave you the holder and insert in the first place.

Andrew

Thanks Neil, will try to increase RPM.

Thanks Andrew. Always good to learn from well experience members here. Not that i don't do research of my own but the forum is just a gold mine and collection of knowledge and years of engineering experience and I find it very useful as everyone here always helps out.

I can see the difference with the insert you posted. The one I have is on the left, unpolished. I will try to get the polished one as suggested. The holder is used but not abused and looks Ok. It was just given to me by a friend who works in a CNC lathe fabrication. Its a tool he is not using and was thankful that he gave it to me for testing. If all works well then maybe I can invest on carbide tools although I honestly still preferred HSS. I'm also willing to give carbide tools ago hence this test. I have a lot to learn and appreciate all the inputs I can get here.

Edited By RAPHAEL VAL GOLEZ 1 on 11/10/2018 22:39:11

The polished inserts I use are designated CCGX.

The third letter is listed as 'tolerance' in most of the charts, but seems to actually be 'cutting edge radius' in practice. So an xxGx is likely to be a polished sharp edge insert, while an xxMx insert is likely to be a honed and/or coated one with 'not sharp' cutting edge. All the other shapes and dimensions will be identical for a given value of x.

Edited By Mark Rand on 14/10/2018 00:25:59

I use ali inserts all the time for copper and concut that the third letter must be G. The shiny ones Andrew pictured are CCGT, you can get a box of 10 for under a tenner from china. They last ok and can be used at relatively low speeds

G = ground

M = moulded

Neil