Endmill smear of metal

My 'logic' is Brass is 'slippery' and with any kind of rounding on the cutting edge it skates off the surface. With lathe tools this can generate a series of cut skate cut events without achieving a stable continuous cut. Sharp tools as in comes to a fine edge at the cutting edge rather than has acute angle geometry.

With your massive cut perhaps you don't notice. You really do feel it when filing.

regards Martin

The woodworkers who can be even more fussy about tool sharpness describe a cutting edge as where two faces meet, the crisper the external corner where they meet the sharper the cutting edge. So even with negative rake if the edge is not really crisp and has any form or rounding due to wear or bad sharpening then you won't get a good cut in brass.

Stuarts very soft gun metal is one of the worse to cut without a burr and a blunt tool can even see thin section parts bend away from the edge being cut so keep things sharp, good HSS flycutter works well as they are easy to sharpen unlike milling cutters that most beginners won't have the machines to sharpen.

Edited By JasonB on 22/03/2021 14:57:34

Exactly. I go as far as honing my brass tools.

regards Martin

Well I had thrown a couple of Stuart bearings into the scrap as I did not use then on the just finishe dVictoria so dug them out and took a couple of cuts. I'm assuming Nick is using the end of the cutter to clean up the 10V parts as there is not much else that needs milling.

First up was a 10mm dia HSS 4-flute cutter of the cheap far eastern type that has been used on a bit of everything and the corners were starting to look a bit worn but it cut quite well and did not leave too massive a burr though you can see it is pushing one along the edge. 2000rpm, 240mm/min feed 0.5mm DOC x 9.5mm width of cut. The SX2P may need a slightly slower feed than my X3.

Not the best side by side by side photo, I've not removed any burrs

But not a bad finish from the ali specific one.

why spend cash on new end mills and carbide bits,when a simple home made flycutter with a hss toolbit or broken centre drill ground up to shape costs next to nothing and will produce a better finish as the tool tip rad,cutting clearances,rake etc can be chosen to suit the job by using a bench grinder.The burr is manly caused by blunt tooling.

As my mill is smaller I have found flycutting a nerve-wracking experience (vibratory!) and avoid it where possible. I use a carbide insert shell mill instead with good results. It was £25 including R8 fitting and it gets used quite a lot, so I don't begrudge the money.

Jason, good experiment, thank you. It does look like took sharpness is the critical factor?

I find I tend to feed too slowly or vary during the cut, what I did was download a metronome app. I set it to tick at twice the speed I need to rotate the feed. Then just follow the ticks top, bottom, top ... when turning the feed.