The material of both bright and black steel are the same the hardness is the T which us the same in both products.

David

As alluded to above, I assume it doesn't need saying that you don't want to let your nice sharp involute cutter anywhere near that nasty black mill scale. It'll knock the edge off the cutter quicker than you can say pickle.

There, I've gone and said it now…

Given both are EN24T it doesn't matter if they're cold drawn or hot rolled. In theory the cold drawn will have internal stresses. But on the assumption that the material is hardened and tempered after drawing that won't be the case.

The question of mill scale isn't really an issue. One, when cutting a spur gear the cutter normally approaches the OD from within the material. So it never has to cut the scale. Two, hot rolled is unlikely to be to size, or even round, so the OD will need to be machined first anyway.

Andrew

Andrew (or others), is gear cutting always carried out by conventional milling – even on large commercial machines?

Clearly, climb milling is not usual for our smaller, less rigid mills – even a bump, and not table movement, might upset the more flimsy rotary tables used by some.

What about hobbing, while on the topic. I suppose this metod of gear cutting has to be done conventionally, just to get started?

.

I don’t buy it, Jason … so I can’t answer that

The reason for my confusion was that Adam asked why ‘black’ was more expensive, and you explained why it was cheaper.

MichaelG.

Must be getting old, I thought I made my 6DP traction engine crankshaft gears from EN8, but looking back I actually made them from EN24T. Gears shown here, before the splines were machined:

If I recall correctly I had to turn at fairly high speeds to get the nice finish with insert tooling; probably 800 or 1200rpm. Depth of cut and feeds were nothing special.

I cut the gears in one pass; anything else is a waste of time and just increases wear on the cutter. Spindle speed would have been around 60rpm. I can't remember what the feedrate was, but I normally aim for around 4 thou per tooth when horizontal milling. Anything much less and the mill shakes. Gear cutting shown here; coolant not essential but it does help cool things down:

The cutter was secondhand, bought from the US via Ebay. A new cutter should cut a complete gear without a problem, although it may depend upon the source of said cutter.

Andrew

Multiply RPM x number of teeth on the cutter x 0.004" and that will give distance per minute feed.

That seems quite a lot of teeth

I would have expected about 12, have you got a picture or link as teeth would be very thin

Edited By JasonB on 10/10/2019 11:54:39