Machining Brass

[Peter Simpson 1Participant @petersimpson1]

Today I started to make two LBSC mechanical lubricators for my loco, I have some 5/16" square brass to start the pump stands. The stands are 1.25" long. I cut two pieces just over length the started to machine them to exactly 1.25" long. I found that using the lathe and a four jaw chuck or the milling machine with a small fly cutter. I found it impossible to gauge the depth of cut. I set both machines to cut 0.007" off the length several times, after each cut I measured the reduction in length only to find approx 0.002" had been removed. Taking the cutter over the brass for a second time no further material was been removed, Why is the cutter not cutting the original 0.007" ?

[Peter Simpson 1Participant @petersimpson1]

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[SillyOldDufferModerator @sillyoldduffer]

Maybe something is moving? Is the cutter good and tight in the fly holder? I occasionally forget to tighten work in the chuck and the cutter pushes the whole job back, blush.

I don't know why I confess simple mistakes – they're embarrassing now I can't really claim to be a beginner! Perhaps one day I'll get it right…

Check the cutting point too. Maybe it's been knocked off.

Dave

[Anonymous]

We all make mistakes. I'm building two traction engines, but I've nearly made enough parts for three.

I'd agree that a mill/flycutter is the wrong setup. The most common brass (CZ121) is easy-peasy to machine. So if it isn't behaving there are several possibilities. The brass isn't free cutting, or may not even be brass, for instance bronze can be horrible to machine. The cutting tools are blunt/broken or have an incorrect geometry. Something is loose. The measurement system is telling porkie pies or doesn't agree with the dials on the machine.

Andrew

[Peter Simpson 1Participant @petersimpson1]

It's not the machines, as I used end mills, small flycutter which gave the best finish and lathe. This does not occur when machining BMS. All gibs were tightened down so I can think it is the tool geometry.

[Bob StevensonParticipant @bobstevenson13909]

Being a clockmaker I keep separate tools for brass with zero top rake…….some people say it’s not important, it is for me.

[Martin ConnellyParticipant @martinconnelly55370]

Use a set up with a mechanical stop. That way there is no chance of the material slipping away from the tool and you can fit and replace the part in the chuck or vice as you cut then measure then cut again.

Martin C

[EmgeeParticipant @emgee]

Posted by SillyOldDuffer on 14/01/2021 15:15:29:

I don't know why I confess simple mistakes – they're embarrassing now I can't really claim to be a beginner! Perhaps one day I'll get it right…

Check the cutting point too. Maybe it's been knocked off.

Dave

Don't feel too bad about it Dave, from another site somewhere "The man who hasn't made a mistake has likely made nothing"

Over the years I have to admit spending many hours machining parts that turned out to be scrap, I think that's what is called gaining experience.

Emgee

[larry phelan 1Participant @larryphelan1]

In that case, I must be one of the most experienced metal bashers on the planet !

Started off with a small scrap box, the current one is almost big enough to hold the lathe.

Learning curve seems to be never ending, more of a long road.

Reminds me of the old song "Keep right on to the end of the road "

Nice to know that I am not alone.

[Tony Wright 1Participant @tonywright1]

I usually keep my mistakes eventually they come in for another job ,so all is not lost .I keep them all in a massive shed 🤣.

[Nick Clarke 3Participant @nickclarke3]

Posted by larry phelan 1 on 14/01/2021 16:59:22:

In that case, I must be one of the most experienced metal bashers on the planet !

Started off with a small scrap box, the current one is almost big enough to hold the lathe.

Shh! don't say that – or no matter what lathe it is, someone will post that's where it belongs!

[old martParticipant @oldmart]

You could check for backlash in the machine leadscrews, not making allowances for it can lead to unexpected errors.

[John ReeseParticipant @johnreese12848]

If backlash is the problem the effects will be exacerbated if the cutting tools are not perfectly sharp. If using insert tools you need a tool designed for aluminum, a perfectly sharp edge and a polished top. If using HSS be sure the tool is honed to a perfectly sharp edge. If an end mill is used for steel it will probably perform poorly in brass. Some machinists keep tools for brass separate from their other cutting tools.

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