Which mill cutter to use?

[Matthew ReedParticipant @matthewreed92137]

As a competent lathe user, now on a steep learning curve with SX2P mill, I have read all the usual books, but still not seen an answer to this sort of question.

I have two blocks of (free cutting) mild steel, 20x30x12mm, need taking down to 19x30x12.

Priority is accuracy, with surface finish secondary, but not bothered about time. Will be held in a vice, on parallels, against an end stop, so set up is repeatable for each block.

Do I cut deep or shallow?

large cutter using less of it, or small using more of it?

I'm inclined to go with the 16mm cutter, cut all 1mm depth in one go, using about 2mm width of cut… but I am guessing.

I've seen something like "go as deep and large as you can without shaking" but…

There is plenty of advice about what speed of feed/spindle will work be best with any of these options, but nothing really to recommend which approach and why.

So how would you do it.

Matthew

[Matthew ReedParticipant @matthewreed92137]

Big or small, deep or shallow?

[Neil WyattModerator @neilwyatt]

Well a 1mm deep cut is well within the capabilities of an SX2.

Face milling capacity is given as 35mm, so in principle you could just make two passes with the 16mm end mill.

With my X2 I would probably use a 1/2" end mill and do it in about four passes.

Neil

[Anonymous]

If the surface finish is poor, then by definition so will be the accuracy.

Since you only appear to be reducing in one dimension by a small amount I'd use the biggest cutter that would fit and take full depth and at least 80% of the width per run, if the mill is up to it.

If your block is cold drawn, and not annealed, all bets are off anyway, as it will distort if you machine off one side.

Andrew

[JasonBModerator @jasonb]

I'd flycut 0.5mm off each opposing face, full width, 1 pass each side. I tend to use a flycutter quite a bit for sizing blocks as they work well for me and are cheap to sharpen.

 

Edited By JasonB on 26/10/2016 20:56:15

[VicParticipant @vic]

I'd use a fly cutter as well but I'd do it in several passes with a finishing cut.

[duncan webster 1Participant @duncanwebster1]

+1 for flycutters, as Jason says at least you can keep them sharp without a load of complicated kit.

[Ian S CParticipant @iansc]

I imagine it is cold rolled steel, take off .5 mm on one side, then turn it over and take off the .5 mm, and with any luck it might not distort. I would use my face cutter it is 50 mm, and uses 3 carbide tips, 2 better than a fly cutter, but a fly cutter will give at least as good finish if not better, and you can make your own.

Ian S C

[JasonBModerator @jasonb]

On such a small block I doubt most of us could measuer teh distortion, it would be more noticable on a larger piece. I just tend to take a bit off both side sas even cold rolled (bright) bar has a few pits in teh surface.

[Neil WyattModerator @neilwyatt]

I haven't the patience for flycutting, If I had a 16mm cutter, I'd use it, plus I've just noticed the cut is only 12mm wide!. A flycutter will just be wasting time cutting air.

Do it in one pass with any endmill over 12mm wide, or if you want to be posh like Jason take one cut off each end.

Neil

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