Milling – difficult to gauge exact cut

[David LittlewoodParticipant @davidlittlewood51847]

Richard,

 

I think you might want to re-think how a 2-slot cutter actually cuts. Looking down at the workpiece from behind the cutter, the tooth at 9 o-clock starts cutting at the same moment that the other tooth is at 3 o-clock and leaving the cut. When the cutting tooth moves towards 12 and the sideways thrust is increasing, there is nothing, other than that tooth, to cut. This is why a slot drill does not cut a wide or wobbly slot. A 4-tooth end mill has at that point got another tooth, now at 9 o-clock, and the sideways thrust causes it to cut the slot wider than the nominal tool diameter. Worse, if the feed is not consistent and the side thrust thus varies, the amount of offset also varies accordingly and the slot is not straight.

 

I find cutting slots with 2-flute cutters, from 2 mm to 12 mm, with a fairly light mill (Emco FB2) gives a good clean and accurate slot.

 

I have often considered how to use a vertical mill as a quasi-horizontal one; the best option seems to be a long angle plate. I have been gathering the material to cut the flutes in some coupling rods this way.

 

David

Edited By David Littlewood on 29/01/2012 17:56:33

[Anonymous]

I wonder what happens to the cutting forces if you use a single flute slot drill? Is it any different to a two flute slot drill?

 

Regards,

 

Andrew

[Anonymous]

David sneaked in before my post appeared; I agree with him regarding the slot drill cutting.

 

On the subject of converting vertical mills to horizontal I think it’s a bit of a waste of time. I do have a horizontal attachment for my vertical mill, but I’ve never used it. I certainly wouldn’t want to take heavy cuts with it, even with a relatively small side and face cutter. Much better to get a real horizontal mill. They’re pretty cheap, as they’re no longer used in industry. My horizontal mill cost £150, and it’s built like the proverbial brick outhouse.

 

Regards,

 

Andrew

[Chris TriceParticipant @christrice43267]

Posted by David Littlewood on 28/01/2012 23:42:55:

Chris,

 

That sideways cut is why you should not use an end mill for slot cutting. With a 2-flute slot drill it doesn’t happen.

 

David

I know but Wolfie said he was using a milling cutter. Even with a slot drill, if it’s a small diameter and the cut quite deep, unless it’s a straight flute version, there’s still a tendency to pull slightly though a lot less and usuall good enough.

[Chris TriceParticipant @christrice43267]

Double post

Edited By Chris Trice on 29/01/2012 18:24:43

[Tony Pratt 1Participant @tonypratt1]

With all things machining you can’t expect to rough and finish a job to any degree of accuracy in 1 operation and 1 tool. The best possible slot will be achieved using a smaller cutter to rough out with and working up to the final size slot, the less metal the final cutter removes the better. A slot drill is usuable preferable but is limited in length and if a precision slot is needed you really need to use a smaller cutter and move either side of the centre line until your required size is reached. This all takes time I know but you will be pleased with the result.

Tony

[Chris TriceParticipant @christrice43267]

I agree with Tony. When it really counts, cut it undersize and then open it out.

[Sub MandrelParticipant @submandrel]

Some folks have been reading GHT on slot drills…

 

Neil

[Author]

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