Machining a long part

This topic has 8 replies, 8 voices, and was last updated 25 April 2019 at 13:34 by Howard Lewis.

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23 April 2019 at 13:39 #406166
Patryk Socha
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@patryksocha88647
Hello. I am very new to machining, and my limited knowledge was sufficient for what I was doing so far, but the recent project proved to be a little bit more challenging.

So what I need is to mill with reasonable precision some features on both ends of long (550mm) workpiece. 550mm exceeds the X travel of my table, therefore I need some way of doing this in two steps. My best idea so far is to make some kind of reference edge in the centre of the part, use it as an origin point, machine features on one end of a part, then flip it 180deg, find origin point again and then machine the second end of the part.

Is there a better way to do this? Tried searching online and in those mach9ining books, I have on the shelf, and could not find much…

Edited By Patryk Socha on 23/04/2019 13:40:09
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23 April 2019 at 13:39 #9633
Patryk Socha
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@patryksocha88647
23 April 2019 at 14:10 #406168
Mick B1
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@mickb1
I don't think your question can be answered without knowing what the workpiece has to fit and where the features need to be datumed from.

In general principle your suggested method seems sound so long as you can locate off the central reference accurately.

Alternatively, if each feature is datumed off some corresponding feature at t'other end, you might calculate the position of your end features from each end of the workpiece at nominal length, measure the actual length to enable you to factor in an offset, then position the features from each end – less winding and less risk of any leadscrew pitch errors, but any such should be inconsiderable anyway in a properly-made machine.

Sometimes there just isn't a perfect or efficient method available, or not one you can think of in the time you've got. Then you just have to do the best you can with what you have and what you know, and figure out how to cope with unintended variations as you come up against them.
23 April 2019 at 14:17 #406171
John Hinkley
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@johnhinkley26699
It also rather depends on the material you are trying to machine. If it's round, I'd clamp it in Vee blocks with a fixed end stop to butt up against and do all the measuring from the end. If it''s flat, just clamp to the mill bed, again using a fixed end stop to locate it and reference from the end again. More food for thought? This all supposes that the material is accurately machined to length to start with.

John
23 April 2019 at 14:28 #406173
Weary
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@weary
As stated above depends what you are machining, accuracy required, shape before and after machining, etc..

But, as a generalisation, what about some variation of:

Position one end of work conveniently for machining.

Machine as required.

Bolt a fixed block to the table hard against end or some similar feature(s). Add more blocks as required against work-piece to define position.

Remove work-piece and change end for end butting un-machined end or features against your fixed blocks.

Remove 'datum' blocks.

Machine to same settings as first end.

btw Nice steam-punk avatar!

Regards,

Phil
23 April 2019 at 14:28 #406174
JasonB
Moderator
@jasonb
I've used Vee blocks and ER Collet blocks in the past. if the block is placed in th emiddle you can locate off the same side of the block which will pick up the length and having a flat surface you can register that to the table so there is no risk of round parts twisting out of position when moved about.
24 April 2019 at 22:22 #406338
John Reese
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@johnreese12848
On the Bridgeport type machines one can swivel the turret and rack the ram in or out to cover both ends of a long part. Sometimes it is necessary to create a reference point on the part or on the machine table so work on opposite ends can be kept in register. I have often used a block with a bored hole as a reference and just clamped it to the table.
24 April 2019 at 23:27 #406343
Neil Lickfold
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@neillickfold44316
Like been said, more is needed to be advised correctly. Does the detail require any radial alignment?

So simple sliding fixtures can be made to hold and support parts that need detail at the end of a long workpiece.

There is numerous ways of indexing a length etc.

Neil
25 April 2019 at 13:34 #406402
Howard Lewis
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@howardlewis46836
If the surface produced has to be at the same level, from end to end a depth stop needs to be set. Whilst roughing out it may not matter if the resulting surface differs very slightly in level, but the finished surface after both cuts will need to be same. Obviously, it is essential that the clamping arrangement ensures that the workpiece is held in the same place, horizontally and vertically.

It may be useful to rough both ends, before taking the finishing cut on one end and then reverse the workpiece, again,for the second finishing cut.. My suggestion would be that the second finishing cut slightly overlaps the first, just to ensure that both are at the same level. A small piece of cigarette paper, stuck to the work with oil, may help. Fag papers are usually about 0.0015 (0.0381 mm ) thick; CHECK!

Howard
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