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Old 16th August 2006, 11:57 PM   #1
bulgin is offline bulgin  South Africa
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Default Milling dead perpendicular

Hello

I have a small home workshop equipped with a small milling machine and a lathe. These machines are set up almost to pefection with analogue clocks in all directions as this is required for what I make. Fitted to the milling machine is a precision milling vise. The item I make has to be drilled absolutely and totally perpendicular along the vertical. Over the years I have devised a few dozen jigs to aid in this requirement. The latest jig is in two parts. The one part fits precisely over whatever has to be milled vertically and the other part fits into the milling chuck. The mill's bed is then manipulated until the jig's two parts fit into each other, while the job is in the vise. Once all is setup to mill deadcentre and perfectly vertically, I take the jig off the chuck and the job and fit a cutter into the chuck and proceed to do the job.

Standing on my head and pulling out my few hairs left, there is always a small offcentre error of a few fractions of a millimeter.

I suspect it could be the vise which tilts the job ever so slightly, but this tool has also been fettled so that there is almost no play on the jaws and if they are closed, you cannot get the finest feeler guage between them.

Getting to the point, do you think it would be possible to fit a redbeam laser into the chuck and then to manipulate the mill's bed so that the beam is deadcentre over the marked position on the job?

My mill's chuck can take up to a 16mm cutter but this will be too costly to use to aim a laser.

I have also made a 16mm precision threaded mandrel onto which is fitted a high precision Jacobs chuck with a capacity of up to 7mm.

I'm thinking along the lines of a laser beam widget that looks similar to say, a Solitaire Maglite, but about 7mm dia. which I can fit into my mill's chuck, aim the beam and manipulate the mill's bed until the job is lined up.

Are there such things?

Replies gratefully accepted!

bulgin
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Old 17th August 2006, 12:23 AM   #2
poobah is offline poobah  United States
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http://www.mcmaster.com/nav/enter.asp?pagenum=2130

Look for wiggler / center finder.

You can also make something simple. Put a plain piece of round stock in your chuck... and file it to a point while the chuck is running.

Or do it on your lathe. You just need a fine point.

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Old 17th August 2006, 01:28 AM   #3
Ron E is offline Ron E  United States
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http://www.finelinehair.com/home/tramming_the_mill.htm
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Old 17th August 2006, 10:32 AM   #4
bulgin is offline bulgin  South Africa
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Default Milling dead centre perpendicular

Hi poobah, ron

I already have all these things - a wiggler, finger clocks and other analogue guages. The job I mill is a component carrier in plastic for moving coil cartridges. This horror is cylindrical in two diameters and square at the back. There are several slots, recesses and threaded holes. I've made jigs to hold the piece while milling or drilling and everything is set up true with clocks.

What I wanted to do was once the 'blank' has been turned on my lathe, was to make 'mark' with a small centredrill before it comes ot of the lathe and then transfer the job to the mill, held by a jig.

To give you an idea of how accurate things should be, the front end is 6mm dia and it has an angled 5mm recess 5mm deep and a threaded 2mm hole further on.

My jigs hold the job securely but I would have thought if you could fit a 1mm red laser device into the milling chuck and manipulate the bed until the beam is dead centre on the guide
mark, then fit whatever cutter is needed.

The wellknown 'wiggler' and analogue machine clocks are fine for normal work but not on the stuff I do. The reason is simple - if your're 'out' by even the smallest fraction of a millimeter, the stylus points offcentre.

Thanks for your replies & kind regards

bulgin
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Old 17th August 2006, 01:17 PM   #5
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How about a dwg or photo so we can understand...

Are you trying to pick up an ID turned on the lathe when it goes over for milling?

Is the ANY chance you are picking up tool deflection in the milling op?

Length & diameter of milling cutter?

Length/diameter ratio of cutter?

This is handy for re-establishing center points on parts to be milled... it clamps on the quill spindle.

http://www.phase2plus.com/details.as...r_Holder&id=90
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Old 17th August 2006, 01:45 PM   #6
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just a stab in the dark, but would the tightness to which you chucked and "vised" have any implications? From my own experience, I know it's darn near inpossible to put anything back precisely once moved. Even using stops are not ultimate many times, depending on how much you tighten or cinch. I also know that setups used for precision are often left alone to do that job in a dedicated fashion because setup is time consuming.
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Old 17th August 2006, 02:30 PM   #7
DaveM is offline DaveM  United States
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Did i understand correctly that you are doing a hole in a cylinder that you prevously turned on your lathe?

If that is the case, and I realise this is obvious but needs to at least be said so we can understand better, why not simply drill the hole necessary while the cylinder in on the lathe using the tail stock to hold a jacobs chuck?
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Old 17th August 2006, 02:39 PM   #8
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Bulgin,

Some pictures would be real handy!

If I understand correctly, you have difficulty in setting out the drill's entry point into the material accurately?

Why not just take a thin silversteel rod, turn it down to a sharp point on one side, and put this into your Jacobs to "feel" the center of the hole? (I can have this CNC cut for you!) This should be simple enough, unless of course I am missing something from your description of the problem!

The maglight laser is a good idea, BUT, you need to ensure that the laser is mounted perfectly at the center, and shoots out perfectly parallel to the sides of the device, thus perpendicular to the mill's table. The former should be fairly easy, but the latter could be very difficult to achieve.

Also bear in mind that even a 1mm dot is relatively big when you are concerned about fractions of milimetres!

Another option:

You get a type of microscopic alignment tool, that attaches to the mill (it has a morse taper attachment), and allows you to align it absloutely perfectly, using crosshairs and a magnified image. I worked at Kentron (Denel) for a while, and we used to use these for absolute precision. My fear is that this might be too expensive for home use though...

Willem
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Old 17th August 2006, 02:41 PM   #9
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You're probably already more familiar with these sites than I am,
but perhaps posting at these forums may help. These guys are
dedicated to making tiny precision parts in their home shops.

http://www.chaski.org/homemachinist/...0aa45ccd23cc94
(There are probably busier miniature I.C. engine builder's forums on the web out there.)

http://www.cnczone.com/forums/forumdisplay.php?f=165
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Old 17th August 2006, 07:45 PM   #10
bulgin is offline bulgin  South Africa
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Default Milling dead centre perpendicular

Hi Chipco3434, RetroAudio, DaveM, Willem Fick & bluebeard

A real brainstrust here I see!! My gratitude and thanks for all the useful suggestions and links. The problem with this little part has also stumped my fellow members at the Cape Town Society of Model and Experimental Engineers.

@ RetroAudio I think you homed-in on part of the problem - the hand-torque applied to my milling vise. After the turned 'blank' comes out of the lathe chuck, it is then inserted into a two-part 'holding jig'. The other part of the jig goes into a precision Jacobs chuck, taper fitted onto a threaded 16mm mandrel with no run out, which in turn is fitted into the collet chuck of the mill. The latter runs perfectly true.

At this time, the job, fitted into the bottom part of the jig is in a vertical position in the vise for the purpose of alignment with the top part of the jig.

I then manipulate the mill's bed until I have 'perfect' alignment with the vised job. In other words, the top part of the jig (in the chuck) has to have perfect alignment with both the jigged job and the bottom part of the jig as well. To make absolutely sure the job is centred, it is sprayed with engineers' blue and the top part of the jig rotated by hand until there are no marks left by this part of the chucked jig.

Now comes the part where all these shanoogles go wrong. Since the 5mm dia x 5mm deep circular cavity to be milled at the tip of a 6mm dia plastic roundbar must be angled @ 20degrees off the vertical, I am now compelled to remove the job (still held in its jig) and tilt it and then 'vice-up' again. I think (as RetroAudio pointed out), the 2nd revising before milling is where things go wrong.

The degree of 'offcentreness' of this cavity (where the cart's magnet goes) is so small that it cannot be seen by the naked eye, but causes all parts inserted to be off centre.

I have in the past (while the blank is in the lathe) pipped a 1mm hole in the tip, which I then lined-up in the milling machine with an identical centredrill in the mill chuck.

Even this is not foolproof as the centredrill and its holding components (The chuck) is steel and the job is engineering plastic of 6mm dia. I think the slightest touching of the job by the steel guide drill, deflects the plastic job.

If such a 1mm (maglite) type chuckable laser beam is available, the job can be inserted already angled and the beam positioned over a pre-marked deadcentre pip which I could colour with engineers's blue.

Btw, each of these little horrors take about 3 hours to turn and mill from start to finish. At present, the reject rate is about 40% and this you discover right at the very end.

As a further aside about the crucial job dia of 6mm, this was ultimately determined by the standardised 1/2" distance between cartridge mounting holes. If I make these parts for an alu bodied cart, I at least have 7mm to play with...

Thanks so much once more for all the kind info and suggestions. I will check them out one by one.

bulgin
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