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CNC Mill Head

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LarryTheKing

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#1
Taking a buddy's advice that I should start documenting my projects, thought I would share a bit.

Brief intro, I've been dreaming of building a CNC mill for a while. I have a closet full of servos, control boards, linear rails, and other misc parts.
I had been designing a weldment frame, but it was proving to be a bit more of a challenge than I had time to tackle - so the project has been shelved for a few years.

And then this showed up on Craigslist:
IMG_20180907_171256.jpg

which reinvigorated the project!

A Bridgeport inspired CNC bed mill frame, complete with ball-screws, hardened ways, and beefing castings (funny how sometimes Craigslist has exactly what you're looking for)
Taking a weekend away from school, I made a trip to look it over, and ended up having a long conversation with the gentleman selling it and arranging to have a good buddy pick it up.

The bed mill is designed to mount a Bridgeport head, however I have a beefy 30 taper cartridge spindle in my collection of parts.
Thus began this project, making a spindle adapter.

IMG_20171102_131745.jpg
- a shot of the bt30 cartridge spindle

Starting with an 88lb round billet:
IMG_20180908_134842.jpg

and turning it round (maxing out the above cross slide swing on this lathe)
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chopping off the end and squaring it up
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and making clearance for the 3" head swivel gear on the student shop Tormach
IMG_20180914_150429.jpg

machining two large 5" flats
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Some quick metrology showed I was easily within 0.001" on my flatness, widths, and parallelism. The surface finish was also beautiful
IMG_20180920_163840.jpg

some long drilling was needed for the 6" bolt circle (these holes were first drilled 3" deep on the mill)
IMG_20180924_100417.jpg
and countersunk for a wide nut and washer
IMG_20180924_123216.jpg

Next began the most interesting part of this project, boring the 90mm hole for the spindle.

a fixture plate was made to bring the part to the appropriate height on the lathe cross slide
IMG_20181001_160058.jpg

and then it was bolted down and drilled (with first a roughly 1/2" through hole, a 2 1/2" and finally a 3" spade)
The spade bits have a morse 4 taper, and lacking an adapter, I purchased a cheap mt4 to r8 adapter and sawed the r8 portion off.
The four jaw chuck does a good job of holding the bit securly on center.

IMG_20181001_164950.jpg
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Next the bore was line bored with a 2" boring bar I made special for this project
IMG_20181002_165815.jpg
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The final bore came out with 0.0008" of clearance and 0.0003" of taper as measured with a tenths reading dial bore gauge.
The fit was great, having 0.0005" of wiggle with the spindle inserted.

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a 106mm bolt circle later and the hardest part of this project look done

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The spindle bore measured to be "dead nuts" square with the flat, however the mounting plate had 0.002" dip over its width.
I'm planning on scraping in the mounting flange so that the spindle is in the same plane, and so that it has good contact with the mill casting.
This will likely be the last step before mounting.

Also, the part now weighs around 48lbs, meaning that close to 40lbs of chips have been swept off the floor :)

The next step is to design the mounting bracket for the pull stud's pneumatic cylinder and the bracket for the 3hp drive motor
Playing around in Fusion360 with some ideas still.

cad.PNG

I have some videos of the setup and machining (including some high speed footage) that I'd like to share soon.
I'm going to try to keep this thread updated as I make progress, however I think it'd be cool to make a 10 minute video of the entire process, or maybe a short series (thoughts?)

Thanks for reading
- Larry
 

LarryTheKing

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#2
Uploaded some of the high speed footage to YouTube.






- the line boring clips seem to have a bit of stuttering in them
 

mattthemuppet2

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#3
dang! what an awesome project! Thank you for sharing it with us and I look forward to some more heavy duty machining. I particularly like your shopping basket pic :)

A question - why drill and line bore the headstock on the lathe instead of in your mill? Were you worried about taper from a long boring bar in a boring head?
 

JimDawson

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#4
I'll be watching this :encourage:

Looking good :)
 

LarryTheKing

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#5
dang! what an awesome project! Thank you for sharing it with us and I look forward to some more heavy duty machining. I particularly like your shopping basket pic :)

A question - why drill and line bore the headstock on the lathe instead of in your mill? Were you worried about taper from a long boring bar in a boring head?
A couple reasons to do this on the lathe, with avoiding taper being a big motivation.

The line boring setup was more rigid than anything I could have rigged up on the mill, and the bore being slightly longer than the quill travel (5.5") means I'd have been cranking the knee up and down for each pass.

Also, there was no way I'd have been able to use these spade drill on the mill - even the lathe at 50 rpm with 3hp stalled a few times pushing the 2 1/2" spade through - so I'd being taking a lot of passes once I maxed out the drill capacity on the mill.

It was actually really easy to make a spacer, square the part up on the lathe and go to town!
 

mattthemuppet2

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#7
very neat, thanks for the details!

Also, after having done my first boring on the mill, I can see why you'd want to do it on the lathe - speed! Can't believe how long boring takes on the mill.
 
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