New VMC build - industrial CNC

[hanermo2]

Further worked on the new yoke for lathe x axis.
7 hours.
Good day today .. yoke is now finish-machined re: ballscrew.

This is what I did:
First picked the screw, a 500 mm 32x5 mm ballscrew from what I have (about 5 25-32 mm D screws).

Start-bored the counterbore for the nut body to 2 mm undersize for chip clearance, better visibility, lighten the workpiece.
48 D x 42.6 mm.

Then bored the through clearance hole for a 32 mm screw to 34 mm.
I had previously drilled it to 24.6 mm +/-.

So deep-bored to 61 mm deep, at 60/12 = 5:1 D/L ratio, in tool steel, on a heavy slightly eccentric workpiece.
Using about 74-76 mm long boring bar of 12 mm diameter with ccmt inserts, 21.51 size.
Had about 2-3 mm clearance on the toolmount-workpiece face.

About 0.1 mm depth of cuts, diameter increasing 0.2/pass.
Went from == 10 m/min css to 60 min/min and 60 mm/min feed from 7-10 m/min feed.
And 120 rpm to == 320 rpm on the spindle.

So one pass took about 24 secs at the end, with 1500 mm/min feed on fast moves, only about 2 secs end-end per pass on the G0 rapids.
Around 44-46 passes iirc, 25.x == 34 mm x 0.2 mm D each.
(I keep rapids dialled way down for now.)

Bored the ballnut hole- needed 4 re-set-ups in the 4 jaw chuck !
The factory ballnut must have an eccentricity or oval or bulge somewhere around 20 mm deep .. or a taper ..
The ballnut simply would not go into the bore with a solid "stop" each time trying to mount it.
Yes, I did it 5 times.
Took about 3 hours of work time.

And I was mostly expanding the bore about 0.02 - 0.04 mm each time, since this always worked in the past 10+ times.
Not this time.
So I did it 4 times, each time lugging the yoke, heavy, about 10 kg, lathe to table to lathe -- 4 jaw -- bore very carefully -- repeat ..

It is hard to do, because the piece is big and I need to use a small bar of 12 mm .. on a hole of 50.00 mm D nominal.
42 mm deep for 2 mm clearance bore at the end.
The ballnut mount hole is 50 mm D or ø and 40 mm deep, so I leave 1-2 mm extra bore at the end.
But a 12 mm tool at 42 mm deep + 2 mm clearance = 44 mm / 12 = 3.6 overhang and it really wants to chatter and has high moment arm.

Then mounted screw, marked first 5 holes (one covered by the clamp), drilled 5 mm + 7 mm, + tapped 8 mm --
fit, all 5 screws, marked last hole, drilled and tapped.
Test fit.

Tapping raises the edges of the holes a bit for around == 2 mm from the edge of the hole in M8 size.
Just a bit, a few hundredths of 0.01 mm up from the flat plane.
I will probably use a random orbital sander and low grit to flatten the surface from the tapped holes.
This leaves a nice random scratchy surface that is flat, and wont round the edges, ime.
Bosch green industrial sander 80 grit or so, 1-2-3 minutes.

I have about 30 hours work into the yoke at this time.
Some minimal finishing, perhaps fast disc-sanding since it is not for sale.
Then finish.
Finish with degrease (twice), boil, blacken, boil, hot-oil to seal, steam/boil, done.
(For this use I might just ghetto-finish it and paint it).

My goal was to illustrate a bit what and how and why some bigger commercial stuff is made in workshops ..
and why it is either slow to do or rather expensive.

I believe a yoke like mine will retail 500-1500$ as a spare part for common industrial cnc machine tools in the 25 kw or 40 hp power area.
Except they are standardised parts unlike my one-off.

I plan to do a pic of the yoke tomorrow - as a sample - and post it here.

[Chaz]

Need pics .....

:-)