Pratt Whitney milling machine progress!

[jim rozen]

Milling machine keeps on happening. This is basically a test fitup of the knee onto the
column, it'll all have to come apart again and the table is just mocked up. For your
enjoyment:





Jim

[Harold_V]

Hey, Jim!

How much are you doing with the mill? Any scraping?

Harold

[jim rozen]

I've been perusing the Connelly book, and the horizontal milling machine section in
particular. The amazing part is, there's actually only a small amount of wear on
the ways on this machine, in spite of it's rather ratty appearance. For example,
somebody had dropped a wrench or something on the in/out ways, so the slide
hung up about halfway along the travel. I was able to remove the ding using
some bluing and a tiny scraper made from a carbide lathe tool that could get
into the tight spot. Now the gibs can be adjusted very tight, and it does not
bind at the ends of the travel, which is where things mostly go to heck.

The other amazing part is, the feedscrews are hardened and ground, and show
basically zero wear. The backlash on the infeed screw for example is about two
thou *total* at both ends of the travel, and in the middle as well!

So my plan is to do a cosmetic/cleanup re-build, and then tackle whatever
scraping jobs have to be done, when it becomes apparent it is needed.

Another approach would be to put this machine in service, and then dismantle
my hardinge UM which has *lots* of wear, everywhere.

Jim

[Harold_V]

Shocking description of the machine. I'd do the same thing---clean it up and put it to work.

It's amazing to find such an old machine in exceptional mechanical condition.

Harold

[jim rozen]

Seeing how this was made, it's no wonder we won ww2. It has the "war production board" tag on the
back of the column. Each of the three feed screws, are run in an angular contact pair bearing! The
elevating screw, that has one bearing pair that the screw itself runs on, and the handle that drives
that screw via bevel gears, also runs in angular contact pairs. Amazing. I have not put the table
back together yet, so I'm not sure really how much those ways are worn.

Jim

[Harold_V]

My initial reaction to the small machine tools is that they are not of great quality. It's a pleasant surprise for me to see such a small machine made so well. Clearly, it was intended for small work, but intended for use in industry.

Be sure to comment again, Jim, as you progress.

Harold

[jim rozen]

The lastest update on this machine, the slides are pretty much together. I had to make the
screws to operate the tapered gib on the cross slide, the ones in there were the wrong shape
and had somewhat rounded over the ends of the gibs. So I made screws with slotted heads,
5/16 diameter and 1/4 inch long heads, 8-32:





Does not look much different except for paint, but the slides are now
pretty tight and could be run as a machine now:



The dial gage was used to check to see how much play was present on the
slides. There's some wear but with the gibs adjusted to give a solid
feel, both slides show about 0.0005 TIR play with a lot of force applied.

My guess is when new that number would be a lot less.

The bad news is, while the cross slide firmed up nice with the existing gib,
the in/out slide did not. The gib screw that draws the gib in, bottomed
out. At that point there was a couple of thou of play. I used a bit of
0.003 inch thick steel shim stock behind the gib, and that was nearly too
much. So there's some wear on that slide.

Jim

[jim rozen]

Forgot to mention last night, after checking the lash in the slides on that machine, I wanted to
see what my hardinge horizontal did. The table traverse, under a thou, but the infeed, several
thou of lash! The gibs were loose, I snugged them up.

Then just for fun wondered what the schaublin cross slide on my small bench lathe
looked like. Zero lash, as shown by that indicator which reads down to about two
tenths or so. Then on to the hardinge cross slide on my second op lathe.

Wow, five thou of motion!!

Wait, the pivot on the compound is moving. One of the hold-down clamps
is doing NOTHING. Another project to look at I guess.

Jim

[Harold_V]

Wait, the pivot on the compound is moving. One of the hold-down clamps
is doing NOTHING. Another project to look at I guess.

Jim

Hasn't that showed up in the way of problems when using the machine?

Harold

[jim rozen]

That machine never gets used for large jobs, but the surface finishes have been rough lately
the last comple of times I've used it. Then again, I don't know exactly when the failure
happened.

There are two nuts that ride in a circular T-slot, and into each of those nuts goes
a vertical post, with a hole crossed drilled into it. The upper part of the slide
has two horizontal holes, with eccentric pins in them. The eccentrics pick up
the cross hole, and turning the pins locks the slide down.

One of the vertical posts had neatly sheared at the threads.

I've not touched those hold-downs in probably two years. So it was "spontaneous
total product failure" I would say. Just one more project to get to!

Jim

[jim rozen]

Ah, a few more photos of the goings-on:



A bit more paint, some more assembly:



It's going to be fitted with a VFD so the location where the motor
control switch used to be, is now going to be the speed pot and
fwd/off/reverse switch:



I really like the wrinkle paint I have to confess. Still to be done, new felt
wipers and a stand.

Jim

[Harold_V]

Looking good, Jim.

I reconditioned an old Troemner triple beam balance some time ago. It was originally the tight crinkle finish, in black, so I tracked down a couple of rattle cans of the same stuff. Turned out great! I like it, too. Covers a multitude of sins, and looks very professional.

Harold