Replacing a milling machine head

[KeithB]

I've had an Enco brand 10' x 54" vertical milling machine since 2000. It has given good service - the ways, table and screws are all in good shape, but the head had suffered some mechanical problems. The powered downfeed gave out, then the low speed gear range broke. Finding parts for a slightly off-spec Taiwanese mill was impractical. Fortunately there are complete replacement heads available so I decided to simply replace the whole head. I wanted a functional mill, not a long term repair project.

Enco 10" x 54" vertical mill with broken step pulley type head. The box end wrench on the front is on one of the clamp bolts, the ratchet on the rear drives a worm to tilt the head left and right.



I settled on a variable speed mechanical head sold by H H Roberts Machinery Limited in Ontario Canada. Very good folks to deal with! They also sell electronic drive heads that can be interfaced with CNC controls but I have a CNC mill and really just need a good mechanical mill thus my choice.

Replacement head from HH Roberts Machinery Limited.





The first step was to remove the old head. After shutting the breaker off at the box I disconnected the four wires at the machine. Then I loosened up the four bolts on the face of the machine head and used the worm screw drive on the head to rotate the head from the vertical to the horizontal orientation. I made a cradle out of some wood and raised the knee up to support the head on the table. With the weight securely supported by the table I took the nuts all the way off and used the Y axis screw to pull the head forward and off the bolts. Then the hydraulic foot lift was used to move the head to a steel table. I did all this myself over a weekend, a lot of it from a wheelchair. Not all that hard if you think things through and use the right tools!

When Scott came in we attempted to put the old head on by doing the reverse - lift the new head up on the cradle with the footlift, sit the cradle on the table and use the knee elevation and the Y axis screw to slide the head over the four bolts, tighten the bolts up until slightly snug and crank the head up to the vertical position. The hardest part was getting four loose bolts sliding around in a circular T-slot to line up with the holes in the head. They even make the holes in the machine head larger than the bolts and then provide bushings to slide over the screws and into the machine head after the bolts are through! It was like herding cats!

We finally got the head on over the bolts (and were exhausted by the effort) when we ran into a problem. The head jammed up when we got it about a half inch away from meeting up with the face of the ram trunnion. My friend Mike - he's a machinery rigger - brought by an electric floor crane and let us use it. It made handling the head a lot easier. We pulled the head back off the bolts and looked at it very carefully. There were indentations on the edges of the opening of the new head that were made by the gear teeth of the gear in the trunnion face. The gear was larger than it should be and wouldn't mate up.

Trying to put head on using footlift. Note spur gear bolted to center of trunnion.


My friend Mike with the CatCart elecric floor crane.


To be continued...

 

[KeithB]

The old gear left indentations in the back of the new head because it was too big. After diagnosing the problem I called HH Roberts and explained the situation. They sent me the proper gear for free! It was nothing like the old gear. It was almost a 1/4" smaller in diameter. shorter, had 33 teeth instead of the 25 on the old gear, and a completely different bolt pattern. Oh drat and darn it.

Indentations on housing of new head because old gear is too large


Old gear on left, new gear on right


Face of ram trunnion with bolt holes and circular T slot.


I thought about several possible solutions but settled on grafting the new gear to the old gear. That way the new gear teeth would mesh properly with the worm on the machine head and the old gear would have the proper mounting holes to mate with the trunnion face.

First step was to turn down the old gear to remove the teeth. The gear was indicated in and the OD was turned down to be just slightly larger than the edges of the screw holes. It was flipped around and the base flange was cut to the right thickness. Then the new gear was indicated in and the center was bored out to barely slip over the old gear. A good grade of epoxy was used to glue the two pieces together. After the glue set I put the hybrid gear in the CNC mill and drilled eight 1/8" diameter holes through the back of the old gear and into the rim of the new gear. Hardened solid steel dowel pins were dropped in place and staked to prevent them from falling out during reassembly.

Old gear indicated in and turned down to minimum possible size


Old gear flipped around to cut flange to proper thickness


New gear bored out for a slip fit over old gear.


Old gear on left, new gear on right


The two gears fitted up prior to gluing them together with epoxy.


The shear pin holes in back of gear assembly. Note they have been staked in place so they don't come loose during reassembly.


Here is hybrid gear bolted into place in face of trunnion.


After bolting the gear back to the trunnion face the electric hoist was used to handle the head. Everything mated up, the head bolted flush to the trunnion face and the worm engaged the gear properly. It only took a minute to crank the head into the vertical position. Nothing broke, everything went smoothly. The only time that gear has any load on it is when it is used to adjust the head "shrug". I never tilted the old head left or right, once I got it squared up I locked it in place and left it alone. The shear pins in the gear have no load on them once the head is clamped in place so I have no worries about this fix.

To be continued...

 

[KeithB]

The last steps were to add the pneumatically powered drawbar and clamp a dial indicator in place to square the head up to the table. Then the electrcian showed up, checked everything out, and got us running.

I really like the powered drawbar! I have used this head now for several days and am really happy with the whole setup. It's nice to change speed w/o changing belts and change tools with ease. And the unit is fairly quiet and runs smoothly.

The yellow cylinder on top of head is powered drawbar. The two buttons on gold panel below power switch actuate air motor.

 

[Joshua]

That is a wonderful solution to the gear problem!

A note on your new Torque-Rite:
I know this isn’t gonna make sense now, when everything is all brand new. But, we have had one of those Torque-Rite pneumatic draw bar pullers go bad on us because the air lines put too much side tension on it! It finally wouldn’t plunge down and engage anymore.

Our machine maintenance guys just replaced the first one. Didn’t even try to diagnose any problems the first time. Just put on a new one on and said they would rebuild the “broken” one with new soft parts and put it on their parts shelf.

About a year later the same problem happened again. They came out, disassembled the year old one, cleaned it, reinstalled it, and it worked like 6 out of every ten attempts. It just didn’t want to plunge every time. I mentioned how the airlines pulled it to one side. We cut a zip tie, which gave the air lines some slack. It started to work just fine once it had enough slack.

And, it is still working fine a year later.

 

[Snakeoil]

You did well dealing with more than one "oh-shit" moment. I also like your hybrid gear solution.

I'm curious here, not being critical. Why couldn't you just have drilled new holes in the new gear? At least in the photos, it appears you would only have needed to drill 2 more holes 120 deg apart. But I'm guessing that the bolt circle is different between the two. No?

 

[JWinAZ]

Very nice, thank you for taking the time to show this to us. I was impressed with the depth of the indentations the old gear made in the head.

 

[KeithB]

@Snakeoil - nothing between the old and new gear lined up. The new gear was smaller and would be a loose fit in the trunnion hole. And there was also a tapered pin hole in the old gear that would have to be drilled and reamed to size and I don't have the proper taper pin reamer.