Longitudinal Handwheel Repair on a Pacemaker

[Fasttrack]

This was the first issue I chose to address on my 1945 Pacemaker. When being moved to its long stint outside, it was placed on a pallet. Naturally, the garden variety pallet could not support the 8000lb brute and it tipped forward into the mast of the forklift, or so I am told.

Anyway, here's a pic of the z-axis handwheel:


First, I wanted to remove the cracked casting**. The handwheel was the first thing to remove. Then, four socket head cap screws needed to be removed and then some gentle prying and tapping to free the casting from the apron. There is a dowel at the bottom that needs to be freed. Once its clear, it should slide right off.

There is a sealed ball bearing installed in this casting. On my lathe, this bearing had seized and worn a groove in the shaft, so it was slated for replacement.



To remove the bent shaft, a nut on the backside of the apron must be removed. There is a lock ring which fits in a miniature keyway on the shaft with a tab that catches the nut. Not sure what the techincal name is for these, but you see them on cars occasionally too. Anyway, if you can get back behind the apron with a screwdriver and then a pair of pliers to get the lock ring free and the nut off your better than I am! I opted to remove the carriage and apron.

To do that, you must first remove the leadscrew/feed rod/clutch rod support. I first removed the caps on either side of the feed rod support to see what was going on in there. The clutch rod and leadscrew just float in brass bushings so no trouble there. Next I removed all the socket head cap screws securing the support to the bed. I suspect there are a few other ways to remove this but I went about it by rocking the whole support back and forwards a bit to loosen the dowel and then removed the dowel. This allowed me to slide the support off from one end.



**Note that this isn't really the best time to do this, since I opted to remove the apron in order to free the shaft. To do that, it requires that the carriage be moved by the handwheel. In this case, it didn't matter too much since the shaft was already bent and damaged.

[Fasttrack]

After that pin was removed, the support was slid off. The bearing remains in place.


With the support out of the way, you can drive the pin out of the collar, allwoing the the bearing and spring to slide off of the feed rod. This is a straight pin.



With the support out of the way, next I planned on cranking the carriage all the way to the end but the safety stop got in the way! These rings on the feed rod are held in place with a stuborn taper pin. Make sure you know which way to hammer to extract it! Also, a little trick I use is to center punch the pin before I begin pounding. It takes alot of blows to finally dislodge these pins and it is easy to mushroom the head of the pin. Then, while filing off the mushroom head, the pin is drawn down to the level of the ring and you can't see where the pin is. (Don't ask me how I know ... ) So, to make it easier, I make sure there is a dimple to mark where the pin is, just incase you can't see the outline.



Now, I noticed that the leadscrew drive pin was sheared. In fact, the original taper pin was missing and the brass straight pin that replaced it was also sheared. I noticed this problem earlier while playing around with the different features, but was unsure whether the problem I noted was in the driving end or the driven end. (This is the first lathe I've taken apart and didn't know what to expect)

I removed the straight pin and then completely removed the leadscrew to get it out of the way. Next, I decided to remove the feed rod from the gearbox since I was unsure how it interacted with the apron and didn't know if i could slide it clear off the rod. The keyway does not continue to the end of the rod, so this is neccessary.
There is one taper pin that drives the feed rod that must be removed. Don't forget to dimple it!

Here is the carriage at the end of the bed:



In retrospect, I should have removed the carriage and apron before removing the cracked casting, since I needed the handwheel to move the carriage to the end of the lathe.

[Fasttrack]

Ok. Make sure you have something to support the carriage! Even after I removed the compound and toolpost, the carriage with taper attachment weighs somewhere on the order of 400 lbs. I used a forklift with a fork slid between the inner V's. This let me slide it off the V's and onto the fork. It balances well with the TA, but make sure you've got some help to balance it, just in case. After it was on the fork, I used a strap to keep it there while I moved it where I wanted it.

To remove the apron, a little shield/coolant tray needs to be removed in order to seperate the apron from the carriage. To do that the auto feed clutch control needs to be removed. This is a simple task of loosening a set screw up near the top of the casting and then loosening the socket head screw that clamps the casting in place. Then, with some gentle prying and tapping, it pops right off exposing the safety clutch and thrust bearing. When that is out of the way, the tray can be removed. It was held in place by a few SHCS.


Note that you can see the stuck plunger that also needs to be addressed in this shot.


Now the apron is free. Here it is from the back:



Notice that I've already removed the bent shaft. In fact, I did that before removing the apron from the carriage or the carriage from the lathe completely.

Here is where that nut normally is [see the red box]:

[Fasttrack]

Now... fixing the bent shaft!

The gear and shaft is all one piece so making a replacement shaft is out of the question. Instead, I decided to cut off the bent section, make a new section and then weld the two sections together. Luckily, the shaft was stepped, allowing me to bore a hole in the original shaft to locate my replacement. The replacement would need 5/8" coarse threads, so I chose a grade five bolt and parted off the head. Next was cutting the keyway. I had one lathe available and one drill press. Thats it. No endmills. So I thought I'd cut the keyway in the lathe but the lathe that was operational had a sheared key in the apron, preventing either auto feed or the handwheel from moving the carriage when under pressure. Obviously, that causes some issues when trying to scratch your own keyway into a shaft with a lathe. I was rather proud of my solution. I had a big drill chuck, max capacity of 3/4", in the tailstock. I held the 5/8" bit of bolt in the drill chuck and then used the leadscrew to drive the carriage. At 118 tpi, it was geared pretty low. Still, I worried about putting alot of strain on the half-nut mechanism but I suppose thats what its made for. Anyway, with the leadscrew set to cut LH threads, the feedscrew drives the carriage to cut the keyway.



Once that was ready to go, it was time to braze! I brazed the stub into the original shaft and brazed the cracked casting. I then replaced the bearing in the casting, but I used a chineese bearing ... I still feel guilty :-)


Thats only the fourth time I've brazed something, but I think it came out ok. There is a key in the apron on the gear that is driven by this shaft. It is sheared on both Pacemakers and I believe it is a weak spot. With this stub brazed in place, I hope that it will fail before that key. This is easy to replace since the apron does not need to be removed to refix the stub. There is a safety clutch on the auto-feed that will protect the key on that end.



Here is the bent shaft before repair:

[torker]

FASTTRACK!!! Settle down! You made a booboo...ooops...nope ya made two

[tattoomike68]

screw welding up the crack, turn it round in the lathe and sweat a nice steel sleave over it. leave the crack and call it a grease groove.

[Fasttrack]

Whew ... I finished!

Two boo-boo's ? What do you mean!?

Actually Mike, I thought about doing something like that, but I decided a little bit of brazing was easier The casting was still "intact" and the bearing still held snug despite the cracks, so I wasn't too concerned.

[torker]

screw welding up the crack, turn it round in the lathe and sweat a nice steel sleave over it. leave the crack and call it a grease groove.

Ya...lets not go down that road again
Mikey.. I see you over on Shop Floor? I like that place.

[lazlo]

Nice job on the repairs Fasttrack!

What's the bevel gear mechanism next to the half nuts? Is that an auto-reverse that trips with those stop rods?

[Fasttrack]

The ATW "high production" models did have that feature, but these bevels are just for the apron feed reverse selector. Its dead handy compared to the ones on the headstock where you have to shut off the lathe to reverse the direction.

This is a pretty plain model. The larger ones came with rapid traverse and you could get the high-production package that would automatically trip and reverse feed. Like a mechanical CNC!