Nifty three jaw trick

Look at this video where the guy repairs a worn motor armature shaft. The narration is heavily accented but bear with it. His words are gold.

Electric Motor Shaft Repair | With Lathe, Welding Machine and CNC-Mill - YouTube

Pretty routine. Turn down the worn area to clean metal, weld up the keyway, then weld build up the diameter, rough machine to 3 mm oversize, then check the set-up and refine the armature to run true. Note he's using a well-used three jaw but has to get the bearing fit at the chuck end to run true. He padded the jaws with copper an excellent choice because copper is malleable.

Note the action and discussion at 4:14. He uses a soft brass punch to tap the jaw. The shock seats the jaw a trifle deeper in the copper moving the armature axis TOWARDS the hammer. Tap succeeds tap, snugging the jaws as you go, and soon the three jaw error has been adjusted out. NEAT trick if the work has mass you can work against.

Afterwards he uses a steady to re-tool the shaft center. Then goes on to finish nachine the shaft to size concentric to the bearing axes, machines the keyseat, etc. Not a thing wrong with his technique. Brisk but careful.

I've been nearly 60 years in this trade and have never seen that three jaw trick nor worked it out for myself though I could have used it a zillion times. Goes to show there's always a new trick even when you think you've see it all.

Hat's off the the Beyond the Press guys. Glad to see they can be skilled workers when necessary and not just YouTube clowns.

OT: I bet they coudn’t imagine that crushing things on hydraulic press would replace their ”real” machinist’s job

Thats brilliant!
Im just done wrapping a boring bar in copper wire holding in an old bell mouthed 3 jaw, so can totally relate how tapping on the jaws can squish the shimming to help centre a something. I liked the jig he used to rotate the armature too

I've seen that done before...but I guess I always considered it a 'shaky' practice because that same malleability is subject to change once you turn the lathe on and/or start working. I'd say it's good for light cuts...but I wouldn't consider it a healthy setup that is unlikely to migrate.

Wouldnt it just as easy to put it in a 4 jaw and dial it in ?
Then you know its not going to move on you.

redlee said:

Wouldnt it just as easy to put it in a 4 jaw and dial it in ?
Then you know its not going to move on you.

Click to expand...

Yes, if you have a chuck that will fit your work but sometimes you just gotta make do.

Sent from my SM-G930R4 using Tapatalk

I like these videos much more than the videos of them crushing stuff.

Pretty neat, I'll remember that trick, but I think I'd rather have a 4 jaw. At work all the lathes except the smallest have 4 jaws all the time. And at the farm I only have one lathe that doesn't have a 4 jaw, again the smallest.

There are plenty of motor endbells that have 3 lobes cast in place, to grip on with the chuck. A 4 jaw simply cannot reach to grab on anywhere else. Hence i use a combination 3 jaw. Substantial offset adjustment is required, no way will an adjust-tru chuck suffice.

On small rotors, I'll use a 5C collet to chuck right on the bearing journal.

In situations where a 4 jaw will work, but the casting has considerable draft, I'll often put the endbell face down on the mill table, and quickly mill 4 flat spots at the quadrant points, cutting deep enough to make a flat about 1/2" deep and 1/2" wide. This saves a considerable amount of time trying to keep the casting from cocking crooked while setting up in the 4 jaw.

GregSY said:

I've seen that done before...but I guess I always considered it a 'shaky' practice because that same malleability is subject to change once you turn the lathe on and/or start working. I'd say it's good for light cuts...but I wouldn't consider it a healthy setup that is unlikely to migrate.

Click to expand...

.
agreed its unstable if roughing the vibration will cause part shift cause of the soft metal. 4 jaw independent chuck never had a problem using

Thanks Forrest, the guys habits are pretty good (don’t like the blow gun, but that’s me). Making that repair from the bench to done in ½ day is as good as anybody I’ve ever seen. I think his english is pretty good also (got “shit” correct anyway).

The old-time brass tooling tags (you stamped the numbers on) work well for knocking as well as aluminum coupons, you just don’t go crazy with it. I like the hand welding jig he made however the really good ones you see have brass rollers over a shaft or a shoulder screw (if someone intends to build their own).

He didn’t say if he moved the keyseat after filling it up and making the roundabout overlay. It’s a good idea as the filler is more ductile than the original in my experience. That’s also about the size shaft you can tack a dummy key in and then overlay to keep the shaft warping down. You can tell he’s used that rig a lot (very good weld for non automated).

Last advice I’d give for people who do a lot of sizing using abrasive cloth is to get a good 14” long angle pattern lathe file. Finishes to 8-16Ra & much less likely to get lobing when reducing at the dreaded .001” material left to go...

Good luck,
Matt

The old crusty ones in the shop I once worked in (Back in the 1970's) used the tapping on a three jaw all the time. So this method has been around a long time, much before the 1970's.

Each lathe in the shop had a hunk of copper and a hunk of lead in the chip pan near the headstock just for this purpose.

I prefer a 4 jaw, as I don't exactly like hammering on chuck jaws, but the method worked for the guys and it was quick. Much faster than changing the 3 jaw out for a 4 jaw.

I have a set of chucks for the tailstock that have brass jaws, specifically for the armature shafts that do not have a center hole. Handy for turning commutators, just what Jacobs made them for and called as such.

I've used shim stock to tweak in a three-jaw. It can be tricky figuring out just what size shim you need.

what "special" center drill might he have used to locate the hole?

dian said:

what "special" center drill might he have used to locate the hole?

Click to expand...

When you true up a center you have to single point it. Long thin braxed carbide is what I use.

thats why i wonder about his "special center drill".

Garwood said:

When you true up a center you have to single point it. Long thin braxed carbide is what I use.

Click to expand...

Yep, we did it this way all the time in the job shop on big centrifugal pump shafts. The millwrights always screwed up the shaft centers when they used a hydraulic puller to remove the couplings. So the first thing we did when a pump shaft came into the shop for repairs was to set it up in the lathe with a steady and recut the centers.

PS, what do the machinists call the "millwrights"?

Answer: "Millwrongs"

SilveradoHauler said:

Yep, we did it this way all the time in the job shop on big centrifugal pump shafts. The millwrights always screwed up the shaft centers when they used a hydraulic puller to remove the couplings. So the first thing we did when a pump shaft came into the shop for repairs was to set it up in the lathe with a steady and recut the centers.

PS, what do the machinists call the "millwrights"?

Answer: "Millwrongs"

Click to expand...

My 50 year old nephew is a millwright (a very good one, in fact). Thanks for the ammo.

OK I have to ask, as I have tried similar projects recutting centers but how do you determine the height of the steady rest , seems to me the bearing surface would run true if it was up or down a bit but not exactly in line with the center line. In this project you can't put the steady next to the chuck , and I never can with my permanent gap Sag 12 . Just curious about the best method to get the center on centerline of a shaft ?

Am I missing something? If the key way was bad, why did he not just mill a new key way let's say 45° from the old one and fill the mutilated old one with solder?
The hammering on the 3 jaw - well ok. The milling of the new key way would be oversize for sure.

Jim Moser said:

OK I have to ask, as I have tried similar projects recutting centers but how do you determine the height of the steady rest , seems to me the bearing surface would run true if it was up or down a bit but not exactly in line with the center line. In this project you can't put the steady next to the chuck , and I never can with my permanent gap Sag 12 . Just curious about the best method to get the center on centerline of a shaft ?

Click to expand...

I don't worry too much about getting the steady set perfectly unless it is actually going to be used while turning a straight journal, because in that circumstance, it has to be perfect, or it will introduce taper to the cut. You have to set it approximately close to correct, or the work will be induced to walk out of the chuck. You can do this rough setting by measuring.

I also run the part slowly when it is being set up in the steady, and feel each steady knob for extreme pressure or looseness. This will tell you if the chuck jaws are trying to apply a restoring pressure to try to get the centerline of the work aligned with the spindle centerline.

If using the steady to rebore the center hole, then close is often good enough, because the error that introduces into the bored angle is reasonably small. The hole will still be on centerline with respect to the journal that the steady rest is resting on. Of course, the other end of the piece MUST be accurately chucked to ensure it runs true at the other end. If not, you are wasting valuable time producing junk.

Considering most people are using rolling bearing centers in the tailstock, it doesn't matter if the center contacts at the front or the back of the center hole, just so long as the center hole is an object of revolution with no offsetting dents. So you bore it to make sure the damage is cleared. If it's 59 degrees or 61 degrees, it won't spoil the job.

I've often rebored centers and still had a thousandth runout and had to shim the center just a little anyways.I use 2 shims spaced at 120 degrees in the center hole. These shims are shaped like an acute triangle. I detect the high spot and place the shims opposite at the 4 and 8 o'clock positions. This can be done with the high spot up, and back the tailcenter slightly back and slide the shims in underneath. Mark the end of the shaft with a marker to indicate the correct shim positions. You need to monitor that these shims stay in position until you're done with the finish cut. For that reason, I install the shims only before the last few thousandths are cut.