PDA

View Full Version : D'ja ever have one of those days?



DICKEYBIRD
01-03-2009, 08:50 PM
This has been one of those "screw up a wheelbarrow" days. It actually started last night.

I've been working on trying to resurrect an old pool pump motor to make a buffer/polisher out of it. The shaft was corroded badly so I turned off the bad stuff and made a repair shaft last weekend that was drilled & reamed for a light press fit. I borrowed some Loctite Primer/Activator from work and my plan was to install the new piece last night so it would be cured enough to finish up today.

I cleaned & primed both pieces and put on a film of Loctite Shaft & bearing mount. I started the new piece on and started tapping it home but it got about 3/4 of the way on & stopped dead. I ran over to my screw-press and tightened it as tight as I dared and started whacking it HARD with a hammer to get it seated. Boy, I says, that was close.

This morning I put it back in the 4-jaw and found I'd bent the shaft during last night's fiasco. Jeez, what to do, what to do! I don't have a steady rest so I ended up putting the motor back together and clamping it on the mill table so I could get a solid read with a DTI on the outboard end of the wobbly shaft. Fortunately the shaft was bent outside of the bearing so I was able to tweak it back straight with a piece of pipe. Three or 4 tweaks back & forth had it down to less than a thou.

Back into the 4-jaw it went and a live center was fitted so I could turn down the end to .5" and ready for the 1/2-20 threads. This was my 1st try at cutting threads on my lathe (or any other lathe for that matter) and was really looking forward to the "experience." My little 8x16 relies on the ol' stack-of gears swap-a-roo so I spent a long time getting the correct combination. The manual is long gone & all I have is a cryptic little nameplate with almost indecipherable columns of hieroglyphics on it. I finally got it right and was ready to go. I envy you guys and your four-on-the-floor, Hurst shifted quick change gearboxes!

The lathe doesn't have a thread dial so I used the ol' "don't ever disengage the half-nut" method. To my amazement, it worked very well. That is until the 4th pass when the half nut jammed & kicked itself off. This was the longest work I've ever put in the lathe and I had to use the unworn far end of the lead screw which made it hard to engage properly due to the tight fit.

It took me a second to realize what happened and the resulting crash buggered the 1st 3/8" of the threads and chipped my freshly sharpened brazed carbide bit....plus got the leadscrew and spindle hopelessly out of sync.

I putzed around for quite a while and somehow chased down the correct alignment and finished up with the chipped bit. I didn't have the gumption to take the bit out, resharpen it and try to start over.

All that said, I am very proud of my very 1st single point threads! The nut spins on effortlessly with very little slack. Me likey! :)

I can't wait for what comes next. I think I better go sit in front of the TV a while to contemplate all the things I "learned" so far this weekend and try again tomorrow.

http://i57.photobucket.com/albums/g227/DBAviation/PumpMotorThreads.jpg

dockrat
01-03-2009, 08:57 PM
I think I better go sit in front of the TV a while to contemplate all the things I "learned" so far this weekend and try again tomorrow.

Don't forget to pour yourself a stiff one...you deserve it. :D Feels good when ya win in the face of adversity dont it???

DICKEYBIRD
01-03-2009, 09:02 PM
Good suggestion D/R. I'm feeling a bit superior due to my newfound threading prowess so I'm having a chat with nice Mr. Merlot from California as we speak.;)

wierdscience
01-03-2009, 09:13 PM
Don't feel bad,pool pump motors are cursed.Believe me,I've had hundreds of them apart to change bearings and none has ever been easy.

My personal favorite is when the centrifugal switch is so rotten it crumbles like a cookie:D

tiptop
01-03-2009, 09:38 PM
Nice looking threads. Glad to hear you mad it past the buggered end ok. Jay

dp
01-03-2009, 09:42 PM
Was waiting for the ba duh bump! moment when you realized you needed a left hand thread :) Nicely done on the recovery and first-time thread. I wonder if the reason the press fit stopped was the pocket was full of Locktite and hydrolocked?

DICKEYBIRD
01-03-2009, 10:20 PM
Oops, the double post faux paux.

DICKEYBIRD
01-03-2009, 10:24 PM
Don't feel bad,pool pump motors are cursed.Believe me,I've had hundreds of them apart to change bearings and none has ever been easy.

My personal favorite is when the centrifugal switch is so rotten it crumbles like a cookie:DYup, that warm, rosy feeling of quality parts is definitely missing on this one too. I have another, better built one but it's a rusty mess and is rated at 220v 14A; more power than I feel safe with. I'll prolly be launching plenty of parts into the dark corners of the shop with this little one anyway.

Thanks Jay, that's a real compliment coming from a vet like you!:) I really enjoyed finally tackling the threading process but the gear swap shuffle is a time wasting pain in the butt. The other thing that snapped into focus was the depth of cut. When reading other's threading instructions, I thought, man, they sure take weenie little cuts but now I see why!

dp you're probably right. Next time I'll drill a "squirt" hole to let the excess juice out.

oil mac
01-04-2009, 08:40 AM
Dickeybird,
You think you had problems! about two years ago, a man i know of the farming persuasion asked me if i could repair a sludge pump for him, Silly me said No Problem! Man puts the damned thing on my lovely clean workbench, takes a spanner loosens a flange out pours the most evil smelling farmyard sludge, which pours down into my tools, through a crack on the bench
Result, harsh words, had to clean all affected tools, ended up with upset stomach for a few days Lesson learned dont be so obliging in future!

John Stevenson
01-04-2009, 08:52 AM
Well I think you did brilliantly and got out of trouble very well, especially for a first time.

Text books never tell you about the cock ups only how to do it right :rolleyes: I have never seen a text book explanation of how to pick threads up and what happens if you need to pick a set up to clean a damaged portion, or change a chipped tool, that's a quite regular job in some places.

It's no good replacing the tool, winding over the thread, engaging the half nuts then setting the tool as you haven't taken into account back lash in the drive.

One answer is to fit the tool, wind just clear of the thread and start the screw cutting operation, when part way down the thread stop the machine, leave everything as it is, half nuts in etc and then reset the tool in the toolpost to fit the thread.

Then restart by hand turning the chuck and you should just take a sliver off, note the reading, wind back and do the next cut under power at this setting, then carry on.

.

Lew Hartswick
01-04-2009, 09:57 AM
I cleaned & primed both pieces and put on a film of Loctite Shaft & bearing mount. I started the new piece on and started tapping it home but it got about 3/4 of the way on & stopped dead.

Whats with this "tapping" bit??? One smoothe CONTINUOUS press
is the only safe way to do that. Isn't it? Else the stuff sets up.
...lew...

DICKEYBIRD
01-04-2009, 10:02 AM
One answer is to fit the tool, wind just clear of the thread and start the screw cutting operation, when part way down the thread stop the machine, leave everything as it is, half nuts in etc and then reset the tool in the toolpost to fit the thread.Ahhh! Never tho't a that. Your way's dead easy.:)

You're right about there not being much written anywhere on how to recover from a threading screw up. Not knowing a better way, I backed off with the cross-feed, turned the spindle by hand and tryed different combinations of half nut engagement positions until the tip of the tool was centered in the groove on the undamaged section. I juggled the compound & cross feed until the tool matched the groove as good as I could get it, viewed through a magnifier.

I then backed way off with the cross-feed, reversed past the start, brought the cross-feed back to zero, backed off on the compound a bit, held my breath and hit the start button. It didn't look right at first and some tortured chips were tearing off of the damaged 1st section but when the tool got over to the undamaged part, it was right on. That's when I yelled YES!!!

Fortunately, the crash occurred early on and after cutting to full depth, you can just barely see evidence of the problem. The whole fiasco is a very good example of my signature line.

My other favorite saying I use a lot at work is "The road to success is paved with failures." My road has been paved more times than the New Jersey Turnpike.;)

Mac, yuck, I know what you mean. A buddy had to fix his septic tank pump that got clogged with dog hair. His wife liked to give her precious dog nice showers every week. He had a glazed look in his eyes for days.

DICKEYBIRD
01-04-2009, 10:07 AM
Lew, you may be right. I've used the stuff many times in the past and never had any quick set-up problems. Come to think of it though, most of those cases were to repair worn stuff. Who knows, the stuff may go hard real quick when squeezed between tight fitting parts.

38_Cal
01-04-2009, 01:14 PM
I think that the difining "whoops" was the use of the Loctite primer/activator. That speeds up the process enough that even if a steady push was used to get the sleeve onto the shaft, it probably would have set up before the OP was ready for it.

David
Montezuma, IA

mark61
01-04-2009, 01:33 PM
I putzed around for quite a while and somehow chased down the correct alignment and finished up with the chipped bit. I didn't have the gumption to take the bit out, resharpen it and try to start over.



Next time you lose the feed nut engagment--DO take the bit out and sharpen it! Then BEFORE reinstalling the bit engage the half nut and STOP the lathe. NOW re-align/ replace the bit so it will cut correctly! No "putzing around"

I don't want to remeber how many times I have had this lesson impressed on me! Threading up to shoulders and blind bottoming threads in holes, using older machines you learn this method!

mark61

DICKEYBIRD
01-05-2009, 11:04 PM
OK, I won't be able to live with myself if I don't share "The Rest of the Story." (Apologies to Paul Harvey.)

As mentioned earlier, I screwed up and the motor repair shaft didn't seat all the way onto the original shaft which left a gap. At first I thought so what, it'll be fine for what I need it to do but later decided I had to (A) Cut it off & start over with a new part or (B) Jury rig a repair that I knew wouldn't be as good as a new one but should be better than leaving it as it was. I decided to go with (B).

I measured the gap carefully and turned 2 bushings that matched the O.D. & I.D. of the repair shaft. I parted them off to a thickness that was within a couple thou of the gap and then carefully worked them down by hand on piece of 320 wet/dry to about .0005" thicker than the gap.

I clamped the 1st one in the vise and milled out a section equal to the dia. of the turned-down original motor shaft. It looked like a fat letter "C" and would be a light press fit over the original shaft and between the 2 faces of the gap.(Unfortunately, I didn't get a picture of the "C" shaped part.)

The other piece was clamped in the vise and a flat was milled on one side that was just shy of breaking through to the I.D. I flipped it over, seating the flat on a parallel as I clamped it in the vise again and then milled the other flat. I was able to take it out, mike it and finish off with a cut that left it at the correct thickness to be a snug, sliding fit into the "C" piece. Here's a pic of that part. I was kinda proud of it. Not too shabby for a guy with my skills. I wouldn't have dreamed of making parts like this a couple years ago!

http://i57.photobucket.com/albums/g227/DBAviation/PumpMotorSpacer.jpg

I primed everything and pressed the 2 parts onto the shaft with a dose of Loctite shaft & bearing mount. The mechanical fit was very satisfying. The small piece took some fiddling to get it started straight but once it was started, a firm squeeze with my big vice-grips seated them into place perfectly!:) I left it clamped overnight and it now seems to be rock solid

http://i57.photobucket.com/albums/g227/DBAviation/PumpMotorSpacer2.jpg

This obviously ain't something I'd do for resale and I don't recommend it to anyone else but hey, I had fun doing it and learned that I can do some precise work when I have to.

I'll report back on how well it holds up after the buffer is running and sees some hard use. If it works loose, I can always make another sleeve to press on over the whole thing. Who knows, it may be a good fix as it is.