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View Full Version : Setting up four jaw chuck workpieces..



.RC.
01-01-2009, 08:21 AM
Today I had to bore out two cast gears that had a worn hole....The part was off a windmill that had been rebuilt only 4 years ago...The engineering establishment that did the rebuild decided rather then bore and bush they would instead knurl the shaft to increase it's size the small amount required to fit the slightly worn parts (The windmill had done over 50 years of continuous work)....While knurling the shaft where these gears ran did not cause any problems in the short term, they also decided to knurl the shaft where the windmill wheel hub connects to the axle and is supposed to be a 20 ton press fit...

Suffice to say we found it with the wheel spinning and the axle stationary as their well fitted key had fallen out as well..We were lucky we found it when we did as there was nothing stopping the wheel (12' in diameter) falling off..Here is a pic of the hub and shaft http://img.photobucket.com/albums/v606/OzRinger/Z12foot012.jpg
and the knurled shaft http://img.photobucket.com/albums/v606/OzRinger/Z12foot013.jpg

Anyway on with the job..

I was thinking on how to do it to keep the bore alignment with these gears while setting them up in the four jaw and this idea popped into my head...

I installed a centre in the headstock like this http://img.photobucket.com/albums/v606/OzRinger/settingupgear001.jpg

Then I installed the four jaw chuck over the centre..

I then placed the gear onto the old shaft it was running on..

This shaft had centre holes at either end which I then put it in the lathe like thus http://img.photobucket.com/albums/v606/OzRinger/settingupgear004.jpg

Then I tightened the four jaws carefully around the gear http://img.photobucket.com/albums/v606/OzRinger/settingupgear006.jpg

Then bored it out to 1.750 inches..

So this might give some people some ideas when it comes to setting up stuff in the four jaw...

Here is what the mill head looks like http://img.photobucket.com/albums/v606/OzRinger/Z12foot018.jpg

Your Old Dog
01-01-2009, 10:58 AM
Thanks for the pics. Interesting looking project. So what was the fix? Did you weldup the shaft similar to what Sir John does on his motor amaturs or did you reduce and then sleeve the shaft? It's only the first day of the year and I'm not up to speed yet!

Sir John, if you're reading this, what weldment do you use for your methode that you are able to machine back to spec? My understanding is that most weldment is really tough to machine.

oil mac
01-01-2009, 03:53 PM
Hello Ringer,
Some time ago, i had a similar excercise to uncobble where some "highly skilled guys"had managed to do some"classical" fitting, In my particular repair, the od of the gear was good,teeth were fine when it left the gearcutters, Pity about the re-bore carried out to modify it for the duty they were applying it to, bore was not concentric to o.d. of gears,
Part 1,i had by me a small off cut of steel from which i bored the centre to a light drive fit over the O.D. of gear teeth, the outer dia of the portion of steel i machined to be concentric with inside bore & parted off a ring about1/2" broad
Part 2 Set up the gear using 4 jaw holding gearwheel, Same way of holding in 4jaw as you did Ringer.
Part 3 tapped on steel ring & clocked up true
part 4 bored out, and pressed in bush and then cut keyway
When fitted gears were running accurately for concentricity

barts
01-01-2009, 04:28 PM
Thanks for the pics. Interesting looking project. So what was the fix? Did you weldup the shaft similar to what Sir John does on his motor amaturs or did you reduce and then sleeve the shaft? It's only the first day of the year and I'm not up to speed yet!

Sir John, if you're reading this, what weldment do you use for your methode that you are able to machine back to spec? My understanding is that most weldment is really tough to machine.

I find MIG welding leaves a nice soft buildup, easily machined. I've fixed various spinning wheel shafts this way.

- Bart

brian Rupnow
01-01-2009, 04:31 PM
Ringer---I read your post early this morning, and I admire your inginuity, and I'm glad that you were able to fix it to your satisfaction. I think you did it wrong!! How did you determine that you had exactly the same clamping force on all four chuck jaws so as not to shift things "out of center" when you tightened the jaws individually? Did you check it with a dial indicator for TIR before you actually did your machining? I think this information you give is incorrect, and will lead other new machinists down the garden path. I hate centering things in a 4 jaw chuck worse than snakes, and I am not very good at it, but what you are advocating is just plain bad advise!! Sorry---I didn't mean to sound so hatefull on the first friggin' day of the year.---Brian

barts
01-01-2009, 04:40 PM
..While knurling the shaft where these gears ran did not cause any problems in the short term, they also decided to knurl the shaft where the windmill wheel hub connects to the axle and is supposed to be a 20 ton press fit...

This is the sort of thing that just screams for a taper bushing & bore during the design phase... easily (dis)assembled and excellent retention.

Nice trick w/ the center.

- Bart

.RC.
01-01-2009, 05:15 PM
I probably forgot to mention that supreme accuracy of the hole position was not a requirement...The gear teeth are not cut on this part but cast. The only machining done to the part at the factory was they drilled the hole in the centre and two cross holes for locking pins...

In fact after I centred the hole the runout on the OD was in the order of several mm..but it has been in service like this for 50+ years now (this particular design has not been built since 1953) so it is obviously acceptable..

LAZYBONES
01-01-2009, 06:59 PM
Seems to me that this would have been a good job for the milling machine instead of a lathe. Or am I missing something here?