Machining advice needed


The drive assembly to my cement mixer has finally given up. Unfortunately
neither I or the previous owner ever used the Zerk fitting to lubricate the
drive. The drive is a 3/4 inch shaft with a 3" gear on one end and an 18"
pulley on the other. Am going to have to machine a new shaft and housing.
Housing will be welded to the frame, as is the existing housing.
This link is a picture of the shaft-gear assembly.
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This link is a close-up of the gear. It is pressed on. My plan is to press
out the old shaft, or, bore it out if I have to.
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This is a picture of the shaft sitting loosely in the housing. The housing
is simply welded to the vertical channel. The larger diameter (rusty area,
middle of the photo) sits in a bolt-on cradle (not shown).
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My plan is as follows:
Remove old shaft from gear.
Make new shaft and mill a flat on one end to lock on pulley.
Make a suitable housing with 3/4"± bore.
After completion slide a short sleeve (2"± outside diameter) onto housing so
I can mount in cradle.
Weld entire assembly back into place.
Questions:
If I can not press out the old shaft, how do I center a 9-tooth gear in the
lathe. I have both 3 and 4 jaw chucks.
Don't have a boring bar 6" long. Can this somehow be done from both ends
and still end up with a concentric bore?
How do I modify the shaft so that it can take grease? Do I file a
continuous spiral? Do I do it to the sleeve? New shaft will have a new
Zerk fitting.
Keep in mind the following. Have 13" lathe and a large mill. This is a
very low rpm assembly and does not require very much torque. Even with drum
full of 200 lbs ± of concrete, you can rotate it quite easily by hand. Drum
IS NOT supported by this mechanism. It is simply a drive.
Thanks for any and all advice.
Ivan Vegvary
Reply to
Ivan Vegvary
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Sorry, no machining advice. But we can help you with your family morality issues
Ivan Vegvary wrote:
9 teeth/3jaw = 3. Should self-center. If not (jaws wider than teeth?), go to the 4-jaw and dial it in.
Drill and ream. Or, make a shop-made boring bar. Fairly simple project. 5/8" drill rod, mill a slot in the end, drill and tap for setscrews.
Groove the sleeve internally, intersecting with the zirk hole. Use your boring bar. You could make a spiral channel in the lathe with a slow speed and a quick crank on the carriage wheel. Are you going to use a bronze or oilite bushing in the sleeve?
Reply to
RB
Eew. You really didn't find the zerk! :-)
Two ways:- 1) Quick and dirty:- Given that it's 9 tooth, grip it in the three jaw chuck. It will probably centre well enough, given the somewhat agricultural tolerances involved in cement mixers. Then part off and bore out the shaft.
2) Perfectionist:- Bore a piece of stock to fit the (coned) shape of the gear. Saw the stock in half. Clamp the gear with the stock in the 4 jaw and centre using a DTI near to the gear and far from the gear. Adjust jaws and shim gear until DTI readings are stable at both ends.
Get one! It'll come in useful next time you need to bore a long hole as well. If you really must bore from both ends, turn the hub of the gear to a known diameter while boring the shaft end of the gear. Then bore a piece of stock to the same diameter and without removing the stock from the chuck, loctite the gear hub into that hole to maintain concentricity.
What form are the bearings that the shaft runs in (other than knackered, that is)? Ideally, they will be either two bronze bushes with a gap either side of the zerk, or a continuous cast iron or bronze bore with a spiral or axial grove most of the way along the length. If not, consider boring out the housing ends so that you can fit a couple of Oilite bushes. I would not modify the shaft other than to make it from something like 4340 or 1040 (depending on what I had in the right size) and harden it to 52HRc or better.
Oh, and after you've rebuilt it. Use the bloody zerk!!!!
That's what I'd do, right or wrong. I'd probably also spend more time on it than the cost of a new mixer was worth :-)
Mark Rand (just glad that my little half bag cement mixer has a toothed belt drive) RTFM
Reply to
Mark Rand
Hi, Ivan. I think if the gear will not press off the shaft, I would make a drawing of the shaft, showing length, length of the flat and diameter of the unworn part of the shaft, then put the shaft in your lathe and drill out the shaft so the gear falls off. Then find a piece of water pipe or thick wall steel tubing that will fit completely through the housing hole. Take the pipe out and drill 3-4 holes somewhere in the old housing so you can weld the pipe in place. Pull or unscrew the old Zerk and drill and tap for a new, Zerk. Then make a new shaft to fit the bushing you just welded in, or turn it before you weld the bushing. Have a big end to fit the gear and the rest to fit through the new bushing. Then mill a flat for the old pulley. You may need to turn another small bushing to fit the old pulley hub.
At any rate, you probably get the picture. Your statement about the low torque and the obvious number of years the thing ran tells me that with regular grease, my fix will last your lifetime!
Let us know how you work out the repair.
Paul Drahn
Reply to
co_farmer
I would weld up the shaft and turn it down. Would be good enough for many years with a little grease.
Reply to
Ralph Henrichs
Heat the gear with a torch and dunk the shaft into cold water. The heat and the cold shaft should allow the gear to practically fall off.
Be careful as most of those gears that I have seen are cast iron.
Then turn your new shaft.
New housing could be made from heavy wall tubing and off the shelf bushings. Wouldn't hurt to make a way to install seals on both ends to keep the cement out of the new bushings.
Reply to
Steve W.
Do you have enough room to use pillow blocks?
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Reply to
Jim Wilkins
Do you have enough room to use pillow blocks?
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Great idea Jim! I think I have an old pair somewhere. Certainly can weld them onto a base plate and then weld the base plate to the frame of the mixer. Would save an awful lot of machining.
Thanks!!! Ivan Vegvary
Reply to
Ivan Vegvary

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