Repairing sheared impeller shaft - JD 47 snowblower attachment

[DanMc77]

Great news, but photo did not come through.

Can you check mock up for runout?

The photo is there this morning. Try again.

I chucked the shaft in the 3 jaw chuck and measured the gear surface that mates with the flange surface, out at the OD. I did not prepare well for making this measurement. I never machined the full length of the shaft, so the section I'm putting in the chuck is rough. Also, my 3 jaw chuck is essentially junk, with typically .010" of runout. The 4 jaw chuck is a cheap Chinese thing. So any time I need accuracy, I have to do everything without re-chucking. I'd love to have a super accurate 6 jaw chuck!!!!!! But you could argue that starting with crappy equipment makes a better machinist in the long run.

Anyway, I put the rough part of the shaft into the 3 jaw chuck and measured anywhere from .013 to .0015 in axial runout measured at the OD on the surface that mates with the shaft flange. I re-chucked it several times and got a different result every time, but that was the range.

I thinking that I should turn the real new shaft between centers so I have a chance of being able to remove the piece from the machine and continue on in the work. I'll have to rough it out and then bring everything into tolerance without removing it even with the centers. I picked up a new tailstock live center since the one that came with the machine is pretty knarled up.

 

[al3]

Must say you’re pretty good at what you are doing if you can hold a Plus/minus .0002 tolerance across a shaft of any length on a typical home lathe. Between material deflection, tooling issues, temperature variation this time of year and typically undersized equipment, it certainly is a challenge. Good work.

Remember having to hold a .0003 plus on a 2-3 inch hole on a manual mill with a boring bar. Walked in the final cut(s) not by tool adjustment but by pressure….

 

[DanMc77]

I'm barely getting by. The lathe is a South Bend 13" machine that spent it's years in a VoTech. It's capable of doing some excellent work if it's dialed in properly and has good tooling. Most of what I do is crude repairs or parts that don't really require much accuracy.

But my tooling is marginal, as I said, I have some pretty crummy chucks, and that limits me to never rechucking a part. I'm not able to hold a tolerance of .0002", or even able to measure such a thing. I'm making my measurements with a Mitutoyo digital caliper which has a resolution of .0005". Still my measurements could be called dubious. Measurements bounce around like crazy depending on how you hold the caliper and how much pressure you apply to the jaws.

Edit: Now that I have embarrassed myself sufficiently, I put in an order for a more accurate micrometer.

 

[DanMc77]

The new shaft is ready for parting. All critical dimensions are right on target to .001". My new micrometer has not arrived, I'm getting by with the Mitutoyo caliper. The measurements are a little better than dubious.

Incidently, the license plate seen in the pic is a chip shield I patched in on the lathe to keep chips from getting into the lead screw to the taper attachment.

 

[jthibodeau89]

Looking great. If the drive end needs a keyway or through hole, you way want to consider leaving the stub on until all operations are complete. It is a convenient place to clamp the part. It is not critical for the parting to be concentric.

 

[DanMc77]

Thanks! I will have to cut in the keyway and drill a hole for a retaining bolt. Great idea to clamp on the scrap portion while it's in the milling machine for those operations.

I have the gear bored out to .002" undersize, relative to the shaft. A reference surface was cut so there's a accurate alignment with the shaft flange. I was a bit terrified that I would do something stupid and bore that out too large and then have to make a whole new shaft.

Incidentally, when looking closely at this gear, the mill marks from machining have not even been worn off the teeth, so this machine has not seen a lot of run time. It makes me wonder if there was a defect in the forging operation of this part.

 

[Tinhack]

...the mill marks from machining have not even been worn off the teeth...

Those are "oil reservoirs".

 

[radios1]

I'm barely getting by. The lathe is a South Bend 13" machine that spent it's years in a VoTech. It's capable of doing some excellent work if it's dialed in properly and has good tooling. Most of what I do is crude repairs or parts that don't really require much accuracy.

But my tooling is marginal, as I said, I have some pretty crummy chucks, and that limits me to never rechucking a part. I'm not able to hold a tolerance of .0002", or even able to measure such a thing. I'm making my measurements with a Mitutoyo digital caliper which has a resolution of .0005". Still my measurements could be called dubious. Measurements bounce around like crazy depending on how you hold the caliper and how much pressure you apply to the jaws.

Edit: Now that I have embarrassed myself sufficiently, I put in an order for a more accurate micrometer.

non CNC chucks are inaccurate, four jaw chucks are more accurate, but it takes a bit to get the right centering. collets are very accurate for rechucking a part, but then you wind up having to buy a whole bunch of collets..

 

[DanMc77]

The house was cool enough this morning to fire up the stove nice and hot so I could heat up the gear. (Stupid photo edit tool - I rotated the image and then saved it, but now it comes up back on its side.)

Rejoice! We had a wedding this morning down in the shop. Mr Shaft and Miss Gear were married for life. If you look closely, you can see that the upper part of the shaft is still cold and frosty from the cold.

 

[DanMc77]

Next step is to put it back in the lathe and machine the hub a little so I can more easily drill 3 holes into the interface for putting in some bolts. I would love to have a super accurate 6 jaw chuck, but a good one would cost as much as I paid for the lathe. So I use a cheap 4 jaw and spend some time dialing it in.

Questions:

What kind of bolts should I put in there?

I was thinking of leaving a little bit of the taper from the tap at the bottom of the hole, so the bolt tightens up. Is that reasonable?

I have used JB weld in the past to strengthen repaired parts. Would that be reasonable to use for locking in the bolts? Or would red locktite be more appropriate? I recall that a spot weld was initially recommended, just exploring options.