Bent arbor

[Sonic EscapeParticipant @sonicescape38234]

One of my milling machine has a bent arbor. It is the Y axis manual feed. Because of this it is very difficult to lift or lower the table. And for the same reason I can’t remove that big nut which in turn covers the screws that hold the arbor in that casing. I tried to use the vise but the bent section is too short and you would need a lot of force to bent it in the other way. How could I fix this?

 

[BazyleParticipant @bazyle]

If you consider the arbor toast, ie you are going to make another rather than try to bend it straight, cut off the bent bit or angle grind the bit that is projecting sideways. In fact if you can grind it down while running in its own bearings – ie the post grind result is reasonably symmetrical you may later be able to true it up and shrink on a new full diameter repair.

[DiogenesParticipant @diogenes]

Is it a ‘screw’ or a plain shaft?

If it’s plain, hacksaw the bent bit off so you can remove it from the housing and make a new one.

If it is a screw, either remove as above and make a new one, or file / grind the bent bit until you can get it out of the housing.

Once it is out, you can either;

..build-up the end with weld and re-machine it.

or

..cut it off and make a new ‘end’ with a spigot fitting a hole you can make in the existing shaft – glue, pin, or weld and clean up..

 

 

[Sonic EscapeParticipant @sonicescape38234]

I drilled a small hole on the edge of that nut. Then I enlarged it with the mini grinder and I was able to remove those screws.

And I was able to remove the arbor. It is looking like this:

Cutting it is a good idea. Actually I’m thinking to cut it only enough to make it easy to bend. Then I could fill the gap by welding. Something like this:

Is it possible that this arbor is made from some high carbon steel that can’t be welded?

How about if I use a long pipe and try to bend it in the vise? My vise is not very big but it is made of steel not cast iron, so it should not break. Would it be strong enough?

 

 

 

[noel shelleyParticipant @noelshelley55608]

VERY careful use of a press may work. As to the  vice – you may have little control and make it as bad as it is in the opposite direction. Noel

[HopperParticipant @hopper]

i would not attempt the welding idea. The molten weld contracts as it cools and exerts VERY powerful pulling forces on the surrounding metal. The shaft would end up bent again, unless you could guess exactly how much contraction would occur and bend the shaft the other way too far. But you can’t get that exactly right so forget welding.

Can you knock the shaft out of the bearing the other direction? Or is the shaft stepped so the bearing can not slide over the long end of the shaft?

If you don’t have a hydraulic press as Noel suggested, you could then heat the shaft with an oxy acetylene torch, or maybe even propane, until red hot and then straighten it in your vice with a piece of pipe. It will be very hard, well nigh impossible, to get it back to dead straight because metal will have been stretched etc during the current bending. But if it is just to mount the handwheel on, you can live with a small amount of wobble.

If you want it dead straight and that does not work, you might have to cut the end off the shaft and make a new end piece and attach to the old shaft with a spigot on the new piece that fits into a hole drilled and reamed up the middle of the old piece. Then carefully secure it with  either Loctite, solder, cross pins or even careful tack welding. Or just make a whole new shaft.

[Pete RimmerParticipant @peterimmer30576]

These shafts are not usually hardened and if that one was it would likely have snapped before getting to that angle.

Even if you straighten it you may still not be able to remove it easily as the section which was bent then straightened will probably be out of round. You may be able to carefully grind it enough to extract it.

As for straightening it, if you want it dead straight and true then your best chance is probably to straighten it as much as you can, weld it up and turn it back straight. Personally, I would just re-make it between centres.

[Howard LewisParticipant @howardlewis46836]

+1 for the risks attached to contraction after welding.

IF the shaft can be pressed through the bearing, (IF not you won’t have much option but to saw it off to get it out, even if it means destroying the bearing. That can be replaced)

Once out,, if the shaft will pass through the Headstock (Use a steady, if it won’t) it can be turned down until it JUST cleans up.

Then turn up a sleeve, back to original OD, with the bore having a slight interference on the turned down shaft diameter (Say 0.0127 mm smaller).  Then fit he sleeve into position using the “Heat and Freeze” tecchnique. With the shaft at -18C, it should fit onto the shaft at about 200C.

If the shaft is too long to fit into a freezer, you will have to heat the sleeve to a higher temperature, and press into place. For this, to minimise damage to the sleeve which will be softemed by the hight teperature, use a dolly to take the pressure from the press.

Oncve everything has soaked back to ambient temperature, you should be in a position to reassemble, and make the machine useable.

Howard

[SillyOldDufferModerator @sillyoldduffer]

From the comfort of my armchair, because I don’t have a torch big enough, but why not make the object red-hot before bending it.   Red-hot, or hotter, steel is considerably softer than when cold, making it much easier to work.   Blacksmiths do it all the time.  Maybe a garage or agricultural repair shop with propane or oxy-acetlylene.   LBSC describes heating largish objects laid on top of a burning coke bed with a paraffin blow-lamp.

Dave

[noel shelleyParticipant @noelshelley55608]

Howard was up before me – it’s sunday ! Machine to truth and then sleeve back to standard. For heating use an oil bath with cooking oil NOT motor engine oil. Before doing this check for a crack where it is bent. Only if you have a large quantity of good luck will welding work and be true. Noel.

[Sonic EscapeParticipant @sonicescape38234]

I just realized that the bent part of the arbor is not subject to too much force. Because the handwheel has some teeth that connect to the nut. So I cut the arbor enough to straighten it. And that’s it, the problem is solved! Now it is spinning very easy.

[Howard LewisParticipant @howardlewis46836]

Glad that you have solved the problem

Thanks for the feedback

Howard

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