Proper way to make this part?

[MikeKParticipant @mikek40713]

I’ve mounted my third attempt on the grinder spindle.  Still didn’t get as good a result as I would have liked…it was about 1 though runout on the face.  The first two attempts were done with a mandrel and resulted in just under 2 thou runout each.  I did undercut the mandrel shoulder, though.  The first attempt was with super glue, which I think caused it to move before setting.  Second attempt was by heating the part for a shrink fit onto a new mandrel, and I think the heat may have caused part deformation?

This third attempt was the simplest of the suggestions, to push the part hard up against the chuck face when tightening.  Runout was about 1 thou, measuring the bush height on a good 3″ granite surface plate.  I decided to go ahead and mount this bushing (and the other side, yet to be made) and mount the spindle in the lathe for truing the bush face.  So right now I’m working on expanding my fixed steady capacity (which was 1″) to hold the spindle bearings (which are 32mm).  Holding the far end spindle bearing in the steady is the only way to make it work and still have access to, um…trim the bush.

Thanks for all the good suggestions, guys.

Mike

 

[RobinParticipant @robin]

This is how our wonderful hobby constantly pulls you in to give your wallet an exploratory squeeze…

If you require tight tolerances, the obvious solution to this is the magnetic chuck on a surface grinder.

All your problems disappear and the parts look beautiful 🙂

Robin

[bernard towersParticipant @bernardtowers37738]

Instead of the expense of a grinder you could have a mag chuck for the lathe then you can turn parts and grind!!!

[JasonBModerator @jasonb]

Or even less expense it to stick with the chuck you have and just get some soft jaws. I was surprised I was the only one who suggested them for getting the front and back face of work running true. Also takes care of concentricity which may be a problem with a mag chuck on a lathe and you are not restricted to magnetic materials

[DiogenesParticipant @diogenes]

I thought someone must have mentioned them already – perfect for this job.

[MikeKParticipant @mikek40713]

I don’t think I can get soft jaws for my cheap Chinese 3-jaw chuck.

[DiogenesParticipant @diogenes]

What chuck is it?  – AFAIK it possible to find soft jaws for most of them, certainly Arc, Warco, and Chester sell them, Rotagrip, Ebay and maybe Chronos or RDG might fill any gaps..

Edit – it’s not only the accuracy that is an advantage, because they give such good grip, it’s possible to hold work securely on the slimmest of margins and with a bit of imagination, allowing more surfaces to be turned at one setting..

..or thin-walled or delicate parts without squashing them..

[JasonBModerator @jasonb]

Rotagrip do soft aws for imported chucks, that is where I got my first set.

Also several options for making soft add ons for standard jaws.

 

[Martin ConnellyParticipant @martinconnelly55370]

Or, on the basis that you are not going to be cranking down hard on small delicate parts, make your own with some mild steel and off the shelf dowels.

Martin C

[Tony Pratt 1Participant @tonypratt1]

Soft jaws are the obvious answer but you could mount the nearly finished part on a tapered mandrel and face off both ends with a RH and LH knife tool, the faces would then have to be parallel.

Tony

[MikeKParticipant @mikek40713]

I did try the mandrel route.  Not sure what went wrong.  I’m also not sure what precision can be had from it, since I still had about 2 thou runout.

I’m making another one, again.  I made one longer, expecting the length to help the part when installed on the shaft, but it was still 1.5 thou runout.  And after monkeying around trying to fit it in the lathe, to finally face the bushing face true, I realized that if I had installed a shorter bushing I could fit the shaft without modifying the steady rest further.

Mike

[MikeK]

On MikeK Said:

I did try the mandrel route.  Not sure what went wrong.  I’m also not sure what precision can be had from it, since I still had about 2 thou runout.

I’m making another one, again.  I made one longer, expecting the length to help the part when installed on the shaft, but it was still 1.5 thou runout.  And after monkeying around trying to fit it in the lathe, to finally face the bushing face true, I realized that if I had installed a shorter bushing I could fit the shaft without modifying the steady rest further.

Mike

Quoting 2 thou runout is meaningless (to readers of this thread) without stating exactly where and what you are measuring, If you are referring to axial runout of a flange then an indication of the diameter that the DTI probe is contacting would be useful to know. Are you measuring the runout of the wheel flange face without the wheel in place?

AIUI you are wanting to make spacer that will sit on a motor shaft between the ball race and the flange that the grinding wheel will sit against, Is that correct?

If this is a plain bush then the method of makings it that ensures an accurate ID and OD and with both ends dead square (because all machining done in one chucking) has already been described earlier in this thread. There is no need for soft jaws, magnetic chucks, surface grinders, mandrels and no special tooling. I’ve just skimmed through this thread but did not spot who described the method but below is my description of the process,

With the stock in the chuck turn the OD, bore and chamfer the ID (depth slightly longer than the finished bush length), then turn the back of the bush almost to the bore diameter so it is held by what is effectively a thin walled tube. Obviously the initial bar stock needs to be long enough to allow entry of a RH facing tool so that the ‘back’ face of the bush can be roughed and then skimmed to ‘almost’ the bore diameter. In practice I would expect that 0.5mm or even less ‘wall’ thickness of the remaining tubular material will be strong enough for the final skim to length until the final skim until the tip of the tool gets close enough to the bore to ‘part off the bush. Hand chamfering/deburring will remove what remains of the tubular support.

Even if the bush is dead parallel between its faces it does not mean that your wheel flange will run dead true as the error could be coming from other parts of the assembly. Making a silk purse out of a mediocre quality sows ear is not simple task but if done sensibly one can achieve a good end result.

Ian P

 

 

 

[MikeKParticipant @mikek40713]

The runout is on the face, in the middle of the ~3/16″ land of the bushing (1″ diameter, 5/8″-ish thru-bore).  I don’t care about OD, and I’m not seeing how the part could be chucked and still turn the OD, but anyway…

There have been plenty of good suggestions here, and I thank you guys.  It’s always nice to get help from Brits, and other Europeans.  Here in the States, most guys would just tell me “You’re an idiot, buy XYZ thing.”  I won’t keep the thread alive unless I have something worth posting about it.

Mike

 

[JasonBModerator @jasonb]

The wobble from the arbor is likely be to the short length of “hole” you have in contact with the arbor. Your part only has 1/8″ length of hole in contact due to the rest being a larger counterbore.

So if your arbor is just using the diameters to hold the part in position it is likely to have wobbly faces due to the ratio of contact length to diameter. Also any clearance between the two diameters will make things worse.

A better way would have been to make the arbor from some more of your 1″ bar. Face the end, turn a spigot that is a light push fit into the larger 5/8″ hole and about 5/16″ long.

You can then push the part onto the spigot with a small amount of locktite and use the tailstock to make sure it is pushed up tight to the shoulder of the arbor.

Once Loctite has set take gentle cuts to face the outer end back to length. Remove arbor and part, heat to break the Loctite bond and you should have parallel faces.

Do not remove an arbor from chuck once it has been machined until job is complete.

[JasonBModerator @jasonb]

I mentioned a light push fit above, this shows the sort of fit that is. For hobby use feel is what is needed not two measurements.

Here is a short 1mm long spigot that has been turned on the inner face of a cylinder end cover. (Softies in use again)

The cyli

With just light hand pressure the cylinder can be pushed onto the spigot and stays there.

 

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