CBN inserts

[Mark Harris 1Participant @markharris1]

I have a large steel hardened  bush that needs 1/4” off the odd. How much will I be able to remove with a CBN insert ? Or will I have to grind it ? Many thanks in advance Mark

[HuubParticipant @huub]

CBN inserts are expensive and very brittle. I would use a half decent cheap insert to cut that hardened steel part. The insert won’t like it and get dull but it will cut hardened steel. Run at modest feed and speed. If you don’t have flood cooling, run it dry because a drop of oil could chip/crack the very hot insert.

[Mark RandParticipant @markrand96270]

They’re not too expensive on fleabay and are very useful when machining hardened steel. It does help to be able to run them at about 300SFM-100m/S. Normally one would limit oneself to 10 thou-.4mm depth of cut but one could go more if the lathe has the power. Coolant doesn’t do any harm at all with a continuous cue (a bit like carbide in that respect) I find them very useful for things like hardened D2 toolsteel etc. Definitely quicker than grinding.

[DC31kParticipant @dc31k]

As above, CBN via eBay and China are acceptably priced. Cheapest UK-supplied is £11.99. The shape of the insert also influences its price (e.g. W 08 – designated ones are are cheapest (£4) I could find). Hence, it might end up more economic to buy a new holder as well as the insert.

Keep in mind the possibility that the bush might not be through hardened. If you are removing 1/4″, by inspection the parent item must be more than 1/4″ thick. You can observe the swarf and it will change character if there is only a hardened surface layer. At that point, you can change back to a normal insert.

[Graham MeekParticipant @grahammeek88282]

Just a couple of thoughts on the proposed task having done something similar in the past.

You might find there is some distortion of the bore after removing such a large amount off the O/D. If the bush could be made with a flange at the original diameter this will help to stop the distortion.

Flood cooling will also get rid of the heat and again reduce the distortion as well as any loss of “Temper”.

Regards

Gray,

[Mark Harris 1Participant @markharris1]

Thank you for the replies I will order some Chinese inserts today. This is a running bush for the horizontal mill I just bought. Got them to throw in a 1 1/4” arbor with it but the running bush is to big hence needing to turn it down. I will see how if I can set up flood coolant. The OD is 2 1/4” so I’m hoping that there will be no distortion but will bare this in mind.

many thanks Mark

[DC31kParticipant @dc31k]

As you call it a ‘running bush’, does it run in anything? In other words, in its new configuration, will the soft surface you reveal by turning away the existing hard surface act as one half of a bearing?

If so, if might be worth investigating enlarging the other half of the bearing (perhaps it is bronze) and preserving the existing hardened surface as it has desirable properties (hardness and ground surface finish) for its intended application.

What is your intention for finishing the surface you turn? It is better think of this before you start rather than after your final cut to diameter leaving the surface like a fresh-ploughed field.

[Mark Harris 1Participant @markharris1]

Unfortunately enlarging the bore of the bronze bone sh is not an option as I have the original 1” arbor which fits the bush. But I will see if it is possible to make this bronze bushe removable so I can swap between sizes. Thanks for the tips many thanks Mark

[SillyOldDufferModerator @sillyoldduffer]

Entirely up to Mark what he does to his machine, but this is the sort of modification I balk at!

The machine’s designer went to a lot of trouble and expense to install a large diameter hardened arbour, and the original customer paid big money for it.   Possibly Mark doesn’t need the feature the extra strength provides, but a future owner might bitterly regret Mark’s modification.  As it’s always much harder to replace metal than remove it, I recommend thinking twice before hacking into anything that’s been deliberately beefed up.    Is there no way of making an adaptor that doesn’t require chopping the machine up with specially extra-hard CBN inserts?

Dave

 

[Mark Harris 1Participant @markharris1]

I’m not sure I explained this well I’ve just purchased a new mill to me. It comes with the over arm support with an 1 7/8” bronze bush. I have an 1” diameter arbor with the correct running bush. As part of the deal they supplied a 1 1/4” arbor that a need for the larger cutters I have to run. It has a 2 1/8” running hardened bush. My original plan was to reduce its diameter to work with the existing bearing. If I can make it so that I can make a new bronze bearing which I can change I will take that option. I will not do anything to the machine that cannot be put back to original spec. But the 1. 1/4” arbor is from another machine. I have looked for other running bushes but tooling for horizontal mills is not easy to find. Many thanks Mark

[HopperParticipant @hopper]

For home use, does the running bush need to be hardened, or would an unhardened mild steel bush do the job for the limited hours of use per year it will get, running in the bronze bush?

Or maybe use something like SAE 4140 high-carbon alloy steel? (No idea what that is in UK grading system.)

If you do turn the original hardened bush down, you might need to grind the final finish on it to get a smooth bearing surface? Whereas, turning up a fresh unhardened bush, a bit of emery paper will give final finish?

[Mark Harris 1]

On Mark Harris 1 Said:

If I can make it so that I can make a new bronze bearing which I can change I will take that option.

A new bronze bearing is a good idea.

Another (possibly remote) option is to see if 1 7/8″ is a standard hydraulic ram diameter. A piece of hard chromed bar with a 1 1/4″ hole bored through it would make a lovely running bush. [Edit: it is, see https://hydraulicandengineering.co.uk/product/chrome-bar-in-various-imperial-sizes-and-material-grades/ hit the additional info. tab]

I do not think silver steel is available in 1 7/8″ or that would be a good start because it is ground.

How long is the bush? Another another option might be a couple of imperial ball bearings (KLNJ7/8) that have 1 7/8″ OD. Remove the balls, cage and inner race and blu-tak them to something with a 1 1/4″ hole in it. Distribute the blu-tak evenly so everything is concentric.

[Mark Harris 1Participant @markharris1]

Thank you for the excellent comment DC31K .  I have now bought a piece of chrome bar of the correct size. They are an excellent company to deal with considering I only wanted 3” long piece of bar returned a quote by email.  paid and am now waiting for it to be delivered.
many thanks Mark

[old martParticipant @oldmart]

I have not seen CBN used on hard steel in conjunction with coolant. Dry, you have to take care to avoid the red hot swarf coming off. A lot of hard steels are only case hardened, once you are through the first 0.01″, 0.25mm then the going gets easier.

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