Burnishing tool

[Sonic EscapeParticipant @sonicescape38234]

I saw some videos with burnishing tools. They can create a mirror like finish. I would like to have one. Some types are using a ball, others a round diamond or a small wheel. I have these round carbide inserts and I was wondering if they could be used for this. Like a wheel. Or they will break?

 

[DiogenesParticipant @diogenes]

I think the edge will chip if you put sideways pressure on it – it’s easy to chip inserts even touching off the end of a workpiece, ask how etc. <crying face>

[Sonic EscapeParticipant @sonicescape38234]

I also chip inserts from time to time. But maybe those inserts are harder. After all they are specified to cut more than 4mm if I remember correctly. Also the round shape should be the strongest. And in the end I don’t have anything better to do with them.

I’m thinking on a more universal tool. So in case the inserts will not work to be able to replace them with some carbon steel wheel or something else.

But I find it difficult to make an arbor for them. There is a taper inside the central hole. I don’t have a tool to measure it. And it I suppose it is to short to try to copy it with an indicator. I’m still thinking on this.

[Neil LickfoldParticipant @neillickfold44316]

Polished bearings on a scissor type knurling tool does work.

[SillyOldDufferModerator @sillyoldduffer]

Sonic takes us well off the beaten track with this question!  The only way to find out is to try it.

Although much is made of the brittleness of carbide inserts, modern ones are tough stuff.  Breakages occur with heavy interrupted cutting, which causes high shock loads unlikely to occur in burnishing.

Most likely cause of failure I feel, is that Sonic’s inserts have a sharp cutting edge on one side.  If this edge comes into contact with the work piece whilst burnishing, it will ruin the job by gouging deep into it.  How likely, or not, it is to gouge depends on the job, how it is held, how the button is applied, and the skill of the operator.

Burnishing is a finishing operation, suggesting a lot of time already invested in making the part.  Is it wise to risk spoiling it with a repurposed tool?  Not done much burnishing, but in both cases I shaped a proper burnishing tool by grinding and polishing HSS.  Key feature of my home-made burnishers – no sharp edges.

Dave

[SillyOldDuffer]

On SillyOldDuffer Said:

… ..Although much is made of the brittleness of carbide inserts, modern ones are tough stuff.  Breakages occur with heavy interrupted cutting, which causes high shock loads unlikely to occur in burnishing.. …

 

Dave

– true only in regard to an insert that is being loaded in the direction for which it was designed.

Under normal conditions, the edge is supported by the entire thickness of the material beneath it.

With pressure applied laterally, there is little or no supporting material immediately behind the edge due to the chip-breaker.

 

[jimmy bParticipant @jimmyb]

<p style=”text-align: left;”>You need a diamond for single point burnishing or the hardened roller type.</p>
You’ll need a fairly good finish before and consistent size.

We do a bit if this at work, on both lathes and milling.

 

The results can be quite amazing.

 

Funnily enough I’m planning on trying this out at home, but will stick to the polished diamond. They can be had for than £20 on ebay.

 

Jimb

[Sonic EscapeParticipant @sonicescape38234]

What is the drawback of a polished diamond? To me it looks like the simplest solution.

[jimmy bParticipant @jimmyb]

The diamond burnishing tools are a diamond with a polished finish.

Jimb

[bernard towersParticipant @bernardtowers37738]

how do you get on with using diamond on ferrous material?

[Robert Atkinson 2Participant @robertatkinson2]

Burnishing should not get anything hot enough to be an issue.

[bernard towersParticipant @bernardtowers37738]

Didnt think it was anything to do with heat just that diamond tools are not recommended on ferrous materials.

[Sonic EscapeParticipant @sonicescape38234]

I read somewhere that diamond tend to disolve in hot steel. That is why diamond grinding wheels are recomended only for carbide tools and CBN for HSS.

[FulmenParticipant @fulmen]

It’s not as simple as that, but yes. Diamond is not compatible with ferrous metals at high temperatures and pressures.

[jimmy bParticipant @jimmyb]

More information on burnishing

 

[jimmy bParticipant @jimmyb]

https://cogsdill.co.uk/products/burnishing-tools/?_gl=1*1atk2mb*_up*MQ..&gclid=Cj0KCQjwo8S3BhDeARIsAFRmkOMmGJSWJEsJeVhtJmh5mCH-M3gQxLpKQ5v2tpa0vdNgOE3PB_8X7coaAlMYEALw_wcB

[duncan webster 1Participant @duncanwebster1]

As far as I can discover diamond reacts with iron in the steel at temperatures above 700C to give iron carbide, which is why I bought  CBN wheel for my little drill sharpening grinder. For light use I doubt it gets that hot. If it gets really hot, the diamond can change it’s crystal form and become graphite, but that is really hot, 1500C.

[jimmy bParticipant @jimmyb]

Burnishing doesn’t create much heat, unless you are doing it wrong!

 

Jimb

[Neil LickfoldParticipant @neillickfold44316]

Does the radius diamond tool spin in it’s holder when used on a lathe?  So the edge is not stationary but rotates with the part?

Neil

[jimmy bParticipant @jimmyb]

The diamond is fixed.

The steel roller type do rotate.

Flood coolant is used too.

 

Jimb

[Sonic EscapeParticipant @sonicescape38234]

I made a quick experiment with a poor man’s burnishing tool. I have a ball bearing that I replaced on a milling machine arbor. I made a small arbor for it and I milled it to have a flat side to be able to hold it in the tool post. I added two C clamps just to be sure.

The resulting surface was a clear improvement over the existing poor finish. I think I’ll rework the tool with a new bearing and a safer holding method.

One thing I discovered is that there is no feedback about how much pressure to apply. When using cutting tools you can feel when the cutting depth is too much. But here no clue.

There is also some kind of axial ripple on the surface. But this might be caused by the bad bearing, unlocked gib, not optimal tool angle or who knows. However I found it a promising method.

What type of bearings do you think is worth trying? And angular contact type I suppose it would better suited to this type of asymmetric load? Or smaller diameter maybe, since it will have a smaller radius on the edge? Is there a type of bearing that has a very large diameter to height ratio?

 

[Harry WilkesParticipant @harrywilkes58467]

There are several versions of this type of tool on youtube and it seems to work well

https://www.youtube.com/watch?v=qXmLxpSZPfU

‘Super Ball Rolling For The Lathe’

H

[duncan webster 1]

On duncan webster 1 Said:

As far as I can discover diamond reacts with iron in the steel at temperatures above 700C to give iron carbide, which is why I bought  CBN wheel for my little drill sharpening grinder. For light use I doubt it gets that hot. If it gets really hot, the diamond can change it’s crystal form and become graphite, but that is really hot, 1500C.

Where did you get the wheel?

[duncan webster 1Participant @duncanwebster1]

Can’t remember, it wad a long time ago

[Clive FosterParticipant @clivefoster55965]

There is a DIY version floating around the internet that uses a decent size ball, maybe 10 mm – 1/2″ Ø methinks, backed up by a ball bearing as the burnishing tool. An attractive thing of this design is the built in oil reservoir. Which should ensure that the burnisher never runs dry. Un-lubricated surfaces are a common cause of problems when burnishing. Although you can burnish dry, lubricating is generally more reliable.

Basic design is a vertical bore with one closed end sized to take the ball close to the tip of the shank. The tip is cut back so the ball protrudes through a longitudinal hole sufficiently to burnish the work.

The rear of the hole is extended into a slot in which a ball bearing mounted on a cross pin spins. The ball bearing is positioned slightly above the centre line so it takes most of the thrust load and holds the burnishing ball down in the hole.

Looks very simple and effective but I imagine there is some positional subtlety concerning the centre lines of bearing and ball to ensue everything spins freely without ejecting the ball.

Clive

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