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Peter.
01-29-2010, 05:59 AM
Who here does burnishing in a lathe? I've seen a few references to it for getting a good finish for seals etc using a roller in a tool holder but how practical is it for a home shop lathe? Does burnishing a turned surface change the part significantly dimensionally?

Ian B
01-29-2010, 07:46 AM
Peter,

Info on roller burnishing:

http://cogsdill.com/PDF/USCatalogs/CompleteCatalogs/USBurnishingCatalog.pdf

Ian

Peter.
01-29-2010, 08:08 AM
Hmm, kinda looks rather hi-tech. I was thinking it might be possible to do it using a regular roller bearing mounted in a toolpost tool. Thanks for the link Ian.

Carm
01-29-2010, 09:39 AM
The Cogsdill tools are top notch, but your home roller will work too. Dimensional change is in the tenths.
Bump style tools put lots of stress on the lathe though.

japcas
01-29-2010, 10:04 AM
We have one at work that uses a spring loaded diamond tip tool that rolls the ridges over on the work to produce a really nice finish. We only use it occasionally but I don't think it would be too hard to cobble something up for home use.

Evan
01-29-2010, 10:26 AM
You don't need a roller at all. You can polish up a carbide bit and use extreme pressure differential lube to prevent galling. I have done many experiments along this line with my shaper and there should be no difference using a lathe. The secret is the lube as it prevents actual contact of the tool with the work.

I will post a picture of the tool a bit later.

japcas
01-29-2010, 10:29 AM
Evan we always use the one at work with a little coolant and it seems to work fine. Never tried any lube but it probably couldn't hurt.

Willy
01-29-2010, 11:32 AM
As Evan noted you don't need a roller at all. I have used exactly the same method he described with good success using EP gear lube as well. The extreme pressure additives in hypoid gear oil will prevent metal to metal contact resulting in a very smooth finish.

I usually use a small roller bearing mounted in a QCTP though as they are so easy and quick to make and require no lube, not that using oil is a significant drawback of any sort.

Cobbled this one together last night because my usual one is out on loan and I needed one in a hurry. The overhang away from the tool holder could have been less but I was in a hurry so the bearing spacers are a little thicker than need be and the bolt should have been a socket head cap screw for a cleaner appearance and less intrusive design. But hey I was in a hurry and it did the job just fine in spite of the design deficiencies.

I usually mount it in the the tool post so that only a small portion of the bearing actually makes contact with the work piece. This way maximum pressure per square inch will be exerted to the work piece with less strain on the lathe. Dimensional changes are negligible depending on the type of material in use and can easily be compensated for in critical applications.

Unfortunately I don't have any before and after photos to illustrate the effects of the roller on a piece of stock, but they are dramatic.
I have a couple of busy days ahead of me but I'll post some as soon as I can drag my carcass out to the shop again.

http://i76.photobucket.com/albums/j31/250willy/DSCN0256.jpg


http://i76.photobucket.com/albums/j31/250willy/DSCN0255.jpg

Peter.
01-29-2010, 01:39 PM
That's great! I have a spindle from an old Drummond roundbed lathe that runs on the cast headstock and the shaft is a little rough, but not too bad. I bought it as spares for another Drummond but found they have not a thing in common so I figured I might make a project of it. Hopefully I can dress the shaft by roller-burnishing - I'll try it out on a non-bearing part of the shaft first and take some pictures.

CCWKen
01-29-2010, 06:28 PM
I've done it similar to Willy but used my clamping knurler with bearings in place of the knurls. Works pretty good but you have to watch overloading the small bearings. I was burnishing aluminum. Might be better to turn your own disks (flat face knurls) for steel.